Add an option for percent-encoding of the padding character to Base64Codec

lib/src/base64.dart

+// Copyright (c) 2012, 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 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,
@@ skipping 12 matching lines @@
 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'
+const List<int> _PAD_BYTES = const [61]; // '='
+const List<int> _ENCODED_PAD_BYTES = const [37, 51, 68]; // '%3D'
+const String _PAD = "=";
+const String _ENCODED_PAD = "%3D";
 
 class Base64Codec extends Codec<List<int>, String> {
 
   final bool _urlSafe;
   final bool _addLineSeparator;
+  final bool _encodePaddingCharacter;
 
   /**
    * 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`.
+   *
+   * If [encodePaddingCharacter] is `true` `encode` converts `=` to `%3D`.
+   * The default value of [encodePaddingCharacter] is `false`.
    */
-  const Base64Codec({bool urlSafe: false, bool addLineSeparator: false})
+  const Base64Codec({bool urlSafe: false,
+                     bool addLineSeparator: false,
+                     bool encodePaddingCharacter: false})
       : _urlSafe = urlSafe,
-        _addLineSeparator = addLineSeparator;
+        _addLineSeparator = addLineSeparator,
+        _encodePaddingCharacter = encodePaddingCharacter;
 
   String get name => "base64";
 
   String encode(List<int> bytes,
                 {bool urlSafe,
-                 bool addLineSeparator}) {
+                 bool addLineSeparator,
+                 bool encodePaddingCharacter}) {
     if (urlSafe == null) urlSafe = _urlSafe;
     if (addLineSeparator == null) addLineSeparator = _addLineSeparator;
-    return new Base64Encoder(urlSafe: urlSafe,
-                   addLineSeparator: addLineSeparator).convert(bytes);
+    if (encodePaddingCharacter == null) {
+      encodePaddingCharacter = _encodePaddingCharacter;
+    }
+    return new Base64Encoder(
+                   urlSafe: urlSafe,
+                   addLineSeparator: addLineSeparator,
+                   encodePaddingCharacter: encodePaddingCharacter)
+                 .convert(bytes);
 
 
   }
 
-  Base64Encoder get encoder => new Base64Encoder(
-                                     urlSafe: _urlSafe,
-                                     addLineSeparator: _addLineSeparator);
+  Base64Encoder get encoder =>
+      new Base64Encoder(urlSafe: _urlSafe,
+                        addLineSeparator: _addLineSeparator,
+                        encodePaddingCharacter: _encodePaddingCharacter);
 
   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;
+  final bool _encodePaddingCharacter;
+  final List<int> _pad;
 
   /**
    * 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`.
+   *
+   * If [encodePaddingCharacter] is `true` `encode` converts `=` to `%3D`.
+   * The default value of [encodePaddingCharacter] is `false`.
    */
-  const Base64Encoder({bool urlSafe: false, bool addLineSeparator: false})
+  const Base64Encoder({bool urlSafe: false,
+                       bool addLineSeparator: false,
+                       bool encodePaddingCharacter: false})
       : _urlSafe = urlSafe,
-        _addLineSeparator = addLineSeparator;
+        _addLineSeparator = addLineSeparator,
+        _encodePaddingCharacter = encodePaddingCharacter,
+        _pad = encodePaddingCharacter == true ? _ENCODED_PAD_BYTES : _PAD_BYTES;
 
   /**
    * 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 remainderOutputLength;
+    if(_encodePaddingCharacter) {
+      remainderOutputLength = ((remainderLength > 0) ? 6 : 0);
+    } else {
+      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) {
@@ skipping 11 matching lines @@
         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;
+      out.setRange(j, j + _pad.length, _pad);
+      out.setRange(j + _pad.length, j + 2 * _pad.length, _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;
+      out.setRange(j, j + _pad.length, _pad);
     }
 
     return new String.fromCharCodes(out);
   }
 
   _Base64EncoderSink startChunkedConversion(Sink<String> sink) {
     StringConversionSink stringSink;
     if (sink is StringConversionSink) {
       stringSink = sink;
     } else {
@@ skipping 46 matching lines @@
  * 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]
    */
   const Base64Decoder();
 
-  List<int> convert(String input, {bool alwaysPadding: false}) {
+  List<int> convert(String input) {
     int length = input.length;
     if (length == 0) {
       return new List<int>(0);
     }
 
+    bool expectedSafe = false;
+    bool expectedUnsafe = false;
+
+    int normalLength = 0;
+    int i = 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) {
+    while (i < length) {
+      int codeUnit = input.codeUnitAt(i);
+      int c = _decodeTable[codeUnit];
+      if (c == -2) {
+        if (codeUnit == _ENCODED_PAD_BYTES[0] &&
+            i < length - 2 &&
+            input.codeUnitAt(i + 1) == _ENCODED_PAD_BYTES[1] &&
+            input.codeUnitAt(i + 2) == _ENCODED_PAD_BYTES[2]) {
+          normalLength++;
+          i += 2;
+        } else {
           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 (c >= 0) normalLength++;
+      i++;
     }
 
-    if ((length - extrasLength) % 4 != 0) {
+    if (normalLength % 4 != 0) {
       throw new FormatException('''Size of Base 64 characters in Input
-          must be a multiple of 4''', input, length - extrasLength);
+          must be a multiple of 4''', input, normalLength);
     }
 
     // Count pad characters.
     int padLength = 0;
-    for (int i = length - 1; i >= 0; i--) {
+    i = length - 1;
+    while(i >= 0) {
       int currentCodeUnit = input.codeUnitAt(i);
-      if (_decodeTable[currentCodeUnit] > 0) break;
-      if (currentCodeUnit == _PAD) padLength++;
+      if (currentCodeUnit == _ENCODED_PAD_BYTES[2] &&
+                i >= 2 &&
+                input.codeUnitAt(i - 1) == _ENCODED_PAD_BYTES[1] &&
+                input.codeUnitAt(i - 2) == _ENCODED_PAD_BYTES[0]) {
+        padLength++;
+        i -= 2;
+      } else if (_decodeTable[currentCodeUnit] > 0) {
+        break;
+      } else if (currentCodeUnit == _PAD_BYTES[0]) {
+        padLength++;
+      }
+      i--;
     }
-    int outputLength = (((length - extrasLength) * 6) >> 3) - padLength;
+    int outputLength = ((normalLength * 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--;
@@ skipping 18 matching lines @@
 }
 
 
 class _Base64DecoderSink extends ChunkedConversionSink<String> {
 
   final Base64Decoder _decoder = new Base64Decoder();
   final ChunkedConversionSink<List<int>> _outSink;
   String _buffer = "";
   bool _isSafe = false;
   bool _isUnsafe = false;
+  int _expectPaddingCount = 3;
 
   _Base64DecoderSink(this._outSink);
 
   void add(String chunk) {
+    if (chunk.isEmpty) return;
+
     int nextBufferLength = (chunk.length + _buffer.length) % 4;
 
+    if (chunk.length >= _expectPaddingCount &&
+        chunk.substring(0, _expectPaddingCount) ==
+          _ENCODED_PAD.substring(3 - _expectPaddingCount, 3)) {
+      chunk = _PAD + chunk.substring(_expectPaddingCount);
+      _expectPaddingCount = 3;
+    } else if(chunk.length < _expectPaddingCount &&
+              chunk == _ENCODED_PAD.substring(
+                         3 - _expectPaddingCount,
+                         3 - _expectPaddingCount + chunk.length)) {
+      _expectPaddingCount -= chunk.length;
+      chunk = "";
+    }
+
+    if (chunk.length > 1 &&
+        chunk[chunk.length - 2] == _ENCODED_PAD[0] &&
+        chunk[chunk.length - 1] == _ENCODED_PAD[1]) {
+      _expectPaddingCount = 1;
+      chunk = chunk.substring(0, chunk.length - 2);
+    } else if (!chunk.isEmpty && chunk[chunk.length - 1] == _ENCODED_PAD[0]) {
+      _expectPaddingCount = 2;
+      chunk = chunk.substring(0, chunk.length - 1);
+    }
+
+    chunk = chunk.replaceAll(_ENCODED_PAD, _PAD);
+
     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) {
+    if (_expectPaddingCount == 0 &&
+        _buffer.length == 3) {
+      _outSink.add(_buffer + _PAD);
+    } else if (_expectPaddingCount < 3 &&
+               _buffer.length + 3 - _expectPaddingCount == 4) {
+      _outSink.add(_buffer + _ENCODED_PAD.substring(0, 3 - _expectPaddingCount));
+    } else if (_expectPaddingCount != 3 || !_buffer.isEmpty) {
       throw new FormatException(
-          "Size of Base 64 input must be a multiple of 4",
-          _buffer,
-          _buffer.length);
+        "Size of Base 64 input must be a multiple of 4",
+        _buffer + _PAD.substring(0, 3 - _expectPaddingCount),
+        _buffer.length + 3 - _expectPaddingCount);
     }
     _outSink.close();
   }
 }
 
+