EmailMultiAlternatives does not properly handle attachments

Example of EmailAlternativesMessage? with support of including, next to alternative views, attachments

Just to be clear on what the result is of the following code for the EmailMultiAlternatives? implementation in Django 1.0 when invoking the following code:

subject, from_email, to = 'hello', 'from@example.com', 'to@example.com'
text_content = 'This is an important message.'
html_content = '<p>This is an <strong>important</strong> message.</p>'
msg = EmailMultiAlternatives(subject, text_content, from_email, [to])
msg.attach_alternative(html_content, "text/html")
msg.attach_file('/tmp/file.pdf')
msg.send()

A message will be sent, with the two views (typically the HTML view will show up in the email client) and the file.pdf attachment is included in the email. However, it cannot be opened in email client because it does not show any attachments (and why should the email client, it is supposed to be an alternative view...)

We should make sure that attach_file() works correctly and actually attaches the file even in the subclass. That should be all that's needed here.

I can't work out what your attachment here is trying to do, since it's a whole file. Can you attach a proper patch if you're trying to fix attach_file()?

Replying to mtredinnick:

We should make sure that attach_file() works correctly and actually attaches the file even in the subclass. That should be all that's needed here. I can't work out what your attachment here is trying to do, since it's a whole file. Can you attach a proper patch if you're trying to fix attach_file()?

Ok. I will submit a patch in the coming days.

Patch has been attached. In the patch the EmailMultiAlternatives? wraps the multipart/alternative views in a multipart/mixed message that also includes the attachments. The changes made to EmailMessage? are merely for reusing code in the derived EmailMutliAlternatives? class. In the original EmailMultiAlternatives? all attachments (including the alternative views) would be attached as multipart/alternative. As a result of this the alternative views are correctly presented in the browser, however the attachments are also considered to be an alternative view (instead of the real attachment they are).

Not sure why this is assigned to me. I'm not going to have time to look at it just yet.

It's still quite difficult to see what the patch does, due to the way diff interprets things, but I've had a proper look. attach_file() doesn't work correctly in the subclass because the subclass works by overriding the value of multipart_subtype, which is used by the base class to build the message. So the fundamental way EmailMultiAlternatives works is broken for normal attachments, hence the need for quite a big patch. But it looks like a good patch.

I've added a test, I'll commit shortly. I'm taking it on trust that this is necessary to fix behaviour in Outlook (the previous format of email worked OK in my mail client, but Outlook's behaviour seems sensible as loekje argues).

(In [10983]) Fixed #9367 - EmailMultiAlternatives? does not properly handle attachments.

Thanks to Loek Engels for the bulk of the patch.

(In [10984]) [1.0.X] Fixed #9367 - EmailMultiAlternatives? does not properly handle attachments.

Thanks to Loek Engels for the bulk of the patch.

Backport of r10983 from trunk