""" Module provides a class allowing to wrap communication over subprocess.Popen input, output, error streams into a meaningfull, non-blocking, concurrent stream processor exposing the output data as an iterator fitting to be a return value passed by a WSGI applicaiton to a WSGI server per PEP 3333. Copyright (c) 2011 Daniel Dotsenko <dotsa[at]hotmail.com> This file is part of git_http_backend.py Project. git_http_backend.py Project is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 2.1 of the License, or (at your option) any later version. git_http_backend.py Project is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with git_http_backend.py Project. If not, see <http://www.gnu.org/licenses/>. """ import os import logging import subprocess32 as subprocess from collections import deque from threading import Event, Thread log = logging.getLogger(__name__) class StreamFeeder(Thread): """ Normal writing into pipe-like is blocking once the buffer is filled. This thread allows a thread to seep data from a file-like into a pipe without blocking the main thread. We close inpipe once the end of the source stream is reached. """ def __init__(self, source): super(StreamFeeder, self).__init__() self.daemon = True filelike = False self.bytes = bytes() if type(source) in (type(''), bytes, bytearray): # string-like self.bytes = bytes(source) else: # can be either file pointer or file-like if type(source) in (int, long): # file pointer it is # converting file descriptor (int) stdin into file-like try: source = os.fdopen(source, 'rb', 16384) except Exception: pass # let's see if source is file-like by now try: filelike = source.read except Exception: pass if not filelike and not self.bytes: raise TypeError("StreamFeeder's source object must be a readable " "file-like, a file descriptor, or a string-like.") self.source = source self.readiface, self.writeiface = os.pipe() def run(self): t = self.writeiface try: if self.bytes: os.write(t, self.bytes) else: s = self.source b = s.read(4096) while b: os.write(t, b) b = s.read(4096) finally: os.close(t) @property def output(self): return self.readiface class InputStreamChunker(Thread): def __init__(self, source, target, buffer_size, chunk_size): super(InputStreamChunker, self).__init__() self.daemon = True # die die die. self.source = source self.target = target self.chunk_count_max = int(buffer_size / chunk_size) + 1 self.chunk_size = chunk_size self.data_added = Event() self.data_added.clear() self.keep_reading = Event() self.keep_reading.set() self.EOF = Event() self.EOF.clear() self.go = Event() self.go.set() def stop(self): self.go.clear() self.EOF.set() try: # this is not proper, but is done to force the reader thread let # go of the input because, if successful, .close() will send EOF # down the pipe. self.source.close() except: pass def run(self): s = self.source t = self.target cs = self.chunk_size chunk_count_max = self.chunk_count_max keep_reading = self.keep_reading da = self.data_added go = self.go try: b = s.read(cs) except ValueError: b = '' timeout_input = 20 while b and go.is_set(): if len(t) > chunk_count_max: keep_reading.clear() keep_reading.wait(timeout_input) if len(t) > chunk_count_max + timeout_input: log.error("Timed out while waiting for input from subprocess.") os._exit(-1) # this will cause the worker to recycle itself t.append(b) da.set() try: b = s.read(cs) except ValueError: b = '' self.EOF.set() da.set() # for cases when done but there was no input. class BufferedGenerator(object): """ Class behaves as a non-blocking, buffered pipe reader. Reads chunks of data (through a thread) from a blocking pipe, and attaches these to an array (Deque) of chunks. Reading is halted in the thread when max chunks is internally buffered. The .next() may operate in blocking or non-blocking fashion by yielding '' if no data is ready to be sent or by not returning until there is some data to send When we get EOF from underlying source pipe we raise the marker to raise StopIteration after the last chunk of data is yielded. """ def __init__(self, source, buffer_size=65536, chunk_size=4096, starting_values=None, bottomless=False): starting_values = starting_values or [] if bottomless: maxlen = int(buffer_size / chunk_size) else: maxlen = None self.data = deque(starting_values, maxlen) self.worker = InputStreamChunker(source, self.data, buffer_size, chunk_size) if starting_values: self.worker.data_added.set() self.worker.start() #################### # Generator's methods #################### def __iter__(self): return self def next(self): while not len(self.data) and not self.worker.EOF.is_set(): self.worker.data_added.clear() self.worker.data_added.wait(0.2) if len(self.data): self.worker.keep_reading.set() return bytes(self.data.popleft()) elif self.worker.EOF.is_set(): raise StopIteration def throw(self, exc_type, value=None, traceback=None): if not self.worker.EOF.is_set(): raise exc_type(value) def start(self): self.worker.start() def stop(self): self.worker.stop() def close(self): try: self.worker.stop() self.throw(GeneratorExit) except (GeneratorExit, StopIteration): pass def __del__(self): self.close() #################### # Threaded reader's infrastructure. #################### @property def input(self): return self.worker.w @property def data_added_event(self): return self.worker.data_added @property def data_added(self): return self.worker.data_added.is_set() @property def reading_paused(self): return not self.worker.keep_reading.is_set() @property def done_reading_event(self): """ Done_reding does not mean that the iterator's buffer is empty. Iterator might have done reading from underlying source, but the read chunks might still be available for serving through .next() method. :returns: An Event class instance. """ return self.worker.EOF @property def done_reading(self): """ Done_reding does not mean that the iterator's buffer is empty. Iterator might have done reading from underlying source, but the read chunks might still be available for serving through .next() method. :returns: An Bool value. """ return self.worker.EOF.is_set() @property def length(self): """ returns int. This is the lenght of the que of chunks, not the length of the combined contents in those chunks. __len__() cannot be meaningfully implemented because this reader is just flying throuh a bottomless pit content and can only know the lenght of what it already saw. If __len__() on WSGI server per PEP 3333 returns a value, the responce's length will be set to that. In order not to confuse WSGI PEP3333 servers, we will not implement __len__ at all. """ return len(self.data) def prepend(self, x): self.data.appendleft(x) def append(self, x): self.data.append(x) def extend(self, o): self.data.extend(o) def __getitem__(self, i): return self.data[i] class SubprocessIOChunker(object): """ Processor class wrapping handling of subprocess IO. .. important:: Watch out for the method `__del__` on this class. If this object is deleted, it will kill the subprocess, so avoid to return the `output` attribute or usage of it like in the following example:: # `args` expected to run a program that produces a lot of output output = ''.join(SubprocessIOChunker( args, shell=False, inputstream=inputstream, env=environ).output) # `output` will not contain all the data, because the __del__ method # has already killed the subprocess in this case before all output # has been consumed. In a way, this is a "communicate()" replacement with a twist. - We are multithreaded. Writing in and reading out, err are all sep threads. - We support concurrent (in and out) stream processing. - The output is not a stream. It's a queue of read string (bytes, not unicode) chunks. The object behaves as an iterable. You can "for chunk in obj:" us. - We are non-blocking in more respects than communicate() (reading from subprocess out pauses when internal buffer is full, but does not block the parent calling code. On the flip side, reading from slow-yielding subprocess may block the iteration until data shows up. This does not block the parallel inpipe reading occurring parallel thread.) The purpose of the object is to allow us to wrap subprocess interactions into and interable that can be passed to a WSGI server as the application's return value. Because of stream-processing-ability, WSGI does not have to read ALL of the subprocess's output and buffer it, before handing it to WSGI server for HTTP response. Instead, the class initializer reads just a bit of the stream to figure out if error ocurred or likely to occur and if not, just hands the further iteration over subprocess output to the server for completion of HTTP response. The real or perceived subprocess error is trapped and raised as one of EnvironmentError family of exceptions Example usage: # try: # answer = SubprocessIOChunker( # cmd, # input, # buffer_size = 65536, # chunk_size = 4096 # ) # except (EnvironmentError) as e: # print str(e) # raise e # # return answer """ # TODO: johbo: This is used to make sure that the open end of the PIPE # is closed in the end. It would be way better to wrap this into an # object, so that it is closed automatically once it is consumed or # something similar. _close_input_fd = None _closed = False def __init__(self, cmd, inputstream=None, buffer_size=65536, chunk_size=4096, starting_values=None, fail_on_stderr=True, fail_on_return_code=True, **kwargs): """ Initializes SubprocessIOChunker :param cmd: A Subprocess.Popen style "cmd". Can be string or array of strings :param inputstream: (Default: None) A file-like, string, or file pointer. :param buffer_size: (Default: 65536) A size of total buffer per stream in bytes. :param chunk_size: (Default: 4096) A max size of a chunk. Actual chunk may be smaller. :param starting_values: (Default: []) An array of strings to put in front of output que. :param fail_on_stderr: (Default: True) Whether to raise an exception in case something is written to stderr. :param fail_on_return_code: (Default: True) Whether to raise an exception if the return code is not 0. """ starting_values = starting_values or [] if inputstream: input_streamer = StreamFeeder(inputstream) input_streamer.start() inputstream = input_streamer.output self._close_input_fd = inputstream self._fail_on_stderr = fail_on_stderr self._fail_on_return_code = fail_on_return_code _shell = kwargs.get('shell', True) kwargs['shell'] = _shell _p = subprocess.Popen(cmd, bufsize=-1, stdin=inputstream, stdout=subprocess.PIPE, stderr=subprocess.PIPE, **kwargs) bg_out = BufferedGenerator(_p.stdout, buffer_size, chunk_size, starting_values) bg_err = BufferedGenerator(_p.stderr, 16000, 1, bottomless=True) while not bg_out.done_reading and not bg_out.reading_paused and not bg_err.length: # doing this until we reach either end of file, or end of buffer. bg_out.data_added_event.wait(1) bg_out.data_added_event.clear() # at this point it's still ambiguous if we are done reading or just full buffer. # Either way, if error (returned by ended process, or implied based on # presence of stuff in stderr output) we error out. # Else, we are happy. _returncode = _p.poll() if ((_returncode and fail_on_return_code) or (fail_on_stderr and _returncode is None and bg_err.length)): try: _p.terminate() except Exception: pass bg_out.stop() bg_err.stop() if fail_on_stderr: err = ''.join(bg_err) raise EnvironmentError( "Subprocess exited due to an error:\n" + err) if _returncode and fail_on_return_code: err = ''.join(bg_err) if not err: # maybe get empty stderr, try stdout instead # in many cases git reports the errors on stdout too err = ''.join(bg_out) raise EnvironmentError( "Subprocess exited with non 0 ret code:%s: stderr:%s" % ( _returncode, err)) self.process = _p self.output = bg_out self.error = bg_err self.inputstream = inputstream def __iter__(self): return self def next(self): # Note: mikhail: We need to be sure that we are checking the return # code after the stdout stream is closed. Some processes, e.g. git # are doing some magic in between closing stdout and terminating the # process and, as a result, we are not getting return code on "slow" # systems. result = None stop_iteration = None try: result = self.output.next() except StopIteration as e: stop_iteration = e if self.process.poll() and self._fail_on_return_code: err = '%s' % ''.join(self.error) raise EnvironmentError( "Subprocess exited due to an error:\n" + err) if stop_iteration: raise stop_iteration return result def throw(self, type, value=None, traceback=None): if self.output.length or not self.output.done_reading: raise type(value) def close(self): if self._closed: return self._closed = True try: self.process.terminate() except: pass if self._close_input_fd: os.close(self._close_input_fd) try: self.output.close() except: pass try: self.error.close() except: pass try: os.close(self.inputstream) except: pass def __del__(self): self.close() def run_command(arguments, env=None): """ Run the specified command and return the stdout. :param arguments: sequence of program arguments (including the program name) :type arguments: list[str] """ cmd = arguments log.debug('Running subprocessio command %s', cmd) try: _opts = {'shell': False, 'fail_on_stderr': False} if env: _opts.update({'env': env}) p = SubprocessIOChunker(cmd, **_opts) stdout = ''.join(p) stderr = ''.join(''.join(p.error)) except (EnvironmentError, OSError) as err: cmd = ' '.join(cmd) # human friendly CMD tb_err = ("Couldn't run subprocessio command (%s).\n" "Original error was:%s\n" % (cmd, err)) log.exception(tb_err) raise Exception(tb_err) return stdout, stderr