Add Resource package.

lib/src/resource.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-library resoure.resource;
-
 import "dart:async" show Future, Stream;
 import "dart:convert" show Encoding;
 import "dart:isolate" show Isolate;
-import "package_resolver.dart";
-import "io.dart" as io;  // Loading strategy. TODO: Be configuration dependent.
-
-/// A strategy for resolving package URIs
-abstract class PackageResolver {
-  /// Cache of the current resolver, accessible directly after it has first
-  /// been found asynchronously.
-  static PackageResolver _current;
-
-  /// The package resolution strategy used by the current isolate.
-  static final Future<PackageResolver> current = _findIsolateResolution();
-
-  PackageResolver();
-
-  /// Creates a resolver using a map from package name to package location.
-  factory PackageResolver.fromMap(Map<String, Uri> packages) = MapResolver;
-
-  /// Creates a resolver using a package root.
-  factory PackageResolver.fromRoot(Uri packageRoot) = RootResolver;
-
-  /// Resolves a package URI to its location.
-  ///
-  /// If [uri] does not have `package` as scheme, it is returned again.
-  /// Otherwise the package name is looked up, and if found, a location
-  /// for the package file is returned.
-  Future<Uri> resolve(Uri uri);
-
-  /// Returns a [Resource] for the [uri] as resolved by this resolver.
-  Resource resource(Uri uri) {
-    return new _UriResource(this, uri);
-  }
-
-  /// Finds the way the current isolate resolves package URIs.
-  ///
-  /// Is only called once, and when it has been called, the [_current]
-  /// resolver is initialized, so [UriResource] will be initialized
-  /// with the resolver directly.
-  static Future<PackageResolver> _findIsolateResolution() async {
-    var pair = await Future.wait([Isolate.packageRoot, Isolate.packageMap]);
-    Uri root = pair[0];
-    if (root != null) {
-      _current = new RootResolver(root);
-    } else {
-      Map<String, Uri> map = pair[1];
-      _current = new MapResolver(map);
-    }
-    return _current;
-  }
-}
+import "loader.dart";
 
 /// A resource that can be read into the program.
 ///
 /// A resource is data that can be located using a URI and read into
 /// the program at runtime.
 /// The URI may use the `package` scheme to read resources provided
 /// along with package sources.
 abstract class Resource {
   /// Creates a resource object with the given [uri] as location.
   ///
-  /// The `uri` is a string containing a valid URI.
+  /// The [uri] must be either a [Uri] or a string containing a valid URI.
   /// If the string is not a valid URI, using any of the functions on
   /// the resource object will fail.
   ///
   /// The URI may be relative, in which case it will be resolved
   /// against [Uri.base] before being used.
   ///
   /// The URI may use the `package` scheme, which is always supported.
   /// Other schemes may also be supported where possible.
-  const factory Resource(String uri) = _StringResource;
+  ///
+  /// If [loader] is provided, it is used to load absolute non-package URIs.
+  /// Package: URIs are resolved to a non-package URI before being loaded, so
+  /// the loader doesn't have to support package: URIs, nor does it need to
+  /// support relative URI references.
+  /// If [loader] is omitted, a default implementation is used which supports
+  /// as many of `http`, `https`, `file` and `data` as are available on the
+  /// current platform.
+  const factory Resource(uri, {ResourceLoader loader}) = _Resource;
 
-  /// Creates a resource object with the given [uri] as location.
-  ///
-  /// The URI may be relative, in which case it will be resolved
-  /// against [Uri.base] before being used.
-  ///
-  /// The URI may use the `package` scheme, which is always supported.
-  /// Other schemes may also be supported where possible.
-  factory Resource.forUri(Uri uri) =>
-      new _UriResource(PackageResolver._current, uri);
-
-  /// The location `uri` of this resource.
+  /// The location URI of this resource.
   ///
   /// This is a [Uri] of the `uri` parameter given to the constructor.
-  /// If the parameter was not a valid URI, reading `uri` may fail.
+  /// If the parameter was a string that did not contain a valid URI,
+  /// reading `uri` will fail.
   Uri get uri;
 
+  /// Reads the resource content as a stream of bytes.
   Stream<List<int>> openRead();
 
+  /// Reads the resource content as a single list of bytes.
   Future<List<int>> readAsBytes();
 
-  /// Read the resource content as a string.
+  /// Reads the resource content as a string.
   ///
   /// The content is decoded into a string using an [Encoding].
   /// If no other encoding is provided, it defaults to UTF-8.
   Future<String> readAsString({Encoding encoding});
 }
 
-class _StringResource implements Resource {
-  final String _uri;
-
-  const _StringResource(String uri) : _uri = uri;
-
-  Uri get uri => Uri.parse(_uri);
-
-  Stream<List<int>> openRead() {
-    return new _UriResource(PackageResolver._current, uri).openRead();
-  }
-  Future<List<int>> readAsBytes() {
-    return new _UriResource(PackageResolver._current, uri).readAsBytes();
-  }
-  Future<String> readAsString({Encoding encoding}) {
-    return new _UriResource(PackageResolver._current, uri)
-                   .readAsString(encoding: encoding);
-  }
-}
-
-class _UriResource implements Resource {
-  /// The strategy for resolving package: URIs.
-  ///
-  /// May be null intially. If so, the [PackageResolver.current] resolver is
-  /// used (and cached for later use).
-  PackageResolver _resolver;
+class _Resource implements Resource {
+  /// Loading strategy for the resource.
+  final ResourceLoader _loader;
 
   /// The URI of the resource.
-  final Uri uri;
+  final _uri;
 
-  _UriResource(this.resolver, Uri uri);
+  const _Resource(uri, {ResourceLoader loader})
+      : _uri = uri, _loader = (loader != null) ? loader : const DefaultLoader();
+  // TODO: Make this `loader ?? const DefaultLoader()` when ?? is const.
+
+  Uri get uri => (_uri is String) ? Uri.parse(_uri) : (_uri as Uri);
 
   Stream<List<int>> openRead() async* {
-    Uri uri = await _resolve(this.uri);
-    return io.readAsStream(uri);
+    Uri uri = await _resolvedUri;
+    yield* _loader.openRead(uri);
   }
 
   Future<List<int>> readAsBytes() async {
-    Uri uri = await _resolve(this.uri);
-    return io.readAsBytes(uri);
+    Uri uri = await _resolvedUri;
+    return _loader.readAsBytes(uri);
   }
 
   Future<String> readAsString({Encoding encoding}) async {
-    Uri uri = await _resolve(this.uri);
-    return io.readAsString(uri, encoding);
+    Uri uri = await _resolvedUri;
+    return _loader.readAsString(uri, encoding: encoding);
   }
 
-  static void _checkPackageUri(Uri uri) {
-    if (uri.scheme != "package") {
-      throw new ArgumentError.value(uri, "Not a package: URI");
-    }
-    if (uri.hasAuthority) {
-      throw new ArgumentError.value(uri,
-          "A package: URI must not have an authority part");
-    }
-    if (uri.path.isEmpty || uri.path.startsWith('/')) {
-      throw new ArgumentError.value(uri,
-          "A package: URI must have the form "
-          "'package:packageName/packagePath'");
-    }
-    if (uri.hasQuery) {
-      throw new ArgumentError.value(uri,
-          "A package: URI must not have a query part");
-    }
-    if (uri.hasFragment) {
-      throw new ArgumentError.value(uri,
-          "A package: URI must not have a fragment part");
-    }
-  }
-
-  Future<Uri> _resolve(Uri uri) async {
-    if (uri.scheme != "package") {
-      return Uri.base.resolveUri(uri);
-    }
-    _checkPackageUri(uri);
-    _resolver ??= await PackageResolver._current;
-    return _resolver.resolve(uri);
-  }
+  Future<Uri> get _resolvedUri => resolveUri(uri);
 }
-
-/// A [PackageResolver] based on a packags map.
-class MapResolver extends PackageResolver {
-  Map<String, Uri> _mapping;
-
-  MapResolver(this._mapping);
-
-  Uri resolve(Uri uri) {
-    if (uri.scheme != "package") return uri;
-    var path = uri.path;
-    int slashIndex = path.indexOf('/');
-    if (slashIndex <= 0) {
-      throw new ArgumentError.value(uri, "Invalid package URI");
-    }
-    int packageName = path.substring(0, slashIndex);
-    var base = _mapping[packageName];
-    if (base != null) {
-      int packagePath = path.substring(slashIndex + 1);
-      return base.resolveUri(new Uri(path: packagePath));
-    }
-    throw new UnsupportedError("No package named '$packageName' found");
-  }
-}
-
-/// A [PackageResolver] based on a package root.
-class RootResolver extends PackageResolver {
-  Uri _root;
-  RootResolver(this._root);
-
-  Uri resolve(Uri uri) {
-    if (uri.scheme != "package") return uri;
-    return _root.resolve(uri.path);
-  }
-}