view hgdemandimport/tracing.py @ 39816:ae20f52437e9

wireprotov2: advertise recognized path filter prefixes

While the wire protocol doesn't yet support it, we'll eventually
have commands that accept narrow patterns to specify the set of
files relevant to a command.

For security and performance reasons, only specific filter types
are allowed.

This commit teaches the server to advertise the set of allowed
filter types. By doing so, clients can e.g. validate user-specified
patterns against the server's abilities without having to send
a command to retrieve data.

Having the data in the capabilities data structure will also serve
as a check against unwanted BC.

Differential Revision: https://phab.mercurial-scm.org/D4616

# 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