ssoma-mda: Unfold folding whitespace in message subjects

For the RFC specs on folding whitespace, see [1] and [2].  For the
decision to preserve the original folding in Python headers, here's
R. David Murray's comment from 2011-04-18 [3]:

  I have, by the way, come around to the view that we should never be
  introducing or deleting whitespace except when RFC 2047
  encoding/decoding...we are still deleting it in a couple places, and
  I will address that by and by

[1]: https://tools.ietf.org/html/rfc5322#section-2.2.3
[2]: https://tools.ietf.org/html/rfc5322#section-3.2.2
[3]: http://bugs.python.org/issue1372770#msg133974

diff --git a/ssoma-mda b/ssoma-mda
index 10b8d3d917a38da4e27d96533840588166974955..39bed3eb2ad187ddc317be65da993c69ac2a210a 100755 (executable)
--- a/ssoma-mda
+++ b/ssoma-mda
@@ -50,6 +50,7 @@ import email.utils as _email_utils
 import hashlib as _hashlib
 import logging as _logging
 import os.path as _os_path
+import re as _re
 import sys as _sys
 import pygit2 as _pygit2
 
@@ -61,6 +62,7 @@ _LOG.setLevel(_logging.ERROR)
 _LOG.addHandler(_logging.StreamHandler())
 
 _COMMIT_MESSAGE_ENCODING = 'UTF-8'
+_FOLDING_WHITESPACE_REGEX = _re.compile('\s*\n\s*')
 
 
 class DirtyIndex(RuntimeError):
@@ -258,6 +260,8 @@ def deliver(message=None, message_bytes=None, **kwargs):
     path = message_id_path(message_id=message_id)
     _LOG.info('deliver {} to {}'.format(message_id, path))
     commit_message = message.get('Subject', '<no subject>')
+    if '\n' in commit_message:
+        commit_message = _FOLDING_WHITESPACE_REGEX.sub(' ', commit_message)
     author = get_author(message=message)
     repository = _pygit2.Repository(_os_path.curdir)
     append(