First version of Codecs and Converters.

sdk/lib/codec/codec.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 dart.codec;
+
+import 'dart:convert';
+
+part 'encoding.dart';
+part 'json.dart';
+
+/**
+ * A [Codec] encodes and (if supported) decodes data.
+ *
+ * Codecs can be fused. For example fusing [JSON] and [UTF8] produces
+ * an encoder that can convert Json objects directly to bytes, or can decode
+ * bytes directly to json objects.
+ *
+ * Fused codecs generally attempt to optimize the operations and can be faster
+ * than executing each step of an encoding separately.
+ *
+ * *Codecs are still experimental and are subject to change without notice.*
+ */
+abstract class Codec<S, T> {
+  const Codec();
+
+  T encode(S input) => encoder.convert(input);
+  S decode(T encoded) => decoder.convert(encoded);
+
+  /**
+   * Returns the encoder from [S] to [T].
+   *
+   * It may be stateful and should not be reused.
+   */
+  Converter<S, T> get encoder;
+  /**
+   * Returns the decoder of `this`, converting from [T] to [S].
+   *
+   * It may be stateful an should not be reused.
+   */
+  Converter<T, S> get decoder;
+
+  /**
+   * Fuses `this` with `other`.
+   *
+   * When encoding, the resulting codec encodes with `this` before
+   * encoding with [other].
+   *
+   * When decoding, the resulting codec decodes with [other] before decoding
+   * with `this`.
+   *
+   * In some cases one needs to use the [inverted] codecs to be able to fuse
+   * them correctly. That is, the output type of `this` ([T]) must match the
+   * input type of the second codec [other].
+   *
+   * Examples:
+   *
+   *     final JSON_TO_BYTES = JSON.fuse(UTF8);
+   *     List<int> bytes = JSON_TO_BYTES.encode(["json-object"]);
+   *     var decoded = JSON_TO_BYTES.decode(bytes);
+   *     assert(decoded is List && decoded[0] == "json-object");
+   *
+   *     var inverted = JSON.inverted;
+   *     var jsonIdentity = JSON.fuse(inverted);
+   *     var jsonObject = jsonIdentity.encode(["1", 2]);
+   *     assert(jsonObject is List && jsonObject[0] == "1" && jsonObject[1] == 2);
+   */
+  // TODO(floitsch): use better example with line-splitter once that one is
+  // in this library.
+  Codec<S, dynamic> fuse(Codec<T, dynamic> other) {
+    return new _FusedCodec<S, T, dynamic>(this, other);
+  }
+
+  /**
+   * Inverts `this`.
+   *
+   * The [encoder] and [decoder] of the resulting codec are swapped.
+   */
+  Codec<T, S> get inverted => new _InvertedCodec<T, S>(this);
+}
+
+/**
+ * Fuses the given codecs.
+ *
+ * In the non-chunked conversion simply invokes the non-chunked conversions in
+ * sequence.
+ */
+class _FusedCodec<S, M, T> extends Codec<S, T> {
+  final Codec<S, M> _first;
+  final Codec<M, T> _second;
+
+  Converter<S, T> get encoder => _first.encoder.fuse(_second.encoder);
+  Converter<T, S> get decoder => _second.decoder.fuse(_first.decoder);
+
+  _FusedCodec(this._first, this._second);
+}
+
+class _InvertedCodec<T, S> extends Codec<T, S> {
+  final Codec<S, T> _codec;
+
+  _InvertedCodec(Codec<S, T> codec) : _codec = codec;
+
+  Converter<T, S> get encoder => _codec.decoder;
+  Converter<S, T> get decoder => _codec.encoder;
+
+  Codec<S, T> get inverted => _codec;
+}