view hgdemandimport/tracing.py @ 41466:4d5aae86c9bd

tests: log sendall() operations and port test-http-bad-server.t

Python 3's HTTP server layer buffers output and uses sendall()
instead of write(). In order to make test-http-bad-server.t pass
on Python 3, we needed to teach our socket proxy to log sendall()
events and to abort future sends if we reached our send limit.

The tests using `tail` were difficult to port with inline output
conditionals since the number of lines varied. So we now use
`#if py3` for these tests.

test-http-bad-server.t now passes on Python 3.6 and 3.7 on at
least Linux. However, it does not yet pass on Python 3.5 because
of low-level differences to how the HTTP server is implemented.

Differential Revision: https://phab.mercurial-scm.org/D5753

# Support code for event tracing in Mercurial. Lives in demandimport
# so it can also be used in demandimport.
#
# Copyright 2018 Google LLC.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import

import contextlib
import os

_pipe = None
_checked = False

@contextlib.contextmanager
def log(whencefmt, *whenceargs):
    global _pipe, _session, _checked
    if _pipe is None:
        if _checked:
            yield
            return
        _checked = True
        if 'HGCATAPULTSERVERPIPE' not in os.environ:
            yield
            return
        _pipe = open(os.environ['HGCATAPULTSERVERPIPE'], 'w', 1)
        _session = os.environ.get('HGCATAPULTSESSION', 'none')
    whence = whencefmt % whenceargs
    try:
        # Both writes to the pipe are wrapped in try/except to ignore
        # errors, as we can see mysterious errors in here if the pager
        # is active. Presumably other conditions could trigger
        # problems too.
        try:
            _pipe.write('START %s %s\n' % (_session, whence))
        except IOError:
            pass
        yield
    finally:
        try:
            _pipe.write('END %s %s\n' % (_session, whence))
        except IOError:
            pass