GH-48623: [CI][Archery][Dev] Add missing headers to email reports

[kou]

Rationale for this change

Our email reports miss the following headers:

• MIME-Version: 1.0
• Content-Type: text/plain; charset="utf-8"
• Message-Id: ${AUTO_GENERATED_MESSAGE_ID}
• Date: ${DATE_IN_RFC_2822}

What changes are included in this PR?

Add these headers.

Are these changes tested?

Yes.

Are there any user-facing changes?

No.

• GitHub Issue: [CI][Archery][Dev] Add missing headers to email reports #48623

[github-actions]

⚠️ GitHub issue #48623 has been automatically assigned in GitHub to PR creator.

[sebbASF]

From #48623 (comment)

It looks as though all the headers can (and should) be populated in the ReportUtils.send_email method.

Could you explain the reason? If we use the approach, it's (a bit) difficult to implement dry-run. (We need to pass more arguments to ReportUtils.send_email.)

At present, the headers have to be generated in lots of places, which means more maintenance and more testing.

As to doing a dry-run, that depends on whether you need to see all the headers or just the body.

The Python email library builds up the message for sending, and you can just print the message instead of sending it.

[sebbASF]

AFAICT when you refer to dry-run, you mean using something like output.write(email_report.render("workflow_report"))

If the templates no longer contain the headers, then of course they won't be shown.

I think the simplest way round this is to add a includeHeadersparameter to JinjaReport.render, with default False. If True, the response should include the relevant header values.

The dry-run code would then need to be changed to

output.write(email_report.render("workflow_report"), True)

[kou]

Thanks. I understand your point. We should provide a function for general headers generation, right?

How about the 6b31c32 approach? EmailReport.render(template_name, headers) generates email.message.EmailMessage. It also fills the default header values such as Message-Id.