Binary assets and more unit tests for Asset.

pkg/barback/lib/src/asset.dart

Index: pkg/barback/lib/src/asset.dart
diff --git a/pkg/barback/lib/src/asset.dart b/pkg/barback/lib/src/asset.dart
index 83def7408156e78863f86359befafeaf503b80f0..05a2202dfa612aa62c94d3d57b82f2941bd83ef1 100644
--- a/pkg/barback/lib/src/asset.dart
+++ b/pkg/barback/lib/src/asset.dart
@@ -6,8 +6,10 @@ library barback.asset;
 
 import 'dart:async';
 import 'dart:io';
+import 'dart:utf';
 
 import 'asset_id.dart';
+import 'utils.dart';
 
 /// A blob of content.
 ///
@@ -19,39 +21,80 @@ abstract class Asset {
 
   Asset(this.id);
 
-  factory Asset.fromFile(AssetId id, File file) {
-    return new _FileAsset(id, file);
-  }
+  factory Asset.fromBytes(AssetId id, List<int> bytes) =>
+      new _BinaryAsset(id, bytes);
 
-  factory Asset.fromString(AssetId id, String content) {
-    return new _StringAsset(id, content);
-  }
+  factory Asset.fromFile(AssetId id, File file) =>
+      new _FileAsset(id, file);
 
-  factory Asset.fromPath(AssetId id, String path) {
-    return new _FileAsset(id, new File(path));
-  }
+  factory Asset.fromString(AssetId id, String content) =>
+      new _StringAsset(id, content);
+
+  factory Asset.fromPath(AssetId id, String path) =>
+      new _FileAsset(id, new File(path));
+
+  /// 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 [Encoding.UTF_8].
+  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.
+  Stream<List<int>> read();
+}
+
+/// An asset whose data is stored in a list of bytes.
+class _BinaryAsset extends Asset {
+  final List<int> _contents;
+
+  _BinaryAsset(AssetId id, this._contents)
+      : super(id);
 
-  // TODO(rnystrom): This prevents users from defining their own
-  // implementations of Asset. Use serialization package instead.
-  factory Asset.deserialize(data) {
-    // TODO(rnystrom): Handle errors.
-    var id = new AssetId.parse(data[1]);
-    switch (data[0]) {
-      case "file": return new _FileAsset(id, new File(data[2])); break;
-      case "string": return new _StringAsset(id, data[2]); break;
+  Future<String> readAsString({Encoding encoding}) {
+    if (encoding == null) encoding = Encoding.UTF_8;
+
+    // TODO(rnystrom): When #6284 is fixed, just use that. Until then, only
+    // UTF-8 is supported. :(
+    if (encoding != Encoding.UTF_8) {
+      throw new UnsupportedError(
+          "${encoding.name} is not a supported encoding.");
     }
+
+    return new Future.value(decodeUtf8(_contents));
   }
 
-  /// Returns the contents of the asset as a string.
-  // TODO(rnystrom): Figure out how binary assets should be handled.
-  Future<String> readAsString();
+  Stream<List<int>> read() => new Future<List<int>>.value(_contents).asStream();
 
-  /// Streams the contents of the asset.
-  Stream<List<int>> read();
+  String toString() {
+    var buffer = new StringBuffer();
+    buffer.write("Bytes [");
+
+    // Don't show the whole list if it's long.
+    if (_contents.length > 11) {
+      for (var i = 0; i < 5; i++) {
+        buffer.write(byteToHex(_contents[i]));
+        buffer.write(" ");
+      }
+
+      buffer.write("...");
+
+      for (var i = _contents.length - 5; i < _contents.length; i++) {
+        buffer.write(" ");
+        buffer.write(byteToHex(_contents[i]));
+      }
+    } else {
+      for (var i = 0; i < _contents.length; i++) {
+        if (i > 0) buffer.write(" ");
+        buffer.write(byteToHex(_contents[i]));
+      }
+    }
 
-  /// Serializes this [Asset] to an object that can be sent across isolates
-  /// and passed to [deserialize].
-  Object serialize();
+    buffer.write("]");
+    return buffer.toString();
+  }
 }
 
 /// An asset backed by a file on the local file system.
@@ -60,26 +103,28 @@ class _FileAsset extends Asset {
   _FileAsset(AssetId id, this._file)
       : super(id);
 
-  Future<String> readAsString() => _file.readAsString();
+  Future<String> readAsString({Encoding encoding}) {
+    if (encoding == null) encoding = Encoding.UTF_8;
+    return _file.readAsString(encoding: encoding);
+  }
+
   Stream<List<int>> read() => _file.openRead();
 
   String toString() => 'File "${_file.path}"';
-
-  Object serialize() => ["file", id.serialize(), _file.path];
 }
 
 /// An asset whose data is stored in a string.
-// TODO(rnystrom): Have something similar for in-memory binary assets.
 class _StringAsset extends Asset {
   final String _contents;
 
   _StringAsset(AssetId id, this._contents)
       : super(id);
 
-  Future<String> readAsString() => new Future.value(_contents);
+  Future<String> readAsString({Encoding encoding}) =>
+      new Future.value(_contents);
 
-  // TODO(rnystrom): Implement this and handle encoding.
-  Stream<List<int>> read() => throw new UnimplementedError();
+  Stream<List<int>> read() =>
+      new Future<List<int>>.value(encodeUtf8(_contents)).asStream();
 
   String toString() {
     // Don't show the whole string if it's long.
@@ -93,8 +138,6 @@ class _StringAsset extends Asset {
     return 'String "$contents"';
   }
 
-  Object serialize() => ["string", id.serialize(), _contents];
-
   String _escape(String string) {
     return string
         .replaceAll("\"", r'\"')