bug #553 Fix base64 encoding with streams (apinstein)

This PR was merged into the 5.3-dev branch.

Discussion
----------

Fix base64 encoding with streams

Fixes [gh-207].

Commits
-------

ce0aa52 Fix bug when read() does not return a buffer of length 3n which caused the base64 stream to be truncated.
36219af Adjust Swift_Mime_ContentEncoder_Base64ContentEncoder read() to non-triplet aligned number to make test fail.

lib/classes/Swift/Mime/ContentEncoder/Base64ContentEncoder.php

@@ -30,9 +30,42 @@ public function encodeByteStream(Swift_OutputByteStream $os, Swift_InputByteStre
         }
 
         $remainder = 0;
+        $base64ReadBufferRemainderBytes = NULL;
 
-        while (false !== $bytes = $os->read(8190)) {
-            $encoded = base64_encode($bytes);
+        // To reduce memory usage, the output buffer is streamed to the input buffer like so:
+        //   Output Stream => base64encode => wrap line length => Input Stream
+        // HOWEVER it's important to note that base64_encode() should only be passed whole triplets of data (except for the final chunk of data)
+        // otherwise it will assume the input data has *ended* and it will incorrectly pad/terminate the base64 data mid-stream.
+        // We use $base64ReadBufferRemainderBytes to carry over 1-2 "remainder" bytes from the each chunk from OutputStream and pre-pend those onto the
+        // chunk of bytes read in the next iteration.
+        // When the OutputStream is empty, we must flush any remainder bytes.
+        while (true) {
+            $readBytes = $os->read(8192);
+            $atEOF = ($readBytes === false);
+
+            if ($atEOF) {
+                $streamTheseBytes = $base64ReadBufferRemainderBytes;
+            } else {
+                $streamTheseBytes = $base64ReadBufferRemainderBytes . $readBytes;
+            }
+            $base64ReadBufferRemainderBytes = NULL;
+            $bytesLength = strlen($streamTheseBytes);
+
+            if ($bytesLength === 0) { // no data left to encode
+                break;
+            }
+
+            // if we're not on the last block of the ouput stream, make sure $streamTheseBytes ends with a complete triplet of data
+            // and carry over remainder 1-2 bytes to the next loop iteration
+            if (!$atEOF) {
+                $excessBytes = $bytesLength % 3;
+                if ($excessBytes !== 0) {
+                    $base64ReadBufferRemainderBytes = substr($streamTheseBytes, -$excessBytes);
+                    $streamTheseBytes = substr($streamTheseBytes, 0, $bytesLength - $excessBytes);
+                }
+            }
+
+            $encoded = base64_encode($streamTheseBytes);
             $encodedTransformed = '';
             $thisMaxLineLength = $maxLineLength - $remainder - $firstLineOffset;
 
@@ -51,6 +84,10 @@ public function encodeByteStream(Swift_OutputByteStream $os, Swift_InputByteStre
             }
 
             $is->write($encodedTransformed);
+
+            if ($atEOF) {
+                break;
+            }
         }
     }