First version of Codecs and Converters.

sdk/lib/convert/json.dart

Index: sdk/lib/convert/json.dart
diff --git a/sdk/lib/convert/json.dart b/sdk/lib/convert/json.dart
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+// 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.
+
+part of dart.convert;
+
+/**
+ * A [JsonEncoder] converts JSON objects to strings.
+ */
+class JsonEncoder extends Converter<Object, String> {
+  JsonEncoder();
+
+  /**
+   * Converts the given object [o] to its JSON representation.
+   *
+   * Directly serializable values are [num], [String], [bool], and [Null], as
+   * well as some [List] and [Map] values.
+   * For [List], the elements must all be serializable.
+   * For [Map], the keys must be [String] and the values must be serializable.
+   *
+   * If a value is any other type is attempted serialized, a "toJson()" method
+   * is invoked on the object and the result, which must be a directly
+   * serializable value, is serialized instead of the original value.
+   *
+   * If the object does not support this method, throws, or returns a
+   * value that is not directly serializable, a [JsonUnsupportedObjectError]
+   * exception is thrown. If the call throws (including the case where there
+   * is no nullary "toJson" method, the error is caught and stored in the
+   * [JsonUnsupportedObjectError]'s [:cause:] field.
+   *
+   * If a [List] or [Map] contains a reference to itself, directly or through
+   * other lists or maps, it cannot be serialized and a [JsonCyclicError] is
+   * thrown.
+   *
+   * Json Objects should not change during serialization.
+   * If an object is serialized more than once, [stringify] is allowed to cache
+   * the JSON text for it. I.e., if an object changes after it is first
+   * serialized, the new values may or may not be reflected in the result.
+   */
+  String convert(Object o) => OLD_JSON_LIB.stringify(o);
+}
+
+typedef _Reviver(var key, var value);
+
+
+/**
+ * A [JsonDecoder] parses JSON strings and builds the corresponding objects.
+ */
+class JsonDecoder extends Converter<String, Object> {
+  final _Reviver _reviver;
+  /**
+   * Constructs a new JsonDecoder.
+   *
+   * The [reviver] may be `null`.
+   */
+  JsonDecoder(reviver(var key, var value)) : this._reviver = reviver;
+
+  /**
+   * Converts the given Json-string [input] to its corresponding object.
+   *
+   * Parsed JSON values are of the types [num], [String], [bool], [Null],
+   * [List]s of parsed JSON values or [Map]s from [String] to parsed
+   * JSON values.
+   *
+   * If `this` was initialized with a reviver, then the parsing operation
+   * invokes the reviver on every object or list property that has been parsed.
+   * The arguments are the property name ([String]) or list index ([int]), and
+   * the value is the parsed value. The return value of the reviver is used as
+   * the value of that property instead the parsed value.
+   *
+   * Throws [FormatException] if the input is not valid JSON text.
+   */
+  Object convert(String input) => OLD_JSON_LIB.parse(input, _reviver);
+}