jodd-mail: SendMailSession.createAttachmentBodyPart(): Content-Disposition and Content-ID should be independent from each other

[JensPiegsa]

Use case:

• Sending emails with embedded images that do not show up as attachments

The problem:

• In general it is up to the mail client whether / how to present inline attachments
• For decorative images, it is not intended to make them visible as attachments
• To support the intended behaviour, it seems to be a common practice to explicitly not set the Content-Disposition but only the Content-ID in the image mail part header

Suggestions:

• adjust SendMailSession.createAttachmentBodyPart() to test for attachment.isInline() and attachment.getContentId() != null independently
• introduce EmailAttachmentBuilder.setContentId(String contentId) which sets contentId but does not touch inline

[igr]

Hey @JensPiegsa! If I understood right, your suggestion is to separate setting inline and contentId flag. Few questions, just to be sure:

• setting inline without setting contentId does not have much sense, right? I mean, embedding attachments without contentId make no sense, so I wonder if I can join these methods into one:

     setContentId(String contentId, boolean inline)

(Of course, overloaded 1-argument version would be available).

• The following two attachments would be different:

	.embed(attachment().bytes(new File(PNG)).setContentId("jodd1.png"))
	.embed(attachment().bytes(new File(PNG)).setContentId("jodd2.png").setInline(true))

I don't see any difference in Gmail web client, both inline and non-inline shows as 'embedded', i.e. attachment is not shown. But again, as you said, its just email client. Do you have a public one, just to test?

• I prepared changes, but this time it might be smart if someone else check them. Would you be so kind to review the changes if I push them to a separate branch?

Thank you, I think this is all for now :)

[JensPiegsa]

Hi @igr !

I completely agree with your ideas - that's how it should be.

The different behaviour was observed with Group Office and Outlook.

I'd be happy to review / test this change.

Jens

[igr]

Hey @JensPiegsa

If you can find some time to review: https://github.com/oblac/jodd/tree/email-404

It would be super cool! 🥇

[JensPiegsa]

Hey @igr

I build and tested the branch and want to give you a short update about this issue.

I'm still puzzled here. Eliminating the spotted difference between the working and the non-working email did not lead to the expected solution. There seems to be something else causing the wanted behaviour. Maybe it's about the kind of nesting of multi-parts.

Given that this is a rather minor issue, we should propably leave it well alone, until there is a clear way to solve it with plain java-mail.

Thanks again for the effort!

[JensPiegsa]

PS: some unit test are not compatible with Windows:

jodd.io.FileNameUtilTest > testGetRelativePaths FAILED
org.junit.ComparisonFailure at FileNameUtilTest.java:157

org.junit.ComparisonFailure: expected:<..[/../b/]c> but was:<..[..\b]c>

jodd.io.FileNameUtilTest > testResolveHome FAILED
org.junit.ComparisonFailure at FileNameUtilTest.java:151

org.junit.ComparisonFailure: expected:<[C:\Users\piegsaj]/> but was:<[~]/>

jodd.util.PathUtilTest > testResolve FAILED
org.junit.ComparisonFailure at PathUtilTest.java:43

org.junit.ComparisonFailure: expected:<[/aaa/bbb/]ccc> but was:<[\aaa\bbb]ccc>

[igr]

@JensPiegsa if you find such email you can download it to EML format (plaintext) and send it to me, so I can check the headers...

Thanx for testing!

[JensPiegsa]

• see: index.txt

.. I xed out the addresses.

[igr]

Thanx @JensPiegsa, this one has just content-ID set, no inlines.

More I think I believe that the branch change is good overall. In my tests, both inline and content-id behaves the same, in Gmail web client and in few local clients.

[igr]

Also, see: https://github.com/oblac/jodd/blob/a334b475b15198e9fb9db5b8738324b97c86c60e/jodd-mail/src/test/java/jodd/mail/InlineVsContentTest.java

[igr]

After reading some RFCs and discussions I can conclude the following:

• inline and content-ID can be set separately.
• embedded images should be set using Content-Disposition. Of course, setting content-ID is required if you want to use them
• I could not find any text about having just inline and not content-ID.

So I guess, the embed() method should set both content-ID and inline for user.

[igr]

Added to the mail FAQ.