Add support for file URIs and extracting the file path from file URIs

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 73ce45b906d466733aa000276c1a4b5fa424c034..fbc4ba7845e69b6c597d15d43036c2b3e8c546ab 100644
--- a/sdk/lib/core/uri.dart
+++ b/sdk/lib/core/uri.dart
@@ -263,6 +263,191 @@ class Uri {
   }
 
   /**
+   * Creates a new `file` URI from an absolute or relative file path.

[ahe, 2013/08/06 14:14:30]

I think backquotes are for code snippets, I'm not sure it is the right thing to
use here.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+   *
+   * The file path is passed in [path].
+   *
+   * This path is interpreted using either Windows or non-Windows
+   * semantics. For Windows semantics the backslash or slash separator
+   * is used to separate path segments.

[ahe, 2013/08/06 14:14:30]

Remove the rest of this paragraph from "For Windows semantics ...". It is
redundant with the paragraph below.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+   *
+   * With non-Windows semantics the slash `/` is used to separate path

[ahe, 2013/08/06 14:14:30]

I'm not sure about this use of backquotes either. It would make more sense if it
was: `"/"`

[Søren Gjesse, 2013/08/07 12:08:00]

Ended up using ("/") and ("\").

+   * segments.
+   *
+   * With Windows semantics both the backslash `\` and the slash `/`
+   * are is used to separate path segments. An exception is when the
+   * path is prefixed with `\\?\` in which case only the backslash `\`

[ahe, 2013/08/06 14:14:30]

You could replace "is prefixed with" by "starts with".

You could also rewrite it to something like:

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.

[Søren Gjesse, 2013/08/07 12:08:00]

Thanks for rephrasing.

+   * is treated as a path separator.

[ahe, 2013/08/06 14:14:30]

Ditto for the backquotes in above paragraph.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+   *
+   * 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 with Windows semantics and a path which starts
+   * with a drive letter then an absolute URI is created.

[ahe, 2013/08/06 14:14:30]

This specification does not match the example below: new Uri.file(r"C:") throws
an exception.

[Søren Gjesse, 2013/08/07 12:08:00]

Extended the comment to say that the drive letter must be followed by a colon
and a path separator to become absolute with Windows semantics.

+   *
+   * 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 the browser non-Windows

[ahe, 2013/08/06 14:14:30]

"the browser" -> "a browser".

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+   * semantics is always used.
+   *
+   * To override the automatic detection of which semantics to use pass
+   * a value for [windowsPath]. Passing `true` will use Windows
+   * semantics and passing `false` will use non-Windows semantics.
+   *
+   * Examples using non-Windows semantics (resulting URI in comment):
+   *
+   *     new Uri.file("xxx/yyy");  // xxx/yyy
+   *     new Uri.file("xxx/yyy/");  // xxx/yyy/
+   *     new Uri.file("/xxx/yyy");  // file:///xxx/yyy
+   *     new Uri.file("/xxx/yyy/");  // file:///xxx/yyy/
+   *     new Uri.file("C:");  // C:
+   *
+   * Examples using Windows semantics (resulting URI in comment):
+   *
+   *     new Uri.file(r"xxx\yyy");  // xxx/yyy
+   *     new Uri.file(r"xxx\yyy\");  // xxx/yyy/
+   *     new Uri.file(r"\xxx\yyy");  // file:///xxx/yyy
+   *     new Uri.file(r"\xxx\yyy/");  // file:///xxx/yyy/
+   *     new Uri.file(r"C:\xxx\yyy");  // file:///C:/xxx/yyy
+   *     new Uri.file(r"C:xxx\yyy");  // file:///C:/xxx/yyy
+   *     new Uri.file(r"\\server\share\file");  // file://server/share/file
+   *     new Uri.file(r"C:");  // Throws as path with drive letter is not absolute.

[ahe, 2013/08/06 14:14:30]

Long line.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+   *
+   * If the path passed is not a legal file path [ArgumentError] is thrown.
+   */
+  factory Uri.file(String path, {bool windowsPath}) {
+    windowsPath = windowsPath == null ? Uri._isWindows : windowsPath;

[ahe, 2013/08/06 14:14:30]

Remove Uri. prefix.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+    return windowsPath ? _makeWindowsFileUrl(path) : _makeFileUri(path);
+  }
+
+  external static bool get _isWindowsPlatform;
+
+  static final bool _isWindows = _isWindowsPlatform;

[ahe, 2013/08/06 14:14:30]

For dart2js, this code is suboptimal. I think it would be best if there was just
one external getter for _isWindows (you can cache the result in the VM patch
file).

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+
+  // Characters which are not allowed in file names on Windows.
+  static final _windowsPathReservedCharacters = [
+    _DOUBLE_QUOTE,
+    _ASTERISK,
+    _SLASH,
+    _COLON,  // Colon is only allowed after drive letter.
+    _LESS,
+    _GREATER,
+    _QUESTION,
+    _BACKSLASH,  // Backslash can only be separator.
+    _BAR,
+  ];
+
+  static _checkNonWindowsPathReservedCharacters(List<String> segments,
+                                         bool argumentError) {

[ahe, 2013/08/06 14:14:30]

Indentation.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+    for (var segment in segments) {
+      if (segment.contains("/")) {
+        if (argumentError) {
+          throw new ArgumentError("Illegal path character $segment");
+        } else {
+          throw new UnsupportedError("Illegal path character $segment");
+        }
+      }
+    }
+  }
+
+  static _checkWindowsPathReservedCharacters(List<String> segments,
+                                             bool argumentError,
+                                             [int firstSegment = 0]) {
+    for (int i = firstSegment; i < segments.length; i++) {
+      var segment = segments[i];
+      for (int j = 0; j < segment.length; j++) {
+        if (_windowsPathReservedCharacters.contains(segment.codeUnitAt(j))) {

[ahe, 2013/08/06 14:14:30]

I suspect that regular expressions would be faster for dart2js.

This code feels simpler:

segments.skip(firstSegment).forEach((segment) {
  if (segment.contains(new RegExp(r'["*/:<>?\|]'))) {
    throw ...
  }
});

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+          if (argumentError) {
+            throw new ArgumentError("Illegal path character ${segment[j]}");
+          } else {
+            throw new UnsupportedError("Illegal path character ${segment[j]}");
+          }
+        }
+      }
+    }
+  }
+
+  static _checkWindowsDriveLetter(int charCode, bool argumentError) {
+    if ((_UPPER_CASE_A <= charCode && charCode <= _UPPER_CASE_Z) ||
+        (_LOWER_CASE_A <= charCode && charCode <= _LOWER_CASE_Z)) {
+      return;
+    }
+    if (argumentError) {
+      throw new ArgumentError("Illegal drive letter " +
+                              new String.fromCharCode(charCode));
+    } else {
+      throw new UnsupportedError("Illegal drive letter " +
+                              new String.fromCharCode(charCode));
+    }
+  }
+
+  static _makeFileUri(String path) {
+    String sep = "/";
+    if (path.length > 0 && path[0] == sep) {
+      // Absolute file:// URI.
+      return new Uri(scheme: "file", pathSegments: path.split(sep));
+    } else {
+      // Relative URI.
+      return new Uri(pathSegments: path.split(sep));
+    }
+  }
+
+  static _makeWindowsFileUrl(String path) {
+    if (path.startsWith("\\\\?\\")) {
+      if (path.startsWith("\\\\?\\UNC\\")) {
+        path = "\\${path.substring(7)}";
+      } else {
+        path = path.substring(4);
+        if (path.length < 3 ||
+            path.codeUnitAt(1) != _COLON ||
+            path.codeUnitAt(2) != _BACKSLASH) {
+          throw new ArgumentError(
+              "Windows paths with \\\\?\\ prefix must be absolute");
+        }
+      }
+    } else {
+      path = path.replaceAll("/", "\\");
+    }
+    String sep = "\\";
+    if (path.length > 1 && path[1] == ":") {
+      _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);
+      _checkWindowsPathReservedCharacters(pathSegments, true, 1);
+      return new Uri(scheme: "file", pathSegments: pathSegments);
+    }
+
+    if (path.length > 0 && path[0] == sep) {
+      if (path.length > 1 && path[1] == sep) {
+        // Absolute file:// URI with host.
+        int pathStart = path.indexOf("\\", 2);
+        String hostPart =
+            pathStart == -1 ? path.substring(2) : path.substring(2, pathStart);
+        String pathPart =
+            pathStart == -1 ? "" : path.substring(pathStart + 1);
+        var pathSegments = pathPart.split(sep);
+        _checkWindowsPathReservedCharacters(pathSegments, true);
+        return new Uri(
+            scheme: "file", host: hostPart, pathSegments: pathSegments);
+      } else {
+        // Absolute file:// URI.
+        var pathSegments = path.split(sep);
+        _checkWindowsPathReservedCharacters(pathSegments, true);
+        return new Uri(scheme: "file", pathSegments: pathSegments);
+      }
+    } else {
+      // Relative URI.
+      var pathSegments = path.split(sep);
+      _checkWindowsPathReservedCharacters(pathSegments, true);
+      return new Uri(pathSegments: pathSegments);
+    }
+  }
+
+  /**
    * 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
@@ -651,6 +836,120 @@ class Uri {
     return "$scheme://$host:$port";
   }
 
+  /**
+   * Returns the file path from a file URI.
+   *
+   * The returned path has either Windows or non-Windows
+   * semantics.
+   *
+   * For Windows semantics the backslash separator is used to separate
+   * path segments.
+   *
+   * For non-Windows semantics the slash 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 the browser non-Windows

[ahe, 2013/08/06 14:14:30]

the browser -> a browser.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+   * semantics is always used.
+   *
+   * To override the automatic detection of which semantics to use pass
+   * a value for [windowsPath]. 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 return
+   * `c:\abc` and *not* `c:abc`.

[ahe, 2013/08/06 14:14:30]

I thought this would throw.

[Søren Gjesse, 2013/08/07 12:08:00]

It now throws.

As discussed before I was not sure how to handle this. E.g. when entering
file:///c:adb in Chrome it turned into file:///C:/abc.

After thinking about it again it now throws, and I don't try to do artificial
splitting of the first path segment if it contains a colon.

+   *
+   * Examples using non-Windows semantics (resulting of calling toFilePath in comment):

[ahe, 2013/08/06 14:14:30]

Long line.

[Søren Gjesse, 2013/08/07 12:08:00]

Done.

+   *
+   *     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");  // C:\xxx\yyy
+   *     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].
+   */
+  String toFilePath({bool windowsPath}) {
+    if (scheme != "" && scheme != "file") {
+      throw new UnsupportedError(
+          "Cannot extract a file path from a $scheme URI");
+    }
+    if (windowsPath == null) windowsPath = _isWindows;
+    return windowsPath ? _toWindowsFilePath() : _toFilePath();

[ahe, 2013/08/06 14:14:30]

You should probably check that all other fields but host and path are empty.

[Søren Gjesse, 2013/08/07 12:08:00]

Done and added tests.

+  }
+
+  String _toFilePath() {
+    if (host != "") {
+      throw new UnsupportedError(
+          "Cannot extract a non-Windows file path from a file URI "
+          "with an authority");
+    }
+    _checkNonWindowsPathReservedCharacters(pathSegments, false);
+    var result = new StringBuffer();
+    if (isAbsolute) result.write("/");
+    result.writeAll(pathSegments, "/");
+    return result.toString();
+  }
+
+  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);
+      if (segments[0].length > 2) {
+        var originalSegments = segments;
+        segments = new List<String>(originalSegments.length + 1);
+        segments[0] = originalSegments[0].substring(0, 2);
+        segments[1] = originalSegments[0].substring(2);
+        segments.setRange(2, segments.length, originalSegments, 1);
+      }
+      _checkWindowsPathReservedCharacters(segments, false, 1);
+      hasDriveLetter = true;
+    } else {
+      _checkWindowsPathReservedCharacters(segments, false);
+    }
+    var result = new StringBuffer();
+    if (isAbsolute && !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();
+  }
+
   void _writeAuthority(StringSink ss) {
     _addIfNonEmpty(ss, userInfo, userInfo, "@");
     ss.write(host == null ? "null" :
@@ -840,17 +1139,26 @@ class Uri {
   }
 
   // Frequently used character codes.
+  static const int _DOUBLE_QUOTE = 0x22;
   static const int _PERCENT = 0x25;
+  static const int _ASTERISK = 0x2A;
   static const int _PLUS = 0x2B;
   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 _BACKSLASH = 0x5C;
   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;
 
   /**
    * This is the internal implementation of JavaScript's encodeURI function.