Last week I came across a showstopper bug on Mailman 2.1.9-7, the current version of Mailman package distributed with Debian Etch.

Here is the python traceback (from /var/log/mailman/error logfile) I get each time I’ve sent a mail to my brand new mailing-list:

Dec 20 01:20:04 2008 (14275) Uncaught runner exception: len() of unsized object
Dec 20 01:20:04 2008 (14275) Traceback (most recent call last):
  File "/usr/lib/mailman/Mailman/Queue/Runner.py", line 112, in _oneloop
    self._onefile(msg, msgdata)
  File "/usr/lib/mailman/Mailman/Queue/Runner.py", line 170, in _onefile
    keepqueued = self._dispose(mlist, msg, msgdata)
  File "/usr/lib/mailman/Mailman/Queue/IncomingRunner.py", line 130, in _dispose
    more = self._dopipeline(mlist, msg, msgdata, pipeline)
  File "/usr/lib/mailman/Mailman/Queue/IncomingRunner.py", line 153, in _dopipeline
    sys.modules[modname].process(mlist, msg, msgdata)
  File "/usr/lib/mailman/Mailman/Handlers/ToDigest.py", line 81, in process
    mbox.AppendMessage(msg)
  File "/usr/lib/mailman/Mailman/Mailbox.py", line 69, in AppendMessage
    g.flatten(msg, unixfrom=True)
  File "/usr/lib/mailman/pythonlib/email/Generator.py", line 101, in flatten
    self._write(msg)
  File "/usr/lib/mailman/pythonlib/email/Generator.py", line 136, in _write
    self._write_headers(msg)
  File "/usr/lib/mailman/pythonlib/email/Generator.py", line 182, in _write_headers
    header_name=h, continuation_ws='\t').encode()
  File "/usr/lib/mailman/pythonlib/email/Header.py", line 412, in encode
    newchunks += self._split(s, charset, targetlen, splitchars)
  File "/usr/lib/mailman/pythonlib/email/Header.py", line 297, in _split
    elen = charset.encoded_header_len(encoded)
  File "/usr/lib/mailman/pythonlib/email/Charset.py", line 354, in encoded_header_len
    raise repr(s)
TypeError: len() of unsized object

Dec 20 01:20:04 2008 (14275) SHUNTING: 1229732404.1069181+dcd89a08bf7911dac2db804b76cd42d20564c71c

Here is the corresponding (anonymized) mail sent to the mailing list from a Gmail account:

Received: by 10.180.244.13 with HTTP; Fri, 19 Dec 2008 16:32:22 -0800 (PST)
Message-ID: <1f7b086f0812192632x7427c0f7u2048609ddd50673@mail.gmail.com>
Date: Sat, 20 Dec 2008 01:32:22 +0100
From: "Kevin" <kevin@my-domain.com>
To: my-ml@lists.my-domain.com
Subject: sqdfqsdfqsfd
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: base64
Content-Disposition: inline
Delivered-To: kevin@my-domain.com

LS0KS2V2LgogIOKAoiBiYW5kOiBodHRwOi8vY29vbGNhdmVtZW4uY29tCiAg4oCiIGJsb2c6IGh0
dHA6Ly9rZXZpbi5kZWxkeWNrZS5jb20K

And now my hackish tale. Based on a quick look at Mailman’s source code, I made an educated guess that this error is just a side effect of the wrong assumption that the s variable in the Charset.encoded_header_len() method is always a string. So I came up with the following evil patch to handle (gracefully, I hope) the case of s being None.

Here is the resulting patch of my python-fu:

--- /usr/lib/mailman/pythonlib/email/Charset.py.orig   2008-12-28 19:46:23.000000000 +0100
+++ /usr/lib/mailman/pythonlib/email/Charset.py        2008-12-20 01:42:37.000000000 +0100
@@ -351,6 +351,7 @@
             lenqp = email.quopriMIME.header_quopri_len(s)
             return min(lenb64, lenqp) + len(cset) + MISC_LEN
         else:
+            return s is not None and len(str(s)) or 0
             return len(s)

     def header_encode(self, s, convert=False):

And it do the trick! Of course I can’t guarantee that this patch is the way to definitely fix the bug. And it may corrupt data. So use it only if you’re as crazy as me! :D

But I know, I know… As a responsible and serious hacker (sigh), I should report this bug to the Debian or Mailman project. But I’m still not familiar with Dedian’s way of reporting bugs (and to be honest, I feel lazy these days :p ). Maybe, one day…

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