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# the problem of watching a stdout pipe from
# openvpn binary: using subprocess and coroutines
# acting as event consumers
from __future__ import division, print_function
import logging
from subprocess import PIPE, Popen
import sys
from threading import Thread
logger = logging.getLogger(__name__)
ON_POSIX = 'posix' in sys.builtin_module_names
#
# Coroutines goodies
#
def coroutine(func):
def start(*args, **kwargs):
cr = func(*args, **kwargs)
cr.next()
return cr
return start
@coroutine
def process_events(callback):
"""
coroutine loop that receives
events sent and dispatch the callback.
:param callback: callback to be called\
for each event
:type callback: callable
"""
try:
while True:
m = (yield)
if callable(callback):
callback(m)
else:
logger.debug('not a callable passed')
except GeneratorExit:
return
#
# Threads
#
def launch_thread(target, args):
"""
launch and demonize thread.
:param target: target function that will run in thread
:type target: function
:param args: args to be passed to thread
:type args: list
"""
t = Thread(target=target,
args=args)
t.daemon = True
t.start()
return t
def watch_output(out, observers):
"""
initializes dict of observer coroutines
and pushes lines to each of them as they are received
from the watched output.
:param out: stdout of a process.
:type out: fd
:param observers: tuple of coroutines to send data\
for each event
:type observers: tuple
"""
observer_dict = dict(((observer, process_events(observer))
for observer in observers))
for line in iter(out.readline, b''):
for obs in observer_dict:
observer_dict[obs].send(line)
out.close()
def spawn_and_watch_process(command, args, observers=None):
"""
spawns a subprocess with command, args, and launch
a watcher thread.
:param command: command to be executed in the subprocess
:type command: str
:param args: arguments
:type args: list
:param observers: tuple of observer functions to be called \
for each line in the subprocess output.
:type observers: tuple
:return: a tuple containing the child process instance, and watcher_thread,
:rtype: (Subprocess, Thread)
"""
subp = Popen([command] + args,
stdout=PIPE,
stderr=PIPE,
bufsize=1,
close_fds=ON_POSIX)
watcher = launch_thread(
watch_output,
(subp.stdout, observers))
return subp, watcher
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