view CONTRIBUTING @ 36534:5faeabb07cf5

debugcommands: support for triggering push protocol

The mechanism for pushing to a remote is a bit more complicated
than other commands. On SSH, we wait for a positive reply from
the server before we start sending the bundle payload.

This commit adds a mechanism to the "command" action in
`hg debugwireproto` to trigger the "push protocol" and to
specify a file whose contents should be submitted as the command
payload.

With this new feature, we implement a handful of tests for the
"unbundle" command. We try to cover various server failures and
hook/output scenarios so protocol behavior is as comprehensively
tested as possible. Even with so much test output, we only cover
bundle1 with Python hooks. There's still a lot of test coverage
that needs to be implemented. But this is certainly a good start.

Because there are so many new tests, we split these tests into their
own test file.

In order to make output deterministic, we need to disable the
doublepipe primitive. We add an option to `hg debugwireproto`
to do that. Because something in the bowels of the peer does a
read of stderr, we still capture read I/O from stderr. So there
is test coverage of what the server emits.

The tests around I/O capture some wonkiness. For example,
interleaved ui.write() and ui.write_err() calls are emitted in
order. However, (presumably due to buffering), print() to
sys.stdout and sys.stderr aren't in order.

We currently only test bundle1 because bundle2 is substantially
harder to test because it is more complicated (the server responds
with a stream containing a bundle2 instead of a frame).

Differential Revision: https://phab.mercurial-scm.org/D2471

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