Add base 64 encoding to the crypto library utils.

Add base 64 encoding to the crypto library utils.

It is clearly useful for Crypto APIs. Whether or not we should move
base64 encoding somewhere else can be discussed. However, at least
it is available now.

R=sgjesse@google.com
BUG=dartbug.com/2458
TEST=tests/lib/crypto/base64_test.dart

Committed: https://code.google.com/p/dart/source/detail?r=8108

[Søren Gjesse, 2012-05-30 13:40:08]

LGTM with line breaking fixed.

http://codereview.chromium.org/10456028/diff/1/lib/crypto/crypto_utils.dart
File lib/crypto/crypto_utils.dart (right):

http://codereview.chromium.org/10456028/diff/1/lib/crypto/crypto_utils.dart#n...
lib/crypto/crypto_utils.dart:34: result.add(table[b2 & 0x3f]);
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".

http://codereview.chromium.org/10456028/diff/1/tests/lib/crypto/base64_test.dart
File tests/lib/crypto/base64_test.dart (right):

http://codereview.chromium.org/10456028/diff/1/tests/lib/crypto/base64_test.d...
tests/lib/crypto/base64_test.dart:14: const [ '', 'Zg==', 'Zm8=', 'Zm9v',
'Zm9vYg==', 'Zm9vYmE=', 'Zm9vYmFy' ];
There is a longer example in tests/standalone/crypto/base64_test.dart

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

http://codereview.chromium.org/10456028/diff/1/lib/crypto/crypto_utils.dart
File lib/crypto/crypto_utils.dart (right):

http://codereview.chromium.org/10456028/diff/1/lib/crypto/crypto_utils.dart#n...
lib/crypto/crypto_utils.dart:34: result.add(table[b2 & 0x3f]);
On 2012/05/30 13:40:08, Søren Gjesse wrote:
> 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".

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.

http://codereview.chromium.org/10456028/diff/1/tests/lib/crypto/base64_test.dart
File tests/lib/crypto/base64_test.dart (right):

http://codereview.chromium.org/10456028/diff/1/tests/lib/crypto/base64_test.d...
tests/lib/crypto/base64_test.dart:14: const [ '', 'Zg==', 'Zm8=', 'Zm9v',
'Zm9vYg==', 'Zm9vYmE=', 'Zm9vYmFy' ];
On 2012/05/30 13:40:08, Søren Gjesse wrote:
> There is a longer example in tests/standalone/crypto/base64_test.dart

Thanks!