Reapply fast-URI patch.

sdk/lib/core/uri.dart

Index: sdk/lib/core/uri.dart
diff --git a/sdk/lib/core/uri.dart b/sdk/lib/core/uri.dart
index 456bcb7589769a20d1e84d41f915517caa11b7f0..51d66cfa8052a64fb1ad6235f4afee31e1c4a918 100644
--- a/sdk/lib/core/uri.dart
+++ b/sdk/lib/core/uri.dart
@@ -4,6 +4,24 @@
 
 part of dart.core;
 
+// Frequently used character codes.
+const int _SPACE = 0x20;
+const int _PERCENT = 0x25;
+const int _PLUS = 0x2B;
+const int _DOT = 0x2E;
+const int _SLASH = 0x2F;
+const int _COLON = 0x3A;
+const int _UPPER_CASE_A = 0x41;
+const int _UPPER_CASE_Z = 0x5A;
+const int _LEFT_BRACKET = 0x5B;
+const int _BACKSLASH = 0x5C;
+const int _RIGHT_BRACKET = 0x5D;
+const int _LOWER_CASE_A = 0x61;
+const int _LOWER_CASE_F = 0x66;
+const int _LOWER_CASE_Z = 0x7A;
+
+const String _hexDigits = "0123456789ABCDEF";
+
 /**
  * A parsed URI, such as a URL.
  *
@@ -15,77 +33,17 @@ part of dart.core;
  * [uris]: https://www.dartlang.org/docs/dart-up-and-running/ch03.html#uris
  * [libtour]: https://www.dartlang.org/docs/dart-up-and-running/contents/ch03.html
  */
-class Uri {
-  /**
-   * The scheme component of the URI.
-   *
-   * Returns the empty string if there is no scheme component.
-   *
-   * A URI scheme is case insensitive.
-   * The returned scheme is canonicalized to lowercase letters.
-   */
-  // We represent the missing scheme as an empty string.
-  // A valid scheme cannot be empty.
-  final String scheme;
-
-  /**
-   * The user-info part of the authority.
-   *
-   * Does not distinguish between an empty user-info and an absent one.
-   * The value is always non-null.
-   * Is considered absent if [_host] is `null`.
-   */
-  final String _userInfo;
-
-  /**
-   * The host name of the URI.
-   *
-   * Set to `null` if there is no authority in the URI.
-   * The host name is the only mandatory part of an authority, so we use
-   * it to mark whether an authority part was present or not.
-   */
-  final String _host;
-
+abstract class Uri {
   /**
-   * The port number part of the authority.
+   * Returns the natural base URI for the current platform.
    *
-   * The port. Set to null if there is no port. Normalized to null if
-   * the port is the default port for the scheme.
-   */
-  int _port;
-
-  /**
-   * The path of the URI.
+   * When running in a browser this is the current URL of the current page
+   * (from `window.location.href`).
    *
-   * Always non-null.
-   */
-  String _path;
-
-  // The query content, or null if there is no query.
-  final String _query;
-
-  // The fragment content, or null if there is no fragment.
-  final String _fragment;
-
-  /**
-   * Cache the computed return value of [pathSegements].
-   */
-  List<String> _pathSegments;
-
-  /**
-   * Cache the computed return value of [queryParameters].
+   * When not running in a browser this is the file URI referencing
+   * the current working directory.
    */
-  Map<String, String> _queryParameters;
-  Map<String, List<String>> _queryParameterLists;
-
-  /// Internal non-verifying constructor. Only call with validated arguments.
-  Uri._internal(this.scheme,
-                this._userInfo,
-                this._host,
-                this._port,
-                this._path,
-                this._query,
-                this._fragment);
+  external static Uri get base;
 
   /**
    * Creates a new URI from its components.
@@ -158,39 +116,15 @@ class Uri {
    * general delimiters, are escaped if necessary.
    * If `fragment` is omitted or `null`, the URI has no fragment part.
    */
-  factory Uri({String scheme : "",
-               String userInfo : "",
+  factory Uri({String scheme,
+               String userInfo,
                String host,
                int port,
                String path,
                Iterable<String> pathSegments,
                String query,
                Map<String, dynamic/*String|Iterable<String>*/> queryParameters,
-               String fragment}) {
-    scheme = _makeScheme(scheme, 0, _stringOrNullLength(scheme));
-    userInfo = _makeUserInfo(userInfo, 0, _stringOrNullLength(userInfo));
-    host = _makeHost(host, 0, _stringOrNullLength(host), false);
-    // Special case this constructor for backwards compatibility.
-    if (query == "") query = null;
-    query = _makeQuery(query, 0, _stringOrNullLength(query), queryParameters);
-    fragment = _makeFragment(fragment, 0, _stringOrNullLength(fragment));
-    port = _makePort(port, scheme);
-    bool isFile = (scheme == "file");
-    if (host == null &&
-        (userInfo.isNotEmpty || port != null || isFile)) {
-      host = "";
-    }
-    bool hasAuthority = (host != null);
-    path = _makePath(path, 0, _stringOrNullLength(path), pathSegments,
-                     scheme, hasAuthority);
-    if (scheme.isEmpty && host == null && !path.startsWith('/')) {
-      path = _normalizeRelativePath(path);
-    } else {
-      path = _removeDotSegments(path);
-    }
-    return new Uri._internal(scheme, userInfo, host, port,
-                             path, query, fragment);
-  }
+               String fragment}) = _Uri;
 
   /**
    * Creates a new `http` URI from authority, path and query.
@@ -227,9 +161,7 @@ class Uri {
    */
   factory Uri.http(String authority,
                    String unencodedPath,
-                   [Map<String, String> queryParameters]) {
-    return _makeHttpUri("http", authority, unencodedPath, queryParameters);
-  }
+                   [Map<String, String> queryParameters]) = _Uri.http;
 
   /**
    * Creates a new `https` URI from authority, path and query.
@@ -239,531 +171,106 @@ class Uri {
    */
   factory Uri.https(String authority,
                     String unencodedPath,
-                    [Map<String, String> queryParameters]) {
-    return _makeHttpUri("https", authority, unencodedPath, queryParameters);
-  }
+                    [Map<String, String> queryParameters]) = _Uri.https;
 
   /**
-   * Returns the authority component.
+   * Creates a new file URI from an absolute or relative file path.
    *
-   * The authority is formatted from the [userInfo], [host] and [port]
-   * parts.
+   * The file path is passed in [path].
    *
-   * Returns the empty string if there is no authority component.
-   */
-  String get authority {
-    if (!hasAuthority) return "";
-    var sb = new StringBuffer();
-    _writeAuthority(sb);
-    return sb.toString();
-  }
-
-  /**
-   * Returns the user info part of the authority component.
+   * This path is interpreted using either Windows or non-Windows
+   * semantics.
    *
-   * Returns the empty string if there is no user info in the
-   * authority component.
-   */
-  String get userInfo => _userInfo;
-
-  /**
-   * Returns the host part of the authority component.
+   * With non-Windows semantics the slash ("/") is used to separate
+   * path segments.
    *
-   * Returns the empty string if there is no authority component and
-   * hence no host.
+   * With Windows semantics, backslash ("\\") and forward-slash ("/")
+   * are used to separate path segments, except if the path starts
+   * with "\\\\?\\" in which case, only backslash ("\\") separates path
+   * segments.
    *
-   * If the host is an IP version 6 address, the surrounding `[` and `]` is
-   * removed.
+   * If the path starts with a path separator an absolute URI is
+   * created. Otherwise a relative URI is created. One exception from
+   * this rule is that when Windows semantics is used and the path
+   * starts with a drive letter followed by a colon (":") and a
+   * path separator then an absolute URI is created.
    *
-   * The host string is case-insensitive.
-   * The returned host name is canonicalized to lower-case
-   * with upper-case percent-escapes.
-   */
-  String get host {
-    if (_host == null) return "";
-    if (_host.startsWith('[')) {
-      return _host.substring(1, _host.length - 1);
-    }
-    return _host;
-  }
-
-  /**
-   * Returns the port part of the authority component.
+   * The default for whether to use Windows or non-Windows semantics
+   * determined from the platform Dart is running on. When running in
+   * the standalone VM this is detected by the VM based on the
+   * operating system. When running in a browser non-Windows semantics
+   * is always used.
    *
-   * Returns the defualt port if there is no port number in the authority
-   * component. That's 80 for http, 443 for https, and 0 for everything else.
-   */
-  int get port {
-    if (_port == null) return _defaultPort(scheme);
-    return _port;
-  }
-
-  // The default port for the scheme of this Uri..
-  static int _defaultPort(String scheme) {
-    if (scheme == "http") return 80;
-    if (scheme == "https") return 443;
-    return 0;
-  }
-
-  /**
-   * Returns the path component.
+   * To override the automatic detection of which semantics to use pass
+   * a value for [windows]. Passing `true` will use Windows
+   * semantics and passing `false` will use non-Windows semantics.
    *
-   * The returned path is encoded. To get direct access to the decoded
-   * path use [pathSegments].
+   * Examples using non-Windows semantics:
    *
-   * Returns the empty string if there is no path component.
-   */
-  String get path => _path;
-
-  /**
-   * Returns the query component. The returned query is encoded. To get
-   * direct access to the decoded query use [queryParameters].
+   * ```
+   * // xxx/yyy
+   * new Uri.file("xxx/yyy", windows: false);
    *
-   * Returns the empty string if there is no query component.
+   * // xxx/yyy/
+   * new Uri.file("xxx/yyy/", windows: false);
+   *
+   * // file:///xxx/yyy
+   * new Uri.file("/xxx/yyy", windows: false);
+   *
+   * // file:///xxx/yyy/
+   * new Uri.file("/xxx/yyy/", windows: false);
+   *
+   * // C:
+   * new Uri.file("C:", windows: false);
+   * ```
+   *
+   * Examples using Windows semantics:
+   *
+   * ```
+   * // xxx/yyy
+   * new Uri.file(r"xxx\yyy", windows: true);
+   *
+   * // xxx/yyy/
+   * new Uri.file(r"xxx\yyy\", windows: true);
+   *
+   * file:///xxx/yyy
+   * new Uri.file(r"\xxx\yyy", windows: true);
+   *
+   * file:///xxx/yyy/
+   * new Uri.file(r"\xxx\yyy/", windows: true);
+   *
+   * // file:///C:/xxx/yyy
+   * new Uri.file(r"C:\xxx\yyy", windows: true);
+   *
+   * // This throws an error. A path with a drive letter is not absolute.
+   * new Uri.file(r"C:", windows: true);
+   *
+   * // This throws an error. A path with a drive letter is not absolute.
+   * new Uri.file(r"C:xxx\yyy", windows: true);
+   *
+   * // file://server/share/file
+   * new Uri.file(r"\\server\share\file", windows: true);
+   * ```
+   *
+   * If the path passed is not a legal file path [ArgumentError] is thrown.
    */
-  String get query => (_query == null) ? "" : _query;
+  factory Uri.file(String path, {bool windows}) = _Uri.file;
 
   /**
-   * Returns the fragment identifier component.
+   * Like [Uri.file] except that a non-empty URI path ends in a slash.
    *
-   * Returns the empty string if there is no fragment identifier
-   * component.
+   * If [path] is not empty, and it doesn't end in a directory separator,
+   * then a slash is added to the returned URI's path.
+   * In all other cases, the result is the same as returned by `Uri.file`.
    */
-  String get fragment => (_fragment == null) ? "" : _fragment;
+  factory Uri.directory(String path, {bool windows}) = _Uri.directory;
 
   /**
-   * Creates a new `Uri` object by parsing a URI string.
+   * Creates a `data:` URI containing the [content] string.
    *
-   * If [start] and [end] are provided, only the substring from `start`
-   * to `end` is parsed as a URI.
-   *
-   * If the string is not valid as a URI or URI reference,
-   * a [FormatException] is thrown.
-   */
-  static Uri parse(String uri, [int start = 0, int end]) {
-    // This parsing will not validate percent-encoding, IPv6, etc.
-    // When done splitting into parts, it will call, e.g., [_makeFragment]
-    // to do the final parsing.
-    //
-    // Important parts of the RFC 3986 used here:
-    // URI           = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
-    //
-    // hier-part     = "//" authority path-abempty
-    //               / path-absolute
-    //               / path-rootless
-    //               / path-empty
-    //
-    // URI-reference = URI / relative-ref
-    //
-    // absolute-URI  = scheme ":" hier-part [ "?" query ]
-    //
-    // relative-ref  = relative-part [ "?" query ] [ "#" fragment ]
-    //
-    // relative-part = "//" authority path-abempty
-    //               / path-absolute
-    //               / path-noscheme
-    //               / path-empty
-    //
-    // scheme        = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
-    //
-    // authority     = [ userinfo "@" ] host [ ":" port ]
-    // userinfo      = *( unreserved / pct-encoded / sub-delims / ":" )
-    // host          = IP-literal / IPv4address / reg-name
-    // port          = *DIGIT
-    // reg-name      = *( unreserved / pct-encoded / sub-delims )
-    //
-    // path          = path-abempty    ; begins with "/" or is empty
-    //               / path-absolute   ; begins with "/" but not "//"
-    //               / path-noscheme   ; begins with a non-colon segment
-    //               / path-rootless   ; begins with a segment
-    //               / path-empty      ; zero characters
-    //
-    // path-abempty  = *( "/" segment )
-    // path-absolute = "/" [ segment-nz *( "/" segment ) ]
-    // path-noscheme = segment-nz-nc *( "/" segment )
-    // path-rootless = segment-nz *( "/" segment )
-    // path-empty    = 0<pchar>
-    //
-    // segment       = *pchar
-    // segment-nz    = 1*pchar
-    // segment-nz-nc = 1*( unreserved / pct-encoded / sub-delims / "@" )
-    //               ; non-zero-length segment without any colon ":"
-    //
-    // pchar         = unreserved / pct-encoded / sub-delims / ":" / "@"
-    //
-    // query         = *( pchar / "/" / "?" )
-    //
-    // fragment      = *( pchar / "/" / "?" )
-    const int EOI = -1;
-
-    String scheme = "";
-    String userinfo = "";
-    String host = null;
-    int port = null;
-    String path = null;
-    String query = null;
-    String fragment = null;
-    if (end == null) end = uri.length;
-
-    int index = start;
-    int pathStart = start;
-    // End of input-marker.
-    int char = EOI;
-
-    void parseAuth() {
-      if (index == end) {
-        char = EOI;
-        return;
-      }
-      int authStart = index;
-      int lastColon = -1;
-      int lastAt = -1;
-      char = uri.codeUnitAt(index);
-      while (index < end) {
-        char = uri.codeUnitAt(index);
-        if (char == _SLASH || char == _QUESTION || char == _NUMBER_SIGN) {
-          break;
-        }
-        if (char == _AT_SIGN) {
-          lastAt = index;
-          lastColon = -1;
-        } else if (char == _COLON) {
-          lastColon = index;
-        } else if (char == _LEFT_BRACKET) {
-          lastColon = -1;
-          int endBracket = uri.indexOf(']', index + 1);
-          if (endBracket == -1) {
-            index = end;
-            char = EOI;
-            break;
-          } else {
-            index = endBracket;
-          }
-        }
-        index++;
-        char = EOI;
-      }
-      int hostStart = authStart;
-      int hostEnd = index;
-      if (lastAt >= 0) {
-        userinfo = _makeUserInfo(uri, authStart, lastAt);
-        hostStart = lastAt + 1;
-      }
-      if (lastColon >= 0) {
-        int portNumber;
-        if (lastColon + 1 < index) {
-          portNumber = 0;
-          for (int i = lastColon + 1; i < index; i++) {
-            int digit = uri.codeUnitAt(i);
-            if (_ZERO > digit || _NINE < digit) {
-              _fail(uri, i, "Invalid port number");
-            }
-            portNumber = portNumber * 10 + (digit - _ZERO);
-          }
-        }
-        port = _makePort(portNumber, scheme);
-        hostEnd = lastColon;
-      }
-      host = _makeHost(uri, hostStart, hostEnd, true);
-      if (index < end) {
-        char = uri.codeUnitAt(index);
-      }
-    }
-
-    // When reaching path parsing, the current character is known to not
-    // be part of the path.
-    const int NOT_IN_PATH = 0;
-    // When reaching path parsing, the current character is part
-    // of the a non-empty path.
-    const int IN_PATH = 1;
-    // When reaching authority parsing, authority is possible.
-    // This is only true at start or right after scheme.
-    const int ALLOW_AUTH = 2;
-
-    // Current state.
-    // Initialized to the default value that is used when exiting the
-    // scheme loop by reaching the end of input.
-    // All other breaks set their own state.
-    int state = NOT_IN_PATH;
-    int i = index;  // Temporary alias for index to avoid bug 19550 in dart2js.
-    while (i < end) {
-      char = uri.codeUnitAt(i);
-      if (char == _QUESTION || char == _NUMBER_SIGN) {
-        state = NOT_IN_PATH;
-        break;
-      }
-      if (char == _SLASH) {
-        state = (i == start) ? ALLOW_AUTH : IN_PATH;
-        break;
-      }
-      if (char == _COLON) {
-        if (i == start) _fail(uri, start, "Invalid empty scheme");
-        scheme = _makeScheme(uri, start, i);
-        i++;
-        if (scheme == "data") {
-          // This generates a URI that is (potentially) not path normalized.
-          // Applying part normalization to a non-hierarchial URI isn't
-          // meaningful.
-          return UriData._parse(uri, i, null).uri;
-        }
-        pathStart = i;
-        if (i == end) {
-          char = EOI;
-          state = NOT_IN_PATH;
-        } else {
-          char = uri.codeUnitAt(i);
-          if (char == _QUESTION || char == _NUMBER_SIGN) {
-            state = NOT_IN_PATH;
-          } else if (char == _SLASH) {
-            state = ALLOW_AUTH;
-          } else {
-            state = IN_PATH;
-          }
-        }
-        break;
-      }
-      i++;
-      char = EOI;
-    }
-    index = i;  // Remove alias when bug is fixed.
-
-    if (state == ALLOW_AUTH) {
-      assert(char == _SLASH);
-      // Have seen one slash either at start or right after scheme.
-      // If two slashes, it's an authority, otherwise it's just the path.
-      index++;
-      if (index == end) {
-        char = EOI;
-        state = NOT_IN_PATH;
-      } else {
-        char = uri.codeUnitAt(index);
-        if (char == _SLASH) {
-          index++;
-          parseAuth();
-          pathStart = index;
-        }
-        if (char == _QUESTION || char == _NUMBER_SIGN || char == EOI) {
-          state = NOT_IN_PATH;
-        } else {
-          state = IN_PATH;
-        }
-      }
-    }
-
-    assert(state == IN_PATH || state == NOT_IN_PATH);
-    if (state == IN_PATH) {
-      // Characters from pathStart to index (inclusive) are known
-      // to be part of the path.
-      while (++index < end) {
-        char = uri.codeUnitAt(index);
-        if (char == _QUESTION || char == _NUMBER_SIGN) {
-          break;
-        }
-        char = EOI;
-      }
-      state = NOT_IN_PATH;
-    }
-
-    assert(state == NOT_IN_PATH);
-    bool hasAuthority = (host != null);
-    path = _makePath(uri, pathStart, index, null, scheme, hasAuthority);
-
-    if (char == _QUESTION) {
-      int numberSignIndex = -1;
-      for (int i = index + 1; i < end; i++) {
-        if (uri.codeUnitAt(i) == _NUMBER_SIGN) {
-          numberSignIndex = i;
-          break;
-        }
-      }
-      if (numberSignIndex < 0) {
-        query = _makeQuery(uri, index + 1, end, null);
-      } else {
-        query = _makeQuery(uri, index + 1, numberSignIndex, null);
-        fragment = _makeFragment(uri, numberSignIndex + 1, end);
-      }
-    } else if (char == _NUMBER_SIGN) {
-      fragment = _makeFragment(uri, index + 1, end);
-    }
-    return new Uri._internal(scheme,
-                             userinfo,
-                             host,
-                             port,
-                             path,
-                             query,
-                             fragment);
-  }
-
-  // Report a parse failure.
-  static void _fail(String uri, int index, String message) {
-    throw new FormatException(message, uri, index);
-  }
-
-  static Uri _makeHttpUri(String scheme,
-                          String authority,
-                          String unencodedPath,
-                          Map<String, String> queryParameters) {
-    var userInfo = "";
-    var host = null;
-    var port = null;
-
-    if (authority != null && authority.isNotEmpty) {
-      var hostStart = 0;
-      // Split off the user info.
-      bool hasUserInfo = false;
-      for (int i = 0; i < authority.length; i++) {
-        if (authority.codeUnitAt(i) == _AT_SIGN) {
-          hasUserInfo = true;
-          userInfo = authority.substring(0, i);
-          hostStart = i + 1;
-          break;
-        }
-      }
-      var hostEnd = hostStart;
-      if (hostStart < authority.length &&
-          authority.codeUnitAt(hostStart) == _LEFT_BRACKET) {
-        // IPv6 host.
-        for (; hostEnd < authority.length; hostEnd++) {
-          if (authority.codeUnitAt(hostEnd) == _RIGHT_BRACKET) break;
-        }
-        if (hostEnd == authority.length) {
-          throw new FormatException("Invalid IPv6 host entry.",
-                                    authority, hostStart);
-        }
-        parseIPv6Address(authority, hostStart + 1, hostEnd);
-        hostEnd++;  // Skip the closing bracket.
-        if (hostEnd != authority.length &&
-            authority.codeUnitAt(hostEnd) != _COLON) {
-          throw new FormatException("Invalid end of authority",
-                                    authority, hostEnd);
-        }
-      }
-      // Split host and port.
-      bool hasPort = false;
-      for (; hostEnd < authority.length; hostEnd++) {
-        if (authority.codeUnitAt(hostEnd) == _COLON) {
-          var portString = authority.substring(hostEnd + 1);
-          // We allow the empty port - falling back to initial value.
-          if (portString.isNotEmpty) port = int.parse(portString);
-          break;
-        }
-      }
-      host = authority.substring(hostStart, hostEnd);
-    }
-    return new Uri(scheme: scheme,
-                   userInfo: userInfo,
-                   host: host,
-                   port: port,
-                   pathSegments: unencodedPath.split("/"),
-                   queryParameters: queryParameters);
-  }
-
-  /**
-   * Creates a new file URI from an absolute or relative file path.
-   *
-   * The file path is passed in [path].
-   *
-   * This path is interpreted using either Windows or non-Windows
-   * semantics.
-   *
-   * With non-Windows semantics the slash ("/") is used to separate
-   * path segments.
-   *
-   * With Windows semantics, backslash ("\\") and forward-slash ("/")
-   * are used to separate path segments, except if the path starts
-   * with "\\\\?\\" in which case, only backslash ("\\") separates path
-   * segments.
-   *
-   * If the path starts with a path separator an absolute URI is
-   * created. Otherwise a relative URI is created. One exception from
-   * this rule is that when Windows semantics is used and the path
-   * starts with a drive letter followed by a colon (":") and a
-   * path separator then an absolute URI is created.
-   *
-   * The default for whether to use Windows or non-Windows semantics
-   * determined from the platform Dart is running on. When running in
-   * the standalone VM this is detected by the VM based on the
-   * operating system. When running in a browser non-Windows semantics
-   * is always used.
-   *
-   * To override the automatic detection of which semantics to use pass
-   * a value for [windows]. Passing `true` will use Windows
-   * semantics and passing `false` will use non-Windows semantics.
-   *
-   * Examples using non-Windows semantics:
-   *
-   * ```
-   * // xxx/yyy
-   * new Uri.file("xxx/yyy", windows: false);
-   *
-   * // xxx/yyy/
-   * new Uri.file("xxx/yyy/", windows: false);
-   *
-   * // file:///xxx/yyy
-   * new Uri.file("/xxx/yyy", windows: false);
-   *
-   * // file:///xxx/yyy/
-   * new Uri.file("/xxx/yyy/", windows: false);
-   *
-   * // C:
-   * new Uri.file("C:", windows: false);
-   * ```
-   *
-   * Examples using Windows semantics:
-   *
-   * ```
-   * // xxx/yyy
-   * new Uri.file(r"xxx\yyy", windows: true);
-   *
-   * // xxx/yyy/
-   * new Uri.file(r"xxx\yyy\", windows: true);
-   *
-   * file:///xxx/yyy
-   * new Uri.file(r"\xxx\yyy", windows: true);
-   *
-   * file:///xxx/yyy/
-   * new Uri.file(r"\xxx\yyy/", windows: true);
-   *
-   * // file:///C:/xxx/yyy
-   * new Uri.file(r"C:\xxx\yyy", windows: true);
-   *
-   * // This throws an error. A path with a drive letter is not absolute.
-   * new Uri.file(r"C:", windows: true);
-   *
-   * // This throws an error. A path with a drive letter is not absolute.
-   * new Uri.file(r"C:xxx\yyy", windows: true);
-   *
-   * // file://server/share/file
-   * new Uri.file(r"\\server\share\file", windows: true);
-   * ```
-   *
-   * If the path passed is not a legal file path [ArgumentError] is thrown.
-   */
-  factory Uri.file(String path, {bool windows}) {
-    windows = (windows == null) ? Uri._isWindows : windows;
-    return windows ? _makeWindowsFileUrl(path, false)
-                   : _makeFileUri(path, false);
-  }
-
-  /**
-   * Like [Uri.file] except that a non-empty URI path ends in a slash.
-   *
-   * If [path] is not empty, and it doesn't end in a directory separator,
-   * then a slash is added to the returned URI's path.
-   * In all other cases, the result is the same as returned by `Uri.file`.
-   */
-  factory Uri.directory(String path, {bool windows}) {
-    windows = (windows == null) ? Uri._isWindows : windows;
-    return windows ? _makeWindowsFileUrl(path, true)
-                   : _makeFileUri(path, true);
-  }
-
-  /**
-   * Creates a `data:` URI containing the [content] string.
-   *
-   * Converts the content to a bytes using [encoding] or the charset specified
-   * in [parameters] (defaulting to US-ASCII if not specified or unrecognized),
-   * then encodes the bytes into the resulting data URI.
+   * Converts the content to a bytes using [encoding] or the charset specified
+   * in [parameters] (defaulting to US-ASCII if not specified or unrecognized),
+   * then encodes the bytes into the resulting data URI.
    *
    * Defaults to encoding using percent-encoding (any non-ASCII or non-URI-valid
    * bytes is replaced by a percent encoding). If [base64] is true, the bytes
@@ -827,1599 +334,2340 @@ class Uri {
   }
 
   /**
-   * Returns the natural base URI for the current platform.
+   * The scheme component of the URI.
    *
-   * When running in a browser this is the current URL (from
-   * `window.location.href`).
+   * Returns the empty string if there is no scheme component.
    *
-   * When not running in a browser this is the file URI referencing
-   * the current working directory.
+   * A URI scheme is case insensitive.
+   * The returned scheme is canonicalized to lowercase letters.
    */
-  external static Uri get base;
+  String get scheme;
 
-  external static bool get _isWindows;
+  /**
+   * Returns the authority component.
+   *
+   * The authority is formatted from the [userInfo], [host] and [port]
+   * parts.
+   *
+   * Returns the empty string if there is no authority component.
+   */
+  String get authority;
 
-  static _checkNonWindowsPathReservedCharacters(List<String> segments,
-                                                bool argumentError) {
-    segments.forEach((segment) {
-      if (segment.contains("/")) {
-        if (argumentError) {
-          throw new ArgumentError("Illegal path character $segment");
-        } else {
-          throw new UnsupportedError("Illegal path character $segment");
-        }
-      }
-    });
-  }
+  /**
+   * Returns the user info part of the authority component.
+   *
+   * Returns the empty string if there is no user info in the
+   * authority component.
+   */
+  String get userInfo;
 
-  static _checkWindowsPathReservedCharacters(List<String> segments,
-                                             bool argumentError,
-                                             [int firstSegment = 0]) {
-    for (var segment in segments.skip(firstSegment)) {
-      if (segment.contains(new RegExp(r'["*/:<>?\\|]'))) {
-        if (argumentError) {
-          throw new ArgumentError("Illegal character in path");
-        } else {
-          throw new UnsupportedError("Illegal character in path");
-        }
-      }
-    }
-  }
+  /**
+   * Returns the host part of the authority component.
+   *
+   * Returns the empty string if there is no authority component and
+   * hence no host.
+   *
+   * If the host is an IP version 6 address, the surrounding `[` and `]` is
+   * removed.
+   *
+   * The host string is case-insensitive.
+   * The returned host name is canonicalized to lower-case
+   * with upper-case percent-escapes.
+   */
+  String get host;
 
-  static _checkWindowsDriveLetter(int charCode, bool argumentError) {
-    if ((_UPPER_CASE_A <= charCode && charCode <= _UPPER_CASE_Z) ||
-        (_LOWER_CASE_A <= charCode && charCode <= _LOWER_CASE_Z)) {
-      return;
-    }
-    if (argumentError) {
-      throw new ArgumentError("Illegal drive letter " +
-                              new String.fromCharCode(charCode));
-    } else {
-      throw new UnsupportedError("Illegal drive letter " +
-                              new String.fromCharCode(charCode));
-    }
-  }
+  /**
+   * Returns the port part of the authority component.
+   *
+   * Returns the defualt port if there is no port number in the authority
+   * component. That's 80 for http, 443 for https, and 0 for everything else.
+   */
+  int get port;
 
-  static _makeFileUri(String path, bool slashTerminated) {
-    const String sep = "/";
-    var segments = path.split(sep);
-    if (slashTerminated &&
-        segments.isNotEmpty &&
-        segments.last.isNotEmpty) {
-      segments.add("");  // Extra separator at end.
-    }
-    if (path.startsWith(sep)) {
-      // Absolute file:// URI.
-      return new Uri(scheme: "file", pathSegments: segments);
-    } else {
-      // Relative URI.
-      return new Uri(pathSegments: segments);
-    }
-  }
+  /**
+   * Returns the path component.
+   *
+   * The returned path is encoded. To get direct access to the decoded
+   * path use [pathSegments].
+   *
+   * Returns the empty string if there is no path component.
+   */
+  String get path;
 
-  static _makeWindowsFileUrl(String path, bool slashTerminated) {
-    if (path.startsWith(r"\\?\")) {
-      if (path.startsWith(r"UNC\", 4)) {
-        path = path.replaceRange(0, 7, r'\');
-      } else {
-        path = path.substring(4);
-        if (path.length < 3 ||
-            path.codeUnitAt(1) != _COLON ||
-            path.codeUnitAt(2) != _BACKSLASH) {
-          throw new ArgumentError(
-              r"Windows paths with \\?\ prefix must be absolute");
-        }
+  /**
+   * Returns the query component. The returned query is encoded. To get
+   * direct access to the decoded query use [queryParameters].
+   *
+   * Returns the empty string if there is no query component.
+   */
+  String get query;
+
+  /**
+   * Returns the fragment identifier component.
+   *
+   * Returns the empty string if there is no fragment identifier
+   * component.
+   */
+  String get fragment;
+
+  /**
+   * Returns the URI path split into its segments. Each of the segments in the
+   * returned list have been decoded. If the path is empty the empty list will
+   * be returned. A leading slash `/` does not affect the segments returned.
+   *
+   * The returned list is unmodifiable and will throw [UnsupportedError] on any
+   * calls that would mutate it.
+   */
+  List<String> get pathSegments;
+
+  /**
+   * Returns the URI query split into a map according to the rules
+   * specified for FORM post in the [HTML 4.01 specification section
+   * 17.13.4](http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4 "HTML 4.01 section 17.13.4").
+   * Each key and value in the returned map has been decoded.
+   * If there is no query the empty map is returned.
+   *
+   * Keys in the query string that have no value are mapped to the
+   * empty string.
+   * If a key occurs more than once in the query string, it is mapped to
+   * an arbitrary choice of possible value.
+   * The [queryParametersAll] getter can provide a map
+   * that maps keys to all of their values.
+   *
+   * The returned map is unmodifiable.
+   */
+  Map<String, String> get queryParameters;
+
+  /**
+   * Returns the URI query split into a map according to the rules
+   * specified for FORM post in the [HTML 4.01 specification section
+   * 17.13.4](http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4 "HTML 4.01 section 17.13.4").
+   * Each key and value in the returned map has been decoded. If there is no
+   * query the empty map is returned.
+   *
+   * Keys are mapped to lists of their values. If a key occurs only once,
+   * its value is a singleton list. If a key occurs with no value, the
+   * empty string is used as the value for that occurrence.
+   *
+   * The returned map and the lists it contains are unmodifiable.
+   */
+  Map<String, List<String>> get queryParametersAll;
+
+  /**
+   * Returns whether the URI is absolute.
+   *
+   * A URI is an absolute URI in the sense of RFC 3986 if it has a scheme
+   * and no fragment.
+   */
+  bool get isAbsolute;
+
+  /**
+   * Returns whether the URI has a [scheme] component.
+   */
+  bool get hasScheme => scheme.isNotEmpty;
+
+  /**
+   * Returns whether the URI has an [authority] component.
+   */
+  bool get hasAuthority;
+
+  /**
+   * Returns whether the URI has an explicit port.
+   *
+   * If the port number is the default port number
+   * (zero for unrecognized schemes, with http (80) and https (443) being
+   * recognized),
+   * then the port is made implicit and omitted from the URI.
+   */
+  bool get hasPort;
+
+  /**
+   * Returns whether the URI has a query part.
+   */
+  bool get hasQuery;
+
+  /**
+   * Returns whether the URI has a fragment part.
+   */
+  bool get hasFragment;
+
+  /**
+   * Returns whether the URI has an empty path.
+   */
+  bool get hasEmptyPath;
+
+  /**
+   * Returns whether the URI has an absolute path (starting with '/').
+   */
+  bool get hasAbsolutePath;
+
+  /**
+   * Returns the origin of the URI in the form scheme://host:port for the
+   * schemes http and https.
+   *
+   * It is an error if the scheme is not "http" or "https".
+   *
+   * See: http://www.w3.org/TR/2011/WD-html5-20110405/origin-0.html#origin
+   */
+  String get origin;
+
+  /**
+   * Returns the file path from a file URI.
+   *
+   * The returned path has either Windows or non-Windows
+   * semantics.
+   *
+   * For non-Windows semantics the slash ("/") is used to separate
+   * path segments.
+   *
+   * For Windows semantics the backslash ("\\") separator is used to
+   * separate path segments.
+   *
+   * If the URI is absolute the path starts with a path separator
+   * unless Windows semantics is used and the first path segment is a
+   * drive letter. When Windows semantics is used a host component in
+   * the uri in interpreted as a file server and a UNC path is
+   * returned.
+   *
+   * The default for whether to use Windows or non-Windows semantics
+   * determined from the platform Dart is running on. When running in
+   * the standalone VM this is detected by the VM based on the
+   * operating system. When running in a browser non-Windows semantics
+   * is always used.
+   *
+   * To override the automatic detection of which semantics to use pass
+   * a value for [windows]. Passing `true` will use Windows
+   * semantics and passing `false` will use non-Windows semantics.
+   *
+   * If the URI ends with a slash (i.e. the last path component is
+   * empty) the returned file path will also end with a slash.
+   *
+   * With Windows semantics URIs starting with a drive letter cannot
+   * be relative to the current drive on the designated drive. That is
+   * for the URI `file:///c:abc` calling `toFilePath` will throw as a
+   * path segment cannot contain colon on Windows.
+   *
+   * Examples using non-Windows semantics (resulting of calling
+   * toFilePath in comment):
+   *
+   *     Uri.parse("xxx/yyy");  // xxx/yyy
+   *     Uri.parse("xxx/yyy/");  // xxx/yyy/
+   *     Uri.parse("file:///xxx/yyy");  // /xxx/yyy
+   *     Uri.parse("file:///xxx/yyy/");  // /xxx/yyy/
+   *     Uri.parse("file:///C:");  // /C:
+   *     Uri.parse("file:///C:a");  // /C:a
+   *
+   * Examples using Windows semantics (resulting URI in comment):
+   *
+   *     Uri.parse("xxx/yyy");  // xxx\yyy
+   *     Uri.parse("xxx/yyy/");  // xxx\yyy\
+   *     Uri.parse("file:///xxx/yyy");  // \xxx\yyy
+   *     Uri.parse("file:///xxx/yyy/");  // \xxx\yyy/
+   *     Uri.parse("file:///C:/xxx/yyy");  // C:\xxx\yyy
+   *     Uri.parse("file:C:xxx/yyy");  // Throws as a path segment
+   *                                   // cannot contain colon on Windows.
+   *     Uri.parse("file://server/share/file");  // \\server\share\file
+   *
+   * If the URI is not a file URI calling this throws
+   * [UnsupportedError].
+   *
+   * If the URI cannot be converted to a file path calling this throws
+   * [UnsupportedError].
+   */
+  // TODO(lrn): Deprecate and move functionality to File class or similar.
+  // The core libraries should not worry about the platform.
+  String toFilePath({bool windows});
+
+  /**
+   * Access the structure of a `data:` URI.
+   *
+   * Returns a [UriData] object for `data:` URIs and `null` for all other
+   * URIs.
+   * The [UriData] object can be used to access the media type and data
+   * of a `data:` URI.
+   */
+  UriData get data;
+
+  /// Returns a hash code computed as `toString().hashCode`.
+  ///
+  /// This guarantees that URIs with the same normalized
+  int get hashCode;
+
+  /// A URI is equal to another URI with the same normalized representation.
+  bool operator==(Object other);
+
+  /// Returns the normalized string representation of the URI.
+  String toString();
+
+  /**
+   * Returns a new `Uri` based on this one, but with some parts replaced.
+   *
+   * This method takes the same parameters as the [new Uri] constructor,
+   * and they have the same meaning.
+   *
+   * At most one of [path] and [pathSegments] must be provided.
+   * Likewise, at most one of [query] and [queryParameters] must be provided.
+   *
+   * Each part that is not provided will default to the corresponding
+   * value from this `Uri` instead.
+   *
+   * This method is different from [Uri.resolve] which overrides in a
+   * hierarchial manner,
+   * and can instead replace each part of a `Uri` individually.
+   *
+   * Example:
+   *
+   *     Uri uri1 = Uri.parse("a://b@c:4/d/e?f#g");
+   *     Uri uri2 = uri1.replace(scheme: "A", path: "D/E/E", fragment: "G");
+   *     print(uri2);  // prints "A://b@c:4/D/E/E/?f#G"
+   *
+   * This method acts similarly to using the `new Uri` constructor with
+   * some of the arguments taken from this `Uri` . Example:
+   *
+   *     Uri uri3 = new Uri(
+   *         scheme: "A",
+   *         userInfo: uri1.userInfo,
+   *         host: uri1.host,
+   *         port: uri1.port,
+   *         path: "D/E/E",
+   *         query: uri1.query,
+   *         fragment: "G");
+   *     print(uri3);  // prints "A://b@c:4/D/E/E/?f#G"
+   *     print(uri2 == uri3);  // prints true.
+   *
+   * Using this method can be seen as a shorthand for the `Uri` constructor
+   * call above, but may also be slightly faster because the parts taken
+   * from this `Uri` need not be checked for validity again.
+   */
+  Uri replace({String scheme,
+               String userInfo,
+               String host,
+               int port,
+               String path,
+               Iterable<String> pathSegments,
+               String query,
+               Map<String, dynamic/*String|Iterable<String>*/> queryParameters,
+               String fragment});
+
+  /**
+   * Returns a `Uri` that differs from this only in not having a fragment.
+   *
+   * If this `Uri` does not have a fragment, it is itself returned.
+   */
+  Uri removeFragment();
+
+  /**
+   * Resolve [reference] as an URI relative to `this`.
+   *
+   * First turn [reference] into a URI using [Uri.parse]. Then resolve the
+   * resulting URI relative to `this`.
+   *
+   * Returns the resolved URI.
+   *
+   * See [resolveUri] for details.
+   */
+  Uri resolve(String reference);
+
+  /**
+   * Resolve [reference] as an URI relative to `this`.
+   *
+   * Returns the resolved URI.
+   *
+   * The algorithm "Transform Reference" for resolving a reference is described
+   * in [RFC-3986 Section 5](http://tools.ietf.org/html/rfc3986#section-5 "RFC-1123").
+   *
+   * Updated to handle the case where the base URI is just a relative path -
+   * that is: when it has no scheme or authority and the path does not start
+   * with a slash.
+   * In that case, the paths are combined without removing leading "..", and
+   * an empty path is not converted to "/".
+   */
+  Uri resolveUri(Uri reference);
+
+  /**
+   * Returns a URI where the path has been normalized.
+   *
+   * A normalized path does not contain `.` segments or non-leading `..`
+   * segments.
+   * Only a relative path with no scheme or authority may contain
+   * leading `..` segments,
+   * a path that starts with `/` will also drop any leading `..` segments.
+   *
+   * This uses the same normalization strategy as `new Uri().resolve(this)`.
+   *
+   * Does not change any part of the URI except the path.
+   *
+   * The default implementation of `Uri` always normalizes paths, so calling
+   * this function has no effect.
+   */
+  Uri normalizePath();
+
+  /**
+   * Creates a new `Uri` object by parsing a URI string.
+   *
+   * If [start] and [end] are provided, only the substring from `start`
+   * to `end` is parsed as a URI.
+   *
+   * If the string is not valid as a URI or URI reference,
+   * a [FormatException] is thrown.
+   */
+  static Uri parse(String uri, [int start = 0, int end]) {
+    // This parsing will not validate percent-encoding, IPv6, etc.
+    // When done splitting into parts, it will call, e.g., [_makeFragment]
+    // to do the final parsing.
+    //
+    // Important parts of the RFC 3986 used here:
+    // URI           = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
+    //
+    // hier-part     = "//" authority path-abempty
+    //               / path-absolute
+    //               / path-rootless
+    //               / path-empty
+    //
+    // URI-reference = URI / relative-ref
+    //
+    // absolute-URI  = scheme ":" hier-part [ "?" query ]
+    //
+    // relative-ref  = relative-part [ "?" query ] [ "#" fragment ]
+    //
+    // relative-part = "//" authority path-abempty
+    //               / path-absolute
+    //               / path-noscheme
+    //               / path-empty
+    //
+    // scheme        = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
+    //
+    // authority     = [ userinfo "@" ] host [ ":" port ]
+    // userinfo      = *( unreserved / pct-encoded / sub-delims / ":" )
+    // host          = IP-literal / IPv4address / reg-name
+    // port          = *DIGIT
+    // reg-name      = *( unreserved / pct-encoded / sub-delims )
+    //
+    // path          = path-abempty    ; begins with "/" or is empty
+    //               / path-absolute   ; begins with "/" but not "//"
+    //               / path-noscheme   ; begins with a non-colon segment
+    //               / path-rootless   ; begins with a segment
+    //               / path-empty      ; zero characters
+    //
+    // path-abempty  = *( "/" segment )
+    // path-absolute = "/" [ segment-nz *( "/" segment ) ]
+    // path-noscheme = segment-nz-nc *( "/" segment )
+    // path-rootless = segment-nz *( "/" segment )
+    // path-empty    = 0<pchar>
+    //
+    // segment       = *pchar
+    // segment-nz    = 1*pchar
+    // segment-nz-nc = 1*( unreserved / pct-encoded / sub-delims / "@" )
+    //               ; non-zero-length segment without any colon ":"
+    //
+    // pchar         = unreserved / pct-encoded / sub-delims / ":" / "@"
+    //
+    // query         = *( pchar / "/" / "?" )
+    //
+    // fragment      = *( pchar / "/" / "?" )
+    end ??= uri.length;
+
+    // Special case data:URIs. Ignore case when testing.
+    if (end >= start + 5) {
+      int dataDelta = _startsWithData(uri, start);
+      if (dataDelta == 0) {
+        // The case is right.
+        if (start > 0 || end < uri.length) uri = uri.substring(start, end);
+        return UriData._parse(uri, 5, null).uri;
+      } else if (dataDelta == 0x20) {
+        return UriData._parse(uri.substring(start + 5, end), 0, null).uri;
       }
-    } else {
-      path = path.replaceAll("/", r'\');
+      // Otherwise the URI doesn't start with "data:" or any case variant of it.
     }
-    const String sep = r'\';
-    if (path.length > 1 && path.codeUnitAt(1) == _COLON) {
-      _checkWindowsDriveLetter(path.codeUnitAt(0), true);
-      if (path.length == 2 || path.codeUnitAt(2) != _BACKSLASH) {
-        throw new ArgumentError(
-            "Windows paths with drive letter must be absolute");
-      }
-      // Absolute file://C:/ URI.
-      var pathSegments = path.split(sep);
-      if (slashTerminated &&
-          pathSegments.last.isNotEmpty) {
-        pathSegments.add("");  // Extra separator at end.
-      }
-      _checkWindowsPathReservedCharacters(pathSegments, true, 1);
-      return new Uri(scheme: "file", pathSegments: pathSegments);
+
+    // The following index-normalization belongs with the scanning, but is
+    // easier to do here because we already have extracted variables from the
+    // indices list.
+    var indices = new List<int>(8);//new List<int>.filled(8, start - 1);
+
+    // Set default values for each position.
+    // The value will either be correct in some cases where it isn't set
+    // by the scanner, or it is clearly recognizable as an unset value.
+    indices
+      ..[0] = 0
+      ..[_schemeEndIndex] = start - 1
+      ..[_hostStartIndex] = start - 1
+      ..[_notSimpleIndex] = start - 1
+      ..[_portStartIndex] = start
+      ..[_pathStartIndex] = start
+      ..[_queryStartIndex] = end
+      ..[_fragmentStartIndex] = end;
+    var state = _scan(uri, start, end, _uriStart, indices);
+    // Some states that should be non-simple, but the URI ended early.
+    // Paths that end at a ".." must be normalized to end in "../".
+    if (state >= _nonSimpleEndStates) {
+      indices[_notSimpleIndex] = end;
+    }
+    int schemeEnd = indices[_schemeEndIndex];
+    if (schemeEnd >= start) {
+      // Rescan the scheme part now that we know it's not a path.
+      state = _scan(uri, start, schemeEnd, _schemeStart, indices);
+      if (state == _schemeStart) {
+        // Empty scheme.
+        indices[_notSimpleIndex] = schemeEnd;
+      }
     }
-
-    if (path.startsWith(sep)) {
-      if (path.startsWith(sep, 1)) {
-        // Absolute file:// URI with host.
-        int pathStart = path.indexOf(r'\', 2);
-        String hostPart =
-            (pathStart < 0) ? path.substring(2) : path.substring(2, pathStart);
-        String pathPart =
-            (pathStart < 0) ? "" : path.substring(pathStart + 1);
-        var pathSegments = pathPart.split(sep);
-        _checkWindowsPathReservedCharacters(pathSegments, true);
-        if (slashTerminated &&
-            pathSegments.last.isNotEmpty) {
-          pathSegments.add("");  // Extra separator at end.
-        }
-        return new Uri(
-            scheme: "file", host: hostPart, pathSegments: pathSegments);
+    // The returned positions are limited by the scanners ability to write only
+    // one position per character, and only the current position.
+    // Scanning from left to right, we only know whether something is a scheme
+    // or a path when we see a `:` or `/`, and likewise we only know if the first
+    // `/` is part of the path or is leading an authority component when we see
+    // the next character.
+
+    int hostStart     = indices[_hostStartIndex] + 1;
+    int portStart     = indices[_portStartIndex];
+    int pathStart     = indices[_pathStartIndex];
+    int queryStart    = indices[_queryStartIndex];
+    int fragmentStart = indices[_fragmentStartIndex];
+
+    // We may discover scheme while handling special cases.
+    String scheme;
+
+    // Derive some positions that weren't set to normalize the indices.
+    // If pathStart isn't set (it's before scheme end or host start), then
+    // the path is empty.
+    if (fragmentStart < queryStart) queryStart = fragmentStart;
+    if (pathStart < hostStart || pathStart <= schemeEnd) {
+      pathStart = queryStart;
+    }
+    // If there is an authority with no port, set the port position
+    // to be at the end of the authority (equal to pathStart).
+    // This also handles a ":" in a user-info component incorrectly setting
+    // the port start position.
+    if (portStart < hostStart) portStart = pathStart;
+
+    assert(hostStart == start || schemeEnd <= hostStart);
+    assert(hostStart <= portStart);
+    assert(schemeEnd <= pathStart);
+    assert(portStart <= pathStart);
+    assert(pathStart <= queryStart);
+    assert(queryStart <= fragmentStart);
+
+    bool isSimple = indices[_notSimpleIndex] < start;
+
+    if (isSimple) {
+      // Check/do normalizations that weren't detected by the scanner.
+      // This includes removal of empty port or userInfo,
+      // or scheme specific port and path normalizations.
+      if (hostStart > schemeEnd + 3) {
+        // Always be non-simple if URI contains user-info.
+        // The scanner doesn't set the not-simple position in this case because
+        // it's setting the host-start position instead.
+        isSimple = false;
+      } else if (portStart > start && portStart + 1 == pathStart) {
+        // If the port is empty, it should be omitted.
+        // Pathological case, don't bother correcting it.
+        isSimple = false;
+      } else if (queryStart < end &&
+                 (queryStart == pathStart + 2 &&
+                  uri.startsWith("..", pathStart)) ||
+                 (queryStart > pathStart + 2 &&
+                  uri.startsWith("/..", queryStart - 3))) {
+        // The path ends in a ".." segment. This should be normalized to "../".
+        // We didn't detect this while scanning because a query or fragment was
+        // detected at the same time (which is why we only need to check this
+        // if there is something after the path).
+        isSimple = false;
       } else {
-        // Absolute file:// URI.
-        var pathSegments = path.split(sep);
-        if (slashTerminated &&
-            pathSegments.last.isNotEmpty) {
-          pathSegments.add("");  // Extra separator at end.
+        // There are a few scheme-based normalizations that
+        // the scanner couldn't check.
+        // That means that the input is very close to simple, so just do
+        // the normalizations.
+        if (schemeEnd == start + 4) {
+          // Do scheme based normalizations for file, http.
+          if (uri.startsWith("file", start)) {
+            scheme = "file";
+            if (hostStart <= start) {
+              // File URIs should have an authority.
+              // Paths after an authority should be absolute.
+              String schemeAuth = "file://";
+              int delta = 2;
+              if (!uri.startsWith("/", pathStart)) {
+                schemeAuth = "file:///";
+                delta = 3;
+              }
+              uri = schemeAuth + uri.substring(pathStart, end);
+              schemeEnd -= start;
+              hostStart = 7;
+              portStart = 7;
+              pathStart = 7;
+              queryStart += delta - start;
+              fragmentStart += delta - start;
+              start = 0;
+              end = uri.length;
+            } else if (pathStart == queryStart) {
+              // Uri has authority and empty path. Add "/" as path.
+              if (start == 0 && end == uri.length) {
+                uri = uri.replaceRange(pathStart, queryStart, "/");
+                queryStart += 1;
+                fragmentStart += 1;
+                end += 1;
+              } else {
+                uri = "${uri.substring(start, pathStart)}/"
+                      "${uri.substring(queryStart, end)}";
+                schemeEnd -= start;
+                hostStart -= start;
+                portStart -= start;
+                pathStart -= start;
+                queryStart += 1 - start;
+                fragmentStart += 1 - start;
+                start = 0;
+                end = uri.length;
+              }
+            }
+          } else if (uri.startsWith("http", start)) {
+            scheme = "http";
+            // HTTP URIs should not have an explicit port of 80.
+            if (portStart > start && portStart + 3 == pathStart &&
+                uri.startsWith("80", portStart + 1)) {
+              if (start == 0 && end == uri.length) {
+                uri = uri.replaceRange(portStart, pathStart, "");
+                pathStart -= 3;
+                queryStart -= 3;
+                fragmentStart -= 3;
+                end -= 3;
+              } else {
+                uri = uri.substring(start, portStart) +
+                      uri.substring(pathStart, end);
+                schemeEnd -= start;
+                hostStart -= start;
+                portStart -= start;
+                pathStart -= 3 + start;
+                queryStart -= 3 + start;
+                fragmentStart -= 3 + start;
+                start = 0;
+                end = uri.length;
+              }
+            }
+          }
+        } else if (schemeEnd == start + 5 && uri.startsWith("https", start)) {
+          scheme = "https";
+          // HTTPS URIs should not have an explicit port of 443.
+          if (portStart > start && portStart + 4 == pathStart &&
+              uri.startsWith("443", portStart + 1)) {
+            if (start == 0 && end == uri.length) {
+              uri = uri.replaceRange(portStart, pathStart, "");
+              pathStart -= 4;
+              queryStart -= 4;
+              fragmentStart -= 4;
+              end -= 3;
+            } else {
+              uri = uri.substring(start, portStart) +
+                    uri.substring(pathStart, end);
+              schemeEnd -= start;
+              hostStart -= start;
+              portStart -= start;
+              pathStart -= 4 + start;
+              queryStart -= 4 + start;
+              fragmentStart -= 4 + start;
+              start = 0;
+              end = uri.length;
+            }
+          }
         }
-        _checkWindowsPathReservedCharacters(pathSegments, true);
-        return new Uri(scheme: "file", pathSegments: pathSegments);
       }
-    } else {
-      // Relative URI.
-      var pathSegments = path.split(sep);
-      _checkWindowsPathReservedCharacters(pathSegments, true);
-      if (slashTerminated &&
-          pathSegments.isNotEmpty &&
-          pathSegments.last.isNotEmpty) {
-        pathSegments.add("");  // Extra separator at end.
+    }
+
+    if (isSimple) {
+      if (start > 0 || end < uri.length) {
+        uri = uri.substring(start, end);
+        schemeEnd -= start;
+        hostStart -= start;
+        portStart -= start;
+        pathStart -= start;
+        queryStart -= start;
+        fragmentStart -= start;
       }
-      return new Uri(pathSegments: pathSegments);
+      return new _SimpleUri(uri, schemeEnd, hostStart, portStart, pathStart,
+                            queryStart, fragmentStart, scheme);
+
     }
+
+    return new _Uri.notSimple(uri, start, end, schemeEnd, hostStart, portStart,
+                              pathStart, queryStart, fragmentStart, scheme);
   }
 
   /**
-   * Returns a new `Uri` based on this one, but with some parts replaced.
-   *
-   * This method takes the same parameters as the [new Uri] constructor,
-   * and they have the same meaning.
+   * Encode the string [component] using percent-encoding to make it
+   * safe for literal use as a URI component.
    *
-   * At most one of [path] and [pathSegments] must be provided.
-   * Likewise, at most one of [query] and [queryParameters] must be provided.
+   * All characters except uppercase and lowercase letters, digits and
+   * the characters `-_.!~*'()` are percent-encoded. This is the
+   * set of characters specified in RFC 2396 and the which is
+   * specified for the encodeUriComponent in ECMA-262 version 5.1.
    *
-   * Each part that is not provided will default to the corresponding
-   * value from this `Uri` instead.
+   * When manually encoding path segments or query components remember
+   * to encode each part separately before building the path or query
+   * string.
    *
-   * This method is different from [Uri.resolve] which overrides in a
-   * hierarchial manner,
-   * and can instead replace each part of a `Uri` individually.
+   * For encoding the query part consider using
+   * [encodeQueryComponent].
    *
-   * Example:
+   * To avoid the need for explicitly encoding use the [pathSegments]
+   * and [queryParameters] optional named arguments when constructing
+   * a [Uri].
+   */
+  static String encodeComponent(String component) {
+    return _Uri._uriEncode(_Uri._unreserved2396Table, component, UTF8, false);
+  }
+
+  /**
+   * Encode the string [component] according to the HTML 4.01 rules
+   * for encoding the posting of a HTML form as a query string
+   * component.
    *
-   *     Uri uri1 = Uri.parse("a://b@c:4/d/e?f#g");
-   *     Uri uri2 = uri1.replace(scheme: "A", path: "D/E/E", fragment: "G");
-   *     print(uri2);  // prints "A://b@c:4/D/E/E/?f#G"
+   * Encode the string [component] according to the HTML 4.01 rules
+   * for encoding the posting of a HTML form as a query string
+   * component.
+
+   * The component is first encoded to bytes using [encoding].
+   * The default is to use [UTF8] encoding, which preserves all
+   * the characters that don't need encoding.
+
+   * Then the resulting bytes are "percent-encoded". This transforms
+   * spaces (U+0020) to a plus sign ('+') and all bytes that are not
+   * the ASCII decimal digits, letters or one of '-._~' are written as
+   * a percent sign '%' followed by the two-digit hexadecimal
+   * representation of the byte.
+
+   * Note that the set of characters which are percent-encoded is a
+   * superset of what HTML 4.01 requires, since it refers to RFC 1738
+   * for reserved characters.
    *
-   * This method acts similarly to using the `new Uri` constructor with
-   * some of the arguments taken from this `Uri` . Example:
+   * When manually encoding query components remember to encode each
+   * part separately before building the query string.
    *
-   *     Uri uri3 = new Uri(
-   *         scheme: "A",
-   *         userInfo: uri1.userInfo,
-   *         host: uri1.host,
-   *         port: uri1.port,
-   *         path: "D/E/E",
-   *         query: uri1.query,
-   *         fragment: "G");
-   *     print(uri3);  // prints "A://b@c:4/D/E/E/?f#G"
-   *     print(uri2 == uri3);  // prints true.
+   * To avoid the need for explicitly encoding the query use the
+   * [queryParameters] optional named arguments when constructing a
+   * [Uri].
    *
-   * Using this method can be seen as a shorthand for the `Uri` constructor
-   * call above, but may also be slightly faster because the parts taken
-   * from this `Uri` need not be checked for validity again.
+   * See http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.2 for more
+   * details.
    */
-  Uri replace({String scheme,
-               String userInfo,
-               String host,
-               int port,
-               String path,
-               Iterable<String> pathSegments,
-               String query,
-               Map<String, dynamic/*String|Iterable<String>*/> queryParameters,
-               String fragment}) {
-    // Set to true if the scheme has (potentially) changed.
-    // In that case, the default port may also have changed and we need
-    // to check even the existing port.
-    bool schemeChanged = false;
-    if (scheme != null) {
-      scheme = _makeScheme(scheme, 0, scheme.length);
-      schemeChanged = true;
-    } else {
-      scheme = this.scheme;
-    }
-    bool isFile = (scheme == "file");
-    if (userInfo != null) {
-      userInfo = _makeUserInfo(userInfo, 0, userInfo.length);
-    } else {
-      userInfo = this._userInfo;
-    }
-    if (port != null) {
-      port = _makePort(port, scheme);
-    } else {
-      port = this._port;
-      if (schemeChanged) {
-        // The default port might have changed.
-        port = _makePort(port, scheme);
-      }
-    }
-    if (host != null) {
-      host = _makeHost(host, 0, host.length, false);
-    } else if (this.hasAuthority) {
-      host = this._host;
-    } else if (userInfo.isNotEmpty || port != null || isFile) {
-      host = "";
-    }
-
-    bool hasAuthority = host != null;
-    if (path != null || pathSegments != null) {
-      path = _makePath(path, 0, _stringOrNullLength(path), pathSegments,
-                       scheme, hasAuthority);
-    } else {
-      path = this._path;
-      if ((isFile || (hasAuthority && !path.isEmpty)) &&
-          !path.startsWith('/')) {
-        path = "/" + path;
-      }
-    }
-
-    if (query != null || queryParameters != null) {
-      query = _makeQuery(query, 0, _stringOrNullLength(query), queryParameters);
-    } else {
-      query = this._query;
-    }
-
-    if (fragment != null) {
-      fragment = _makeFragment(fragment, 0, fragment.length);
-    } else {
-      fragment = this._fragment;
-    }
+  static String encodeQueryComponent(String component,
+                                     {Encoding encoding: UTF8}) {
+    return _Uri._uriEncode(_Uri._unreservedTable, component, encoding, true);
+  }
 
-    return new Uri._internal(
-        scheme, userInfo, host, port, path, query, fragment);
+  /**
+   * Decodes the percent-encoding in [encodedComponent].
+   *
+   * Note that decoding a URI component might change its meaning as
+   * some of the decoded characters could be characters with are
+   * delimiters for a given URI componene type. Always split a URI
+   * component using the delimiters for the component before decoding
+   * the individual parts.
+   *
+   * For handling the [path] and [query] components consider using
+   * [pathSegments] and [queryParameters] to get the separated and
+   * decoded component.
+   */
+  static String decodeComponent(String encodedComponent) {
+    return _Uri._uriDecode(encodedComponent, 0, encodedComponent.length,
+                           UTF8, false);
   }
 
   /**
-   * Returns a `Uri` that differs from this only in not having a fragment.
+   * Decodes the percent-encoding in [encodedComponent], converting
+   * pluses to spaces.
    *
-   * If this `Uri` does not have a fragment, it is itself returned.
+   * It will create a byte-list of the decoded characters, and then use
+   * [encoding] to decode the byte-list to a String. The default encoding is
+   * UTF-8.
    */
-  Uri removeFragment() {
-    if (!this.hasFragment) return this;
-    return new Uri._internal(scheme, _userInfo, _host, _port,
-                             _path, _query, null);
+  static String decodeQueryComponent(
+      String encodedComponent,
+      {Encoding encoding: UTF8}) {
+    return _Uri._uriDecode(encodedComponent, 0, encodedComponent.length,
+                           encoding, true);
   }
 
   /**
-   * Returns the URI path split into its segments. Each of the segments in the
-   * returned list have been decoded. If the path is empty the empty list will
-   * be returned. A leading slash `/` does not affect the segments returned.
+   * Encode the string [uri] using percent-encoding to make it
+   * safe for literal use as a full URI.
    *
-   * The returned list is unmodifiable and will throw [UnsupportedError] on any
-   * calls that would mutate it.
+   * All characters except uppercase and lowercase letters, digits and
+   * the characters `!#$&'()*+,-./:;=?@_~` are percent-encoded. This
+   * is the set of characters specified in in ECMA-262 version 5.1 for
+   * the encodeURI function .
    */
-  List<String> get pathSegments {
-    var result = _pathSegments;
-    if (result != null) return result;
+  static String encodeFull(String uri) {
+    return _Uri._uriEncode(_Uri._encodeFullTable, uri, UTF8, false);
+  }
 
-    var pathToSplit = path;
-    if (pathToSplit.isNotEmpty && pathToSplit.codeUnitAt(0) == _SLASH) {
-      pathToSplit = pathToSplit.substring(1);
-    }
-    result = (pathToSplit == "")
-        ? const<String>[]
-        : new List<String>.unmodifiable(
-              pathToSplit.split("/").map(Uri.decodeComponent));
-    _pathSegments = result;
-    return result;
+  /**
+   * Decodes the percent-encoding in [uri].
+   *
+   * Note that decoding a full URI might change its meaning as some of
+   * the decoded characters could be reserved characters. In most
+   * cases an encoded URI should be parsed into components using
+   * [Uri.parse] before decoding the separate components.
+   */
+  static String decodeFull(String uri) {
+    return _Uri._uriDecode(uri, 0, uri.length, UTF8, false);
   }
 
   /**
-   * Returns the URI query split into a map according to the rules
+   * Returns the [query] split into a map according to the rules
    * specified for FORM post in the [HTML 4.01 specification section
    * 17.13.4](http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4 "HTML 4.01 section 17.13.4").
-   * Each key and value in the returned map has been decoded.
-   * If there is no query the empty map is returned.
+   * Each key and value in the returned map has been decoded. If the [query]
+   * is the empty string an empty map is returned.
    *
    * Keys in the query string that have no value are mapped to the
    * empty string.
-   * If a key occurs more than once in the query string, it is mapped to
-   * an arbitrary choice of possible value.
-   * The [queryParametersAll] getter can provide a map
-   * that maps keys to all of their values.
    *
-   * The returned map is unmodifiable.
+   * Each query component will be decoded using [encoding]. The default encoding
+   * is UTF-8.
    */
-  Map<String, String> get queryParameters {
-    if (_queryParameters == null) {
-      _queryParameters =
-          new UnmodifiableMapView<String, String>(splitQueryString(query));
-    }
-    return _queryParameters;
+  static Map<String, String> splitQueryString(String query,
+                                              {Encoding encoding: UTF8}) {
+    return query.split("&").fold({}, (map, element) {
+      int index = element.indexOf("=");
+      if (index == -1) {
+        if (element != "") {
+          map[decodeQueryComponent(element, encoding: encoding)] = "";
+        }
+      } else if (index != 0) {
+        var key = element.substring(0, index);
+        var value = element.substring(index + 1);
+        map[decodeQueryComponent(key, encoding: encoding)] =
+            decodeQueryComponent(value, encoding: encoding);
+      }
+      return map;
+    });
   }
 
+
   /**
-   * Returns the URI query split into a map according to the rules
-   * specified for FORM post in the [HTML 4.01 specification section
-   * 17.13.4](http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4 "HTML 4.01 section 17.13.4").
-   * Each key and value in the returned map has been decoded. If there is no
-   * query the empty map is returned.
-   *
-   * Keys are mapped to lists of their values. If a key occurs only once,
-   * its value is a singleton list. If a key occurs with no value, the
-   * empty string is used as the value for that occurrence.
+   * Parse the [host] as an IP version 4 (IPv4) address, returning the address
+   * as a list of 4 bytes in network byte order (big endian).
    *
-   * The returned map and the lists it contains are unmodifiable.
+   * Throws a [FormatException] if [host] is not a valid IPv4 address
+   * representation.
    */
-  Map<String, List<String>> get queryParametersAll {
-    if (_queryParameterLists == null) {
-      Map queryParameterLists = _splitQueryStringAll(query);
-      for (var key in queryParameterLists.keys) {
-        queryParameterLists[key] =
-            new List<String>.unmodifiable(queryParameterLists[key]);
+  static List<int> parseIPv4Address(String host) =>
+       _parseIPv4Address(host, 0, host.length);
+
+  /// Implementation of [parseIPv4Address] that can work on a substring.
+  static List<int> _parseIPv4Address(String host, int start, int end) {
+    void error(String msg, int position) {
+      throw new FormatException('Illegal IPv4 address, $msg', host, position);
+    }
+
+    var result = new Uint8List(4);
+    int partIndex = 0;
+    int partStart = start;
+    for (int i = start; i < end; i++) {
+      int char = host.codeUnitAt(i);
+      if (char != _DOT) {
+        if (char ^ 0x30 > 9) {
+          // Fail on a non-digit character.
+          error("invalid character", i);
+        }
+      } else {
+        if (partIndex == 3) {
+          error('IPv4 address should contain exactly 4 parts', i);
+        }
+        int part = int.parse(host.substring(partStart, i));
+        if (part > 255) {
+          error("each part must be in the range 0..255", partStart);
+        }
+        result[partIndex++] = part;
+        partStart = i + 1;
       }
-      _queryParameterLists =
-          new Map<String, List<String>>.unmodifiable(queryParameterLists);
     }
-    return _queryParameterLists;
+
+    if (partIndex != 3) {
+      error('IPv4 address should contain exactly 4 parts', end);
+    }
+
+    int part = int.parse(host.substring(partStart, end));
+    if (part > 255) {
+      error("each part must be in the range 0..255", partStart);
+    }
+    result[partIndex] = part;
+
+    return result;
   }
 
   /**
-   * Returns a URI where the path has been normalized.
-   *
-   * A normalized path does not contain `.` segments or non-leading `..`
-   * segments.
-   * Only a relative path with no scheme or authority may contain
-   * leading `..` segments,
-   * a path that starts with `/` will also drop any leading `..` segments.
+   * Parse the [host] as an IP version 6 (IPv6) address, returning the address
+   * as a list of 16 bytes in network byte order (big endian).
    *
-   * This uses the same normalization strategy as `new Uri().resolve(this)`.
+   * Throws a [FormatException] if [host] is not a valid IPv6 address
+   * representation.
    *
-   * Does not change any part of the URI except the path.
+   * Acts on the substring from [start] to [end]. If [end] is omitted, it
+   * defaults ot the end of the string.
    *
-   * The default implementation of `Uri` always normalizes paths, so calling
-   * this function has no effect.
+   * Some examples of IPv6 addresses:
+   *  * ::1
+   *  * FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
+   *  * 3ffe:2a00:100:7031::1
+   *  * ::FFFF:129.144.52.38
+   *  * 2010:836B:4179::836B:4179
    */
-  Uri normalizePath() {
-    String path = _normalizePath(_path, scheme, hasAuthority);
-    if (identical(path, _path)) return this;
-    return this.replace(path: path);
-  }
+  static List<int> parseIPv6Address(String host, [int start = 0, int end]) {
+    if (end == null) end = host.length;
+    // An IPv6 address consists of exactly 8 parts of 1-4 hex digits, separated
+    // by `:`'s, with the following exceptions:
+    //
+    //  - One (and only one) wildcard (`::`) may be present, representing a fill
+    //    of 0's. The IPv6 `::` is thus 16 bytes of `0`.
+    //  - The last two parts may be replaced by an IPv4 "dotted-quad" address.
 
-  static int _makePort(int port, String scheme) {
-    // Perform scheme specific normalization.
-    if (port != null && port == _defaultPort(scheme)) return null;
-    return port;
-  }
+    // Helper function for reporting a badly formatted IPv6 address.
+    void error(String msg, [position]) {
+      throw new FormatException('Illegal IPv6 address, $msg', host, position);
+    }
 
-  /**
-   * Check and normalize a host name.
-   *
-   * If the host name starts and ends with '[' and ']', it is considered an
-   * IPv6 address. If [strictIPv6] is false, the address is also considered
-   * an IPv6 address if it contains any ':' character.
-   *
-   * If it is not an IPv6 address, it is case- and escape-normalized.
-   * This escapes all characters not valid in a reg-name,
-   * and converts all non-escape upper-case letters to lower-case.
-   */
-  static String _makeHost(String host, int start, int end, bool strictIPv6) {
-    // TODO(lrn): Should we normalize IPv6 addresses according to RFC 5952?
-    if (host == null) return null;
-    if (start == end) return "";
-    // Host is an IPv6 address if it starts with '[' or contains a colon.
-    if (host.codeUnitAt(start) == _LEFT_BRACKET) {
-      if (host.codeUnitAt(end - 1) != _RIGHT_BRACKET) {
-        _fail(host, start, 'Missing end `]` to match `[` in host');
+    // Parse a hex block.
+    int parseHex(int start, int end) {
+      if (end - start > 4) {
+        error('an IPv6 part can only contain a maximum of 4 hex digits', start);
       }
-      parseIPv6Address(host, start + 1, end - 1);
-      // RFC 5952 requires hex digits to be lower case.
-      return host.substring(start, end).toLowerCase();
-    }
-    if (!strictIPv6) {
-      // TODO(lrn): skip if too short to be a valid IPv6 address?
-      for (int i = start; i < end; i++) {
-        if (host.codeUnitAt(i) == _COLON) {
-          parseIPv6Address(host, start, end);
-          return '[$host]';
-        }
+      int value = int.parse(host.substring(start, end), radix: 16);
+      if (value < 0 || value > 0xFFFF) {
+        error('each part must be in the range of `0x0..0xFFFF`', start);
       }
+      return value;
     }
-    return _normalizeRegName(host, start, end);
-  }
-
-  static bool _isRegNameChar(int char) {
-    return char < 127 && (_regNameTable[char >> 4] & (1 << (char & 0xf))) != 0;
-  }
-
-  /**
-   * Validates and does case- and percent-encoding normalization.
-   *
-   * The [host] must be an RFC3986 "reg-name". It is converted
-   * to lower case, and percent escapes are converted to either
-   * lower case unreserved characters or upper case escapes.
-   */
-  static String _normalizeRegName(String host, int start, int end) {
-    StringBuffer buffer;
-    int sectionStart = start;
-    int index = start;
-    // Whether all characters between sectionStart and index are normalized,
-    bool isNormalized = true;
 
-    while (index < end) {
-      int char = host.codeUnitAt(index);
-      if (char == _PERCENT) {
-        // The _regNameTable contains "%", so we check that first.
-        String replacement = _normalizeEscape(host, index, true);
-        if (replacement == null && isNormalized) {
-          index += 3;
-          continue;
-        }
-        if (buffer == null) buffer = new StringBuffer();
-        String slice = host.substring(sectionStart, index);
-        if (!isNormalized) slice = slice.toLowerCase();
-        buffer.write(slice);
-        int sourceLength = 3;
-        if (replacement == null) {
-          replacement = host.substring(index, index + 3);
-        } else if (replacement == "%") {
-          replacement = "%25";
-          sourceLength = 1;
-        }
-        buffer.write(replacement);
-        index += sourceLength;
-        sectionStart = index;
-        isNormalized = true;
-      } else if (_isRegNameChar(char)) {
-        if (isNormalized && _UPPER_CASE_A <= char && _UPPER_CASE_Z >= char) {
-          // Put initial slice in buffer and continue in non-normalized mode
-          if (buffer == null) buffer = new StringBuffer();
-          if (sectionStart < index) {
-            buffer.write(host.substring(sectionStart, index));
-            sectionStart = index;
+    if (host.length < 2) error('address is too short');
+    List<int> parts = [];
+    bool wildcardSeen = false;
+    // Set if seeing a ".", suggesting that there is an IPv4 address.
+    bool seenDot = false;
+    int partStart = start;
+    // Parse all parts, except a potential last one.
+    for (int i = start; i < end; i++) {
+      int char = host.codeUnitAt(i);
+      if (char == _COLON) {
+        if (i == start) {
+          // If we see a `:` in the beginning, expect wildcard.
+          i++;
+          if (host.codeUnitAt(i) != _COLON) {
+            error('invalid start colon.', i);
           }
-          isNormalized = false;
+          partStart = i;
         }
-        index++;
-      } else if (_isGeneralDelimiter(char)) {
-        _fail(host, index, "Invalid character");
-      } else {
-        int sourceLength = 1;
-        if ((char & 0xFC00) == 0xD800 && (index + 1) < end) {
-          int tail = host.codeUnitAt(index + 1);
-          if ((tail & 0xFC00) == 0xDC00) {
-            char = 0x10000 | ((char & 0x3ff) << 10) | (tail & 0x3ff);
-            sourceLength = 2;
+        if (i == partStart) {
+          // Wildcard. We only allow one.
+          if (wildcardSeen) {
+            error('only one wildcard `::` is allowed', i);
           }
+          wildcardSeen = true;
+          parts.add(-1);
+        } else {
+          // Found a single colon. Parse [partStart..i] as a hex entry.
+          parts.add(parseHex(partStart, i));
         }
-        if (buffer == null) buffer = new StringBuffer();
-        String slice = host.substring(sectionStart, index);
-        if (!isNormalized) slice = slice.toLowerCase();
-        buffer.write(slice);
-        buffer.write(_escapeChar(char));
-        index += sourceLength;
-        sectionStart = index;
+        partStart = i + 1;
+      } else if (char == _DOT) {
+        seenDot = true;
+      }
+    }
+    if (parts.length == 0) error('too few parts');
+    bool atEnd = (partStart == end);
+    bool isLastWildcard = (parts.last == -1);
+    if (atEnd && !isLastWildcard) {
+      error('expected a part after last `:`', end);
+    }
+    if (!atEnd) {
+      if (!seenDot) {
+        parts.add(parseHex(partStart, end));
+      } else {
+        List<int> last = _parseIPv4Address(host, partStart, end);
+        parts.add(last[0] << 8 | last[1]);
+        parts.add(last[2] << 8 | last[3]);
+      }
+    }
+    if (wildcardSeen) {
+      if (parts.length > 7) {
+        error('an address with a wildcard must have less than 7 parts');
       }
+    } else if (parts.length != 8) {
+      error('an address without a wildcard must contain exactly 8 parts');
     }
-    if (buffer == null) return host.substring(start, end);
-    if (sectionStart < end) {
-      String slice = host.substring(sectionStart, end);
-      if (!isNormalized) slice = slice.toLowerCase();
-      buffer.write(slice);
+    List<int> bytes = new Uint8List(16);
+    for (int i = 0, index = 0; i < parts.length; i++) {
+      int value = parts[i];
+      if (value == -1) {
+        int wildCardLength = 9 - parts.length;
+        for (int j = 0; j < wildCardLength; j++) {
+          bytes[index] = 0;
+          bytes[index + 1] = 0;
+          index += 2;
+        }
+      } else {
+        bytes[index] = value >> 8;
+        bytes[index + 1] = value & 0xff;
+        index += 2;
+      }
     }
-    return buffer.toString();
+    return bytes;
   }
+}
+
+class _Uri implements Uri {
+  // We represent the missing scheme as an empty string.
+  // A valid scheme cannot be empty.
+  final String scheme;
 
   /**
-   * Validates scheme characters and does case-normalization.
+   * The user-info part of the authority.
    *
-   * Schemes are converted to lower case. They cannot contain escapes.
+   * Does not distinguish between an empty user-info and an absent one.
+   * The value is always non-null.
+   * Is considered absent if [_host] is `null`.
    */
-  static String _makeScheme(String scheme, int start, int end) {
-    if (start == end) return "";
-    final int firstCodeUnit = scheme.codeUnitAt(start);
-    if (!_isAlphabeticCharacter(firstCodeUnit)) {
-      _fail(scheme, start, "Scheme not starting with alphabetic character");
+  final String _userInfo;
+
+  /**
+   * The host name of the URI.
+   *
+   * Set to `null` if there is no authority in the URI.
+   * The host name is the only mandatory part of an authority, so we use
+   * it to mark whether an authority part was present or not.
+   */
+  final String _host;
+
+  /**
+   * The port number part of the authority.
+   *
+   * The port. Set to null if there is no port. Normalized to null if
+   * the port is the default port for the scheme.
+   */
+  int _port;
+
+  /**
+   * The path of the URI.
+   *
+   * Always non-null.
+   */
+  String _path;
+
+  // The query content, or null if there is no query.
+  final String _query;
+
+  // The fragment content, or null if there is no fragment.
+  final String _fragment;
+
+  /**
+   * Cache the computed return value of [pathSegements].
+   */
+  List<String> _pathSegments;
+
+  /**
+   * Cache of the full normalized text representation of the URI.
+   */
+  String _text;
+
+  /**
+   * Cache of the hashCode of [_text].
+   *
+   * Is null until computed.
+   */
+  int _hashCodeCache;
+
+  /**
+   * Cache the computed return value of [queryParameters].
+   */
+  Map<String, String> _queryParameters;
+  Map<String, List<String>> _queryParameterLists;
+
+  /// Internal non-verifying constructor. Only call with validated arguments.
+  _Uri._internal(this.scheme,
+                 this._userInfo,
+                 this._host,
+                 this._port,
+                 this._path,
+                 this._query,
+                 this._fragment);
+
+  /// Create a [_Uri] from parts of [uri].
+  ///
+  /// The parameters specify the start/end of particular components of the URI.
+  /// The [scheme] may contain a string representing a normalized scheme
+  /// component if one has already been discovered.
+  factory _Uri.notSimple(String uri, int start, int end, int schemeEnd,
+                        int hostStart, int portStart, int pathStart,
+                        int queryStart, int fragmentStart, String scheme) {
+    if (scheme == null) {
+      scheme = "";
+      if (schemeEnd > start) {
+        scheme = _makeScheme(uri, start, schemeEnd);
+      } else if (schemeEnd == start) {
+        _fail(uri, start, "Invalid empty scheme");
+      }
     }
-    bool containsUpperCase = false;
-    for (int i = start; i < end; i++) {
-      final int codeUnit = scheme.codeUnitAt(i);
-      if (!_isSchemeCharacter(codeUnit)) {
-        _fail(scheme, i, "Illegal scheme character");
+    String userInfo = "";
+    String host;
+    int port;
+    if (hostStart > start) {
+      int userInfoStart = schemeEnd + 3;
+      if (userInfoStart < hostStart) {
+        userInfo = _makeUserInfo(uri, userInfoStart, hostStart - 1);
       }
-      if (_UPPER_CASE_A <= codeUnit && codeUnit <= _UPPER_CASE_Z) {
-        containsUpperCase = true;
+      host = _makeHost(uri, hostStart, portStart, false);
+      if (portStart + 1 < pathStart) {
+        // Should throw because invalid.
+        port = int.parse(uri.substring(portStart + 1, pathStart), onError: (_) {
+          throw new FormatException("Invalid port", uri, portStart + 1);
+        });
+        port = _makePort(port, scheme);
       }
     }
-    scheme = scheme.substring(start, end);
-    if (containsUpperCase) scheme = scheme.toLowerCase();
-    return scheme;
-  }
-
-  static String _makeUserInfo(String userInfo, int start, int end) {
-    if (userInfo == null) return "";
-    return _normalize(userInfo, start, end, _userinfoTable);
+    String path = _makePath(uri, pathStart, queryStart, null,
+                            scheme, host != null);
+    String query;
+    if (queryStart < fragmentStart) {
+      query = _makeQuery(uri, queryStart + 1, fragmentStart, null);
+    }
+    String fragment;
+    if (fragmentStart < end) {
+      fragment = _makeFragment(uri, fragmentStart + 1, end);
+    }
+    return new _Uri._internal(scheme,
+                              userInfo,
+                              host,
+                              port,
+                              path,
+                              query,
+                              fragment);
   }
 
-  static String _makePath(String path, int start, int end,
-                          Iterable<String> pathSegments,
-                          String scheme,
-                          bool hasAuthority) {
+  /// Implementation of [Uri.Uri].
+  factory _Uri({String scheme,
+                String userInfo,
+                String host,
+                int port,
+                String path,
+                Iterable<String> pathSegments,
+                String query,
+                Map<String, dynamic/*String|Iterable<String>*/> queryParameters,
+                String fragment}) {
+    scheme = _makeScheme(scheme, 0, _stringOrNullLength(scheme));
+    userInfo = _makeUserInfo(userInfo, 0, _stringOrNullLength(userInfo));
+    host = _makeHost(host, 0, _stringOrNullLength(host), false);
+    // Special case this constructor for backwards compatibility.
+    if (query == "") query = null;
+    query = _makeQuery(query, 0, _stringOrNullLength(query), queryParameters);
+    fragment = _makeFragment(fragment, 0, _stringOrNullLength(fragment));
+    port = _makePort(port, scheme);
     bool isFile = (scheme == "file");
-    bool ensureLeadingSlash = isFile || hasAuthority;
-    if (path == null && pathSegments == null) return isFile ? "/" : "";
-    if (path != null && pathSegments != null) {
-      throw new ArgumentError('Both path and pathSegments specified');
+    if (host == null &&
+        (userInfo.isNotEmpty || port != null || isFile)) {
+      host = "";
     }
-    var result;
-    if (path != null) {
-      result = _normalize(path, start, end, _pathCharOrSlashTable);
+    bool hasAuthority = (host != null);
+    path = _makePath(path, 0, _stringOrNullLength(path), pathSegments,
+                     scheme, hasAuthority);
+    if (scheme.isEmpty && host == null && !path.startsWith('/')) {
+      path = _normalizeRelativePath(path);
     } else {
-      result = pathSegments.map((s) =>
-          _uriEncode(_pathCharTable, s, UTF8, false)).join("/");
+      path = _removeDotSegments(path);
     }
-    if (result.isEmpty) {
-      if (isFile) return "/";
-    } else if (ensureLeadingSlash && !result.startsWith('/')) {
-      result = "/" + result;
+    return new _Uri._internal(scheme, userInfo, host, port,
+                              path, query, fragment);
+  }
+
+  /// Implementation of [Uri.http].
+  factory _Uri.http(String authority,
+                    String unencodedPath,
+                    [Map<String, String> queryParameters]) {
+    return _makeHttpUri("http", authority, unencodedPath, queryParameters);
+  }
+
+  /// Implementation of [Uri.https].
+  factory _Uri.https(String authority,
+                     String unencodedPath,
+                     [Map<String, String> queryParameters]) {
+    return _makeHttpUri("https", authority, unencodedPath, queryParameters);
+  }
+
+  String get authority {
+    if (!hasAuthority) return "";
+    var sb = new StringBuffer();
+    _writeAuthority(sb);
+    return sb.toString();
+  }
+
+  String get userInfo => _userInfo;
+
+  String get host {
+    if (_host == null) return "";
+    if (_host.startsWith('[')) {
+      return _host.substring(1, _host.length - 1);
     }
-    result = _normalizePath(result, scheme, hasAuthority);
-    return result;
+    return _host;
   }
 
-  /// Performs path normalization (remove dot segments) on a path.
-  ///
-  /// If the URI has neither scheme nor authority, it's considered a
-  /// "pure path" and normalization won't remove leading ".." segments.
-  /// Otherwise it follows the RFC 3986 "remove dot segments" algorithm.
-  static String _normalizePath(String path, String scheme, bool hasAuthority) {
-    if (scheme.isEmpty && !hasAuthority && !path.startsWith('/')) {
-      return _normalizeRelativePath(path);
+  int get port {
+    if (_port == null) return _defaultPort(scheme);
+    return _port;
+  }
+
+  // The default port for the scheme of this Uri.
+  static int _defaultPort(String scheme) {
+    if (scheme == "http") return 80;
+    if (scheme == "https") return 443;
+    return 0;
+  }
+
+  String get path => _path;
+
+  String get query => _query ?? "";
+
+  String get fragment => _fragment ?? "";
+
+  // Report a parse failure.
+  static void _fail(String uri, int index, String message) {
+    throw new FormatException(message, uri, index);
+  }
+
+  static Uri _makeHttpUri(String scheme,
+                          String authority,
+                          String unencodedPath,
+                          Map<String, String> queryParameters) {
+    var userInfo = "";
+    var host = null;
+    var port = null;
+
+    if (authority != null && authority.isNotEmpty) {
+      var hostStart = 0;
+      // Split off the user info.
+      bool hasUserInfo = false;
+      for (int i = 0; i < authority.length; i++) {
+        const int atSign = 0x40;
+        if (authority.codeUnitAt(i) == atSign) {
+          hasUserInfo = true;
+          userInfo = authority.substring(0, i);
+          hostStart = i + 1;
+          break;
+        }
+      }
+      var hostEnd = hostStart;
+      if (hostStart < authority.length &&
+          authority.codeUnitAt(hostStart) == _LEFT_BRACKET) {
+        // IPv6 host.
+        for (; hostEnd < authority.length; hostEnd++) {
+          if (authority.codeUnitAt(hostEnd) == _RIGHT_BRACKET) break;
+        }
+        if (hostEnd == authority.length) {
+          throw new FormatException("Invalid IPv6 host entry.",
+                                    authority, hostStart);
+        }
+        Uri.parseIPv6Address(authority, hostStart + 1, hostEnd);
+        hostEnd++;  // Skip the closing bracket.
+        if (hostEnd != authority.length &&
+            authority.codeUnitAt(hostEnd) != _COLON) {
+          throw new FormatException("Invalid end of authority",
+                                    authority, hostEnd);
+        }
+      }
+      // Split host and port.
+      bool hasPort = false;
+      for (; hostEnd < authority.length; hostEnd++) {
+        if (authority.codeUnitAt(hostEnd) == _COLON) {
+          var portString = authority.substring(hostEnd + 1);
+          // We allow the empty port - falling back to initial value.
+          if (portString.isNotEmpty) port = int.parse(portString);
+          break;
+        }
+      }
+      host = authority.substring(hostStart, hostEnd);
     }
-    return _removeDotSegments(path);
+    return new Uri(scheme: scheme,
+                   userInfo: userInfo,
+                   host: host,
+                   port: port,
+                   pathSegments: unencodedPath.split("/"),
+                   queryParameters: queryParameters);
+  }
+
+  /// Implementation of [Uri.file].
+  factory _Uri.file(String path, {bool windows}) {
+    windows = (windows == null) ? _Uri._isWindows : windows;
+    return windows ? _makeWindowsFileUrl(path, false)
+                   : _makeFileUri(path, false);
   }
 
-  static String _makeQuery(
-      String query, int start, int end,
-      Map<String, dynamic/*String|Iterable<String>*/> queryParameters) {
-    if (query == null && queryParameters == null) return null;
-    if (query != null && queryParameters != null) {
-      throw new ArgumentError('Both query and queryParameters specified');
-    }
-    if (query != null) return _normalize(query, start, end, _queryCharTable);
+  /// Implementation of [Uri.directory].
+  factory _Uri.directory(String path, {bool windows}) {
+    windows = (windows == null) ? _Uri._isWindows : windows;
+    return windows ? _makeWindowsFileUrl(path, true)
+                   : _makeFileUri(path, true);
+  }
 
-    var result = new StringBuffer();
-    var separator = "";
 
-    void writeParameter(String key, String value) {
-      result.write(separator);
-      separator = "&";
-      result.write(Uri.encodeQueryComponent(key));
-      if (value != null && value.isNotEmpty) {
-        result.write("=");
-        result.write(Uri.encodeQueryComponent(value));
-      }
-    }
+  /// Used internally in path-related constructors.
+  external static bool get _isWindows;
 
-    queryParameters.forEach((key, value) {
-      if (value == null || value is String) {
-        writeParameter(key, value);
-      } else {
-        Iterable values = value;
-        for (String value in values) {
-          writeParameter(key, value);
+  static _checkNonWindowsPathReservedCharacters(List<String> segments,
+                                                bool argumentError) {
+    segments.forEach((segment) {
+      if (segment.contains("/")) {
+        if (argumentError) {
+          throw new ArgumentError("Illegal path character $segment");
+        } else {
+          throw new UnsupportedError("Illegal path character $segment");
         }
       }
     });
-    return result.toString();
   }
 
-  static String _makeFragment(String fragment, int start, int end) {
-    if (fragment == null) return null;
-    return _normalize(fragment, start, end, _queryCharTable);
+  static _checkWindowsPathReservedCharacters(List<String> segments,
+                                             bool argumentError,
+                                             [int firstSegment = 0]) {
+    for (var segment in segments.skip(firstSegment)) {
+      if (segment.contains(new RegExp(r'["*/:<>?\\|]'))) {
+        if (argumentError) {
+          throw new ArgumentError("Illegal character in path");
+        } else {
+          throw new UnsupportedError("Illegal character in path");
+        }
+      }
+    }
   }
 
-  static int _stringOrNullLength(String s) => (s == null) ? 0 : s.length;
+  static _checkWindowsDriveLetter(int charCode, bool argumentError) {
+    if ((_UPPER_CASE_A <= charCode && charCode <= _UPPER_CASE_Z) ||
+        (_LOWER_CASE_A <= charCode && charCode <= _LOWER_CASE_Z)) {
+      return;
+    }
+    if (argumentError) {
+      throw new ArgumentError("Illegal drive letter " +
+                              new String.fromCharCode(charCode));
+    } else {
+      throw new UnsupportedError("Illegal drive letter " +
+                              new String.fromCharCode(charCode));
+    }
+  }
 
-  /**
-   * Performs RFC 3986 Percent-Encoding Normalization.
-   *
-   * Returns a replacement string that should be replace the original escape.
-   * Returns null if no replacement is necessary because the escape is
-   * not for an unreserved character and is already non-lower-case.
-   *
-   * Returns "%" if the escape is invalid (not two valid hex digits following
-   * the percent sign). The calling code should replace the percent
-   * sign with "%25", but leave the following two characters unmodified.
-   *
-   * If [lowerCase] is true, a single character returned is always lower case,
-   */
-  static String _normalizeEscape(String source, int index, bool lowerCase) {
-    assert(source.codeUnitAt(index) == _PERCENT);
-    if (index + 2 >= source.length) {
-      return "%";  // Marks the escape as invalid.
+  static _makeFileUri(String path, bool slashTerminated) {
+    const String sep = "/";
+    var segments = path.split(sep);
+    if (slashTerminated &&
+        segments.isNotEmpty &&
+        segments.last.isNotEmpty) {
+      segments.add("");  // Extra separator at end.
     }
-    int firstDigit = source.codeUnitAt(index + 1);
-    int secondDigit = source.codeUnitAt(index + 2);
-    int firstDigitValue = _parseHexDigit(firstDigit);
-    int secondDigitValue = _parseHexDigit(secondDigit);
-    if (firstDigitValue < 0 || secondDigitValue < 0) {
-      return "%";  // Marks the escape as invalid.
+    if (path.startsWith(sep)) {
+      // Absolute file:// URI.
+      return new Uri(scheme: "file", pathSegments: segments);
+    } else {
+      // Relative URI.
+      return new Uri(pathSegments: segments);
     }
-    int value = firstDigitValue * 16 + secondDigitValue;
-    if (_isUnreservedChar(value)) {
-      if (lowerCase && _UPPER_CASE_A <= value && _UPPER_CASE_Z >= value) {
-        value |= 0x20;
+  }
+
+  static _makeWindowsFileUrl(String path, bool slashTerminated) {
+    if (path.startsWith(r"\\?\")) {
+      if (path.startsWith(r"UNC\", 4)) {
+        path = path.replaceRange(0, 7, r'\');
+      } else {
+        path = path.substring(4);
+        if (path.length < 3 ||
+            path.codeUnitAt(1) != _COLON ||
+            path.codeUnitAt(2) != _BACKSLASH) {
+          throw new ArgumentError(
+              r"Windows paths with \\?\ prefix must be absolute");
+        }
       }
-      return new String.fromCharCode(value);
+    } else {
+      path = path.replaceAll("/", r'\');
     }
-    if (firstDigit >= _LOWER_CASE_A || secondDigit >= _LOWER_CASE_A) {
-      // Either digit is lower case.
-      return source.substring(index, index + 3).toUpperCase();
+    const String sep = r'\';
+    if (path.length > 1 && path.codeUnitAt(1) == _COLON) {
+      _checkWindowsDriveLetter(path.codeUnitAt(0), true);
+      if (path.length == 2 || path.codeUnitAt(2) != _BACKSLASH) {
+        throw new ArgumentError(
+            "Windows paths with drive letter must be absolute");
+      }
+      // Absolute file://C:/ URI.
+      var pathSegments = path.split(sep);
+      if (slashTerminated &&
+          pathSegments.last.isNotEmpty) {
+        pathSegments.add("");  // Extra separator at end.
+      }
+      _checkWindowsPathReservedCharacters(pathSegments, true, 1);
+      return new Uri(scheme: "file", pathSegments: pathSegments);
     }
-    // Escape is retained, and is already non-lower case, so return null to
-    // represent "no replacement necessary".
-    return null;
-  }
 
-  // Converts a UTF-16 code-unit to its value as a hex digit.
-  // Returns -1 for non-hex digits.
-  static int _parseHexDigit(int char) {
-    int digit = char ^ Uri._ZERO;
-    if (digit <= 9) return digit;
-    int lowerCase = char | 0x20;
-    if (Uri._LOWER_CASE_A <= lowerCase && lowerCase <= _LOWER_CASE_F) {
-      return lowerCase - (_LOWER_CASE_A - 10);
+    if (path.startsWith(sep)) {
+      if (path.startsWith(sep, 1)) {
+        // Absolute file:// URI with host.
+        int pathStart = path.indexOf(r'\', 2);
+        String hostPart =
+            (pathStart < 0) ? path.substring(2) : path.substring(2, pathStart);
+        String pathPart =
+            (pathStart < 0) ? "" : path.substring(pathStart + 1);
+        var pathSegments = pathPart.split(sep);
+        _checkWindowsPathReservedCharacters(pathSegments, true);
+        if (slashTerminated &&
+            pathSegments.last.isNotEmpty) {
+          pathSegments.add("");  // Extra separator at end.
+        }
+        return new Uri(
+            scheme: "file", host: hostPart, pathSegments: pathSegments);
+      } else {
+        // Absolute file:// URI.
+        var pathSegments = path.split(sep);
+        if (slashTerminated &&
+            pathSegments.last.isNotEmpty) {
+          pathSegments.add("");  // Extra separator at end.
+        }
+        _checkWindowsPathReservedCharacters(pathSegments, true);
+        return new Uri(scheme: "file", pathSegments: pathSegments);
+      }
+    } else {
+      // Relative URI.
+      var pathSegments = path.split(sep);
+      _checkWindowsPathReservedCharacters(pathSegments, true);
+      if (slashTerminated &&
+          pathSegments.isNotEmpty &&
+          pathSegments.last.isNotEmpty) {
+        pathSegments.add("");  // Extra separator at end.
+      }
+      return new Uri(pathSegments: pathSegments);
     }
-    return -1;
   }
 
-  static String _escapeChar(int char) {
-    assert(char <= 0x10ffff);  // It's a valid unicode code point.
-    List<int> codeUnits;
-    if (char < 0x80) {
-      // ASCII, a single percent encoded sequence.
-      codeUnits = new List(3);
-      codeUnits[0] = _PERCENT;
-      codeUnits[1] = _hexDigits.codeUnitAt(char >> 4);
-      codeUnits[2] = _hexDigits.codeUnitAt(char & 0xf);
+  Uri replace({String scheme,
+               String userInfo,
+               String host,
+               int port,
+               String path,
+               Iterable<String> pathSegments,
+               String query,
+               Map<String, dynamic/*String|Iterable<String>*/> queryParameters,
+               String fragment}) {
+    // Set to true if the scheme has (potentially) changed.
+    // In that case, the default port may also have changed and we need
+    // to check even the existing port.
+    bool schemeChanged = false;
+    if (scheme != null) {
+      scheme = _makeScheme(scheme, 0, scheme.length);
+      schemeChanged = (scheme != this.scheme);
     } else {
-      // Do UTF-8 encoding of character, then percent encode bytes.
-      int flag = 0xc0;  // The high-bit markers on the first byte of UTF-8.
-      int encodedBytes = 2;
-      if (char > 0x7ff) {
-        flag = 0xe0;
-        encodedBytes = 3;
-        if (char > 0xffff) {
-          encodedBytes = 4;
-          flag = 0xf0;
-        }
-      }
-      codeUnits = new List(3 * encodedBytes);
-      int index = 0;
-      while (--encodedBytes >= 0) {
-        int byte = ((char >> (6 * encodedBytes)) & 0x3f) | flag;
-        codeUnits[index] = _PERCENT;
-        codeUnits[index + 1] = _hexDigits.codeUnitAt(byte >> 4);
-        codeUnits[index + 2] = _hexDigits.codeUnitAt(byte & 0xf);
-        index += 3;
-        flag = 0x80;  // Following bytes have only high bit set.
+      scheme = this.scheme;
+    }
+    bool isFile = (scheme == "file");
+    if (userInfo != null) {
+      userInfo = _makeUserInfo(userInfo, 0, userInfo.length);
+    } else {
+      userInfo = this._userInfo;
+    }
+    if (port != null) {
+      port = _makePort(port, scheme);
+    } else {
+      port = this._port;
+      if (schemeChanged) {
+        // The default port might have changed.
+        port = _makePort(port, scheme);
       }
     }
-    return new String.fromCharCodes(codeUnits);
-  }
+    if (host != null) {
+      host = _makeHost(host, 0, host.length, false);
+    } else if (this.hasAuthority) {
+      host = this._host;
+    } else if (userInfo.isNotEmpty || port != null || isFile) {
+      host = "";
+    }
 
-  /**
-   * Runs through component checking that each character is valid and
-   * normalize percent escapes.
-   *
-   * Uses [charTable] to check if a non-`%` character is allowed.
-   * Each `%` character must be followed by two hex digits.
-   * If the hex-digits are lower case letters, they are converted to
-   * upper case.
-   */
-  static String _normalize(String component, int start, int end,
-                           List<int> charTable) {
-    StringBuffer buffer;
-    int sectionStart = start;
-    int index = start;
-    // Loop while characters are valid and escapes correct and upper-case.
-    while (index < end) {
-      int char = component.codeUnitAt(index);
-      if (char < 127 && (charTable[char >> 4] & (1 << (char & 0x0f))) != 0) {
-        index++;
-      } else {
-        String replacement;
-        int sourceLength;
-        if (char == _PERCENT) {
-          replacement = _normalizeEscape(component, index, false);
-          // Returns null if we should keep the existing escape.
-          if (replacement == null) {
-            index += 3;
-            continue;
-          }
-          // Returns "%" if we should escape the existing percent.
-          if ("%" == replacement) {
-            replacement = "%25";
-            sourceLength = 1;
-          } else {
-            sourceLength = 3;
-          }
-        } else if (_isGeneralDelimiter(char)) {
-          _fail(component, index, "Invalid character");
-        } else {
-          sourceLength = 1;
-          if ((char & 0xFC00) == 0xD800) {
-            // Possible lead surrogate.
-            if (index + 1 < end) {
-              int tail = component.codeUnitAt(index + 1);
-              if ((tail & 0xFC00) == 0xDC00) {
-                // Tail surrogat.
-                sourceLength = 2;
-                char = 0x10000 | ((char & 0x3ff) << 10) | (tail & 0x3ff);
-              }
-            }
-          }
-          replacement = _escapeChar(char);
-        }
-        if (buffer == null) buffer = new StringBuffer();
-        buffer.write(component.substring(sectionStart, index));
-        buffer.write(replacement);
-        index += sourceLength;
-        sectionStart = index;
+    bool hasAuthority = host != null;
+    if (path != null || pathSegments != null) {
+      path = _makePath(path, 0, _stringOrNullLength(path), pathSegments,
+                       scheme, hasAuthority);
+    } else {
+      path = this._path;
+      if ((isFile || (hasAuthority && !path.isEmpty)) &&
+          !path.startsWith('/')) {
+        path = "/" + path;
       }
     }
-    if (buffer == null) {
-      // Makes no copy if start == 0 and end == component.length.
-      return component.substring(start, end);
+
+    if (query != null || queryParameters != null) {
+      query = _makeQuery(query, 0, _stringOrNullLength(query), queryParameters);
+    } else {
+      query = this._query;
     }
-    if (sectionStart < end) {
-      buffer.write(component.substring(sectionStart, end));
+
+    if (fragment != null) {
+      fragment = _makeFragment(fragment, 0, fragment.length);
+    } else {
+      fragment = this._fragment;
     }
-    return buffer.toString();
-  }
 
-  static bool _isSchemeCharacter(int ch) {
-    return ch < 128 && ((_schemeTable[ch >> 4] & (1 << (ch & 0x0f))) != 0);
+    return new _Uri._internal(
+        scheme, userInfo, host, port, path, query, fragment);
   }
 
-  static bool _isGeneralDelimiter(int ch) {
-    return ch <= _RIGHT_BRACKET &&
-        ((_genDelimitersTable[ch >> 4] & (1 << (ch & 0x0f))) != 0);
+  Uri removeFragment() {
+    if (!this.hasFragment) return this;
+    return new _Uri._internal(scheme, _userInfo, _host, _port,
+                             _path, _query, null);
   }
 
-  /**
-   * Returns whether the URI is absolute.
-   */
-  bool get isAbsolute => scheme != "" && fragment == "";
+  List<String> get pathSegments {
+    var result = _pathSegments;
+    if (result != null) return result;
 
-  String _mergePaths(String base, String reference) {
-    // Optimize for the case: absolute base, reference beginning with "../".
-    int backCount = 0;
-    int refStart = 0;
-    // Count number of "../" at beginning of reference.
-    while (reference.startsWith("../", refStart)) {
-      refStart += 3;
-      backCount++;
+    var pathToSplit = path;
+    if (pathToSplit.isNotEmpty && pathToSplit.codeUnitAt(0) == _SLASH) {
+      pathToSplit = pathToSplit.substring(1);
     }
+    result = (pathToSplit == "")
+        ? const<String>[]
+        : new List<String>.unmodifiable(
+              pathToSplit.split("/").map(Uri.decodeComponent));
+    _pathSegments = result;
+    return result;
+  }
 
-    // Drop last segment - everything after last '/' of base.
-    int baseEnd = base.lastIndexOf('/');
-    // Drop extra segments for each leading "../" of reference.
-    while (baseEnd > 0 && backCount > 0) {
-      int newEnd = base.lastIndexOf('/', baseEnd - 1);
-      if (newEnd < 0) {
-        break;
-      }
-      int delta = baseEnd - newEnd;
-      // If we see a "." or ".." segment in base, stop here and let
-      // _removeDotSegments handle it.
-      if ((delta == 2 || delta == 3) &&
-          base.codeUnitAt(newEnd + 1) == _DOT &&
-          (delta == 2 || base.codeUnitAt(newEnd + 2) == _DOT)) {
-        break;
+  Map<String, String> get queryParameters {
+    if (_queryParameters == null) {
+      _queryParameters =
+          new UnmodifiableMapView<String, String>(Uri.splitQueryString(query));
+    }
+    return _queryParameters;
+  }
+
+  Map<String, List<String>> get queryParametersAll {
+    if (_queryParameterLists == null) {
+      Map queryParameterLists = _splitQueryStringAll(query);
+      for (var key in queryParameterLists.keys) {
+        queryParameterLists[key] =
+            new List<String>.unmodifiable(queryParameterLists[key]);
       }
-      baseEnd = newEnd;
-      backCount--;
+      _queryParameterLists =
+          new Map<String, List<String>>.unmodifiable(queryParameterLists);
     }
-    return base.replaceRange(baseEnd + 1, null,
-                             reference.substring(refStart - 3 * backCount));
+    return _queryParameterLists;
   }
 
-  /// Make a guess at whether a path contains a `..` or `.` segment.
-  ///
-  /// This is a primitive test that can cause false positives.
-  /// It's only used to avoid a more expensive operation in the case where
-  /// it's not necessary.
-  static bool _mayContainDotSegments(String path) {
-    if (path.startsWith('.')) return true;
-    int index = path.indexOf("/.");
-    return index != -1;
+  Uri normalizePath() {
+    String path = _normalizePath(_path, scheme, hasAuthority);
+    if (identical(path, _path)) return this;
+    return this.replace(path: path);
   }
 
-  /// Removes '.' and '..' segments from a path.
-  ///
-  /// Follows the RFC 2986 "remove dot segments" algorithm.
-  /// This algorithm is only used on paths of URIs with a scheme,
-  /// and it treats the path as if it is absolute (leading '..' are removed).
-  static String _removeDotSegments(String path) {
-    if (!_mayContainDotSegments(path)) return path;
-    assert(path.isNotEmpty);  // An empty path would not have dot segments.
-    List<String> output = [];
-    bool appendSlash = false;
-    for (String segment in path.split("/")) {
-      appendSlash = false;
-      if (segment == "..") {
-        if (output.isNotEmpty) {
-          output.removeLast();
-          if (output.isEmpty) {
-            output.add("");
-          }
-        }
-        appendSlash = true;
-      } else if ("." == segment) {
-        appendSlash = true;
-      } else {
-        output.add(segment);
-      }
-    }
-    if (appendSlash) output.add("");
-    return output.join("/");
+  static int _makePort(int port, String scheme) {
+    // Perform scheme specific normalization.
+    if (port != null && port == _defaultPort(scheme)) return null;
+    return port;
   }
 
-  /// Removes all `.` segments and any non-leading `..` segments.
-  ///
-  /// Removing the ".." from a "bar/foo/.." sequence results in "bar/"
-  /// (trailing "/"). If the entire path is removed (because it contains as
-  /// many ".." segments as real segments), the result is "./".
-  /// This is different from an empty string, which represents "no path",
-  /// when you resolve it against a base URI with a path with a non-empty
-  /// final segment.
-  static String _normalizeRelativePath(String path) {
-    assert(!path.startsWith('/'));  // Only get called for relative paths.
-    if (!_mayContainDotSegments(path)) return path;
-    assert(path.isNotEmpty);  // An empty path would not have dot segments.
-    List<String> output = [];
-    bool appendSlash = false;
-    for (String segment in path.split("/")) {
-      appendSlash = false;
-      if (".." == segment) {
-        if (!output.isEmpty && output.last != "..") {
-          output.removeLast();
-          appendSlash = true;
-        } else {
-          output.add("..");
-        }
-      } else if ("." == segment) {
-        appendSlash = true;
-      } else {
-        output.add(segment);
+  /**
+   * Check and normalize a host name.
+   *
+   * If the host name starts and ends with '[' and ']', it is considered an
+   * IPv6 address. If [strictIPv6] is false, the address is also considered
+   * an IPv6 address if it contains any ':' character.
+   *
+   * If it is not an IPv6 address, it is case- and escape-normalized.
+   * This escapes all characters not valid in a reg-name,
+   * and converts all non-escape upper-case letters to lower-case.
+   */
+  static String _makeHost(String host, int start, int end, bool strictIPv6) {
+    // TODO(lrn): Should we normalize IPv6 addresses according to RFC 5952?
+    if (host == null) return null;
+    if (start == end) return "";
+    // Host is an IPv6 address if it starts with '[' or contains a colon.
+    if (host.codeUnitAt(start) == _LEFT_BRACKET) {
+      if (host.codeUnitAt(end - 1) != _RIGHT_BRACKET) {
+        _fail(host, start, 'Missing end `]` to match `[` in host');
+      }
+      Uri.parseIPv6Address(host, start + 1, end - 1);
+      // RFC 5952 requires hex digits to be lower case.
+      return host.substring(start, end).toLowerCase();
+    }
+    if (!strictIPv6) {
+      // TODO(lrn): skip if too short to be a valid IPv6 address?
+      for (int i = start; i < end; i++) {
+        if (host.codeUnitAt(i) == _COLON) {
+          Uri.parseIPv6Address(host, start, end);
+          return '[$host]';
+        }
       }
     }
-    if (output.isEmpty || (output.length == 1 && output[0].isEmpty)) {
-      return "./";
-    }
-    if (appendSlash || output.last == '..') output.add("");
-    return output.join("/");
+    return _normalizeRegName(host, start, end);
   }
 
-  /**
-   * Resolve [reference] as an URI relative to `this`.
-   *
-   * First turn [reference] into a URI using [Uri.parse]. Then resolve the
-   * resulting URI relative to `this`.
-   *
-   * Returns the resolved URI.
-   *
-   * See [resolveUri] for details.
-   */
-  Uri resolve(String reference) {
-    return resolveUri(Uri.parse(reference));
+  static bool _isRegNameChar(int char) {
+    return char < 127 && (_regNameTable[char >> 4] & (1 << (char & 0xf))) != 0;
   }
 
   /**
-   * Resolve [reference] as an URI relative to `this`.
-   *
-   * Returns the resolved URI.
-   *
-   * The algorithm "Transform Reference" for resolving a reference is described
-   * in [RFC-3986 Section 5](http://tools.ietf.org/html/rfc3986#section-5 "RFC-1123").
+   * Validates and does case- and percent-encoding normalization.
    *
-   * Updated to handle the case where the base URI is just a relative path -
-   * that is: when it has no scheme or authority and the path does not start
-   * with a slash.
-   * In that case, the paths are combined without removing leading "..", and
-   * an empty path is not converted to "/".
+   * The [host] must be an RFC3986 "reg-name". It is converted
+   * to lower case, and percent escapes are converted to either
+   * lower case unreserved characters or upper case escapes.
    */
-  Uri resolveUri(Uri reference) {
-    // From RFC 3986.
-    String targetScheme;
-    String targetUserInfo = "";
-    String targetHost;
-    int targetPort;
-    String targetPath;
-    String targetQuery;
-    if (reference.scheme.isNotEmpty) {
-      targetScheme = reference.scheme;
-      if (reference.hasAuthority) {
-        targetUserInfo = reference.userInfo;
-        targetHost = reference.host;
-        targetPort = reference.hasPort ? reference.port : null;
-      }
-      targetPath = _removeDotSegments(reference.path);
-      if (reference.hasQuery) {
-        targetQuery = reference.query;
-      }
-    } else {
-      targetScheme = this.scheme;
-      if (reference.hasAuthority) {
-        targetUserInfo = reference.userInfo;
-        targetHost = reference.host;
-        targetPort = _makePort(reference.hasPort ? reference.port : null,
-                               targetScheme);
-        targetPath = _removeDotSegments(reference.path);
-        if (reference.hasQuery) targetQuery = reference.query;
-      } else {
-        targetUserInfo = this._userInfo;
-        targetHost = this._host;
-        targetPort = this._port;
-        if (reference.path == "") {
-          targetPath = this._path;
-          if (reference.hasQuery) {
-            targetQuery = reference.query;
-          } else {
-            targetQuery = this._query;
+  static String _normalizeRegName(String host, int start, int end) {
+    StringBuffer buffer;
+    int sectionStart = start;
+    int index = start;
+    // Whether all characters between sectionStart and index are normalized,
+    bool isNormalized = true;
+
+    while (index < end) {
+      int char = host.codeUnitAt(index);
+      if (char == _PERCENT) {
+        // The _regNameTable contains "%", so we check that first.
+        String replacement = _normalizeEscape(host, index, true);
+        if (replacement == null && isNormalized) {
+          index += 3;
+          continue;
+        }
+        if (buffer == null) buffer = new StringBuffer();
+        String slice = host.substring(sectionStart, index);
+        if (!isNormalized) slice = slice.toLowerCase();
+        buffer.write(slice);
+        int sourceLength = 3;
+        if (replacement == null) {
+          replacement = host.substring(index, index + 3);
+        } else if (replacement == "%") {
+          replacement = "%25";
+          sourceLength = 1;
+        }
+        buffer.write(replacement);
+        index += sourceLength;
+        sectionStart = index;
+        isNormalized = true;
+      } else if (_isRegNameChar(char)) {
+        if (isNormalized && _UPPER_CASE_A <= char && _UPPER_CASE_Z >= char) {
+          // Put initial slice in buffer and continue in non-normalized mode
+          if (buffer == null) buffer = new StringBuffer();
+          if (sectionStart < index) {
+            buffer.write(host.substring(sectionStart, index));
+            sectionStart = index;
           }
-        } else {
-          if (reference.hasAbsolutePath) {
-            targetPath = _removeDotSegments(reference.path);
-          } else {
-            // This is the RFC 3986 behavior for merging.
-            if (this.hasEmptyPath) {
-              if (!this.hasScheme && !this.hasAuthority) {
-                // Keep the path relative if no scheme or authority.
-                targetPath = reference.path;
-              } else {
-                // Add path normalization on top of RFC algorithm.
-                targetPath = _removeDotSegments("/" + reference.path);
-              }
-            } else {
-              var mergedPath = _mergePaths(this._path, reference.path);
-              if (this.hasScheme || this.hasAuthority || this.hasAbsolutePath) {
-                targetPath = _removeDotSegments(mergedPath);
-              } else {
-                // Non-RFC 3986 beavior. If both base and reference are relative
-                // path, allow the merged path to start with "..".
-                // The RFC only specifies the case where the base has a scheme.
-                targetPath = _normalizeRelativePath(mergedPath);
-              }
-            }
+          isNormalized = false;
+        }
+        index++;
+      } else if (_isGeneralDelimiter(char)) {
+        _fail(host, index, "Invalid character");
+      } else {
+        int sourceLength = 1;
+        if ((char & 0xFC00) == 0xD800 && (index + 1) < end) {
+          int tail = host.codeUnitAt(index + 1);
+          if ((tail & 0xFC00) == 0xDC00) {
+            char = 0x10000 | ((char & 0x3ff) << 10) | (tail & 0x3ff);
+            sourceLength = 2;
           }
-          if (reference.hasQuery) targetQuery = reference.query;
         }
+        if (buffer == null) buffer = new StringBuffer();
+        String slice = host.substring(sectionStart, index);
+        if (!isNormalized) slice = slice.toLowerCase();
+        buffer.write(slice);
+        buffer.write(_escapeChar(char));
+        index += sourceLength;
+        sectionStart = index;
       }
     }
-    String fragment = reference.hasFragment ? reference.fragment : null;
-    return new Uri._internal(targetScheme,
-                             targetUserInfo,
-                             targetHost,
-                             targetPort,
-                             targetPath,
-                             targetQuery,
-                             fragment);
+    if (buffer == null) return host.substring(start, end);
+    if (sectionStart < end) {
+      String slice = host.substring(sectionStart, end);
+      if (!isNormalized) slice = slice.toLowerCase();
+      buffer.write(slice);
+    }
+    return buffer.toString();
   }
 
   /**
-   * Returns whether the URI has a [scheme] component.
+   * Validates scheme characters and does case-normalization.
+   *
+   * Schemes are converted to lower case. They cannot contain escapes.
    */
-  bool get hasScheme => scheme.isNotEmpty;
+  static String _makeScheme(String scheme, int start, int end) {
+    if (start == end) return "";
+    final int firstCodeUnit = scheme.codeUnitAt(start);
+    if (!_isAlphabeticCharacter(firstCodeUnit)) {
+      _fail(scheme, start, "Scheme not starting with alphabetic character");
+    }
+    bool containsUpperCase = false;
+    for (int i = start; i < end; i++) {
+      final int codeUnit = scheme.codeUnitAt(i);
+      if (!_isSchemeCharacter(codeUnit)) {
+        _fail(scheme, i, "Illegal scheme character");
+      }
+      if (_UPPER_CASE_A <= codeUnit && codeUnit <= _UPPER_CASE_Z) {
+        containsUpperCase = true;
+      }
+    }
+    scheme = scheme.substring(start, end);
+    if (containsUpperCase) scheme = scheme.toLowerCase();
+    return _canonicalizeScheme(scheme);
+  }
 
-  /**
-   * Returns whether the URI has an [authority] component.
-   */
-  bool get hasAuthority => _host != null;
+  // Canonicalize a few often-used scheme strings.
+  //
+  // This improves memory usage and makes comparison faster.
+  static String _canonicalizeScheme(String scheme) {
+    if (scheme == "http") return "http";
+    if (scheme == "file") return "file";
+    if (scheme == "https") return "https";
+    if (scheme == "package") return "package";
+    return scheme;
+  }
 
-  /**
-   * Returns whether the URI has an explicit port.
-   *
-   * If the port number is the default port number
-   * (zero for unrecognized schemes, with http (80) and https (443) being
-   * recognized),
-   * then the port is made implicit and omitted from the URI.
-   */
-  bool get hasPort => _port != null;
+  static String _makeUserInfo(String userInfo, int start, int end) {
+    if (userInfo == null) return "";
+    return _normalize(userInfo, start, end, _userinfoTable);
+  }
 
-  /**
-   * Returns whether the URI has a query part.
-   */
-  bool get hasQuery => _query != null;
+  static String _makePath(String path, int start, int end,
+                          Iterable<String> pathSegments,
+                          String scheme,
+                          bool hasAuthority) {
+    bool isFile = (scheme == "file");
+    bool ensureLeadingSlash = isFile || hasAuthority;
+    if (path == null && pathSegments == null) return isFile ? "/" : "";
+    if (path != null && pathSegments != null) {
+      throw new ArgumentError('Both path and pathSegments specified');
+    }
+    var result;
+    if (path != null) {
+      result = _normalize(path, start, end, _pathCharOrSlashTable);
+    } else {
+      result = pathSegments.map((s) =>
+          _uriEncode(_pathCharTable, s, UTF8, false)).join("/");
+    }
+    if (result.isEmpty) {
+      if (isFile) return "/";
+    } else if (ensureLeadingSlash && !result.startsWith('/')) {
+      result = "/" + result;
+    }
+    result = _normalizePath(result, scheme, hasAuthority);
+    return result;
+  }
 
-  /**
-   * Returns whether the URI has a fragment part.
-   */
-  bool get hasFragment => _fragment != null;
+  /// Performs path normalization (remove dot segments) on a path.
+  ///
+  /// If the URI has neither scheme nor authority, it's considered a
+  /// "pure path" and normalization won't remove leading ".." segments.
+  /// Otherwise it follows the RFC 3986 "remove dot segments" algorithm.
+  static String _normalizePath(String path, String scheme, bool hasAuthority) {
+    if (scheme.isEmpty && !hasAuthority && !path.startsWith('/')) {
+      return _normalizeRelativePath(path);
+    }
+    return _removeDotSegments(path);
+  }
 
-  /**
-   * Returns whether the URI has an empty path.
-   */
-  bool get hasEmptyPath => _path.isEmpty;
+  static String _makeQuery(
+      String query, int start, int end,
+      Map<String, dynamic/*String|Iterable<String>*/> queryParameters) {
+    if (query == null && queryParameters == null) return null;
+    if (query != null && queryParameters != null) {
+      throw new ArgumentError('Both query and queryParameters specified');
+    }
+    if (query != null) return _normalize(query, start, end, _queryCharTable);
 
-  /**
-   * Returns whether the URI has an absolute path (starting with '/').
-   */
-  bool get hasAbsolutePath => _path.startsWith('/');
+    var result = new StringBuffer();
+    var separator = "";
 
-  /**
-   * Returns the origin of the URI in the form scheme://host:port for the
-   * schemes http and https.
-   *
-   * It is an error if the scheme is not "http" or "https".
-   *
-   * See: http://www.w3.org/TR/2011/WD-html5-20110405/origin-0.html#origin
-   */
-  String get origin {
-    if (scheme == "" || _host == null || _host == "") {
-      throw new StateError("Cannot use origin without a scheme: $this");
-    }
-    if (scheme != "http" && scheme != "https") {
-      throw new StateError(
-        "Origin is only applicable schemes http and https: $this");
+    void writeParameter(String key, String value) {
+      result.write(separator);
+      separator = "&";
+      result.write(Uri.encodeQueryComponent(key));
+      if (value != null && value.isNotEmpty) {
+        result.write("=");
+        result.write(Uri.encodeQueryComponent(value));
+      }
     }
-    if (_port == null) return "$scheme://$_host";
-    return "$scheme://$_host:$_port";
+
+    queryParameters.forEach((key, value) {
+      if (value == null || value is String) {
+        writeParameter(key, value);
+      } else {
+        Iterable values = value;
+        for (String value in values) {
+          writeParameter(key, value);
+        }
+      }
+    });
+    return result.toString();
+  }
+
+  static String _makeFragment(String fragment, int start, int end) {
+    if (fragment == null) return null;
+    return _normalize(fragment, start, end, _queryCharTable);
   }
 
   /**
-   * Returns the file path from a file URI.
-   *
-   * The returned path has either Windows or non-Windows
-   * semantics.
-   *
-   * For non-Windows semantics the slash ("/") is used to separate
-   * path segments.
-   *
-   * For Windows semantics the backslash ("\\") separator is used to
-   * separate path segments.
-   *
-   * If the URI is absolute the path starts with a path separator
-   * unless Windows semantics is used and the first path segment is a
-   * drive letter. When Windows semantics is used a host component in
-   * the uri in interpreted as a file server and a UNC path is
-   * returned.
-   *
-   * The default for whether to use Windows or non-Windows semantics
-   * determined from the platform Dart is running on. When running in
-   * the standalone VM this is detected by the VM based on the
-   * operating system. When running in a browser non-Windows semantics
-   * is always used.
-   *
-   * To override the automatic detection of which semantics to use pass
-   * a value for [windows]. Passing `true` will use Windows
-   * semantics and passing `false` will use non-Windows semantics.
-   *
-   * If the URI ends with a slash (i.e. the last path component is
-   * empty) the returned file path will also end with a slash.
-   *
-   * With Windows semantics URIs starting with a drive letter cannot
-   * be relative to the current drive on the designated drive. That is
-   * for the URI `file:///c:abc` calling `toFilePath` will throw as a
-   * path segment cannot contain colon on Windows.
-   *
-   * Examples using non-Windows semantics (resulting of calling
-   * toFilePath in comment):
-   *
-   *     Uri.parse("xxx/yyy");  // xxx/yyy
-   *     Uri.parse("xxx/yyy/");  // xxx/yyy/
-   *     Uri.parse("file:///xxx/yyy");  // /xxx/yyy
-   *     Uri.parse("file:///xxx/yyy/");  // /xxx/yyy/
-   *     Uri.parse("file:///C:");  // /C:
-   *     Uri.parse("file:///C:a");  // /C:a
-   *
-   * Examples using Windows semantics (resulting URI in comment):
+   * Performs RFC 3986 Percent-Encoding Normalization.
    *
-   *     Uri.parse("xxx/yyy");  // xxx\yyy
-   *     Uri.parse("xxx/yyy/");  // xxx\yyy\
-   *     Uri.parse("file:///xxx/yyy");  // \xxx\yyy
-   *     Uri.parse("file:///xxx/yyy/");  // \xxx\yyy/
-   *     Uri.parse("file:///C:/xxx/yyy");  // C:\xxx\yyy
-   *     Uri.parse("file:C:xxx/yyy");  // Throws as a path segment
-   *                                   // cannot contain colon on Windows.
-   *     Uri.parse("file://server/share/file");  // \\server\share\file
+   * Returns a replacement string that should be replace the original escape.
+   * Returns null if no replacement is necessary because the escape is
+   * not for an unreserved character and is already non-lower-case.
    *
-   * If the URI is not a file URI calling this throws
-   * [UnsupportedError].
+   * Returns "%" if the escape is invalid (not two valid hex digits following
+   * the percent sign). The calling code should replace the percent
+   * sign with "%25", but leave the following two characters unmodified.
    *
-   * If the URI cannot be converted to a file path calling this throws
-   * [UnsupportedError].
+   * If [lowerCase] is true, a single character returned is always lower case,
    */
-  String toFilePath({bool windows}) {
-    if (scheme != "" && scheme != "file") {
-      throw new UnsupportedError(
-          "Cannot extract a file path from a $scheme URI");
+  static String _normalizeEscape(String source, int index, bool lowerCase) {
+    assert(source.codeUnitAt(index) == _PERCENT);
+    if (index + 2 >= source.length) {
+      return "%";  // Marks the escape as invalid.
     }
-    if (query != "") {
-      throw new UnsupportedError(
-          "Cannot extract a file path from a URI with a query component");
+    int firstDigit = source.codeUnitAt(index + 1);
+    int secondDigit = source.codeUnitAt(index + 2);
+    int firstDigitValue = _parseHexDigit(firstDigit);
+    int secondDigitValue = _parseHexDigit(secondDigit);
+    if (firstDigitValue < 0 || secondDigitValue < 0) {
+      return "%";  // Marks the escape as invalid.
     }
-    if (fragment != "") {
-      throw new UnsupportedError(
-          "Cannot extract a file path from a URI with a fragment component");
+    int value = firstDigitValue * 16 + secondDigitValue;
+    if (_isUnreservedChar(value)) {
+      if (lowerCase && _UPPER_CASE_A <= value && _UPPER_CASE_Z >= value) {
+        value |= 0x20;
+      }
+      return new String.fromCharCode(value);
     }
-    if (windows == null) windows = _isWindows;
-    return windows ? _toWindowsFilePath() : _toFilePath();
+    if (firstDigit >= _LOWER_CASE_A || secondDigit >= _LOWER_CASE_A) {
+      // Either digit is lower case.
+      return source.substring(index, index + 3).toUpperCase();
+    }
+    // Escape is retained, and is already non-lower case, so return null to
+    // represent "no replacement necessary".
+    return null;
   }
 
-  String _toFilePath() {
-    if (host != "") {
-      throw new UnsupportedError(
-          "Cannot extract a non-Windows file path from a file URI "
-          "with an authority");
+  // Converts a UTF-16 code-unit to its value as a hex digit.
+  // Returns -1 for non-hex digits.
+  static int _parseHexDigit(int char) {
+    const int zeroDigit = 0x30;
+    int digit = char ^ zeroDigit;
+    if (digit <= 9) return digit;
+    int lowerCase = char | 0x20;
+    if (_LOWER_CASE_A <= lowerCase && lowerCase <= _LOWER_CASE_F) {
+      return lowerCase - (_LOWER_CASE_A - 10);
     }
-    _checkNonWindowsPathReservedCharacters(pathSegments, false);
-    var result = new StringBuffer();
-    if (_isPathAbsolute) result.write("/");
-    result.writeAll(pathSegments, "/");
-    return result.toString();
+    return -1;
   }
 
-  String _toWindowsFilePath() {
-    bool hasDriveLetter = false;
-    var segments = pathSegments;
-    if (segments.length > 0 &&
-        segments[0].length == 2 &&
-        segments[0].codeUnitAt(1) == _COLON) {
-      _checkWindowsDriveLetter(segments[0].codeUnitAt(0), false);
-      _checkWindowsPathReservedCharacters(segments, false, 1);
-      hasDriveLetter = true;
+  static String _escapeChar(int char) {
+    assert(char <= 0x10ffff);  // It's a valid unicode code point.
+    List<int> codeUnits;
+    if (char < 0x80) {
+      // ASCII, a single percent encoded sequence.
+      codeUnits = new List(3);
+      codeUnits[0] = _PERCENT;
+      codeUnits[1] = _hexDigits.codeUnitAt(char >> 4);
+      codeUnits[2] = _hexDigits.codeUnitAt(char & 0xf);
     } else {
-      _checkWindowsPathReservedCharacters(segments, false);
+      // Do UTF-8 encoding of character, then percent encode bytes.
+      int flag = 0xc0;  // The high-bit markers on the first byte of UTF-8.
+      int encodedBytes = 2;
+      if (char > 0x7ff) {
+        flag = 0xe0;
+        encodedBytes = 3;
+        if (char > 0xffff) {
+          encodedBytes = 4;
+          flag = 0xf0;
+        }
+      }
+      codeUnits = new List(3 * encodedBytes);
+      int index = 0;
+      while (--encodedBytes >= 0) {
+        int byte = ((char >> (6 * encodedBytes)) & 0x3f) | flag;
+        codeUnits[index] = _PERCENT;
+        codeUnits[index + 1] = _hexDigits.codeUnitAt(byte >> 4);
+        codeUnits[index + 2] = _hexDigits.codeUnitAt(byte & 0xf);
+        index += 3;
+        flag = 0x80;  // Following bytes have only high bit set.
+      }
+    }
+    return new String.fromCharCodes(codeUnits);
+  }
+
+  /**
+   * Runs through component checking that each character is valid and
+   * normalize percent escapes.
+   *
+   * Uses [charTable] to check if a non-`%` character is allowed.
+   * Each `%` character must be followed by two hex digits.
+   * If the hex-digits are lower case letters, they are converted to
+   * upper case.
+   */
+  static String _normalize(String component, int start, int end,
+                           List<int> charTable) {
+    StringBuffer buffer;
+    int sectionStart = start;
+    int index = start;
+    // Loop while characters are valid and escapes correct and upper-case.
+    while (index < end) {
+      int char = component.codeUnitAt(index);
+      if (char < 127 && (charTable[char >> 4] & (1 << (char & 0x0f))) != 0) {
+        index++;
+      } else {
+        String replacement;
+        int sourceLength;
+        if (char == _PERCENT) {
+          replacement = _normalizeEscape(component, index, false);
+          // Returns null if we should keep the existing escape.
+          if (replacement == null) {
+            index += 3;
+            continue;
+          }
+          // Returns "%" if we should escape the existing percent.
+          if ("%" == replacement) {
+            replacement = "%25";
+            sourceLength = 1;
+          } else {
+            sourceLength = 3;
+          }
+        } else if (_isGeneralDelimiter(char)) {
+          _fail(component, index, "Invalid character");
+        } else {
+          sourceLength = 1;
+          if ((char & 0xFC00) == 0xD800) {
+            // Possible lead surrogate.
+            if (index + 1 < end) {
+              int tail = component.codeUnitAt(index + 1);
+              if ((tail & 0xFC00) == 0xDC00) {
+                // Tail surrogate.
+                sourceLength = 2;
+                char = 0x10000 | ((char & 0x3ff) << 10) | (tail & 0x3ff);
+              }
+            }
+          }
+          replacement = _escapeChar(char);
+        }
+        if (buffer == null) buffer = new StringBuffer();
+        buffer.write(component.substring(sectionStart, index));
+        buffer.write(replacement);
+        index += sourceLength;
+        sectionStart = index;
+      }
     }
-    var result = new StringBuffer();
-    if (_isPathAbsolute && !hasDriveLetter) result.write("\\");
-    if (host != "") {
-      result.write("\\");
-      result.write(host);
-      result.write("\\");
-    }
-    result.writeAll(segments, "\\");
-    if (hasDriveLetter && segments.length == 1) result.write("\\");
-    return result.toString();
+    if (buffer == null) {
+      // Makes no copy if start == 0 and end == component.length.
+      return component.substring(start, end);
+    }
+    if (sectionStart < end) {
+      buffer.write(component.substring(sectionStart, end));
+    }
+    return buffer.toString();
   }
 
-  bool get _isPathAbsolute {
-    if (path == null || path.isEmpty) return false;
-    return path.startsWith('/');
+  static bool _isSchemeCharacter(int ch) {
+    return ch < 128 && ((_schemeTable[ch >> 4] & (1 << (ch & 0x0f))) != 0);
   }
 
-  void _writeAuthority(StringSink ss) {
-    if (_userInfo.isNotEmpty) {
-      ss.write(_userInfo);
-      ss.write("@");
-    }
-    if (_host != null) ss.write(_host);
-    if (_port != null) {
-      ss.write(":");
-      ss.write(_port);
-    }
+  static bool _isGeneralDelimiter(int ch) {
+    return ch <= _RIGHT_BRACKET &&
+        ((_genDelimitersTable[ch >> 4] & (1 << (ch & 0x0f))) != 0);
   }
 
   /**
-   * Access the structure of a `data:` URI.
-   *
-   * Returns a [UriData] object for `data:` URIs and `null` for all other
-   * URIs.
-   * The [UriData] object can be used to access the media type and data
-   * of a `data:` URI.
+   * Returns whether the URI is absolute.
    */
-  UriData get data => (scheme == "data") ? new UriData.fromUri(this) : null;
+  bool get isAbsolute => scheme != "" && fragment == "";
 
-  String toString() {
-    StringBuffer sb = new StringBuffer();
-    _addIfNonEmpty(sb, scheme, scheme, ':');
-    if (hasAuthority || path.startsWith("//") || (scheme == "file")) {
-      // File URIS always have the authority, even if it is empty.
-      // The empty URI means "localhost".
-      sb.write("//");
-      _writeAuthority(sb);
+  String _mergePaths(String base, String reference) {
+    // Optimize for the case: absolute base, reference beginning with "../".
+    int backCount = 0;
+    int refStart = 0;
+    // Count number of "../" at beginning of reference.
+    while (reference.startsWith("../", refStart)) {
+      refStart += 3;
+      backCount++;
     }
-    sb.write(path);
-    if (_query != null) { sb..write("?")..write(_query); }
-    if (_fragment != null) { sb..write("#")..write(_fragment); }
-    return sb.toString();
+
+    // Drop last segment - everything after last '/' of base.
+    int baseEnd = base.lastIndexOf('/');
+    // Drop extra segments for each leading "../" of reference.
+    while (baseEnd > 0 && backCount > 0) {
+      int newEnd = base.lastIndexOf('/', baseEnd - 1);
+      if (newEnd < 0) {
+        break;
+      }
+      int delta = baseEnd - newEnd;
+      // If we see a "." or ".." segment in base, stop here and let
+      // _removeDotSegments handle it.
+      if ((delta == 2 || delta == 3) &&
+          base.codeUnitAt(newEnd + 1) == _DOT &&
+          (delta == 2 || base.codeUnitAt(newEnd + 2) == _DOT)) {
+        break;
+      }
+      baseEnd = newEnd;
+      backCount--;
+    }
+    return base.replaceRange(baseEnd + 1, null,
+                             reference.substring(refStart - 3 * backCount));
   }
 
-  bool operator==(other) {
-    if (other is! Uri) return false;
-    Uri uri = other;
-    return scheme       == uri.scheme       &&
-           hasAuthority == uri.hasAuthority &&
-           userInfo     == uri.userInfo     &&
-           host         == uri.host         &&
-           port         == uri.port         &&
-           path         == uri.path         &&
-           hasQuery     == uri.hasQuery     &&
-           query        == uri.query        &&
-           hasFragment  == uri.hasFragment  &&
-           fragment     == uri.fragment;
+  /// Make a guess at whether a path contains a `..` or `.` segment.
+  ///
+  /// This is a primitive test that can cause false positives.
+  /// It's only used to avoid a more expensive operation in the case where
+  /// it's not necessary.
+  static bool _mayContainDotSegments(String path) {
+    if (path.startsWith('.')) return true;
+    int index = path.indexOf("/.");
+    return index != -1;
   }
 
-  int get hashCode {
-    int combine(part, current) {
-      // The sum is truncated to 30 bits to make sure it fits into a Smi.
-      return (current * 31 + part.hashCode) & 0x3FFFFFFF;
+  /// Removes '.' and '..' segments from a path.
+  ///
+  /// Follows the RFC 2986 "remove dot segments" algorithm.
+  /// This algorithm is only used on paths of URIs with a scheme,
+  /// and it treats the path as if it is absolute (leading '..' are removed).
+  static String _removeDotSegments(String path) {
+    if (!_mayContainDotSegments(path)) return path;
+    assert(path.isNotEmpty);  // An empty path would not have dot segments.
+    List<String> output = [];
+    bool appendSlash = false;
+    for (String segment in path.split("/")) {
+      appendSlash = false;
+      if (segment == "..") {
+        if (output.isNotEmpty) {
+          output.removeLast();
+          if (output.isEmpty) {
+            output.add("");
+          }
+        }
+        appendSlash = true;
+      } else if ("." == segment) {
+        appendSlash = true;
+      } else {
+        output.add(segment);
+      }
     }
-    return combine(scheme, combine(userInfo, combine(host, combine(port,
-        combine(path, combine(query, combine(fragment, 1)))))));
+    if (appendSlash) output.add("");
+    return output.join("/");
   }
 
-  static void _addIfNonEmpty(StringBuffer sb, String test,
-                             String first, String second) {
-    if ("" != test) {
-      sb.write(first);
-      sb.write(second);
+  /// Removes all `.` segments and any non-leading `..` segments.
+  ///
+  /// Removing the ".." from a "bar/foo/.." sequence results in "bar/"
+  /// (trailing "/"). If the entire path is removed (because it contains as
+  /// many ".." segments as real segments), the result is "./".
+  /// This is different from an empty string, which represents "no path",
+  /// when you resolve it against a base URI with a path with a non-empty
+  /// final segment.
+  static String _normalizeRelativePath(String path) {
+    assert(!path.startsWith('/'));  // Only get called for relative paths.
+    if (!_mayContainDotSegments(path)) return path;
+    assert(path.isNotEmpty);  // An empty path would not have dot segments.
+    List<String> output = [];
+    bool appendSlash = false;
+    for (String segment in path.split("/")) {
+      appendSlash = false;
+      if (".." == segment) {
+        if (!output.isEmpty && output.last != "..") {
+          output.removeLast();
+          appendSlash = true;
+        } else {
+          output.add("..");
+        }
+      } else if ("." == segment) {
+        appendSlash = true;
+      } else {
+        output.add(segment);
+      }
     }
+    if (output.isEmpty || (output.length == 1 && output[0].isEmpty)) {
+      return "./";
+    }
+    if (appendSlash || output.last == '..') output.add("");
+    return output.join("/");
   }
 
-  /**
-   * Encode the string [component] using percent-encoding to make it
-   * safe for literal use as a URI component.
-   *
-   * All characters except uppercase and lowercase letters, digits and
-   * the characters `-_.!~*'()` are percent-encoded. This is the
-   * set of characters specified in RFC 2396 and the which is
-   * specified for the encodeUriComponent in ECMA-262 version 5.1.
-   *
-   * When manually encoding path segments or query components remember
-   * to encode each part separately before building the path or query
-   * string.
-   *
-   * For encoding the query part consider using
-   * [encodeQueryComponent].
-   *
-   * To avoid the need for explicitly encoding use the [pathSegments]
-   * and [queryParameters] optional named arguments when constructing
-   * a [Uri].
-   */
-  static String encodeComponent(String component) {
-    return _uriEncode(_unreserved2396Table, component, UTF8, false);
+  Uri resolve(String reference) {
+    return resolveUri(Uri.parse(reference));
   }
 
-  /**
-   * Encode the string [component] according to the HTML 4.01 rules
-   * for encoding the posting of a HTML form as a query string
-   * component.
-   *
-   * Encode the string [component] according to the HTML 4.01 rules
-   * for encoding the posting of a HTML form as a query string
-   * component.
-
-   * The component is first encoded to bytes using [encoding].
-   * The default is to use [UTF8] encoding, which preserves all
-   * the characters that don't need encoding.
-
-   * Then the resulting bytes are "percent-encoded". This transforms
-   * spaces (U+0020) to a plus sign ('+') and all bytes that are not
-   * the ASCII decimal digits, letters or one of '-._~' are written as
-   * a percent sign '%' followed by the two-digit hexadecimal
-   * representation of the byte.
-
-   * Note that the set of characters which are percent-encoded is a
-   * superset of what HTML 4.01 requires, since it refers to RFC 1738
-   * for reserved characters.
-   *
-   * When manually encoding query components remember to encode each
-   * part separately before building the query string.
-   *
-   * To avoid the need for explicitly encoding the query use the
-   * [queryParameters] optional named arguments when constructing a
-   * [Uri].
-   *
-   * See http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.2 for more
-   * details.
-   */
-  static String encodeQueryComponent(String component,
-                                     {Encoding encoding: UTF8}) {
-    return _uriEncode(_unreservedTable, component, encoding, true);
+  Uri resolveUri(Uri reference) {
+    // From RFC 3986.
+    String targetScheme;
+    String targetUserInfo = "";
+    String targetHost;
+    int targetPort;
+    String targetPath;
+    String targetQuery;
+    if (reference.scheme.isNotEmpty) {
+      targetScheme = reference.scheme;
+      if (reference.hasAuthority) {
+        targetUserInfo = reference.userInfo;
+        targetHost = reference.host;
+        targetPort = reference.hasPort ? reference.port : null;
+      }
+      targetPath = _removeDotSegments(reference.path);
+      if (reference.hasQuery) {
+        targetQuery = reference.query;
+      }
+    } else {
+      targetScheme = this.scheme;
+      if (reference.hasAuthority) {
+        targetUserInfo = reference.userInfo;
+        targetHost = reference.host;
+        targetPort = _makePort(reference.hasPort ? reference.port : null,
+                               targetScheme);
+        targetPath = _removeDotSegments(reference.path);
+        if (reference.hasQuery) targetQuery = reference.query;
+      } else {
+        targetUserInfo = this._userInfo;
+        targetHost = this._host;
+        targetPort = this._port;
+        if (reference.path == "") {
+          targetPath = this._path;
+          if (reference.hasQuery) {
+            targetQuery = reference.query;
+          } else {
+            targetQuery = this._query;
+          }
+        } else {
+          if (reference.hasAbsolutePath) {
+            targetPath = _removeDotSegments(reference.path);
+          } else {
+            // This is the RFC 3986 behavior for merging.
+            if (this.hasEmptyPath) {
+              if (!this.hasAuthority) {
+                if (!this.hasScheme) {
+                  // Keep the path relative if no scheme or authority.
+                  targetPath = reference.path;
+                } else {
+                  // Remove leading dot-segments if the path is put
+                  // beneath a scheme.
+                  targetPath = _removeDotSegments(reference.path);
+                }
+              } else {
+                // RFC algorithm for base with authority and empty path.
+                targetPath = _removeDotSegments("/" + reference.path);
+              }
+            } else {
+              var mergedPath = _mergePaths(this._path, reference.path);
+              if (this.hasScheme || this.hasAuthority || this.hasAbsolutePath) {
+                targetPath = _removeDotSegments(mergedPath);
+              } else {
+                // Non-RFC 3986 behavior.
+                // If both base and reference are relative paths,
+                // allow the merged path to start with "..".
+                // The RFC only specifies the case where the base has a scheme.
+                targetPath = _normalizeRelativePath(mergedPath);
+              }
+            }
+          }
+          if (reference.hasQuery) targetQuery = reference.query;
+        }
+      }
+    }
+    String fragment = reference.hasFragment ? reference.fragment : null;
+    return new _Uri._internal(targetScheme,
+                              targetUserInfo,
+                              targetHost,
+                              targetPort,
+                              targetPath,
+                              targetQuery,
+                              fragment);
   }
 
-  /**
-   * Decodes the percent-encoding in [encodedComponent].
-   *
-   * Note that decoding a URI component might change its meaning as
-   * some of the decoded characters could be characters with are
-   * delimiters for a given URI componene type. Always split a URI
-   * component using the delimiters for the component before decoding
-   * the individual parts.
-   *
-   * For handling the [path] and [query] components consider using
-   * [pathSegments] and [queryParameters] to get the separated and
-   * decoded component.
-   */
-  static String decodeComponent(String encodedComponent) {
-    return _uriDecode(encodedComponent, 0, encodedComponent.length,
-                      UTF8, false);
-  }
+  bool get hasScheme => scheme.isNotEmpty;
 
-  /**
-   * Decodes the percent-encoding in [encodedComponent], converting
-   * pluses to spaces.
-   *
-   * It will create a byte-list of the decoded characters, and then use
-   * [encoding] to decode the byte-list to a String. The default encoding is
-   * UTF-8.
-   */
-  static String decodeQueryComponent(
-      String encodedComponent,
-      {Encoding encoding: UTF8}) {
-    return _uriDecode(encodedComponent, 0, encodedComponent.length,
-                      encoding, true);
-  }
+  bool get hasAuthority => _host != null;
 
-  /**
-   * Encode the string [uri] using percent-encoding to make it
-   * safe for literal use as a full URI.
-   *
-   * All characters except uppercase and lowercase letters, digits and
-   * the characters `!#$&'()*+,-./:;=?@_~` are percent-encoded. This
-   * is the set of characters specified in in ECMA-262 version 5.1 for
-   * the encodeURI function .
-   */
-  static String encodeFull(String uri) {
-    return _uriEncode(_encodeFullTable, uri, UTF8, false);
-  }
+  bool get hasPort => _port != null;
 
-  /**
-   * Decodes the percent-encoding in [uri].
-   *
-   * Note that decoding a full URI might change its meaning as some of
-   * the decoded characters could be reserved characters. In most
-   * cases an encoded URI should be parsed into components using
-   * [Uri.parse] before decoding the separate components.
-   */
-  static String decodeFull(String uri) {
-    return _uriDecode(uri, 0, uri.length, UTF8, false);
-  }
+  bool get hasQuery => _query != null;
 
-  /**
-   * Returns the [query] split into a map according to the rules
-   * specified for FORM post in the [HTML 4.01 specification section
-   * 17.13.4](http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4 "HTML 4.01 section 17.13.4").
-   * Each key and value in the returned map has been decoded. If the [query]
-   * is the empty string an empty map is returned.
-   *
-   * Keys in the query string that have no value are mapped to the
-   * empty string.
-   *
-   * Each query component will be decoded using [encoding]. The default encoding
-   * is UTF-8.
-   */
-  static Map<String, String> splitQueryString(String query,
-                                              {Encoding encoding: UTF8}) {
-    return query.split("&").fold({}, (map, element) {
-      int index = element.indexOf("=");
-      if (index == -1) {
-        if (element != "") {
-          map[decodeQueryComponent(element, encoding: encoding)] = "";
-        }
-      } else if (index != 0) {
-        var key = element.substring(0, index);
-        var value = element.substring(index + 1);
-        map[Uri.decodeQueryComponent(key, encoding: encoding)] =
-            decodeQueryComponent(value, encoding: encoding);
-      }
-      return map;
-    });
-  }
+  bool get hasFragment => _fragment != null;
 
-  static List _createList() => [];
+  bool get hasEmptyPath => _path.isEmpty;
 
-  static Map _splitQueryStringAll(
-      String query, {Encoding encoding: UTF8}) {
-    Map result = {};
-    int i = 0;
-    int start = 0;
-    int equalsIndex = -1;
+  bool get hasAbsolutePath => _path.startsWith('/');
 
-    void parsePair(int start, int equalsIndex, int end) {
-      String key;
-      String value;
-      if (start == end) return;
-      if (equalsIndex < 0) {
-        key =  _uriDecode(query, start, end, encoding, true);
-        value = "";
-      } else {
-        key = _uriDecode(query, start, equalsIndex, encoding, true);
-        value = _uriDecode(query, equalsIndex + 1, end, encoding, true);
-      }
-      result.putIfAbsent(key, _createList).add(value);
+  String get origin {
+    if (scheme == "" || _host == null || _host == "") {
+      throw new StateError("Cannot use origin without a scheme: $this");
     }
-
-    const int _equals = 0x3d;
-    const int _ampersand = 0x26;
-    while (i < query.length) {
-      int char = query.codeUnitAt(i);
-      if (char == _equals) {
-        if (equalsIndex < 0) equalsIndex = i;
-      } else if (char == _ampersand) {
-        parsePair(start, equalsIndex, i);
-        start = i + 1;
-        equalsIndex = -1;
-      }
-      i++;
+    if (scheme != "http" && scheme != "https") {
+      throw new StateError(
+        "Origin is only applicable schemes http and https: $this");
     }
-    parsePair(start, equalsIndex, i);
-    return result;
+    if (_port == null) return "$scheme://$_host";
+    return "$scheme://$_host:$_port";
   }
 
-  /**
-   * Parse the [host] as an IP version 4 (IPv4) address, returning the address
-   * as a list of 4 bytes in network byte order (big endian).
-   *
-   * Throws a [FormatException] if [host] is not a valid IPv4 address
-   * representation.
-   */
-  static List<int> parseIPv4Address(String host) {
-    void error(String msg) {
-      throw new FormatException('Illegal IPv4 address, $msg');
+  String toFilePath({bool windows}) {
+    if (scheme != "" && scheme != "file") {
+      throw new UnsupportedError(
+          "Cannot extract a file path from a $scheme URI");
     }
-    var bytes = host.split('.');
-    if (bytes.length != 4) {
-      error('IPv4 address should contain exactly 4 parts');
+    if (query != "") {
+      throw new UnsupportedError(
+          "Cannot extract a file path from a URI with a query component");
     }
-    // TODO(ajohnsen): Consider using Uint8List.
-    return bytes
-        .map((byteString) {
-          int byte = int.parse(byteString);
-          if (byte < 0 || byte > 255) {
-            error('each part must be in the range of `0..255`');
-          }
-          return byte;
-        })
-        .toList();
+    if (fragment != "") {
+      throw new UnsupportedError(
+          "Cannot extract a file path from a URI with a fragment component");
+    }
+    if (windows == null) windows = _isWindows;
+    return windows ? _toWindowsFilePath(this) : _toFilePath();
   }
 
-  /**
-   * Parse the [host] as an IP version 6 (IPv6) address, returning the address
-   * as a list of 16 bytes in network byte order (big endian).
-   *
-   * Throws a [FormatException] if [host] is not a valid IPv6 address
-   * representation.
-   *
-   * Acts on the substring from [start] to [end]. If [end] is omitted, it
-   * defaults ot the end of the string.
-   *
-   * Some examples of IPv6 addresses:
-   *  * ::1
-   *  * FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
-   *  * 3ffe:2a00:100:7031::1
-   *  * ::FFFF:129.144.52.38
-   *  * 2010:836B:4179::836B:4179
-   */
-  static List<int> parseIPv6Address(String host, [int start = 0, int end]) {
-    if (end == null) end = host.length;
-    // An IPv6 address consists of exactly 8 parts of 1-4 hex digits, seperated
-    // by `:`'s, with the following exceptions:
-    //
-    //  - One (and only one) wildcard (`::`) may be present, representing a fill
-    //    of 0's. The IPv6 `::` is thus 16 bytes of `0`.
-    //  - The last two parts may be replaced by an IPv4 address.
-    void error(String msg, [position]) {
-      throw new FormatException('Illegal IPv6 address, $msg', host, position);
+  String _toFilePath() {
+    if (hasAuthority && host != "") {
+      throw new UnsupportedError(
+          "Cannot extract a non-Windows file path from a file URI "
+          "with an authority");
     }
-    int parseHex(int start, int end) {
-      if (end - start > 4) {
-        error('an IPv6 part can only contain a maximum of 4 hex digits', start);
-      }
-      int value = int.parse(host.substring(start, end), radix: 16);
-      if (value < 0 || value > (1 << 16) - 1) {
-        error('each part must be in the range of `0x0..0xFFFF`', start);
-      }
-      return value;
+    // Use path segments to have any escapes unescaped.
+    var pathSegments = this.pathSegments;
+    _checkNonWindowsPathReservedCharacters(pathSegments, false);
+    var result = new StringBuffer();
+    if (hasAbsolutePath) result.write("/");
+    result.writeAll(pathSegments, "/");
+    return result.toString();
+  }
+
+  static String _toWindowsFilePath(Uri uri) {
+    bool hasDriveLetter = false;
+    var segments = uri.pathSegments;
+    if (segments.length > 0 &&
+        segments[0].length == 2 &&
+        segments[0].codeUnitAt(1) == _COLON) {
+      _checkWindowsDriveLetter(segments[0].codeUnitAt(0), false);
+      _checkWindowsPathReservedCharacters(segments, false, 1);
+      hasDriveLetter = true;
+    } else {
+      _checkWindowsPathReservedCharacters(segments, false, 0);
     }
-    if (host.length < 2) error('address is too short');
-    List<int> parts = [];
-    bool wildcardSeen = false;
-    int partStart = start;
-    // Parse all parts, except a potential last one.
-    for (int i = start; i < end; i++) {
-      if (host.codeUnitAt(i) == _COLON) {
-        if (i == start) {
-          // If we see a `:` in the beginning, expect wildcard.
-          i++;
-          if (host.codeUnitAt(i) != _COLON) {
-            error('invalid start colon.', i);
-          }
-          partStart = i;
-        }
-        if (i == partStart) {
-          // Wildcard. We only allow one.
-          if (wildcardSeen) {
-            error('only one wildcard `::` is allowed', i);
-          }
-          wildcardSeen = true;
-          parts.add(-1);
-        } else {
-          // Found a single colon. Parse [partStart..i] as a hex entry.
-          parts.add(parseHex(partStart, i));
-        }
-        partStart = i + 1;
+    var result = new StringBuffer();
+    if (uri.hasAbsolutePath && !hasDriveLetter) result.write(r"\");
+    if (uri.hasAuthority) {
+      var host = uri.host;
+      if (host.isNotEmpty) {
+        result.write(r"\");
+        result.write(host);
+        result.write(r"\");
       }
     }
-    if (parts.length == 0) error('too few parts');
-    bool atEnd = (partStart == end);
-    bool isLastWildcard = (parts.last == -1);
-    if (atEnd && !isLastWildcard) {
-      error('expected a part after last `:`', end);
+    result.writeAll(segments, r"\");
+    if (hasDriveLetter && segments.length == 1) result.write(r"\");
+    return result.toString();
+  }
+
+  bool get _isPathAbsolute {
+    return _path != null && _path.startsWith('/');
+  }
+
+  void _writeAuthority(StringSink ss) {
+    if (_userInfo.isNotEmpty) {
+      ss.write(_userInfo);
+      ss.write("@");
+    }
+    if (_host != null) ss.write(_host);
+    if (_port != null) {
+      ss.write(":");
+      ss.write(_port);
+    }
+  }
+
+  /**
+   * Access the structure of a `data:` URI.
+   *
+   * Returns a [UriData] object for `data:` URIs and `null` for all other
+   * URIs.
+   * The [UriData] object can be used to access the media type and data
+   * of a `data:` URI.
+   */
+  UriData get data => (scheme == "data") ? new UriData.fromUri(this) : null;
+
+  String toString() {
+    return _text ??= _initializeText();
+  }
+
+  String _initializeText() {
+    assert(_text == null);
+    StringBuffer sb = new StringBuffer();
+    if (scheme.isNotEmpty) sb..write(scheme)..write(":");
+    if (hasAuthority || path.startsWith("//") || (scheme == "file")) {
+      // File URIS always have the authority, even if it is empty.
+      // The empty URI means "localhost".
+      sb.write("//");
+      _writeAuthority(sb);
     }
-    if (!atEnd) {
-      try {
-        parts.add(parseHex(partStart, end));
-      } catch (e) {
-        // Failed to parse the last chunk as hex. Try IPv4.
-        try {
-          List<int> last = parseIPv4Address(host.substring(partStart, end));
-          parts.add(last[0] << 8 | last[1]);
-          parts.add(last[2] << 8 | last[3]);
-        } catch (e) {
-          error('invalid end of IPv6 address.', partStart);
-        }
-      }
+    sb.write(path);
+    if (_query != null) sb..write("?")..write(_query);
+    if (_fragment != null) sb..write("#")..write(_fragment);
+    return sb.toString();
+  }
+
+  bool operator==(other) {
+    if (identical(this, other)) return true;
+    if (other is Uri) {
+      Uri uri = other;
+      return scheme       == uri.scheme       &&
+             hasAuthority == uri.hasAuthority &&
+             userInfo     == uri.userInfo     &&
+             host         == uri.host         &&
+             port         == uri.port         &&
+             path         == uri.path         &&
+             hasQuery     == uri.hasQuery     &&
+             query        == uri.query        &&
+             hasFragment  == uri.hasFragment  &&
+             fragment     == uri.fragment;
     }
-    if (wildcardSeen) {
-      if (parts.length > 7) {
-        error('an address with a wildcard must have less than 7 parts');
+    return false;
+  }
+
+  int get hashCode {
+    return _hashCodeCache ??= toString().hashCode;
+  }
+
+  static List _createList() => [];
+
+  static Map _splitQueryStringAll(
+      String query, {Encoding encoding: UTF8}) {
+    Map result = {};
+    int i = 0;
+    int start = 0;
+    int equalsIndex = -1;
+
+    void parsePair(int start, int equalsIndex, int end) {
+      String key;
+      String value;
+      if (start == end) return;
+      if (equalsIndex < 0) {
+        key =  _uriDecode(query, start, end, encoding, true);
+        value = "";
+      } else {
+        key = _uriDecode(query, start, equalsIndex, encoding, true);
+        value = _uriDecode(query, equalsIndex + 1, end, encoding, true);
       }
-    } else if (parts.length != 8) {
-      error('an address without a wildcard must contain exactly 8 parts');
+      result.putIfAbsent(key, _createList).add(value);
     }
-    List<int> bytes = new Uint8List(16);
-    for (int i = 0, index = 0; i < parts.length; i++) {
-      int value = parts[i];
-      if (value == -1) {
-        int wildCardLength = 9 - parts.length;
-        for (int j = 0; j < wildCardLength; j++) {
-          bytes[index] = 0;
-          bytes[index + 1] = 0;
-          index += 2;
-        }
-      } else {
-        bytes[index] = value >> 8;
-        bytes[index + 1] = value & 0xff;
-        index += 2;
+
+    const int _equals = 0x3d;
+    const int _ampersand = 0x26;
+    while (i < query.length) {
+      int char = query.codeUnitAt(i);
+      if (char == _equals) {
+        if (equalsIndex < 0) equalsIndex = i;
+      } else if (char == _ampersand) {
+        parsePair(start, equalsIndex, i);
+        start = i + 1;
+        equalsIndex = -1;
       }
+      i++;
     }
-    return bytes;
+    parsePair(start, equalsIndex, i);
+    return result;
   }
 
-  // Frequently used character codes.
-  static const int _SPACE = 0x20;
-  static const int _DOUBLE_QUOTE = 0x22;
-  static const int _NUMBER_SIGN = 0x23;
-  static const int _PERCENT = 0x25;
-  static const int _ASTERISK = 0x2A;
-  static const int _PLUS = 0x2B;
-  static const int _DOT = 0x2E;
-  static const int _SLASH = 0x2F;
-  static const int _ZERO = 0x30;
-  static const int _NINE = 0x39;
-  static const int _COLON = 0x3A;
-  static const int _LESS = 0x3C;
-  static const int _GREATER = 0x3E;
-  static const int _QUESTION = 0x3F;
-  static const int _AT_SIGN = 0x40;
-  static const int _UPPER_CASE_A = 0x41;
-  static const int _UPPER_CASE_F = 0x46;
-  static const int _UPPER_CASE_Z = 0x5A;
-  static const int _LEFT_BRACKET = 0x5B;
-  static const int _BACKSLASH = 0x5C;
-  static const int _RIGHT_BRACKET = 0x5D;
-  static const int _LOWER_CASE_A = 0x61;
-  static const int _LOWER_CASE_F = 0x66;
-  static const int _LOWER_CASE_Z = 0x7A;
-  static const int _BAR = 0x7C;
-
-  static const String _hexDigits = "0123456789ABCDEF";
-
   external static String _uriEncode(List<int> canonicalTable,
                                     String text,
                                     Encoding encoding,
@@ -2941,13 +3189,13 @@ class UriData {
         throw new ArgumentError.value(mimeType, "mimeType",
                                       "Invalid MIME type");
       }
-      buffer.write(Uri._uriEncode(_tokenCharTable,
-                                  mimeType.substring(0, slashIndex),
-                                  UTF8, false));
+      buffer.write(_Uri._uriEncode(_tokenCharTable,
+                                   mimeType.substring(0, slashIndex),
+                                   UTF8, false));
       buffer.write("/");
-      buffer.write(Uri._uriEncode(_tokenCharTable,
-                                  mimeType.substring(slashIndex + 1),
-                                  UTF8, false));
+      buffer.write(_Uri._uriEncode(_tokenCharTable,
+                                   mimeType.substring(slashIndex + 1),
+                                   UTF8, false));
     }
     if (charsetName != null) {
       if (indices != null) {
@@ -2955,7 +3203,7 @@ class UriData {
                ..add(buffer.length + 8);
       }
       buffer.write(";charset=");
-      buffer.write(Uri._uriEncode(_tokenCharTable, charsetName, UTF8, false));
+      buffer.write(_Uri._uriEncode(_tokenCharTable, charsetName, UTF8, false));
     }
     parameters?.forEach((var key, var value) {
       if (key.isEmpty) {
@@ -2968,10 +3216,10 @@ class UriData {
       if (indices != null) indices.add(buffer.length);
       buffer.write(';');
       // Encode any non-RFC2045-token character and both '%' and '#'.
-      buffer.write(Uri._uriEncode(_tokenCharTable, key, UTF8, false));
+      buffer.write(_Uri._uriEncode(_tokenCharTable, key, UTF8, false));
       if (indices != null) indices.add(buffer.length);
       buffer.write('=');
-      buffer.write(Uri._uriEncode(_tokenCharTable, value, UTF8, false));
+      buffer.write(_Uri._uriEncode(_tokenCharTable, value, UTF8, false));
     });
   }
 
@@ -2988,7 +3236,7 @@ class UriData {
     int slashIndex = -1;
     for (int i = 0; i < mimeType.length; i++) {
       var char = mimeType.codeUnitAt(i);
-      if (char != Uri._SLASH) continue;
+      if (char != _SLASH) continue;
       if (slashIndex < 0) {
         slashIndex = i;
         continue;
@@ -3008,7 +3256,7 @@ class UriData {
    * ````
    *
    * where `type`, `subtype`, `attribute` and `value` are specified in RFC-2045,
-   * and `data` is a sequnce of URI-characters (RFC-2396 `uric`).
+   * and `data` is a sequence of URI-characters (RFC-2396 `uric`).
    *
    * This means that all the characters must be ASCII, but the URI may contain
    * percent-escapes for non-ASCII byte values that need an interpretation
@@ -3019,13 +3267,22 @@ class UriData {
    * and `,` delimiters.
    *
    * Accessing the individual parts may fail later if they turn out to have
-   * content that can't be decoded sucessfully as a string.
+   * content that can't be decoded successfully as a string.
    */
   static UriData parse(String uri) {
-    if (!uri.startsWith("data:")) {
-      throw new FormatException("Does not start with 'data:'", uri, 0);
+    if (uri.length >= 5) {
+      int dataDelta = _startsWithData(uri, 0);
+      if (dataDelta == 0) {
+        // Exact match on "data:".
+        return _parse(uri, 5, null);
+      }
+      if (dataDelta == 0x20) {
+        // Starts with a non-normalized "data" scheme containing upper-case
+        // letters. Parse anyway, but throw away the scheme.
+        return _parse(uri.substring(5), 0, null);
+      }
     }
-    return _parse(uri, 5, null);
+    throw new FormatException("Does not start with 'data:'", uri, 0);
   }
 
   /**
@@ -3050,7 +3307,7 @@ class UriData {
     // That's perfectly reasonable - data URIs are not hierarchical,
     // but it may make some consumers stumble.
     // Should we at least do escape normalization?
-    _uriCache = new Uri._internal("data", "", null, null, path, query, null);
+    _uriCache = new _Uri._internal("data", "", null, null, path, query, null);
     return _uriCache;
   }
 
@@ -3075,7 +3332,7 @@ class UriData {
     int start = _separatorIndices[0] + 1;
     int end = _separatorIndices[1];
     if (start == end) return "text/plain";
-    return Uri._uriDecode(_text, start, end, UTF8, false);
+    return _Uri._uriDecode(_text, start, end, UTF8, false);
   }
 
   /**
@@ -3096,8 +3353,8 @@ class UriData {
       var keyStart = _separatorIndices[i] + 1;
       var keyEnd = _separatorIndices[i + 1];
       if (keyEnd == keyStart + 7 && _text.startsWith("charset", keyStart)) {
-        return Uri._uriDecode(_text, keyEnd + 1, _separatorIndices[i + 2],
-                              UTF8, false);
+        return _Uri._uriDecode(_text, keyEnd + 1, _separatorIndices[i + 2],
+                               UTF8, false);
       }
     }
     return "US-ASCII";
@@ -3155,8 +3412,8 @@ class UriData {
         result[index++] = codeUnit;
       } else {
         if (i + 2 < text.length) {
-          var digit1 = Uri._parseHexDigit(text.codeUnitAt(i + 1));
-          var digit2 = Uri._parseHexDigit(text.codeUnitAt(i + 2));
+          var digit1 = _Uri._parseHexDigit(text.codeUnitAt(i + 1));
+          var digit2 = _Uri._parseHexDigit(text.codeUnitAt(i + 2));
           if (digit1 >= 0 && digit2 >= 0) {
             int byte = digit1 * 16 + digit2;
             result[index++] = byte;
@@ -3177,7 +3434,7 @@ class UriData {
    * If the content is Base64 encoded, it will be decoded to bytes and then
    * decoded to a string using [encoding].
    * If encoding is omitted, the value of a `charset` parameter is used
-   * if it is recongized by [Encoding.getByName], otherwise it defaults to
+   * if it is recognized by [Encoding.getByName], otherwise it defaults to
    * the [ASCII] encoding, which is the default encoding for data URIs
    * that do not specify an encoding.
    *
@@ -3199,7 +3456,7 @@ class UriData {
       var converter = BASE64.decoder.fuse(encoding.decoder);
       return converter.convert(text.substring(start));
     }
-    return Uri._uriDecode(text, start, text.length, encoding, false);
+    return _Uri._uriDecode(text, start, text.length, encoding, false);
   }
 
   /**
@@ -3222,8 +3479,8 @@ class UriData {
       var start = _separatorIndices[i - 2] + 1;
       var equals = _separatorIndices[i - 1];
       var end = _separatorIndices[i];
-      String key = Uri._uriDecode(_text, start, equals, UTF8, false);
-      String value = Uri._uriDecode(_text,equals + 1, end, UTF8, false);
+      String key = _Uri._uriDecode(_text, start, equals, UTF8, false);
+      String value = _Uri._uriDecode(_text,equals + 1, end, UTF8, false);
       result[key] = value;
     }
     return result;
@@ -3306,9 +3563,9 @@ class UriData {
           ((canonicalTable[byte >> 4] & (1 << (byte & 0x0f))) != 0)) {
         buffer.writeCharCode(byte);
       } else {
-        buffer.writeCharCode(Uri._PERCENT);
-        buffer.writeCharCode(Uri._hexDigits.codeUnitAt(byte >> 4));
-        buffer.writeCharCode(Uri._hexDigits.codeUnitAt(byte & 0x0f));
+        buffer.writeCharCode(_PERCENT);
+        buffer.writeCharCode(_hexDigits.codeUnitAt(byte >> 4));
+        buffer.writeCharCode(_hexDigits.codeUnitAt(byte & 0x0f));
       }
     }
     if ((byteOr & ~0xFF) != 0) {
@@ -3357,5 +3614,852 @@ class UriData {
   //  mark        =  "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")"
   //
   // This is the same characters as in a URI query (which is URI pchar plus '?')
-  static const _uricTable = Uri._queryCharTable;
+  static const _uricTable = _Uri._queryCharTable;
+}
+
+// --------------------------------------------------------------------
+// Constants used to read the scanner result.
+// The indices points into the table filled by [_scan] which contains
+// recognized positions in the scanned URI.
+// The `0` index is only used internally.
+
+/// Index of the position of that `:` after a scheme.
+const int _schemeEndIndex     = 1;
+/// Index of the position of the character just before the host name.
+const int _hostStartIndex     = 2;
+/// Index of the position of the `:` before a port value.
+const int _portStartIndex     = 3;
+/// Index of the position of the first character of a path.
+const int _pathStartIndex     = 4;
+/// Index of the position of the `?` before a query.
+const int _queryStartIndex    = 5;
+/// Index of the position of the `#` before a fragment.
+const int _fragmentStartIndex = 6;
+/// Index of a position where the URI was determined to be "non-simple".
+const int _notSimpleIndex     = 7;
+
+// Initial state for scanner.
+const int _uriStart           = 00;
+
+// If scanning of a URI terminates in this state or above,
+// consider the URI non-simple
+const int _nonSimpleEndStates = 14;
+
+// Initial state for scheme validation.
+const int _schemeStart        = 20;
+
+/// Transition tables used to scan a URI to determine its structure.
+///
+/// The tables represent a state machine with output.
+///
+/// To scan the URI, start in the [_uriStart] state, then read each character
+/// of the URI in order, from start to end, and for each character perform a
+/// transition to a new state while writing the current position into the output
+/// buffer at a designated index.
+///
+/// Each state, represented by an integer which is an index into
+/// [_scannerTables], has a set of transitions, one for each character.
+/// The transitions are encoded as a 5-bit integer representing the next state
+/// and a 3-bit index into the output table.
+///
+/// For URI scanning, only characters in the range U+0020 through U+007E are
+/// interesting, all characters outside that range are treated the same.
+/// The tables only contain 96 entries, representing that characters in the
+/// interesting range, plus one more to represent all values outside the range.
+/// The character entries are stored in one `Uint8List` per state, with the
+/// transition for a character at position `character ^ 0x60`,
+/// which maps the range U+0020 .. U+007F into positions 0 .. 95.
+/// All remaining characters are mapped to position 31 (`0x7f ^ 0x60`) which
+/// represents the transition for all remaining characters.
+final List<Uint8List> _scannerTables = _createTables();
+
+// ----------------------------------------------------------------------
+// Code to create the URI scanner table.
+
+/// Creates the tables for [_scannerTables] used by [Uri.parse].
+///
+/// See [_scannerTables] for the generated format.
+///
+/// The concrete tables are chosen as a trade-off between the number of states
+/// needed and the precision of the result.
+/// This allows definitely recognizing the general structure of the URI
+/// (presence and location of scheme, user-info, host, port, path, query and
+/// fragment) while at the same time detecting that some components are not
+/// in canonical form (anything containing a `%`, a host-name containing a
+/// capital letter). Since the scanner doesn't know whether something is a
+/// scheme or a path until it sees `:`, or user-info or host until it sees
+/// a `@`, a second pass is needed to validate the scheme and any user-info
+/// is considered non-canonical by default.
+///
+/// The states (starting from [_uriStart]) write positions while scanning
+/// a string from `start` to `end` as follows:
+///
+/// - [_schemeEndIndex]: Should be initialized to `start-1`.
+///   If the URI has a scheme, it is set to the position of the `:` after
+///   the scheme.
+/// - [_hostStartIndex]: Should be initialized to `start - 1`.
+///   If the URI has an authority, it is set to the character before the
+///   host name - either the second `/` in the `//` leading the authority,
+///   or the `@` after a user-info. Comparing this value to the scheme end
+///   position can be used to detect that there is a user-info component.
+/// - [_portStartIndex]: Should be initialized to `start`.
+///   Set to the position of the last `:` in an authority, and unchanged
+///   if there is no authority or no `:` in an authority.
+///   If this position is after the host start, there is a port, otherwise it
+///   is just marking a colon in the user-info component.
+/// - [_pathStartIndex]: Should be initialized to `start`.
+///   Is set to the first path character unless the path is empty.
+///   If the path is empty, the position is either unchanged (`start`) or
+///   the first slash of an authority. So, if the path start is before a
+///   host start or scheme end, the path is empty.
+/// - [_queryStartIndex]: Should be initialized to `end`.
+///   The position of the `?` leading a query if the URI contains a query.
+/// - [_fragmentStartIndex]: Should be initialized to `end`.
+///   The position of the `#` leading a fragment if the URI contains a fragment.
+/// - [_notSimpleIndex]: Should be initialized to `start - 1`.
+///   Set to another value if the URI is considered "not simple".
+///   This is elaborated below.
+///
+/// # Simple URIs
+/// A URI is considered "simple" if it is in a normalized form containing no
+/// escapes. This allows us to skip normalization and checking whether escapes
+/// are valid, and to extract components without worrying about unescaping.
+///
+/// The scanner computes a conservative approximation of being "simple".
+/// It rejects any URI with an escape, with a user-info component (mainly
+/// because they are rare and would increase the number of states in the
+/// scanner significantly), with an IPV6 host or with a capital letter in
+/// the scheme or host name (the scheme is handled in a second scan using
+/// a separate two-state table).
+/// Further, paths containing `..` or `.` path segments are considered
+/// non-simple except for pure relative paths (no scheme or authority) starting
+/// with a sequence of "../" segments.
+///
+/// The transition tables cannot detect a trailing ".." in the path,
+/// followed by a query or fragment, because the segment is not known to be
+/// complete until we are past it, and we then need to store the query/fragment
+/// start instead. This cast is checked manually post-scanning (such a path
+/// needs to be normalized to end in "../", so the URI shouldn't be considered
+/// simple).
+List<Uint8List> _createTables() {
+  // TODO(lrn): Use a precomputed table.
+
+  // Total number of states for the scanner.
+  const int stateCount         = 22;
+
+  // States used to scan a URI from scratch.
+  const int schemeOrPath       = 01;
+  const int authOrPath         = 02;
+  const int authOrPathSlash    = 03;
+  const int uinfoOrHost0       = 04;
+  const int uinfoOrHost        = 05;
+  const int uinfoOrPort0       = 06;
+  const int uinfoOrPort        = 07;
+  const int ipv6Host           = 08;
+  const int relPathSeg         = 09;
+  const int pathSeg            = 10;
+  const int path               = 11;
+  const int query              = 12;
+  const int fragment           = 13;
+  const int schemeOrPathDot    = 14;
+  const int schemeOrPathDot2   = 15;
+  const int relPathSegDot      = 16;
+  const int relPathSegDot2     = 17;
+  const int pathSegDot         = 18;
+  const int pathSegDot2        = 19;
+
+  // States used to validate a scheme after its end position has been found.
+  const int scheme0            = _schemeStart;
+  const int scheme             = 21;
+
+  // Constants encoding the write-index for the state transition into the top 5
+  // bits of a byte.
+  const int schemeEnd          = _schemeEndIndex     << 5;
+  const int hostStart          = _hostStartIndex     << 5;
+  const int portStart          = _portStartIndex     << 5;
+  const int pathStart          = _pathStartIndex     << 5;
+  const int queryStart         = _queryStartIndex    << 5;
+  const int fragmentStart      = _fragmentStartIndex << 5;
+  const int notSimple          = _notSimpleIndex     << 5;
+
+  /// The `unreserved` characters of RFC 3986.
+  const unreserved =
+      "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-._~"  ;
+  /// The `sub-delim` characters of RFC 3986.
+  const subDelims = r"!$&'()*+,;=";
+  // The `pchar` characters of RFC 3986: characters that may occur in a path,
+  // excluding escapes.
+  const pchar = "$unreserved$subDelims";
+
+  var tables = new List<Uint8List>.generate(stateCount,
+      (_) => new Uint8List(96));
+
+  // Helper function which initialize the table for [state] with a default
+  // transition and returns the table.
+  Uint8List build(state, defaultTransition) =>
+      tables[state]..fillRange(0, 96, defaultTransition);
+
+  // Helper function which sets the transition for each character in [chars]
+  // to [transition] in the [target] table.
+  // The [chars] string must contain only characters in the U+0020 .. U+007E
+  // range.
+  void setChars(Uint8List target, String chars, int transition) {
+    for (int i = 0; i < chars.length; i++) {
+      var char = chars.codeUnitAt(i);
+      target[char ^ 0x60] = transition;
+    }
+  }
+
+  /// Helper function which sets the transition for all characters in the
+  /// range from `range[0]` to `range[1]` to [transition] in the [target] table.
+  ///
+  /// The [range] must be a two-character string where both characters are in
+  /// the U+0020 .. U+007E range and the former character must have a lower
+  /// code point than the latter.
+  void setRange(Uint8List target, String range, int transition) {
+    for (int i = range.codeUnitAt(0), n = range.codeUnitAt(1); i <= n; i++) {
+      target[i ^ 0x60] = transition;
+    }
+  }
+
+  // Create the transitions for each state.
+  var b;
+
+  // Validate as path, if it is a scheme, we handle it later.
+  b = build(_uriStart, schemeOrPath | notSimple);
+  setChars(b, pchar, schemeOrPath);
+  setChars(b, ".", schemeOrPathDot);
+  setChars(b, ":", authOrPath | schemeEnd);  // Handle later.
+  setChars(b, "/", authOrPathSlash);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(schemeOrPathDot, schemeOrPath | notSimple);
+  setChars(b, pchar, schemeOrPath);
+  setChars(b, ".", schemeOrPathDot2);
+  setChars(b, ':', authOrPath | schemeEnd);
+  setChars(b, "/", pathSeg | notSimple);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(schemeOrPathDot2, schemeOrPath | notSimple);
+  setChars(b, pchar, schemeOrPath);
+  setChars(b, "%", schemeOrPath | notSimple);
+  setChars(b, ':', authOrPath | schemeEnd);
+  setChars(b, "/", relPathSeg);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(schemeOrPath, schemeOrPath | notSimple);
+  setChars(b, pchar, schemeOrPath);
+  setChars(b, ':', authOrPath | schemeEnd);
+  setChars(b, "/", pathSeg);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(authOrPath, path | notSimple);
+  setChars(b, pchar, path | pathStart);
+  setChars(b, "/", authOrPathSlash | pathStart);
+  setChars(b, ".", pathSegDot | pathStart);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(authOrPathSlash, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, "/", uinfoOrHost0 | hostStart);
+  setChars(b, ".", pathSegDot);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(uinfoOrHost0, uinfoOrHost | notSimple);
+  setChars(b, pchar, uinfoOrHost);
+  setRange(b, "AZ", uinfoOrHost | notSimple);
+  setChars(b, ":", uinfoOrPort0 | portStart);
+  setChars(b, "@", uinfoOrHost0 | hostStart);
+  setChars(b, "[", ipv6Host | notSimple);
+  setChars(b, "/", pathSeg | pathStart);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(uinfoOrHost, uinfoOrHost | notSimple);
+  setChars(b, pchar, uinfoOrHost);
+  setRange(b, "AZ", uinfoOrHost | notSimple);
+  setChars(b, ":", uinfoOrPort0 | portStart);
+  setChars(b, "@", uinfoOrHost0 | hostStart);
+  setChars(b, "/", pathSeg | pathStart);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(uinfoOrPort0, uinfoOrPort | notSimple);
+  setRange(b, "19", uinfoOrPort);
+  setChars(b, "@", uinfoOrHost0 | hostStart);
+  setChars(b, "/", pathSeg | pathStart);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(uinfoOrPort, uinfoOrPort | notSimple);
+  setRange(b, "09", uinfoOrPort);
+  setChars(b, "@", uinfoOrHost0 | hostStart);
+  setChars(b, "/", pathSeg | pathStart);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(ipv6Host, ipv6Host);
+  setChars(b, "]", uinfoOrHost);
+
+  b = build(relPathSeg, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, ".", relPathSegDot);
+  setChars(b, "/", pathSeg | notSimple);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(relPathSegDot, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, ".", relPathSegDot2);
+  setChars(b, "/", pathSeg | notSimple);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(relPathSegDot2, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, "/", relPathSeg);
+  setChars(b, "?", query | queryStart);  // This should be non-simple.
+  setChars(b, "#", fragment | fragmentStart);  // This should be non-simple.
+
+  b = build(pathSeg, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, ".", pathSegDot);
+  setChars(b, "/", pathSeg | notSimple);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(pathSegDot, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, ".", pathSegDot2);
+  setChars(b, "/", pathSeg | notSimple);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(pathSegDot2, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, "/", pathSeg | notSimple);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(path, path | notSimple);
+  setChars(b, pchar, path);
+  setChars(b, "/", pathSeg);
+  setChars(b, "?", query | queryStart);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(query, query | notSimple);
+  setChars(b, pchar, query);
+  setChars(b, "?", query);
+  setChars(b, "#", fragment | fragmentStart);
+
+  b = build(fragment, fragment | notSimple);
+  setChars(b, pchar, fragment);
+  setChars(b, "?", fragment);
+
+  // A separate two-state validator for lower-case scheme names.
+  // Any non-scheme character or upper-case letter is marked as non-simple.
+  b = build(scheme0, scheme | notSimple);
+  setRange(b, "az", scheme);
+
+  b = build(scheme, scheme | notSimple);
+  setRange(b, "az", scheme);
+  setRange(b, "09", scheme);
+  setChars(b, "+-.", scheme);
+
+  return tables;
+}
+
+// --------------------------------------------------------------------
+// Code that uses the URI scanner table.
+
+/// Scan a string using the [_scannerTables] state machine.
+///
+/// Scans [uri] from [start] to [end], startig in state [state] and
+/// writing output into [indices].
+///
+/// Returns the final state.
+int _scan(String uri, int start, int end, int state, List<int> indices) {
+  var tables = _scannerTables;
+  assert(end <= uri.length);
+  for (int i = start; i < end; i++) {
+    var table = tables[state];
+    // Xor with 0x60 to move range 0x20-0x7f into 0x00-0x5f
+    int char = uri.codeUnitAt(i) ^ 0x60;
+    // Use 0x1f (nee 0x7f) to represent all unhandled characters.
+    if (char > 0x5f) char = 0x1f;
+    int transition = table[char];
+    state = transition & 0x1f;
+    indices[transition >> 5] = i;
+  }
+  return state;
+}
+
+class _SimpleUri implements Uri {
+  final String _uri;
+  final int _schemeEnd;
+  final int _hostStart;
+  final int _portStart;
+  final int _pathStart;
+  final int _queryStart;
+  final int _fragmentStart;
+  /// The scheme is often used to distinguish URIs.
+  /// To make comparisons more efficient, we cache the value, and
+  /// canonicalize a few known types.
+  String _schemeCache;
+  int _hashCodeCache;
+
+  _SimpleUri(
+      this._uri,
+      this._schemeEnd,
+      this._hostStart,
+      this._portStart,
+      this._pathStart,
+      this._queryStart,
+      this._fragmentStart,
+      this._schemeCache);
+
+  bool get hasScheme => _schemeEnd > 0;
+  bool get hasAuthority => _hostStart > 0;
+  bool get hasUserInfo => _hostStart > _schemeEnd + 4;
+  bool get hasPort => _hostStart > 0 && _portStart + 1 < _pathStart;
+  bool get hasQuery => _queryStart < _fragmentStart;
+  bool get hasFragment => _fragmentStart < _uri.length;
+
+  bool get _isFile => _schemeEnd == 4 && _uri.startsWith("file");
+  bool get _isHttp => _schemeEnd == 4 && _uri.startsWith("http");
+  bool get _isHttps => _schemeEnd == 5 && _uri.startsWith("https");
+  bool get _isPackage => _schemeEnd == 7 && _uri.startsWith("package");
+  bool _isScheme(String scheme) =>
+    _schemeEnd == scheme.length && _uri.startsWith(scheme);
+
+  bool get hasAbsolutePath => _uri.startsWith("/", _pathStart);
+  bool get hasEmptyPath => _pathStart == _queryStart;
+
+  bool get isAbsolute => hasScheme && !hasFragment;
+
+  String get scheme {
+    if (_schemeEnd <= 0) return "";
+    if (_schemeCache != null) return _schemeCache;
+    if (_isHttp) {
+      _schemeCache = "http";
+    } else if (_isHttps) {
+      _schemeCache = "https";
+    } else if (_isFile) {
+      _schemeCache = "file";
+    } else if (_isPackage) {
+      _schemeCache = "package";
+    } else {
+      _schemeCache = _uri.substring(0, _schemeEnd);
+    }
+    return _schemeCache;
+  }
+  String get authority => _hostStart > 0 ?
+      _uri.substring(_schemeEnd + 3, _pathStart) : "";
+  String get userInfo => (_hostStart > _schemeEnd + 3) ?
+      _uri.substring(_schemeEnd + 3, _hostStart - 1) : "";
+  String get host =>
+      _hostStart > 0 ? _uri.substring(_hostStart, _portStart) : "";
+  int get port {
+    if (hasPort) return int.parse(_uri.substring(_portStart + 1, _pathStart));
+    if (_isHttp) return 80;
+    if (_isHttps) return 443;
+    return 0;
+  }
+  String get path =>_uri.substring(_pathStart, _queryStart);
+  String get query => (_queryStart < _fragmentStart) ?
+     _uri.substring(_queryStart + 1, _fragmentStart) : "";
+  String get fragment => (_fragmentStart < _uri.length) ?
+     _uri.substring(_fragmentStart + 1) : "";
+
+  String get origin {
+    // Check original behavior - W3C spec is wonky!
+    bool isHttp = _isHttp;
+    if (_schemeEnd < 0 || _hostStart == _portStart) {
+      throw new StateError("Cannot use origin without a scheme: $this");
+    }
+    if (!isHttp && !_isHttps) {
+      throw new StateError(
+        "Origin is only applicable schemes http and https: $this");
+    }
+    if (_hostStart == _schemeEnd + 3) {
+      return _uri.substring(0, _pathStart);
+    }
+    // Need to drop anon-empty userInfo.
+    return _uri.substring(0, _schemeEnd + 3) +
+           _uri.substring(_hostStart, _pathStart);
+  }
+
+  List<String> get pathSegments {
+    int start = _pathStart;
+    int end = _queryStart;
+    if (_uri.startsWith("/", start)) start++;
+    if (start == end) return const <String>[];
+    List<String> parts = [];
+    for (int i = start; i < end; i++) {
+      var char = _uri.codeUnitAt(i);
+      if (char == _SLASH) {
+        parts.add(_uri.substring(start, i));
+        start = i + 1;
+      }
+    }
+    parts.add(_uri.substring(start, end));
+    return new List<String>.unmodifiable(parts);
+  }
+
+  Map<String, String> get queryParameters {
+    if (!hasQuery) return const <String, String>{};
+    return new UnmodifiableMapView<String, String>(
+        Uri.splitQueryString(query));
+  }
+
+  Map<String, List<String>> get queryParametersAll {
+    if (!hasQuery) return const <String, List<String>>{};
+    Map queryParameterLists = _Uri._splitQueryStringAll(query);
+    for (var key in queryParameterLists.keys) {
+      queryParameterLists[key] =
+          new List<String>.unmodifiable(queryParameterLists[key]);
+    }
+    return new Map<String, List<String>>.unmodifiable(queryParameterLists);
+  }
+
+  bool _isPort(String port) {
+    int portDigitStart = _portStart + 1;
+    return portDigitStart + port.length == _pathStart &&
+           _uri.startsWith(port, portDigitStart);
+  }
+
+  Uri normalizePath() => this;
+
+  Uri removeFragment() {
+    if (!hasFragment) return this;
+    return new _SimpleUri(
+      _uri.substring(0, _fragmentStart),
+      _schemeEnd, _hostStart, _portStart,
+      _pathStart, _queryStart, _fragmentStart, _schemeCache);
+  }
+
+  Uri replace({String scheme,
+               String userInfo,
+               String host,
+               int port,
+               String path,
+               Iterable<String> pathSegments,
+               String query,
+               Map<String, dynamic/*String|Iterable<String>*/> queryParameters,
+               String fragment}) {
+    bool schemeChanged = false;
+    if (scheme != null) {
+      scheme = _Uri._makeScheme(scheme, 0, scheme.length);
+      schemeChanged = !_isScheme(scheme);
+    } else {
+      scheme = this.scheme;
+    }
+    bool isFile = (scheme == "file");
+    if (userInfo != null) {
+      userInfo = _Uri._makeUserInfo(userInfo, 0, userInfo.length);
+    } else if (_hostStart > 0) {
+      userInfo = _uri.substring(_schemeEnd + 3, _hostStart);
+    } else {
+      userInfo = "";
+    }
+    if (port != null) {
+      port = _Uri._makePort(port, scheme);
+    } else {
+      port = this.hasPort ? this.port : null;
+      if (schemeChanged) {
+        // The default port might have changed.
+        port = _Uri._makePort(port, scheme);
+      }
+    }
+    if (host != null) {
+      host = _Uri._makeHost(host, 0, host.length, false);
+    } else if (_hostStart > 0) {
+      host = _uri.substring(_hostStart, _portStart);
+    } else if (userInfo.isNotEmpty || port != null || isFile) {
+      host = "";
+    }
+
+    bool hasAuthority = host != null;
+    if (path != null || pathSegments != null) {
+      path = _Uri._makePath(path, 0, _stringOrNullLength(path), pathSegments,
+                           scheme, hasAuthority);
+    } else {
+      path = _uri.substring(_pathStart, _queryStart);
+      if ((isFile || (hasAuthority && !path.isEmpty)) &&
+          !path.startsWith('/')) {
+        path = "/" + path;
+      }
+    }
+
+    if (query != null || queryParameters != null) {
+      query = _Uri._makeQuery(
+          query, 0, _stringOrNullLength(query), queryParameters);
+    } else if (_queryStart < _fragmentStart) {
+      query = _uri.substring(_queryStart + 1, _fragmentStart);
+    }
+
+    if (fragment != null) {
+      fragment = _Uri._makeFragment(fragment, 0, fragment.length);
+    } else if (_fragmentStart < _uri.length) {
+      fragment = _uri.substring(_fragmentStart + 1);
+    }
+
+    return new _Uri._internal(
+        scheme, userInfo, host, port, path, query, fragment);
+  }
+
+  Uri resolve(String reference) {
+    return resolveUri(Uri.parse(reference));
+  }
+
+  Uri resolveUri(Uri reference) {
+    if (reference is _SimpleUri) {
+      return _simpleMerge(this, reference);
+    }
+    return _toNonSimple().resolveUri(reference);
+  }
+
+  // Merge two simple URIs. This should always result in a prefix of
+  // one concatentated with a suffix of the other, possibly with a `/` in
+  // the middle of two merged paths, which is again simple.
+  // In a few cases, there might be a need for extra normalization, when
+  // resolving on top of a known scheme.
+  Uri _simpleMerge(_SimpleUri base, _SimpleUri ref) {
+    if (ref.hasScheme) return ref;
+    if (ref.hasAuthority) {
+      if (!base.hasScheme) return ref;
+      bool isSimple = true;
+      if (base._isFile) {
+        isSimple = !ref.hasEmptyPath;
+      } else if (base._isHttp) {
+        isSimple = !ref._isPort("80");
+      } else if (base._isHttps) {
+        isSimple = !ref._isPort("443");
+      }
+      if (isSimple) {
+        var delta = base._schemeEnd + 1;
+        var newUri = base._uri.substring(0, base._schemeEnd + 1) +
+                     ref._uri.substring(ref._schemeEnd + 1);
+        return new _SimpleUri(newUri,
+           base._schemeEnd,
+           ref._hostStart + delta,
+           ref._portStart + delta,
+           ref._pathStart + delta,
+           ref._queryStart + delta,
+           ref._fragmentStart + delta,
+           base._schemeCache);
+      } else {
+        // This will require normalization, so use the _Uri implementation.
+        return _toNonSimple().resolveUri(ref);
+      }
+    }
+    if (ref.hasEmptyPath) {
+      if (ref.hasQuery) {
+        int delta = base._queryStart - ref._queryStart;
+        var newUri = base._uri.substring(0, base._queryStart) +
+                     ref._uri.substring(ref._queryStart);
+        return new _SimpleUri(newUri,
+           base._schemeEnd,
+           base._hostStart,
+           base._portStart,
+           base._pathStart,
+           ref._queryStart + delta,
+           ref._fragmentStart + delta,
+           base._schemeCache);
+      }
+      if (ref.hasFragment) {
+        int delta = base._fragmentStart - ref._fragmentStart;
+        var newUri = base._uri.substring(0, base._fragmentStart) +
+                     ref._uri.substring(ref._fragmentStart);
+        return new _SimpleUri(newUri,
+           base._schemeEnd,
+           base._hostStart,
+           base._portStart,
+           base._pathStart,
+           base._queryStart,
+           ref._fragmentStart + delta,
+           base._schemeCache);
+      }
+      return base.removeFragment();
+    }
+    if (ref.hasAbsolutePath) {
+      var delta = base._pathStart - ref._pathStart;
+      var newUri = base._uri.substring(0, base._pathStart) +
+                   ref._uri.substring(ref._pathStart);
+      return new _SimpleUri(newUri,
+        base._schemeEnd,
+        base._hostStart,
+        base._portStart,
+        base._pathStart,
+        ref._queryStart + delta,
+        ref._fragmentStart + delta,
+        base._schemeCache);
+    }
+    if (base.hasEmptyPath && base.hasAuthority) {
+      // ref has relative non-empty path.
+      // Add a "/" in front, then leading "/../" segments are folded to "/".
+      int refStart = ref._pathStart;
+      while (ref._uri.startsWith("../", refStart)) {
+        refStart += 3;
+      }
+      var delta = base._pathStart - refStart + 1;
+      var newUri = "${base._uri.substring(0, base._pathStart)}/"
+                   "${ref._uri.substring(refStart)}";
+      return new _SimpleUri(newUri,
+        base._schemeEnd,
+        base._hostStart,
+        base._portStart,
+        base._pathStart,
+        ref._queryStart + delta,
+        ref._fragmentStart + delta,
+        base._schemeCache);
+    }
+    // Merge paths.
+    if (base._uri.startsWith("../", base._pathStart)) {
+      // Complex rare case, go slow.
+      return _toNonSimple().resolveUri(ref);
+    }
+
+    // The RFC 3986 algorithm merges the base path without its final segment
+    // (anything after the final "/", or everything if the base path doesn't
+    // contain any "/"), and the reference path.
+    // Then it removes "." and ".." segments using the remove-dot-segment
+    // algorithm.
+    // This code combines the two steps. It is simplified by knowing that
+    // the base path contains no "." or ".." segments, and the reference
+    // path can only contain leading ".." segments.
+
+    String baseUri = base._uri;
+    String refUri = ref._uri;
+    int baseStart = base._pathStart;
+    int baseEnd = base._queryStart;
+    int refStart = ref._pathStart;
+    int refEnd = ref._queryStart;
+    int backCount = 1;
+
+    int slashCount = 0;
+
+    // Count leading ".." segments in reference path.
+    while (refStart + 3 <= refEnd && refUri.startsWith("../", refStart)) {
+      refStart += 3;
+      backCount += 1;
+    }
+
+    // Extra slash inserted between base and reference path parts if
+    // the base path contains any slashes.
+    // (We could use a slash from the base path in most cases, but not if
+    // we remove the entire base path).
+    String insert = "";
+    while (baseEnd > baseStart) {
+      baseEnd--;
+      int char = baseUri.codeUnitAt(baseEnd);
+      if (char == _SLASH) {
+        insert = "/";
+        backCount--;
+        if (backCount == 0) break;
+      }
+    }
+    // If the base URI has no scheme or authority (`_pathStart == 0`)
+    // and a relative path, and we reached the beginning of the path,
+    // we have a special case.
+    if (baseEnd == 0 && !base.hasAbsolutePath) {
+      // Non-RFC 3986 behavior when resolving a purely relative path on top of
+      // another relative path: Don't make the result absolute.
+      insert = "";
+    }
+
+    var delta = baseEnd - refStart + insert.length;
+    var newUri = "${base._uri.substring(0, baseEnd)}$insert"
+               "${ref._uri.substring(refStart)}";
+
+    return new _SimpleUri(newUri,
+      base._schemeEnd,
+      base._hostStart,
+      base._portStart,
+      base._pathStart,
+      ref._queryStart + delta,
+      ref._fragmentStart + delta,
+      base._schemeCache);
+  }
+
+  String toFilePath({bool windows}) {
+    if (_schemeEnd >= 0 && !_isFile) {
+      throw new UnsupportedError(
+          "Cannot extract a file path from a $scheme URI");
+    }
+    if (_queryStart < _uri.length) {
+      if (_queryStart < _fragmentStart) {
+        throw new UnsupportedError(
+            "Cannot extract a file path from a URI with a query component");
+      }
+      throw new UnsupportedError(
+          "Cannot extract a file path from a URI with a fragment component");
+    }
+    if (windows == null) windows = _Uri._isWindows;
+    return windows ? _Uri._toWindowsFilePath(this) : _toFilePath();
+  }
+
+  String _toFilePath() {
+    if (_hostStart < _portStart) {
+      // Has authority and non-empty host.
+      throw new UnsupportedError(
+        "Cannot extract a non-Windows file path from a file URI "
+        "with an authority");
+    }
+    return this.path;
+  }
+
+  UriData get data {
+    assert(scheme != "data");
+    return null;
+  }
+
+  int get hashCode => _hashCodeCache ??= _uri.hashCode;
+
+  bool operator==(Object other) {
+    if (identical(this, other)) return true;
+    if (other is Uri) return _uri == other.toString();
+    return false;
+  }
+
+  Uri _toNonSimple() {
+    return new _Uri._internal(
+      this.scheme,
+      this.userInfo,
+      this.hasAuthority ? this.host: null,
+      this.hasPort ? this.port : null,
+      this.path,
+      this.hasQuery ? this.query : null,
+      this.hasFragment ? this.fragment : null
+    );
+  }
+
+  String toString() => _uri;
+}
+
+/// Checks whether [text] starts with "data:" at position [start].
+///
+/// The text must be long enough to allow reading five characters
+/// from the [start] position.
+///
+/// Returns an integer value which is zero if text starts with all-lowercase
+/// "data:" and 0x20 if the text starts with "data:" that isn't all lower-case.
+/// All other values means the text starts with some other character.
+int _startsWithData(String text, int start) {
+  // Multiply by 3 to avoid a non-colon character making delta be 0x20.
+  int delta = (text.codeUnitAt(start + 4) ^ _COLON) * 3;
+  delta |= text.codeUnitAt(start)     ^ 0x64 /*d*/;
+  delta |= text.codeUnitAt(start + 1) ^ 0x61 /*a*/;
+  delta |= text.codeUnitAt(start + 2) ^ 0x74 /*t*/;
+  delta |= text.codeUnitAt(start + 3) ^ 0x61 /*a*/;
+  return delta;
 }
+
+/// Helper function returning the length of a string, or `0` for `null`.
+int _stringOrNullLength(String s) => (s == null) ? 0 : s.length;