#13849 ignore last writes done by the ResourceService used in ResourceServlet

[lorban]

Let the ServletChannel do the last write upon completion.

Fixes #13849

[sbordet]

The approach looks good to me, but can we write a test case?

[lorban]

@sbordet sure, I added a test for each environment.

[sbordet]

The tests only test H1, for which we know there was not the problem.

Please move the test to jetty-eeN-test-client-transports so that we have a test for all transports about this.

[lorban]

@sbordet as I wrote here, the problem does happen with H1 too, it just doesn't have any visible effect. But doing two last writes is wrong and these tests catch that problem.

I can write a H2-specific test too but would be more complex as it would involve flow control and would be somewhat redundant with these ones.

[sbordet]

@lorban can you clarify? If it does not have visible effects, then we cannot write a test case that would fail without the fix, which renders the test moot.

I would really try hard to write a test for all the transports.

[lorban]

I meant it doesn't have any visible effect for the client, there obviously are multiple way on the server to figure out that more than one last write was attempted.

I'll add a transport test, just to be safe.