Add "url-safe" encoding to base64 in dart:convert.

sdk/lib/convert/base64.dart

Index: sdk/lib/convert/base64.dart
diff --git a/sdk/lib/convert/base64.dart b/sdk/lib/convert/base64.dart
index eb7519a2710175d9ace3aaaea344e44d9a498f8d..c6cac6ed76cf42f1d7641cebbef604f7de72eb13 100644
--- a/sdk/lib/convert/base64.dart
+++ b/sdk/lib/convert/base64.dart
@@ -5,13 +5,11 @@
 part of dart.convert;
 
 /**
- * An instance of [Base64Codec].
+ * A [base64](https://tools.ietf.org/html/rfc4648) encoder and decoder.
  *
- * This instance provides a convenient access to
- * [base64](https://tools.ietf.org/html/rfc4648) encoding and decoding.
- *
- * It encodes and decodes using the default base64 alphabet, does not allow
- * any invalid characters when decoding, and requires padding.
+ * It encodes using the default base64 alphabet,
+ * decodes using both the base64 and base64url alphabets,
+ * does not allow invalid characters and requires padding.
  *
  * Examples:
  *
@@ -21,6 +19,21 @@ part of dart.convert;
  */
 const Base64Codec BASE64 = const Base64Codec();
 
+/**
+ * A [base64url](https://tools.ietf.org/html/rfc4648) encoder and decoder.
+ *
+ * It encodes and decodes using the base64url alphabet,
+ * decodes using both the base64 and base64url alphabets,
+ * does not allow invalid characters and requires padding.
+ *
+ * Examples:
+ *
+ *     var encoded = BASE64.encode([0x62, 0x6c, 0xc3, 0xa5, 0x62, 0xc3, 0xa6,
+ *                                  0x72, 0x67, 0x72, 0xc3, 0xb8, 0x64]);
+ *     var decoded = BASE64.decode("YmzDpWLDpnJncsO4ZAo=");
+ */
+const Base64Codec BASE64URL = const Base64Codec.urlSafe();
+
 // Constants used in more than one class.
 const int _paddingChar = 0x3d;  // '='.
 
@@ -30,15 +43,18 @@ const int _paddingChar = 0x3d;  // '='.
  * A [Base64Codec] allows base64 encoding bytes into ASCII strings and
  * decoding valid encodings back to bytes.
  *
- * This implementation only handles the simplest RFC 4648 base-64 encoding.
+ * This implementation only handles the simplest RFC 4648 base64 and base64url
+ * encodings.
  * It does not allow invalid characters when decoding and it requires,
  * and generates, padding so that the input is always a multiple of four
  * characters.
  */
 class Base64Codec extends Codec<List<int>, String> {
-  const Base64Codec();
+  final Base64Encoder _encoder;
+  const Base64Codec() : _encoder = const Base64Encoder();
+  const Base64Codec.urlSafe() : _encoder = const Base64Encoder.urlSafe();
 
-  Base64Encoder get encoder => const Base64Encoder();
+  Base64Encoder get encoder => _encoder;
 
   Base64Decoder get decoder => const Base64Decoder();
 }
@@ -48,44 +64,53 @@ class Base64Codec extends Codec<List<int>, String> {
 // ------------------------------------------------------------------------
 
 /**
- * Base-64 encoding converter.
+ * Base64 and base64url encoding converter.
  *
- * Encodes lists of bytes using base64 encoding.
- * The result are ASCII strings using a restricted alphabet.
+ * Encodes lists of bytes using base64 or base64url encoding.
+ *
+ * The results are ASCII strings using a restricted alphabet.
  */
 class Base64Encoder extends Converter<List<int>, String> {
-  const Base64Encoder();
+  final bool _urlSafe;
+
+  const Base64Encoder() : _urlSafe = false;
+  const Base64Encoder.urlSafe() : _urlSafe = true;
 
   String convert(List<int> input) {
     if (input.isEmpty) return "";
-    var encoder = new _Base64Encoder();
+    var encoder = new _Base64Encoder(_urlSafe);
     Uint8List buffer = encoder.encode(input, 0, input.length, true);
     return new String.fromCharCodes(buffer);
   }
 
   ByteConversionSink startChunkedConversion(Sink<String> sink) {
     if (sink is StringConversionSink) {
-      return new _Utf8Base64EncoderSink(sink.asUtf8Sink(false));
+      return new _Utf8Base64EncoderSink(sink.asUtf8Sink(false), _urlSafe);
     }
-    return new _AsciiBase64EncoderSink(sink);
+    return new _AsciiBase64EncoderSink(sink, _urlSafe);
   }
 
   Stream<String> bind(Stream<List<int>> stream) {
     return new Stream<String>.eventTransformed(
         stream,
         (EventSink sink) =>
-            new _ConverterStreamEventSink<List<int>, String>(this, sink));
+            new _ConverterStreamEventSink<List<int>, String>(
+                this, sink));
   }
 }
 
 /**
- * Helper class for encoding bytes to BASE-64.
+ * Helper class for encoding bytes to base64.
  */
 class _Base64Encoder {
   /** The RFC 4648 base64 encoding alphabet. */
   static const String _base64Alphabet =
       "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
+  /** The RFC 4648 base64url encoding alphabet. */
+  static const String _base64urlAlphabet =
+      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
   /** Shift-count to extract the values stored in [_state]. */
   static const int _valueShift = 2;
 
@@ -103,6 +128,12 @@ class _Base64Encoder {
    */
   int _state = 0;
 
+  /** Alphabet used for encoding. */
+  final String _alphabet;
+
+  _Base64Encoder(bool urlSafe)
+      : _alphabet = urlSafe ? _base64urlAlphabet : _base64Alphabet;
+
   /** Encode count and bits into a value to be stored in [_state]. */
   static int _encodeState(int count, int bits) {
     assert(count <= _countMask);
@@ -148,15 +179,17 @@ class _Base64Encoder {
       bufferLength += 4;  // Room for padding.
     }
     var output = createBuffer(bufferLength);
-    _state = encodeChunk(bytes, start, end, isLast, output, 0, _state);
+    _state = encodeChunk(_alphabet, bytes, start, end, isLast,
+                         output, 0, _state);
     if (bufferLength > 0) return output;
     // If the input plus the data in state is still less than three bytes,
     // there may not be any output.
     return null;
   }
 
-  static int encodeChunk(List<int> bytes, int start, int end, bool isLast,
-                          Uint8List output, int outputIndex, int state) {
+  static int encodeChunk(String alphabet,
+                         List<int> bytes, int start, int end, bool isLast,
+                         Uint8List output, int outputIndex, int state) {
     int bits = _stateBits(state);
     // Count number of missing bytes in three-byte chunk.
     int expectedChars = 3 - _stateCount(state);
@@ -172,20 +205,20 @@ class _Base64Encoder {
       expectedChars--;
       if (expectedChars == 0) {
         output[outputIndex++] =
-            _base64Alphabet.codeUnitAt((bits >> 18) & _sixBitMask);
+            alphabet.codeUnitAt((bits >> 18) & _sixBitMask);
         output[outputIndex++] =
-            _base64Alphabet.codeUnitAt((bits >> 12) & _sixBitMask);
+            alphabet.codeUnitAt((bits >> 12) & _sixBitMask);
         output[outputIndex++] =
-            _base64Alphabet.codeUnitAt((bits >> 6) & _sixBitMask);
+            alphabet.codeUnitAt((bits >> 6) & _sixBitMask);
         output[outputIndex++] =
-            _base64Alphabet.codeUnitAt(bits & _sixBitMask);
+            alphabet.codeUnitAt(bits & _sixBitMask);
         expectedChars = 3;
         bits = 0;
       }
     }
     if (byteOr >= 0 && byteOr <= 255) {
       if (isLast && expectedChars < 3) {
-        writeFinalChunk(output, outputIndex, 3 - expectedChars, bits);
+        writeFinalChunk(alphabet, output, outputIndex, 3 - expectedChars, bits);
         return 0;
       }
       return _encodeState(3 - expectedChars, bits);
@@ -208,24 +241,25 @@ class _Base64Encoder {
    * Only used when the [_state] contains a partial (1 or 2 byte)
    * input.
    */
-  static void writeFinalChunk(Uint8List output, int outputIndex,
+  static void writeFinalChunk(String alphabet,
+                              Uint8List output, int outputIndex,
                               int count, int bits) {
     assert(count > 0);
     if (count == 1) {
       output[outputIndex++] =
-          _base64Alphabet.codeUnitAt((bits >> 2) & _sixBitMask);
+          alphabet.codeUnitAt((bits >> 2) & _sixBitMask);
       output[outputIndex++] =
-          _base64Alphabet.codeUnitAt((bits << 4) & _sixBitMask);
+          alphabet.codeUnitAt((bits << 4) & _sixBitMask);
       output[outputIndex++] = _paddingChar;
       output[outputIndex++] = _paddingChar;
     } else {
       assert(count == 2);
       output[outputIndex++] =
-          _base64Alphabet.codeUnitAt((bits >> 10) & _sixBitMask);
+          alphabet.codeUnitAt((bits >> 10) & _sixBitMask);
       output[outputIndex++] =
-          _base64Alphabet.codeUnitAt((bits >> 4) & _sixBitMask);
+          alphabet.codeUnitAt((bits >> 4) & _sixBitMask);
       output[outputIndex++] =
-          _base64Alphabet.codeUnitAt((bits << 2) & _sixBitMask);
+          alphabet.codeUnitAt((bits << 2) & _sixBitMask);
       output[outputIndex++] = _paddingChar;
     }
   }
@@ -240,6 +274,8 @@ class _BufferCachingBase64Encoder extends _Base64Encoder {
    */
   Uint8List bufferCache;
 
+  _BufferCachingBase64Encoder(bool urlSafe) : super(urlSafe);
+
   Uint8List createBuffer(int bufferLength) {
     if (bufferCache == null || bufferCache.length < bufferLength) {
       bufferCache = new Uint8List(bufferLength);
@@ -268,11 +304,11 @@ abstract class _Base64EncoderSink extends ByteConversionSinkBase {
 }
 
 class _AsciiBase64EncoderSink extends _Base64EncoderSink {
-  final _Base64Encoder _encoder = new _BufferCachingBase64Encoder();
-
   final Sink<String> _sink;
+  final _Base64Encoder _encoder;
 
-  _AsciiBase64EncoderSink(this._sink);
+  _AsciiBase64EncoderSink(this._sink, bool urlSafe)
+      : _encoder = new _BufferCachingBase64Encoder(urlSafe);
 
   void _add(List<int> source, int start, int end, bool isLast) {
     Uint8List buffer = _encoder.encode(source, start, end, isLast);
@@ -288,9 +324,10 @@ class _AsciiBase64EncoderSink extends _Base64EncoderSink {
 
 class _Utf8Base64EncoderSink extends _Base64EncoderSink {
   final ByteConversionSink _sink;
-  final _Base64Encoder _encoder = new _Base64Encoder();
+  final _Base64Encoder _encoder;
 
-  _Utf8Base64EncoderSink(this._sink);
+  _Utf8Base64EncoderSink(this._sink, bool urlSafe)
+      : _encoder = new _Base64Encoder(urlSafe);
 
   void _add(List<int> source, int start, int end, bool isLast) {
     Uint8List buffer = _encoder.encode(source, start, end, isLast);
@@ -304,6 +341,13 @@ class _Utf8Base64EncoderSink extends _Base64EncoderSink {
 // Decoder
 // ------------------------------------------------------------------------
 
+/**
+ * Decoder for base64 encoded data.
+ *
+ * This decoder accepts both base64 and base64url ("url-safe") encodings.
+ *
+ * The encoding is required to be properly padded.
+ */
 class Base64Decoder extends Converter<String, List<int>> {
   const Base64Decoder();
 
@@ -349,7 +393,7 @@ class _Base64Decoder {
    *
    * Accepts the "URL-safe" alphabet as well (`-` and `_` are the
    * 62nd and 63rd alphabet characters), and considers `%` a padding
-   * character which mush be followed by `3D`, the percent-escape
+   * character, which mush then be followed by `3D`, the percent-escape
    * for `=`.
    */
   static final List<int> _inverseAlphabet = new Int8List.fromList([
@@ -371,7 +415,7 @@ class _Base64Decoder {
   /**
    * Maintains the intermediate state of a partly-decoded input.
    *
-   * BASE-64 is decoded in chunks of four characters. If a chunk does not
+   * Base64 is decoded in chunks of four characters. If a chunk does not
    * contain a full block, the decoded bits (six per character) of the
    * available characters are stored in [_state] until the next call to
    * [_decode] or [_close].
@@ -618,7 +662,7 @@ class _Base64Decoder {
    * Check that the remainder of the string is valid padding.
    *
    * Valid padding is a correct number (0, 1 or 2) of `=` characters
-   * or `%3D` sequences depending on the number of preceding BASE-64 characters.
+   * or `%3D` sequences depending on the number of preceding base64 characters.
    * The [state] parameter encodes which padding continuations are allowed
    * as the number of expected characters. That number is the number of
    * expected padding characters times 3 minus the number of padding characters