skip events w/ empty stdout when generating stdout downloads

[ryanpetrello]

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[softwarefactory-project-zuul]

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[AlanCoding]

Maybe we should have a section in https://github.com/ansible/awx/blob/devel/docs/job_events.md about line breaks, because I cannot remember what rules would cause the need for this. Since we have events for which start_line==end_line, I assume that \n are given in the stdout field of the event. If that's the case, then any variation of "\n".join([event.stdout for event in job_events]) should fail under some circumstances, whether or not the blank ones are excluded.

But if I dig into the scheme we're using, it seems something is much less obvious than this...

blank event:

            "stdout": "",
            "start_line": 0,
            "end_line": 0,

non-blank event:

            "stdout": "\r\nPLAY [localhost] ***************************************************************",
            "start_line": 0,
            "end_line": 2,

The best possible scheme (given our constraints) would be to enforce that event.stdout.count('\n')==event.end_line-event.start_line. You can see, that presumption is violated by the 2nd above example.

So we're not following the rule that events implicitly have \n inserted between them. We're also not following the rule that event stdout already has all the line breaks in them (and need no insertion of line breaks).

We're following some other rules. The pattern you are following here could be a validation implementation of those rules. But I do not know what those rules are.

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