Add an option to write the listening port to a file

[Vlatombe]

The context for this pull request are test flakes observed both in RealJenkinsRule based tests, as well as running ATH with multiple controllers launched.

In both cases, a random port was generated then passed to winstone. The problem is that by the time Jetty tries to bind this port, it could become used by another instance.

This is taking another aproach:

• pass --httpPort=0 to winstone, let Jetty allocate a random free port
• pass the system property winstone.portFileName. In that case, winstone will write the used port in that file.

This file can then be used by RealJenkinsRule or the ATH to obtain the actual port to use to access the instance.

To test this change

• build winstone
• build jenkins with patched winstone (Update winstone to 5.24 jenkins#5928)
• build jenkins-test-harness with patched Jenkins (Ensure RealJenkinsRule tests always start on a free port jenkins-test-harness#348)
• Can also apply to ath through Use new winstone method to run on a random port acceptance-test-harness#711

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• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[jglick]

This file can then be used by RealJenkinsRule

Unfortunately no, it cannot: jenkinsci/jenkins-test-harness#347 (comment)

[jtnord]

looks good but there is a discrepancy around charsets that the file is written in.

[olamy]

I would prefer a command line option (Option class) but yeah not sure this will be used a lot :) )

[Vlatombe]

not sure this will be used a lot

Yes, I thought this would only be used for testing. I can turn it into an option if you prefer, but for now I wanted to see whether the whole thing was viable.

[olamy]

not sure this will be used a lot

Yes, I thought this would only be used for testing. I can turn it into an option if you prefer, but for now I wanted to see whether the whole thing was viable.

no worries all good

[olamy]

@Vlatombe looks to be ready or still a draft?

[Vlatombe]

looks to be ready or still a draft?

I want to ensure all downstream usages can be converted reasonably before considering this is ready to merge.

[Vlatombe]

Refreshed this work as unfortunately jenkinsci/jenkins-test-harness#347 is not enough to prevent port collisions.