Subject prefixes
Mailing lists can define a subject prefix which gets added to the front of
any Subject
text. This can be used to quickly identify which mailing list
the message was posted to.
>>> from mailman.app.lifecycle import create_list
>>> mlist = create_list('test@example.com')
The default list style gives the mailing list a default prefix.
>>> print(mlist.subject_prefix)
[Test]
This can be changed to anything, but typically ends with a trailing space.
>>> mlist.subject_prefix = '[XTest] '
>>> from mailman.config import config
>>> process = config.handlers['subject-prefix'].process
No Subject
If the original message has no Subject
, then a canned one is used.
>>> from mailman.testing.helpers import (specialized_message_from_string
... as message_from_string)
>>> msg = message_from_string("""\
... From: aperson@example.com
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest] (no subject)
Inserting a prefix
If the original message had a Subject
header, then the prefix is inserted
at the beginning of the header’s value.
>>> msg = message_from_string("""\
... From: aperson@example.com
... Subject: Something important
...
... A message of great import.
... """)
>>> msgdata = {}
>>> process(mlist, msg, msgdata)
>>> print(msg['subject'])
[XTest] Something important
The original Subject
is available in the metadata.
>>> print(msgdata['original_subject'])
Something important
If a Subject
header already has a prefix, usually following a Re:
marker, another one will not be added but the prefix will be moved to the
front of the header text.
>>> msg = message_from_string("""\
... From: aperson@example.com
... Subject: Re: [XTest] Something important
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest] Re: Something important
If the Subject
header has a prefix at the front of the header text, that’s
where it will stay.
>>> msg = message_from_string("""\
... From: aperson@example.com
... Subject: [XTest] Re: Something important
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest] Re: Something important
Sometimes the incoming Subject
header has a pathological sequence of
Re:
like markers. These should all be collapsed up to the first non-Re:
marker.
>>> msg = message_from_string("""\
... From: aperson@example.com
... Subject: [XTest] Re: RE : Re: Re: Re: Re: Re: Something important
...
... A message of great import.
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest] Re: Something important
Internationalized headers
Internationalization adds some interesting twists to the handling of subject prefixes. Part of what makes this interesting is the encoding of i18n headers using RFC 2047, and lists whose preferred language is in a different character set than the encoded header.
>>> msg = message_from_string("""\
... Subject: =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'].encode())
[XTest] =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
>>> print(str(msg['subject']))
[XTest] メールマン
Prefix numbers
Subject prefixes support a placeholder for the numeric post id. Every time a
message is posted to the mailing list, a post id gets incremented. This is
a purely sequential integer that increases monotonically. By added a %d
placeholder to the subject prefix, this post id can be included in the prefix.
>>> mlist.subject_prefix = '[XTest %d] '
>>> mlist.post_id = 456
>>> msg = message_from_string("""\
... Subject: Something important
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest 456] Something important
This works even when the message is a reply, except that in this case, the numeric post id in the generated subject prefix is updated with the new post id.
>>> msg = message_from_string("""\
... Subject: [XTest 123] Re: Something important
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest 456] Re: Something important
If the Subject
header had old style prefixing, the prefix is moved to the
front of the header text.
>>> msg = message_from_string("""\
... Subject: Re: [XTest 123] Something important
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest 456] Re: Something important
And of course, the proper thing is done when posting id numbers are included in the subject prefix, and the subject is encoded non-ASCII.
>>> msg = message_from_string("""\
... Subject: =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'].encode())
[XTest 456] =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
>>> print(msg['subject'])
[XTest 456] メールマン
Even more fun is when the internationalized Subject
header already has a
prefix, possibly with a different posting number.
>>> msg = message_from_string("""\
... Subject: [XTest 123] Re: =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'].encode())
[XTest 456] Re: =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
>>> print(msg['subject'])
[XTest 456] Re: メールマン
As before, old style subject prefixes are re-ordered.
>>> msg = message_from_string("""\
... Subject: Re: [XTest 123] =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'].encode())
[XTest 456] Re:
=?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
>>> print(msg['subject'])
[XTest 456] Re: メールマン
In this test case, we get an extra space between the prefix and the original
subject. It’s because the original is crooked. Note that a Subject
starting with ‘n ‘ is generated by some version of Eudora Japanese edition.
>>> mlist.subject_prefix = '[XTest] '
>>> msg = message_from_string("""\
... Subject:
... Important message
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'])
[XTest] Important message
And again, with an RFC 2047 encoded header.
>>> msg = message_from_string("""\
... Subject:
... =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
...
... """)
>>> process(mlist, msg, {})
>>> print(msg['subject'].encode())
[XTest] =?iso-2022-jp?b?GyRCJWEhPCVrJV4lcxsoQg==?=
>>> print(msg['subject'])
[XTest] メールマン