Fix mbox exports. Fixes #3076.

Sometime in August incoming message format changed.
Messages now include the "From " envelope header
when they didn't before. This resulted in duplicate
envelope headers in the export files, essentially
corrupting them. The export code was changed to only
add the envelope header if it isn't already there.

 - Legacy-Id: 1031

backend/mlarchive/archive/view_funcs.py

@@ -259,9 +259,11 @@ def build_mbox_tar(sqs, tar, basename):
             mbox_list = mlist
 
         with open(result.object.get_file_path(), 'rb') as input:
-            # add envelope header
-            from_line = smart_bytes(result.object.get_from_line()) + b'\n'
-            mbox_file.write(from_line)
+            # add envelope header if missing
+            if not input.read(5) == b'From ':
+                from_line = smart_bytes(result.object.get_from_line()) + b'\n'
+                mbox_file.write(from_line)
+            input.seek(0)
             mbox_file.write(input.read())
             mbox_file.write(b'\n')
 

requirements.txt

@@ -1,6 +1,5 @@
 # -*- conf-mode -*-
 # NOTE: Django 2.0, Celery 5.0 only support Python 3
-setuptools>=18.5                        # Require this first, to prevent later errors
 #
 #bs4			# 4.1.3 was installed
 beautifulsoup4