Add base 64 encoding to the crypto library utils.

lib/crypto/crypto_utils.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.
 
 class _CryptoUtils {
   static String bytesToHex(List<int> bytes) {
     var result = new StringBuffer();
     for (var part in bytes) {
       result.add('${part < 16 ? '0' : ''}${part.toRadixString(16)}');
     }
     return result.toString();
   }
+
+  static String bytesToBase64(List<int> bytes) {
+    final table =
+        const [ 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
+                'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
+                'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
+                'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
+                'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',
+                '8', '9', '+', '/' ];
+
+    var result = new StringBuffer();
+
+    // Encode all full 24-bit blocks.
+    var i = 0;
+    for (; (i + 2) < bytes.length; i += 3) {
+      var b0 = bytes[i] & 0xff;
+      var b1 = bytes[i + 1] & 0xff;
+      var b2 = bytes[i + 2] & 0xff;
+      result.add(table[b0 >> 2]);
+      result.add(table[((b0 << 4) | (b1 >> 4)) & 0x3f]);
+      result.add(table[((b1 << 2) | (b2 >> 6)) & 0x3f]);
+      result.add(table[b2 & 0x3f]);

[Søren Gjesse, 2012/05/30 13:40:08]

You need to insert \r\n for at least every 76 characters (57 bytes or 19
blocks). RFC 2045 page 24 says "The encoded output stream must be represented in
lines of no more than 76 characters each".

[Mads Ager (google), 2012/05/30 15:16:10]

http://tools.ietf.org/html/rfc4648

explicitly says in section 3.1 that implementations MUST NOT add line feeds
unless explicitly stated so. I'll add an optional parameter 'lineLength' which
can be used to specify the 76 char line length if used for MIME.

+    }
+
+    // Deal with the last non-full block if any and add padding '='.
+    if (i == bytes.length - 1) {
+      var b0 = bytes[i] & 0xff;
+      result.add(table[b0 >> 2]);
+      result.add(table[(b0 << 4) & 0x3f]);
+      result.add('=');
+      result.add('=');
+    } else if (i == bytes.length - 2) {
+      var b0 = bytes[i] & 0xff;
+      var b1 = bytes[i + 1] & 0xff;
+      result.add(table[b0 >> 2]);
+      result.add(table[((b0 << 4) | (b1 >> 4)) & 0x3f]);
+      result.add(table[(b1 << 2) & 0x3f]);
+      result.add('=');
+    }
+
+    return result.toString();
+  }
 }