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

    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

    """

    def __init__(self, cmd, inputstream=None, buffer_size=65536,

                 chunk_size=4096, starting_values=None, **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.

        """

        starting_values = starting_values or []

        if inputstream:

            input_streamer = StreamFeeder(inputstream)

            input_streamer.start()

            inputstream = input_streamer.output

        # Note: fragile cmd mangling has been removed for use in Kallithea

        assert isinstance(cmd, list), cmd

        _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:

            # 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 is not None # process has terminated

            and returncode != 0

        ): # and it failed

            bg_out.stop()

            out = b''.join(bg_out)

            bg_err.stop()

            err = b''.join(bg_err)

            if (err.strip() == b'fatal: The remote end hung up unexpectedly' and

                out.startswith(b'0034shallow ')

            ):

                # hack inspired by https://github.com/schacon/grack/pull/7

                bg_out = iter([out])

                _p = None

            elif err:

                raise EnvironmentError("Subprocess exited due to an error: %s" % err)

            else:

                raise EnvironmentError(

                    "Subprocess exited with non 0 ret code: %s" % returncode)

        self.process = _p

        self.output = bg_out

        self.error = bg_err

        self.inputstream = inputstream

    def __iter__(self):

        return self

    def __next__(self):

        if self.process:

            returncode = self.process.poll()

            if (returncode is not None # process has terminated

                and returncode != 0

            ): # and it failed

                self.error.stop()

                err = ''.join(self.error)

                raise EnvironmentError("Subprocess exited due to an error:\n" + err)

        return next(self.output)

    def throw(self, type, value=None, traceback=None):

            raise type(value)

    def close(self):

        try:

        except:

            pass

        try:

        except:

            pass

        try:

            self.error.close()

        except:

            pass

        try:

            os.close(self.inputstream)

        except:

            pass