vcsserver/subprocessio.py

"""
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 collections
import logging
import subprocess
import threading

log = logging.getLogger(__name__)


class StreamFeeder(threading.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 isinstance(source, int):  # file pointer it is
                # converting file descriptor (int) stdin into file-like
                source = os.fdopen(source, 'rb', 16384)
            # let's see if source is file-like by now
            filelike = hasattr(source, 'read')
        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):
        writer = self.writeiface
        try:
            if self.bytes:
                os.write(writer, self.bytes)
            else:
                s = self.source

                while 1:
                    _bytes = s.read(4096)
                    if not _bytes:
                        break
                    os.write(writer, _bytes)

        finally:
            os.close(writer)

    @property
    def output(self):
        return self.readiface


class InputStreamChunker(threading.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 = threading.Event()
        self.data_added.clear()

        self.keep_reading = threading.Event()
        self.keep_reading.set()

        self.EOF = threading.Event()
        self.EOF.clear()

        self.go = threading.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:  # probably "I/O operation on closed file"
                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, name, source, buffer_size=65536, chunk_size=4096,
                 starting_values=None, bottomless=False):
        starting_values = starting_values or []
        self.name = name
        self.buffer_size = buffer_size
        self.chunk_size = chunk_size

        if bottomless:
            maxlen = int(buffer_size / chunk_size)
        else:
            maxlen = None

        self.data_queue = collections.deque(starting_values, maxlen)
        self.worker = InputStreamChunker(source, self.data_queue, buffer_size, chunk_size)
        if starting_values:
            self.worker.data_added.set()
        self.worker.start()

    ####################
    # Generator's methods
    ####################
    def __str__(self):
        return f'BufferedGenerator(name={self.name} chunk: {self.chunk_size} on buffer: {self.buffer_size})'

    def __iter__(self):
        return self

    def __next__(self):

        while not self.length and not self.worker.EOF.is_set():
            self.worker.data_added.clear()
            self.worker.data_added.wait(0.2)

        if self.length:
            self.worker.keep_reading.set()
            return bytes(self.data_queue.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

    ####################
    # 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_reading 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 length of the queue of chunks, not the length of
        the combined contents in those chunks.

        __len__() cannot be meaningfully implemented because this
        reader is just flying through a bottomless pit content and
        can only know the length of what it already saw.

        If __len__() on WSGI server per PEP 3333 returns a value,
        the response'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_queue)

    def prepend(self, x):
        self.data_queue.appendleft(x)

    def append(self, x):
        self.data_queue.append(x)

    def extend(self, o):
        self.data_queue.extend(o)

    def __getitem__(self, i):
        return self.data_queue[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 str)
      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
    an iterable 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 occurred 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
    OSError family of exceptions

    Example usage:
    #    try:
    #        answer = SubprocessIOChunker(
    #            cmd,
    #            input,
    #            buffer_size = 65536,
    #            chunk_size = 4096
    #            )
    #    except (OSError) 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
    _stdout = None
    _stderr = None

    def __init__(self, cmd, input_stream=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 input_stream: (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.
        """

        kwargs['shell'] = kwargs.get('shell', True)

        starting_values = starting_values or []
        if input_stream:
            input_streamer = StreamFeeder(input_stream)
            input_streamer.start()
            input_stream = input_streamer.output
            self._close_input_fd = input_stream

        self._fail_on_stderr = fail_on_stderr
        self._fail_on_return_code = fail_on_return_code
        self.cmd = cmd

        _p = subprocess.Popen(cmd, bufsize=-1, stdin=input_stream, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                              **kwargs)
        self.process = _p

        bg_out = BufferedGenerator('stdout', _p.stdout, buffer_size, chunk_size, starting_values)
        bg_err = BufferedGenerator('stderr', _p.stderr, 10240, 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(0.2)
            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.
        return_code = _p.poll()
        ret_code_ok = return_code in [None, 0]
        ret_code_fail = return_code is not None and return_code != 0
        if (
            (ret_code_fail and fail_on_return_code) or
            (ret_code_ok and fail_on_stderr and bg_err.length)
        ):

            try:
                _p.terminate()
            except Exception:
                pass

            bg_out.stop()
            out = b''.join(bg_out)
            self._stdout = out

            bg_err.stop()
            err = b''.join(bg_err)
            self._stderr = err

            # code from https://github.com/schacon/grack/pull/7
            if err.strip() == b'fatal: The remote end hung up unexpectedly' and out.startswith(b'0034shallow '):
                bg_out = iter([out])
                _p = None
            elif err and fail_on_stderr:
                text_err = err.decode()
                raise OSError(
                    "Subprocess exited due to an error:\n{}".format(text_err))

            if ret_code_fail and fail_on_return_code:
                text_err = err.decode()
                if not err:
                    # maybe get empty stderr, try stdout instead
                    # in many cases git reports the errors on stdout too
                    text_err = out.decode()
                raise OSError(
                    "Subprocess exited with non 0 ret code:{}: stderr:{}".format(return_code, text_err))

        self.stdout = bg_out
        self.stderr = bg_err
        self.inputstream = input_stream

    def __str__(self):
        proc = getattr(self, 'process', 'NO_PROCESS')
        return f'SubprocessIOChunker: {proc}'

    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 = next(self.stdout)
        except StopIteration as e:
            stop_iteration = e

        if self.process:
            return_code = self.process.poll()
            ret_code_fail = return_code is not None and return_code != 0
            if ret_code_fail and self._fail_on_return_code:
                self.stop_streams()
                err = self.get_stderr()
                raise OSError(
                    "Subprocess exited (exit_code:{}) due to an error during iteration:\n{}".format(return_code, err))

        if stop_iteration:
            raise stop_iteration
        return result

    def throw(self, exc_type, value=None, traceback=None):
        if self.stdout.length or not self.stdout.done_reading:
            raise exc_type(value)

    def close(self):
        if self._closed:
            return

        try:
            self.process.terminate()
        except Exception:
            pass
        if self._close_input_fd:
            os.close(self._close_input_fd)
        try:
            self.stdout.close()
        except Exception:
            pass
        try:
            self.stderr.close()
        except Exception:
            pass
        try:
            os.close(self.inputstream)
        except Exception:
            pass

        self._closed = True

    def stop_streams(self):
        getattr(self.stdout, 'stop', lambda: None)()
        getattr(self.stderr, 'stop', lambda: None)()

    def get_stdout(self):
        if self._stdout:
            return self._stdout
        else:
            return b''.join(self.stdout)

    def get_stderr(self):
        if self._stderr:
            return self._stderr
        else:
            return b''.join(self.stderr)


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)
    proc = None
    try:
        _opts = {'shell': False, 'fail_on_stderr': False}
        if env:
            _opts.update({'env': env})
        proc = SubprocessIOChunker(cmd, **_opts)
        return b''.join(proc), b''.join(proc.stderr)
    except 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)
    finally:
        if proc:
            proc.close()