# logtoprocess.py - send ui.log() data to a subprocess

#

# Copyright 2016 Facebook, Inc.

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

"""Send ui.log() data to a subprocess (EXPERIMENTAL)

This extension lets you specify a shell command per ui.log() event,

sending all remaining arguments to as environment variables to that command.

Each positional argument to the method results in a `MSG[N]` key in the

environment, starting at 1 (so `MSG1`, `MSG2`, etc.). Each keyword argument

is set as a `OPT_UPPERCASE_KEY` variable (so the key is uppercased, and

prefixed with `OPT_`). The original event name is passed in the `EVENT`

environment variable, and the process ID of mercurial is given in `HGPID`.

So given a call `ui.log('foo', 'bar', 'baz', spam='eggs'), a script configured

for the `foo` event can expect an environment with `MSG1=bar`, `MSG2=baz`, and

`OPT_SPAM=eggs`.

Scripts are configured in the `[logtoprocess]` section, each key an event name.

For example::

  [logtoprocess]

  commandexception = echo "$MSG2$MSG3" > /var/log/mercurial_exceptions.log

would log the warning message and traceback of any failed command dispatch.

Scripts are run asychronously as detached daemon processes; mercurial will

not ensure that they exit cleanly.

"""

from __future__ import absolute_import

import itertools

import os

import platform

import subprocess

import sys

# Note for extension authors: ONLY specify testedwith = 'internal' for

# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should

# be specifying the version(s) of Mercurial they are tested with, or

# leave the attribute unspecified.

testedwith = 'internal'

def uisetup(ui):

    if platform.system() == 'Windows':

        # no fork on Windows, but we can create a detached process

        # https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863.aspx

        # No stdlib constant exists for this value

        DETACHED_PROCESS = 0x00000008

        _creationflags = DETACHED_PROCESS | subprocess.CREATE_NEW_PROCESS_GROUP

        def runshellcommand(script, env):

            # we can't use close_fds *and* redirect stdin. I'm not sure that we

            # need to because the detached process has no console connection.

            subprocess.Popen(

                script, shell=True, env=env, close_fds=True,

                creationflags=_creationflags)

    else:

        def runshellcommand(script, env):

            # double-fork to completely detach from the parent process

            # based on http://code.activestate.com/recipes/278731

            pid = os.fork()

            if pid:

                # parent

                return

            # subprocess.Popen() forks again, all we need to add is

            # flag the new process as a new session.

            if sys.version_info < (3, 2):

                newsession = {'preexec_fn': os.setsid}

            else:

                newsession = {'start_new_session': True}

            try:

                # connect stdin to devnull to make sure the subprocess can't

                # muck up that stream for mercurial.

                subprocess.Popen(

                    script, shell=True, stdin=open(os.devnull, 'r'), env=env,

                    close_fds=True, **newsession)

            finally:

                # mission accomplished, this child needs to exit and not

                # continue the hg process here.

                os._exit(0)

    class logtoprocessui(ui.__class__):

        def log(self, event, *msg, **opts):

            """Map log events to external commands

            Arguments are passed on as environment variables.

            """

            script = ui.config('logtoprocess', event)

            if script:

                if msg:

                    # try to format the log message given the remaining

                    # arguments

                    try:

                        # Python string formatting with % either uses a

                        # dictionary *or* tuple, but not both. If we have

                        # keyword options, assume we need a mapping.

                        formatted = msg[0] % (opts or msg[1:])

                    except (TypeError, KeyError):

                        # Failed to apply the arguments, ignore

                        formatted = msg[0]

                    messages = (formatted,) + msg[1:]

                else:

                    messages = msg

                # positional arguments are listed as MSG[N] keys in the

                # environment

                msgpairs = (

                    ('MSG{0:d}'.format(i), str(m))

                    for i, m in enumerate(messages, 1))

                # keyword arguments get prefixed with OPT_ and uppercased

                optpairs = (

                    ('OPT_{0}'.format(key.upper()), str(value))

                    for key, value in opts.iteritems())

                env = dict(itertools.chain(os.environ.items(),

                                           msgpairs, optpairs),

                           EVENT=event, HGPID=str(os.getpid()))

                # Connect stdin to /dev/null to prevent child processes messing

                # with mercurial's stdin.

                runshellcommand(script, env)

            return super(logtoprocessui, self).log(event, *msg, **opts)

    # Replace the class for this instance and all clones created from it:

    ui.__class__ = logtoprocessui