Implement a Base64 codec

lib/src/base64.dart

+part of crypto;
+
+const Base64Codec BASE64 = const Base64Codec();
+
+const List<int> _decodeTable =
+      const [ -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -1, -2, -2, -1, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, 62, -2, 62, -2, 63,
+              52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -2, -2, -2,  0, -2, -2,
+              -2,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
+              15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -2, -2, -2, -2, 63,
+              -2, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
+              41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
+              -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2 ];
+
+const String _encodeTableUrlSafe =
+      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+const String _encodeTable =
+      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+const List<String> _URL_SAFE_CHARACTERS = const ['+', '/'];
+const List<String> _URL_UNSAFE_CHARACTERS = const ['-', '_'];
+
+const int _LINE_LENGTH = 76;
+const int _PAD = 61; // '='
+const int _CR = 13;  // '\r'
+const int _LF = 10;  // '\n'
+
+class Base64Codec extends Codec<List<int>, String> {
+
+  final bool _urlSafe;
+  final bool _addLineSeparator;
+
+  /**
+   * Instantiates a new [Base64Codec].
+   *
+   * The optional [urlSafe] argument specifies if [encoder] and [encode]
+   * should generate a string, that is safe to use in an URL.
+   *
+   * If [urlSafe] is `true` (and not overriden at the method invocation)
+   * the [encoder] and [encode] use '-' instead of '+' and '_' instead of '/'.
+   *
+   * The default value of [urlSafe] is `false`.
+   *
+   * The optional [addLineSeparator] argument specifies if the [encoder] and
+   * [encode] should add line separators.
+   *
+   * If `addLineSeparator` is `true` [encode] adds an
+   * optional line separator (CR + LF) for each 76 char output.
+   *
+   * The default value of [addLineSeparator] if `false`.
+   */
+  const Base64Codec({bool urlSafe: false, bool addLineSeparator: false})
+      : _urlSafe = urlSafe,
+        _addLineSeparator = addLineSeparator;
+
+  String get name => "base64";
+
+  String encode(List<int> bytes,
+                {bool urlSafe,
+                 bool addLineSeparator}) {
+    if (urlSafe == null) urlSafe = _urlSafe;
+    if (addLineSeparator == null) addLineSeparator = _addLineSeparator;
+    return new Base64Encoder(urlSafe: urlSafe,
+                   addLineSeparator: addLineSeparator).convert(bytes);
+
+
+  }
+
+  Base64Encoder get encoder => new Base64Encoder(
+                                     urlSafe: _urlSafe,
+                                     addLineSeparator: _addLineSeparator);
+
+  Base64Decoder get decoder => new Base64Decoder();
+
+}
+
+/**
+ * This class encodes byte strings (lists of unsigned
+ * 8-bit integers) to strings according to Base64.
+ */
+class Base64Encoder extends Converter<List<int>, String> {
+  final bool _urlSafe;
+  final bool _addLineSeparator;
+
+  /**
+   * Instantiates a new [Base64Encoder].
+   *
+   * The optional [urlSafe] argument specifies if [convert]
+   * should generate a string, that is safe to use in an URL.
+   *
+   * If it is `true` the [convert] use
+   * '-' instead of '+' and '_' instead of '/'.
+   *
+   * The default value of [urlSafe] is `false`.
+   *
+   * The optional [addLineSeparator] argument specifies if [convert]
+   * should add line separators.
+   *
+   * If it is `true` [convert] adds an optional line separator(CR + LF)
+   * for each 76 char output.
+   *
+   * The default value of [addLineSeparator] if `false`.
+   */
+

[Søren Gjesse, 2015/06/03 09:20:58]

nit: Please remove the empty line after the dartdoc comment.

[Alexander Ivanov, 2015/06/03 09:32:52]

Done.

+  const Base64Encoder({bool urlSafe: false, bool addLineSeparator: false})
+      : _urlSafe = urlSafe,
+        _addLineSeparator = addLineSeparator;
+
+  /**
+   * Converts [bytes] to its Base64 representation as a string.
+   *
+   * if [start] and [end] are provided, only the sublist
+   * `bytes.sublist(start, end)` is converted.
+   */
+
+  String convert(List<int> bytes, [int start = 0, int end]) {
+    int bytes_length = bytes.length;
+    RangeError.checkValidRange(start, end, bytes_length);
+    if (end == null) end = bytes_length;
+    int length = end - start;
+    if (length == 0) {
+      return "";
+    }
+    final String lookup = _urlSafe ? _encodeTableUrlSafe : _encodeTable;
+    // Size of 24 bit chunks.
+    final int remainderLength = length.remainder(3);
+    final int chunkLength = length - remainderLength;
+    // Size of base output.
+    int baseOutputLength = ((length ~/ 3) * 4);
+    int remainderOutputLength = ((remainderLength > 0) ? 4 : 0);
+    int outputLength = baseOutputLength + remainderOutputLength;
+    // Add extra for line separators.
+    if (_addLineSeparator) {
+      outputLength += ((outputLength - 1) ~/ _LINE_LENGTH) << 1;
+    }
+    List<int> out = new List<int>(outputLength);
+
+    // Encode 24 bit chunks.
+    int j = 0, i = start, c = 0;
+    while (i < chunkLength) {
+      int x = ((bytes[i++] << 16) & 0x00FFFFFF) |
+              ((bytes[i++] << 8) & 0x00FFFFFF) |
+                bytes[i++];
+      out[j++] = lookup.codeUnitAt(x >> 18);
+      out[j++] = lookup.codeUnitAt((x >> 12) & 0x3F);
+      out[j++] = lookup.codeUnitAt((x >> 6)  & 0x3F);
+      out[j++] = lookup.codeUnitAt(x & 0x3F);
+      // Add optional line separator for each 76 char output.
+      if (_addLineSeparator && ++c == 19 && j < outputLength - 2) {
+        out[j++] = _CR;
+        out[j++] = _LF;
+        c = 0;
+      }
+    }
+
+    // If input length if not a multiple of 3, encode remaining bytes and
+    // add padding.
+    if (remainderLength == 1) {
+      int x = bytes[i];
+      out[j++] = lookup.codeUnitAt(x >> 2);
+      out[j++] = lookup.codeUnitAt((x << 4) & 0x3F);
+      out[j++] = _PAD;
+      out[j++] = _PAD;
+    } else if (remainderLength == 2) {
+      int x = bytes[i];
+      int y = bytes[i + 1];
+      out[j++] = lookup.codeUnitAt(x >> 2);
+      out[j++] = lookup.codeUnitAt(((x << 4) | (y >> 4)) & 0x3F);
+      out[j++] = lookup.codeUnitAt((y << 2) & 0x3F);
+      out[j++] = _PAD;
+    }
+
+    return new String.fromCharCodes(out);
+  }
+
+  _Base64EncoderSink startChunkedConversion(Sink<String> sink) {
+    StringConversionSink stringSink;
+    if (sink is StringConversionSink) {
+      stringSink = sink;
+    } else {
+      stringSink = new StringConversionSink.from(sink);
+    }
+    return new _Base64EncoderSink(stringSink, _urlSafe, _addLineSeparator);
+  }
+}
+
+class _Base64EncoderSink extends ChunkedConversionSink<List<int>> {
+
+  final Base64Encoder _encoder;
+  final ChunkedConversionSink<String> _outSink;
+  final List<int> _buffer = new List<int>();
+  int _bufferCount = 0;
+
+  _Base64EncoderSink(this._outSink, urlSafe, addLineSeparator)
+      : _encoder = new Base64Encoder(urlSafe: urlSafe,
+                                     addLineSeparator: addLineSeparator);
+
+
+  void add(List<int> chunk) {
+    var nextBufferCount = (chunk.length + _bufferCount) % 3;
+
+    int decodableLength = _bufferCount + chunk.length - nextBufferCount;
+
+    if (_bufferCount + chunk.length > _buffer.length) {
+      _buffer.replaceRange(_bufferCount,
+                           _buffer.length,
+                           chunk.sublist(0, _buffer.length - _bufferCount));
+      _buffer.addAll(chunk.sublist(_buffer.length - _bufferCount));
+    } else {
+      _buffer.replaceRange(_bufferCount, _bufferCount + chunk.length, chunk);
+    }
+
+    _outSink.add(_encoder.convert(_buffer, 0, decodableLength));
+    _buffer.removeRange(0, decodableLength);
+    _bufferCount = nextBufferCount;
+  }
+
+  void close() {
+    if (_bufferCount > 0) {
+      _outSink.add(_encoder.convert(_buffer.sublist(0, _bufferCount)));
+    }
+    _outSink.close();
+  }
+}
+
+/**
+ * This class decodes strings to lists of bytes(lists of
+ * unsigned 8-bit integers) according to Base64.
+ */
+class Base64Decoder extends Converter<String, List<int>> {
+
+  /**
+   * Instantiates a new [Base64Decoder]
+   */
+

[Søren Gjesse, 2015/06/03 09:20:58]

nit: Please remove the empty line after the dartdoc comment.

[Alexander Ivanov, 2015/06/03 09:32:52]

Done.

+  const Base64Decoder();

[Søren Gjesse, 2015/06/03 09:20:58]

Having thought about this, I think the decode should take the optional named
urlSafe argument, and use that for checking instead of the auto-detection of the
encoding.

[Alexander Ivanov, 2015/06/03 09:32:52]

We decided to discuss it in another change.

+
+  List<int> convert(String input, {bool alwaysPadding: false}) {
+    int length = input.length;
+    if (length == 0) {
+      return new List<int>(0);
+    }
+
+    // Count '\r', '\n' and illegal characters, check if
+    // '/', '+' / '-', '_' are used consistently, for illegal characters,
+    // throw an exception.
+    int extrasLength = 0;
+    bool expectedSafe = false;
+    bool expectedUnsafe = false;
+
+    for (int i = 0; i < length; i++) {
+      int c = _decodeTable[input.codeUnitAt(i)];
+      if (c < 0) {
+        extrasLength++;
+        if (c == -2) {
+          throw new FormatException('Invalid character', input, i);
+        }
+      } else if (input[i] == _URL_UNSAFE_CHARACTERS[0] ||
+                 input[i] == _URL_UNSAFE_CHARACTERS[1]) {
+
+        if (expectedSafe) {
+          throw new FormatException('Unsafe character in URL-safe string',
+                                    input, i);
+        }
+        expectedUnsafe = true;
+      } else if (input[i] == _URL_SAFE_CHARACTERS[0] ||
+                 input[i] == _URL_SAFE_CHARACTERS[1]) {
+        if (expectedUnsafe) {
+          throw new FormatException('Invalid character', input, i);
+        }
+        expectedSafe = true;
+      }
+    }
+
+    if ((length - extrasLength) % 4 != 0) {
+      throw new FormatException('''Size of Base 64 characters in Input
+          must be a multiple of 4''', input, length - extrasLength);
+    }
+
+    // Count pad characters.
+    int padLength = 0;
+    for (int i = length - 1; i >= 0; i--) {
+      int currentCodeUnit = input.codeUnitAt(i);
+      if (_decodeTable[currentCodeUnit] > 0) break;
+      if (currentCodeUnit == _PAD) padLength++;
+    }
+    int outputLength = (((length - extrasLength) * 6) >> 3) - padLength;
+    List<int> out = new List<int>(outputLength);
+
+    for (int i = 0, o = 0; o < outputLength; ) {
+      // Accumulate 4 valid 6 bit Base 64 characters into an int.
+      int x = 0;
+      for (int j = 4; j > 0; ) {
+        int c = _decodeTable[input.codeUnitAt(i++)];
+        if (c >= 0) {
+          x = ((x << 6) & 0x00FFFFFF) | c;
+          j--;
+        }
+      }
+      out[o++] = x >> 16;
+      if (o < outputLength) {
+        out[o++] = (x >> 8) & 0xFF;
+        if (o < outputLength) out[o++] = x & 0xFF;
+      }
+    }
+
+    return out;
+  }
+
+  _Base64DecoderSink startChunkedConversion(Sink<List<int>> sink) {
+    if (sink is! ByteConversionSink) {
+      sink = new ByteConversionSink.from(sink);
+    }
+    return new _Base64DecoderSink(sink);
+  }
+}
+
+
+class _Base64DecoderSink extends ChunkedConversionSink<String> {
+
+  final Base64Decoder _decoder = new Base64Decoder();
+  final ChunkedConversionSink<List<int>> _outSink;
+  String _buffer = "";
+  bool _isSafe = false;
+  bool _isUnsafe = false;
+
+  _Base64DecoderSink(this._outSink);
+
+  void add(String chunk) {
+    int nextBufferLength = (chunk.length + _buffer.length) % 4;
+
+    if (chunk.length + _buffer.length >= 4) {
+      int remainder = chunk.length - nextBufferLength;
+      String decodable = _buffer + chunk.substring(0, remainder);
+      _buffer = chunk.substring(remainder);
+
+      for (int i = 0;i < decodable.length; i++) {
+        if (decodable[i] == _URL_UNSAFE_CHARACTERS[0] ||
+            decodable[i] == _URL_UNSAFE_CHARACTERS[1]) {
+          if (_isSafe) {
+            throw new FormatException('Unsafe character in URL-safe string',
+                                       decodable, i);
+          }
+          _isUnsafe = true;
+        } else if (decodable[i] == _URL_SAFE_CHARACTERS[0] ||
+                   decodable[i] == _URL_SAFE_CHARACTERS[1]) {
+          if (_isUnsafe) {
+            throw new FormatException('Invalid character', decodable, i);
+          }
+          _isSafe = true;
+        }
+      }
+
+      _outSink.add(_decoder.convert(decodable));
+    } else {
+      _buffer += chunk;
+    }
+  }
+
+  void close() {
+    if (!_buffer.isEmpty) {
+      throw new FormatException(
+          "Size of Base 64 input must be a multiple of 4",
+          _buffer,
+          _buffer.length);
+    }
+    _outSink.close();
+  }
+}
+