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'''
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Module provides a class allowing to wrap communication over subprocess.Popen
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input, output, error streams into a meaningfull, non-blocking, concurrent
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stream processor exposing the output data as an iterator fitting to be a
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return value passed by a WSGI applicaiton to a WSGI server per PEP 3333.
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Copyright (c) 2011 Daniel Dotsenko <dotsa@hotmail.com>
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This file is part of git_http_backend.py Project.
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git_http_backend.py Project is free software: you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation, either version 2.1 of the License,
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or (at your option) any later version.
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git_http_backend.py Project is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with git_http_backend.py Project.
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If not, see <http://www.gnu.org/licenses/>.
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'''
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import os
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import subprocess
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import threading
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from collections import deque
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class StreamFeeder(threading.Thread):
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"""
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Normal writing into pipe-like is blocking once the buffer is filled.
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This thread allows a thread to seep data from a file-like into a pipe
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without blocking the main thread.
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We close inpipe once the end of the source stream is reached.
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"""
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def __init__(self, source):
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super(StreamFeeder, self).__init__()
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self.daemon = True
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filelike = False
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self.bytes = bytes()
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if type(source) in (type(''), bytes, bytearray): # string-like
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self.bytes = bytes(source)
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else: # can be either file pointer or file-like
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if type(source) in (int, long): # file pointer it is
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## converting file descriptor (int) stdin into file-like
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try:
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source = os.fdopen(source, 'rb', 16384)
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except Exception:
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pass
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# let's see if source is file-like by now
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try:
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filelike = source.read
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except Exception:
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pass
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if not filelike and not self.bytes:
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raise TypeError("StreamFeeder's source object must be a readable "
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"file-like, a file descriptor, or a string-like.")
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self.source = source
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self.readiface, self.writeiface = os.pipe()
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def run(self):
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t = self.writeiface
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if self.bytes:
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os.write(t, self.bytes)
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else:
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s = self.source
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b = s.read(4096)
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while b:
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os.write(t, b)
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b = s.read(4096)
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os.close(t)
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@property
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def output(self):
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return self.readiface
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class InputStreamChunker(threading.Thread):
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def __init__(self, source, target, buffer_size, chunk_size):
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super(InputStreamChunker, self).__init__()
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self.daemon = True # die die die.
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self.source = source
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self.target = target
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self.chunk_count_max = int(buffer_size / chunk_size) + 1
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self.chunk_size = chunk_size
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self.data_added = threading.Event()
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self.data_added.clear()
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self.keep_reading = threading.Event()
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self.keep_reading.set()
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self.EOF = threading.Event()
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self.EOF.clear()
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self.go = threading.Event()
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self.go.set()
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def stop(self):
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self.go.clear()
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self.EOF.set()
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try:
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# this is not proper, but is done to force the reader thread let
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# go of the input because, if successful, .close() will send EOF
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# down the pipe.
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self.source.close()
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except:
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pass
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def run(self):
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s = self.source
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t = self.target
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cs = self.chunk_size
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ccm = self.chunk_count_max
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kr = self.keep_reading
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da = self.data_added
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go = self.go
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b = s.read(cs)
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while b and go.is_set():
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if len(t) > ccm:
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kr.clear()
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kr.wait(2)
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# # this only works on 2.7.x and up
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# if not kr.wait(10):
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# raise Exception("Timed out while waiting for input to be read.")
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# instead we'll use this
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if len(t) > ccm + 3:
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raise IOError("Timed out while waiting for input from subprocess.")
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t.append(b)
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da.set()
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b = s.read(cs)
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self.EOF.set()
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da.set() # for cases when done but there was no input.
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class BufferedGenerator():
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'''
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Class behaves as a non-blocking, buffered pipe reader.
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Reads chunks of data (through a thread)
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from a blocking pipe, and attaches these to an array (Deque) of chunks.
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Reading is halted in the thread when max chunks is internally buffered.
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The .next() may operate in blocking or non-blocking fashion by yielding
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'' if no data is ready
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to be sent or by not returning until there is some data to send
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When we get EOF from underlying source pipe we raise the marker to raise
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StopIteration after the last chunk of data is yielded.
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'''
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def __init__(self, source, buffer_size=65536, chunk_size=4096,
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starting_values=[], bottomless=False):
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if bottomless:
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maxlen = int(buffer_size / chunk_size)
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else:
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maxlen = None
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self.data = deque(starting_values, maxlen)
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self.worker = InputStreamChunker(source, self.data, buffer_size,
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chunk_size)
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if starting_values:
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self.worker.data_added.set()
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self.worker.start()
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####################
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# Generator's methods
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####################
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def __iter__(self):
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return self
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def next(self):
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while not len(self.data) and not self.worker.EOF.is_set():
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self.worker.data_added.clear()
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self.worker.data_added.wait(0.2)
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if len(self.data):
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self.worker.keep_reading.set()
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return bytes(self.data.popleft())
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elif self.worker.EOF.is_set():
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raise StopIteration
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def throw(self, type, value=None, traceback=None):
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if not self.worker.EOF.is_set():
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raise type(value)
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def start(self):
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self.worker.start()
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def stop(self):
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self.worker.stop()
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def close(self):
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try:
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self.worker.stop()
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self.throw(GeneratorExit)
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except (GeneratorExit, StopIteration):
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pass
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def __del__(self):
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self.close()
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####################
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# Threaded reader's infrastructure.
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####################
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@property
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def input(self):
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return self.worker.w
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@property
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def data_added_event(self):
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return self.worker.data_added
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@property
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def data_added(self):
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return self.worker.data_added.is_set()
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@property
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def reading_paused(self):
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return not self.worker.keep_reading.is_set()
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@property
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def done_reading_event(self):
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'''
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Done_reding does not mean that the iterator's buffer is empty.
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Iterator might have done reading from underlying source, but the read
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chunks might still be available for serving through .next() method.
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@return An Event class instance.
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'''
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return self.worker.EOF
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@property
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def done_reading(self):
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'''
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Done_reding does not mean that the iterator's buffer is empty.
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Iterator might have done reading from underlying source, but the read
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chunks might still be available for serving through .next() method.
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@return An Bool value.
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'''
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return self.worker.EOF.is_set()
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@property
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def length(self):
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'''
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returns int.
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This is the lenght of the que of chunks, not the length of
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the combined contents in those chunks.
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|
__len__() cannot be meaningfully implemented because this
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reader is just flying throuh a bottomless pit content and
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can only know the lenght of what it already saw.
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If __len__() on WSGI server per PEP 3333 returns a value,
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|
the responce's length will be set to that. In order not to
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confuse WSGI PEP3333 servers, we will not implement __len__
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at all.
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'''
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return len(self.data)
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def prepend(self, x):
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self.data.appendleft(x)
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def append(self, x):
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self.data.append(x)
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def extend(self, o):
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self.data.extend(o)
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def __getitem__(self, i):
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return self.data[i]
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class SubprocessIOChunker(object):
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'''
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Processor class wrapping handling of subprocess IO.
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In a way, this is a "communicate()" replacement with a twist.
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- We are multithreaded. Writing in and reading out, err are all sep threads.
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- We support concurrent (in and out) stream processing.
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- The output is not a stream. It's a queue of read string (bytes, not unicode)
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chunks. The object behaves as an iterable. You can "for chunk in obj:" us.
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- We are non-blocking in more respects than communicate()
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(reading from subprocess out pauses when internal buffer is full, but
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does not block the parent calling code. On the flip side, reading from
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slow-yielding subprocess may block the iteration until data shows up. This
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does not block the parallel inpipe reading occurring parallel thread.)
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The purpose of the object is to allow us to wrap subprocess interactions into
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and interable that can be passed to a WSGI server as the application's return
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value. Because of stream-processing-ability, WSGI does not have to read ALL
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of the subprocess's output and buffer it, before handing it to WSGI server for
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HTTP response. Instead, the class initializer reads just a bit of the stream
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to figure out if error ocurred or likely to occur and if not, just hands the
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further iteration over subprocess output to the server for completion of HTTP
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response.
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The real or perceived subprocess error is trapped and raised as one of
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EnvironmentError family of exceptions
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|
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|
Example usage:
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# try:
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# answer = SubprocessIOChunker(
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# cmd,
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# input,
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# buffer_size = 65536,
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# chunk_size = 4096
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# )
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# except (EnvironmentError) as e:
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# print str(e)
|
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|
# raise e
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#
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# return answer
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|
|
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|
'''
|
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def __init__(self, cmd, inputstream=None, buffer_size=65536,
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chunk_size=4096, starting_values=[], **kwargs):
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'''
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|
Initializes SubprocessIOChunker
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|
:param cmd: A Subprocess.Popen style "cmd". Can be string or array of strings
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:param inputstream: (Default: None) A file-like, string, or file pointer.
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:param buffer_size: (Default: 65536) A size of total buffer per stream in bytes.
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:param chunk_size: (Default: 4096) A max size of a chunk. Actual chunk may be smaller.
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:param starting_values: (Default: []) An array of strings to put in front of output que.
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'''
|
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if inputstream:
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input_streamer = StreamFeeder(inputstream)
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input_streamer.start()
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|
inputstream = input_streamer.output
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|
_p = subprocess.Popen(cmd,
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bufsize=-1,
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shell=True,
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stdin=inputstream,
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stdout=subprocess.PIPE,
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stderr=subprocess.PIPE,
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**kwargs
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)
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bg_out = BufferedGenerator(_p.stdout, buffer_size, chunk_size, starting_values)
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bg_err = BufferedGenerator(_p.stderr, 16000, 1, bottomless=True)
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while not bg_out.done_reading and not bg_out.reading_paused and not bg_err.length:
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|
# doing this until we reach either end of file, or end of buffer.
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|
bg_out.data_added_event.wait(1)
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|
bg_out.data_added_event.clear()
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|
# at this point it's still ambiguous if we are done reading or just full buffer.
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# Either way, if error (returned by ended process, or implied based on
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# presence of stuff in stderr output) we error out.
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# Else, we are happy.
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|
_returncode = _p.poll()
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|
if _returncode or (_returncode == None and bg_err.length):
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try:
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_p.terminate()
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except:
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pass
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|
bg_out.stop()
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|
bg_err.stop()
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|
raise EnvironmentError("Subprocess exited due to an error.\n" + "".join(bg_err))
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|
self.process = _p
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self.output = bg_out
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self.error = bg_err
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|
|
|
def __iter__(self):
|
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|
return self
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|
|
|
|
def next(self):
|
|
|
if self.process.poll():
|
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|
raise EnvironmentError("Subprocess exited due to an error:\n" + ''.join(self.error))
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|
return self.output.next()
|
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|
|
|
|
def throw(self, type, value=None, traceback=None):
|
|
|
if self.output.length or not self.output.done_reading:
|
|
|
raise type(value)
|
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|
|
|
|
def close(self):
|
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|
try:
|
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|
self.process.terminate()
|
|
|
except:
|
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|
pass
|
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|
try:
|
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|
self.output.close()
|
|
|
except:
|
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|
pass
|
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|
try:
|
|
|
self.error.close()
|
|
|
except:
|
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|
pass
|
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|
|
|
|
def __del__(self):
|
|
|
self.close()
|
|
|
|
