Merged revisions 83690 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/py3k

........
  r83690 | r.david.murray | 2010-08-03 18:14:10 -0400 (Tue, 03 Aug 2010) | 10 lines

  #3196: if needed pad a short base64 encoded word before trying to decode.

  The RFCs encourage following Postel's law: be liberal in what you accept.
  So if someone forgot to pad the base64 encoded word payload to an
  even four bytes, we add the padding before handing it to base64mime.decode.
  Previously, missing padding resulted in a HeaderParseError.

  Patch by Jason Williams.
........

Lib/email/header.py

@@ -94,6 +94,9 @@ def decode_header(header):
             word = email.quoprimime.header_decode(encoded_string)
             decoded_words.append((word, charset))
         elif encoding == 'b':
+            paderr = len(encoded_string) % 4   # Postel's law: add missing padding
+            if paderr:
+                encoded_string += '==='[:4 - paderr]
             try:
                 word = email.base64mime.decode(encoded_string)
             except binascii.Error: