#35033: EmailMessage repeats header if provided via the headers kwargs
-------------------------------------+-------------------------------------
Reporter: Aalekh Patel | Owner: Salvo
| Polizzi
Type: Bug | Status: assigned
Component: Core (Mail) | Version: dev
Severity: Normal | Resolution:
Keywords: email, headers, | Triage Stage: Accepted
compat32 |
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Easy pickings: 0 | UI/UX: 0
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Changes (by Mike Edmunds):
* keywords: email, headers => email, headers, compat32
Comment:
Ah, the forum mentions the ticket I couldn't find: #17444 allowed
different `to=...` and `headers={"To": ...}`
I think this got broken when
`EmailMessage._set_list_header_if_not_empty()` was added. And `cc` and
`reply_to` are likely broken in the same way (based on reading the code).
The problem is that Python's `email.message.Message`
[https://docs.python.org/3/library/email.compat32-message.html#email.message.Message.__setitem__
behaves as a multi-value dict when assigning to header keys], but
[https://docs.python.org/3/library/email.compat32-message.html#email.message.Message.__getitem__
returns only one of the values when reading from keys]. The current logic
in `_set_list_header_if_not_empty()` assumes it works like a regular dict,
and the tests from #17444 were insufficient to catch that mistake.
The minimal and safe fix is something like:
1. First make the existing tests fail on current buggy behavior: update
[https://github.com/django/django/blob/stable/5.1.x/tests/mail/tests.py#L410-L412
test_to_header()] to use
[https://docs.python.org/3/library/email.compat32-message.html#email.message.Message.get_all
get_all("To")] and verify there's only the one correct value in the list.
Same thing in
[https://github.com/django/django/blob/stable/5.1.x/tests/mail/tests.py#L439
test_reply_to_header()]. Wouldn't hurt to update some other nearby tests
in the same way, and add a test_cc_header().
2. Then fix
[https://github.com/django/django/blob/stable/5.1.x/django/core/mail/message.py#L432
this line] in `_set_list_header_if_not_empty()` so it only assigns to the
header if there's not already a header there. (Indent it one level so it
only runs in the except clause.)
I would suggest we ''not try to'' enforce RFC 5322-3.6 email header
counting rules in Django. If/when Django [https://groups.google.com/g
/django-developers/c/2zf9GQtjdIk moves to Python's modern email API],
those (and many other email header restrictions) will be enforced by
Python.
--
Ticket URL: <https://code.djangoproject.com/ticket/35033#comment:33>
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