view CONTRIBUTING @ 36526:7cc4a9b9732a

wireprotoserver: support logging SSH server I/O to a file descriptor

We will soon introduce a debug command and tests for low-level I/O
behavior of the SSH wire protocol.

To facilitate this, we need to instrument the SSH server so it
can log its I/O as events occur.

We teach the SSH server to convert its stdout and stderr file objects
into file object proxies. We configure these proxies to log to a
file descriptor whose file number is specified via a config option.
The idea is to have a future debug command start the SSH server
process with access to an extra file descriptor that can be used
by the server process to log I/O. Monitoring only the write I/O
will be more robust than monitoring both writes and reads from the
client process because read operations are not deterministic. This
will matter for tests that capture raw I/O activity.

Differential Revision: https://phab.mercurial-scm.org/D2463

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