- Some email clients send inline attachments using the `multipart/related` Mime-Type and enmime collects these in the `Envelope.OtherParts` list; until now only Envelope.Attachments and Envelope.Inline were considered while parsing incoming mail.
- As some email clients send attachments without filename, especially in the multipart/related case, this PR implements `constructFilename`, which guesses the filename based on the ContentType.
How the issue was disovered:
I implemented an otherwise unrelated application written in go that parses emails with enmime just like Forgejo does.
I noticed that in a few occasions that system would fail to detect all attachments.
Investigating this issue led me to realize the above described issue.
After implementing a fix for that application, I looked through the Forgejo email parsing code and discovered the same problem.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7136
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: christopher-besch <mail@chris-besch.com>
Co-committed-by: christopher-besch <mail@chris-besch.com>
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