Add an AssetStream class to Barback.

pkg/barback/lib/src/asset.dart

 // Copyright (c) 2013, 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 barback.asset;
 
 import 'dart:async';
 import 'dart:convert' show Encoding, UTF8;
 import 'dart:io';
 import 'dart:utf';
 
 import 'asset_id.dart';
+import 'stream_replayer.dart';
 import 'utils.dart';
 
 /// A blob of content.
 ///
 /// Assets may come from the file system, or as the output of a [Transformer].
 /// They are identified by [AssetId].
 abstract class Asset {
   /// The ID for this asset.
   final AssetId id;
 
   Asset(this.id);
 
   factory Asset.fromBytes(AssetId id, List<int> bytes) =>
       new _BinaryAsset(id, bytes);
 
   factory Asset.fromFile(AssetId id, File file) =>
       new _FileAsset(id, file);
 
   factory Asset.fromString(AssetId id, String content) =>
       new _StringAsset(id, content);
 
   factory Asset.fromPath(AssetId id, String path) =>
       new _FileAsset(id, new File(path));
 
+  /// Creates an asset from a stream.
+  ///
+  /// This immediately starts draining [stream].
+  factory Asset.fromStream(AssetId id, Stream<List<int>> stream) =>
+      new _StreamAsset(id, stream);
+
   /// Returns the contents of the asset as a string.
   ///
   /// If the asset was created from a [String] the original string is always
   /// returned and [encoding] is ignored. Otherwise, the binary data of the
   /// asset is decoded using [encoding], which defaults to [UTF8].
   Future<String> readAsString({Encoding encoding});
 
   /// Streams the binary contents of the asset.
   ///
   /// If the asset was created from a [String], this returns its UTF-8 encoding.
@@ skipping 86 matching lines @@
   }
 
   String _escape(String string) {
     return string
         .replaceAll("\"", r'\"')
         .replaceAll("\n", r"\n")
         .replaceAll("\r", r"\r")
         .replaceAll("\t", r"\t");
   }
 }
+
+/// An asset whose data is available from a stream.
+class _StreamAsset extends Asset {
+  /// A stream replayer that records and replays the contents of the input
+  /// stream.
+  final StreamReplayer<List<int>> _replayer;
+
+  _StreamAsset(AssetId id, Stream<List<int>> stream)
+      : _replayer = new StreamReplayer(stream),
+        super(id);
+
+  Future<String> readAsString({Encoding encoding}) {
+    if (encoding == null) encoding = UTF8;
+    return _replayer.getReplay().toList()
+        .then((chunks) => encoding.decode(flatten(chunks)));
+  }
+
+  Stream<List<int>> read() => _replayer.getReplay();
+
+  String toString() => "Stream";
+}