add workaround for unixfrom bug in Mailman

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = extra-mailman-archivers
-version = 0.0.3
+version = 0.0.4
 author = Max Erenberg
 author_email = merenber@csclub.uwaterloo.ca
 description = Some extra archivers for Mailman 3

src/extra_mailman_archivers/pipermail.py

@@ -31,6 +31,7 @@ from io import BytesIO
 import logging
 import os
 import tempfile
+import time
 
 from flufl.lock import Lock
 from mailman.config import config
@@ -90,6 +91,15 @@ class Pipermail:
         :type mlist: mailman.interfaces.mailinglist.IMailingList
         :type message: mailman.email.message.Message
         """
+        
+        # Workaround for a bug in Mailman which sets unixfrom to an email
+        # address instead of an mbox header
+        # https://gitlab.com/mailman/mailman/-/blob/master/src/mailman/runners/lmtp.py#L139
+        old_unixfrom = msg.get_unixfrom()
+        if old_unixfrom is not None and not old_unixfrom.startswith('From '):
+            # Adapted from https://github.com/python/cpython/blob/3.9/Lib/email/generator.py
+            msg.set_unixfrom('From ' + old_unixfrom + ' ' + time.ctime(time.time()))
+
         # Mangle the 'From ' lines and add the Unix envelope header.
         fp = BytesIO()
         g = BytesGenerator(fp, mangle_from_=True)
@@ -135,5 +145,6 @@ class Pipermail:
         finally:
             lock.unlock(unconditionally=True)
             os.unlink(tempfile_name)
+            msg.set_unixfrom(old_unixfrom)
 
         return None