~bzr-pqm/bzr/bzr.dev

# Copyright (C) 2006, 2007 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

"""Wire-level encoding and decoding of requests and responses for the smart
client and server.
"""

import collections
from cStringIO import StringIO
import struct
import sys
import time

import bzrlib
from bzrlib import debug
from bzrlib import errors
from bzrlib.smart import message, request
from bzrlib.trace import log_exception_quietly, mutter
from bzrlib.bencode import bdecode_as_tuple, bencode


# Protocol version strings.  These are sent as prefixes of bzr requests and
# responses to identify the protocol version being used. (There are no version
# one strings because that version doesn't send any).
REQUEST_VERSION_TWO = 'bzr request 2\n'
RESPONSE_VERSION_TWO = 'bzr response 2\n'

MESSAGE_VERSION_THREE = 'bzr message 3 (bzr 1.6)\n'
RESPONSE_VERSION_THREE = REQUEST_VERSION_THREE = MESSAGE_VERSION_THREE


def _recv_tuple(from_file):
    req_line = from_file.readline()
    return _decode_tuple(req_line)


def _decode_tuple(req_line):
    if req_line is None or req_line == '':
        return None
    if req_line[-1] != '\n':
        raise errors.SmartProtocolError("request %r not terminated" % req_line)
    return tuple(req_line[:-1].split('\x01'))


def _encode_tuple(args):
    """Encode the tuple args to a bytestream."""
    return '\x01'.join(args) + '\n'


class Requester(object):
    """Abstract base class for an object that can issue requests on a smart
    medium.
    """

    def call(self, *args):
        """Make a remote call.

        :param args: the arguments of this call.
        """
        raise NotImplementedError(self.call)

    def call_with_body_bytes(self, args, body):
        """Make a remote call with a body.

        :param args: the arguments of this call.
        :type body: str
        :param body: the body to send with the request.
        """
        raise NotImplementedError(self.call_with_body_bytes)

    def call_with_body_readv_array(self, args, body):
        """Make a remote call with a readv array.

        :param args: the arguments of this call.
        :type body: iterable of (start, length) tuples.
        :param body: the readv ranges to send with this request.
        """
        raise NotImplementedError(self.call_with_body_readv_array)

    def set_headers(self, headers):
        raise NotImplementedError(self.set_headers)


class SmartProtocolBase(object):
    """Methods common to client and server"""

    # TODO: this only actually accomodates a single block; possibly should
    # support multiple chunks?
    def _encode_bulk_data(self, body):
        """Encode body as a bulk data chunk."""
        return ''.join(('%d\n' % len(body), body, 'done\n'))

    def _serialise_offsets(self, offsets):
        """Serialise a readv offset list."""
        txt = []
        for start, length in offsets:
            txt.append('%d,%d' % (start, length))
        return '\n'.join(txt)


class SmartServerRequestProtocolOne(SmartProtocolBase):
    """Server-side encoding and decoding logic for smart version 1."""

    def __init__(self, backing_transport, write_func, root_client_path='/'):
        self._backing_transport = backing_transport
        self._root_client_path = root_client_path
        self.unused_data = ''
        self._finished = False
        self.in_buffer = ''
        self._has_dispatched = False
        self.request = None
        self._body_decoder = None
        self._write_func = write_func

    def accept_bytes(self, bytes):
        """Take bytes, and advance the internal state machine appropriately.

        :param bytes: must be a byte string
        """
        if not isinstance(bytes, str):
            raise ValueError(bytes)
        self.in_buffer += bytes
        if not self._has_dispatched:
            if '\n' not in self.in_buffer:
                # no command line yet
                return
            self._has_dispatched = True
            try:
                first_line, self.in_buffer = self.in_buffer.split('\n', 1)
                first_line += '\n'
                req_args = _decode_tuple(first_line)
                self.request = request.SmartServerRequestHandler(
                    self._backing_transport, commands=request.request_handlers,
                    root_client_path=self._root_client_path)
                self.request.args_received(req_args)
                if self.request.finished_reading:
                    # trivial request
                    self.unused_data = self.in_buffer
                    self.in_buffer = ''
                    self._send_response(self.request.response)
            except KeyboardInterrupt:
                raise
            except errors.UnknownSmartMethod, err:
                protocol_error = errors.SmartProtocolError(
                    "bad request %r" % (err.verb,))
                failure = request.FailedSmartServerResponse(
                    ('error', str(protocol_error)))
                self._send_response(failure)
                return
            except Exception, exception:
                # everything else: pass to client, flush, and quit
                log_exception_quietly()
                self._send_response(request.FailedSmartServerResponse(
                    ('error', str(exception))))
                return

        if self._has_dispatched:
            if self._finished:
                # nothing to do.XXX: this routine should be a single state
                # machine too.
                self.unused_data += self.in_buffer
                self.in_buffer = ''
                return
            if self._body_decoder is None:
                self._body_decoder = LengthPrefixedBodyDecoder()
            self._body_decoder.accept_bytes(self.in_buffer)
            self.in_buffer = self._body_decoder.unused_data
            body_data = self._body_decoder.read_pending_data()
            self.request.accept_body(body_data)
            if self._body_decoder.finished_reading:
                self.request.end_of_body()
                if not self.request.finished_reading:
                    raise AssertionError("no more body, request not finished")
            if self.request.response is not None:
                self._send_response(self.request.response)
                self.unused_data = self.in_buffer
                self.in_buffer = ''
            else:
                if self.request.finished_reading:
                    raise AssertionError(
                        "no response and we have finished reading.")

    def _send_response(self, response):
        """Send a smart server response down the output stream."""
        if self._finished:
            raise AssertionError('response already sent')
        args = response.args
        body = response.body
        self._finished = True
        self._write_protocol_version()
        self._write_success_or_failure_prefix(response)
        self._write_func(_encode_tuple(args))
        if body is not None:
            if not isinstance(body, str):
                raise ValueError(body)
            bytes = self._encode_bulk_data(body)
            self._write_func(bytes)

    def _write_protocol_version(self):
        """Write any prefixes this protocol requires.

        Version one doesn't send protocol versions.
        """

    def _write_success_or_failure_prefix(self, response):
        """Write the protocol specific success/failure prefix.

        For SmartServerRequestProtocolOne this is omitted but we
        call is_successful to ensure that the response is valid.
        """
        response.is_successful()

    def next_read_size(self):
        if self._finished:
            return 0
        if self._body_decoder is None:
            return 1
        else:
            return self._body_decoder.next_read_size()


class SmartServerRequestProtocolTwo(SmartServerRequestProtocolOne):
    r"""Version two of the server side of the smart protocol.

    This prefixes responses with the value of RESPONSE_VERSION_TWO.
    """

    response_marker = RESPONSE_VERSION_TWO
    request_marker = REQUEST_VERSION_TWO

    def _write_success_or_failure_prefix(self, response):
        """Write the protocol specific success/failure prefix."""
        if response.is_successful():
            self._write_func('success\n')
        else:
            self._write_func('failed\n')

    def _write_protocol_version(self):
        r"""Write any prefixes this protocol requires.

        Version two sends the value of RESPONSE_VERSION_TWO.
        """
        self._write_func(self.response_marker)

    def _send_response(self, response):
        """Send a smart server response down the output stream."""
        if (self._finished):
            raise AssertionError('response already sent')
        self._finished = True
        self._write_protocol_version()
        self._write_success_or_failure_prefix(response)
        self._write_func(_encode_tuple(response.args))
        if response.body is not None:
            if not isinstance(response.body, str):
                raise AssertionError('body must be a str')
            if not (response.body_stream is None):
                raise AssertionError(
                    'body_stream and body cannot both be set')
            bytes = self._encode_bulk_data(response.body)
            self._write_func(bytes)
        elif response.body_stream is not None:
            _send_stream(response.body_stream, self._write_func)


def _send_stream(stream, write_func):
    write_func('chunked\n')
    _send_chunks(stream, write_func)
    write_func('END\n')


def _send_chunks(stream, write_func):
    for chunk in stream:
        if isinstance(chunk, str):
            bytes = "%x\n%s" % (len(chunk), chunk)
            write_func(bytes)
        elif isinstance(chunk, request.FailedSmartServerResponse):
            write_func('ERR\n')
            _send_chunks(chunk.args, write_func)
            return
        else:
            raise errors.BzrError(
                'Chunks must be str or FailedSmartServerResponse, got %r'
                % chunk)


class _NeedMoreBytes(Exception):
    """Raise this inside a _StatefulDecoder to stop decoding until more bytes
    have been received.
    """

    def __init__(self, count=None):
        """Constructor.

        :param count: the total number of bytes needed by the current state.
            May be None if the number of bytes needed is unknown.
        """
        self.count = count


class _StatefulDecoder(object):
    """Base class for writing state machines to decode byte streams.

    Subclasses should provide a self.state_accept attribute that accepts bytes
    and, if appropriate, updates self.state_accept to a different function.
    accept_bytes will call state_accept as often as necessary to make sure the
    state machine has progressed as far as possible before it returns.

    See ProtocolThreeDecoder for an example subclass.
    """

    def __init__(self):
        self.finished_reading = False
        self._in_buffer_list = []
        self._in_buffer_len = 0
        self.unused_data = ''
        self.bytes_left = None
        self._number_needed_bytes = None

    def _get_in_buffer(self):
        if len(self._in_buffer_list) == 1:
            return self._in_buffer_list[0]
        in_buffer = ''.join(self._in_buffer_list)
        if len(in_buffer) != self._in_buffer_len:
            raise AssertionError(
                "Length of buffer did not match expected value: %s != %s"
                % self._in_buffer_len, len(in_buffer))
        self._in_buffer_list = [in_buffer]
        return in_buffer

    def _get_in_bytes(self, count):
        """Grab X bytes from the input_buffer.

        Callers should have already checked that self._in_buffer_len is >
        count. Note, this does not consume the bytes from the buffer. The
        caller will still need to call _get_in_buffer() and then
        _set_in_buffer() if they actually need to consume the bytes.
        """
        # check if we can yield the bytes from just the first entry in our list
        if len(self._in_buffer_list) == 0:
            raise AssertionError('Callers must be sure we have buffered bytes'
                ' before calling _get_in_bytes')
        if len(self._in_buffer_list[0]) > count:
            return self._in_buffer_list[0][:count]
        # We can't yield it from the first buffer, so collapse all buffers, and
        # yield it from that
        in_buf = self._get_in_buffer()
        return in_buf[:count]

    def _set_in_buffer(self, new_buf):
        if new_buf is not None:
            self._in_buffer_list = [new_buf]
            self._in_buffer_len = len(new_buf)
        else:
            self._in_buffer_list = []
            self._in_buffer_len = 0

    def accept_bytes(self, bytes):
        """Decode as much of bytes as possible.

        If 'bytes' contains too much data it will be appended to
        self.unused_data.

        finished_reading will be set when no more data is required.  Further
        data will be appended to self.unused_data.
        """
        # accept_bytes is allowed to change the state
        self._number_needed_bytes = None
        # lsprof puts a very large amount of time on this specific call for
        # large readv arrays
        self._in_buffer_list.append(bytes)
        self._in_buffer_len += len(bytes)
        try:
            # Run the function for the current state.
            current_state = self.state_accept
            self.state_accept()
            while current_state != self.state_accept:
                # The current state has changed.  Run the function for the new
                # current state, so that it can:
                #   - decode any unconsumed bytes left in a buffer, and
                #   - signal how many more bytes are expected (via raising
                #     _NeedMoreBytes).
                current_state = self.state_accept
                self.state_accept()
        except _NeedMoreBytes, e:
            self._number_needed_bytes = e.count


class ChunkedBodyDecoder(_StatefulDecoder):
    """Decoder for chunked body data.

    This is very similar the HTTP's chunked encoding.  See the description of
    streamed body data in `doc/developers/network-protocol.txt` for details.
    """

    def __init__(self):
        _StatefulDecoder.__init__(self)
        self.state_accept = self._state_accept_expecting_header
        self.chunk_in_progress = None
        self.chunks = collections.deque()
        self.error = False
        self.error_in_progress = None

    def next_read_size(self):
        # Note: the shortest possible chunk is 2 bytes: '0\n', and the
        # end-of-body marker is 4 bytes: 'END\n'.
        if self.state_accept == self._state_accept_reading_chunk:
            # We're expecting more chunk content.  So we're expecting at least
            # the rest of this chunk plus an END chunk.
            return self.bytes_left + 4
        elif self.state_accept == self._state_accept_expecting_length:
            if self._in_buffer_len == 0:
                # We're expecting a chunk length.  There's at least two bytes
                # left: a digit plus '\n'.
                return 2
            else:
                # We're in the middle of reading a chunk length.  So there's at
                # least one byte left, the '\n' that terminates the length.
                return 1
        elif self.state_accept == self._state_accept_reading_unused:
            return 1
        elif self.state_accept == self._state_accept_expecting_header:
            return max(0, len('chunked\n') - self._in_buffer_len)
        else:
            raise AssertionError("Impossible state: %r" % (self.state_accept,))

    def read_next_chunk(self):
        try:
            return self.chunks.popleft()
        except IndexError:
            return None

    def _extract_line(self):
        in_buf = self._get_in_buffer()
        pos = in_buf.find('\n')
        if pos == -1:
            # We haven't read a complete line yet, so request more bytes before
            # we continue.
            raise _NeedMoreBytes(1)
        line = in_buf[:pos]
        # Trim the prefix (including '\n' delimiter) from the _in_buffer.
        self._set_in_buffer(in_buf[pos+1:])
        return line

    def _finished(self):
        self.unused_data = self._get_in_buffer()
        self._in_buffer_list = []
        self._in_buffer_len = 0
        self.state_accept = self._state_accept_reading_unused
        if self.error:
            error_args = tuple(self.error_in_progress)
            self.chunks.append(request.FailedSmartServerResponse(error_args))
            self.error_in_progress = None
        self.finished_reading = True

    def _state_accept_expecting_header(self):
        prefix = self._extract_line()
        if prefix == 'chunked':
            self.state_accept = self._state_accept_expecting_length
        else:
            raise errors.SmartProtocolError(
                'Bad chunked body header: "%s"' % (prefix,))

    def _state_accept_expecting_length(self):
        prefix = self._extract_line()
        if prefix == 'ERR':
            self.error = True
            self.error_in_progress = []
            self._state_accept_expecting_length()
            return
        elif prefix == 'END':
            # We've read the end-of-body marker.
            # Any further bytes are unused data, including the bytes left in
            # the _in_buffer.
            self._finished()
            return
        else:
            self.bytes_left = int(prefix, 16)
            self.chunk_in_progress = ''
            self.state_accept = self._state_accept_reading_chunk

    def _state_accept_reading_chunk(self):
        in_buf = self._get_in_buffer()
        in_buffer_len = len(in_buf)
        self.chunk_in_progress += in_buf[:self.bytes_left]
        self._set_in_buffer(in_buf[self.bytes_left:])
        self.bytes_left -= in_buffer_len
        if self.bytes_left <= 0:
            # Finished with chunk
            self.bytes_left = None
            if self.error:
                self.error_in_progress.append(self.chunk_in_progress)
            else:
                self.chunks.append(self.chunk_in_progress)
            self.chunk_in_progress = None
            self.state_accept = self._state_accept_expecting_length

    def _state_accept_reading_unused(self):
        self.unused_data += self._get_in_buffer()
        self._in_buffer_list = []


class LengthPrefixedBodyDecoder(_StatefulDecoder):
    """Decodes the length-prefixed bulk data."""

    def __init__(self):
        _StatefulDecoder.__init__(self)
        self.state_accept = self._state_accept_expecting_length
        self.state_read = self._state_read_no_data
        self._body = ''
        self._trailer_buffer = ''

    def next_read_size(self):
        if self.bytes_left is not None:
            # Ideally we want to read all the remainder of the body and the
            # trailer in one go.
            return self.bytes_left + 5
        elif self.state_accept == self._state_accept_reading_trailer:
            # Just the trailer left
            return 5 - len(self._trailer_buffer)
        elif self.state_accept == self._state_accept_expecting_length:
            # There's still at least 6 bytes left ('\n' to end the length, plus
            # 'done\n').
            return 6
        else:
            # Reading excess data.  Either way, 1 byte at a time is fine.
            return 1

    def read_pending_data(self):
        """Return any pending data that has been decoded."""
        return self.state_read()

    def _state_accept_expecting_length(self):
        in_buf = self._get_in_buffer()
        pos = in_buf.find('\n')
        if pos == -1:
            return
        self.bytes_left = int(in_buf[:pos])
        self._set_in_buffer(in_buf[pos+1:])
        self.state_accept = self._state_accept_reading_body
        self.state_read = self._state_read_body_buffer

    def _state_accept_reading_body(self):
        in_buf = self._get_in_buffer()
        self._body += in_buf
        self.bytes_left -= len(in_buf)
        self._set_in_buffer(None)
        if self.bytes_left <= 0:
            # Finished with body
            if self.bytes_left != 0:
                self._trailer_buffer = self._body[self.bytes_left:]
                self._body = self._body[:self.bytes_left]
            self.bytes_left = None
            self.state_accept = self._state_accept_reading_trailer

    def _state_accept_reading_trailer(self):
        self._trailer_buffer += self._get_in_buffer()
        self._set_in_buffer(None)
        # TODO: what if the trailer does not match "done\n"?  Should this raise
        # a ProtocolViolation exception?
        if self._trailer_buffer.startswith('done\n'):
            self.unused_data = self._trailer_buffer[len('done\n'):]
            self.state_accept = self._state_accept_reading_unused
            self.finished_reading = True

    def _state_accept_reading_unused(self):
        self.unused_data += self._get_in_buffer()
        self._set_in_buffer(None)

    def _state_read_no_data(self):
        return ''

    def _state_read_body_buffer(self):
        result = self._body
        self._body = ''
        return result


class SmartClientRequestProtocolOne(SmartProtocolBase, Requester,
                                    message.ResponseHandler):
    """The client-side protocol for smart version 1."""

    def __init__(self, request):
        """Construct a SmartClientRequestProtocolOne.

        :param request: A SmartClientMediumRequest to serialise onto and
            deserialise from.
        """
        self._request = request
        self._body_buffer = None
        self._request_start_time = None
        self._last_verb = None
        self._headers = None

    def set_headers(self, headers):
        self._headers = dict(headers)

    def call(self, *args):
        if 'hpss' in debug.debug_flags:
            mutter('hpss call:   %s', repr(args)[1:-1])
            if getattr(self._request._medium, 'base', None) is not None:
                mutter('             (to %s)', self._request._medium.base)
            self._request_start_time = time.time()
        self._write_args(args)
        self._request.finished_writing()
        self._last_verb = args[0]

    def call_with_body_bytes(self, args, body):
        """Make a remote call of args with body bytes 'body'.

        After calling this, call read_response_tuple to find the result out.
        """
        if 'hpss' in debug.debug_flags:
            mutter('hpss call w/body: %s (%r...)', repr(args)[1:-1], body[:20])
            if getattr(self._request._medium, '_path', None) is not None:
                mutter('                  (to %s)', self._request._medium._path)
            mutter('              %d bytes', len(body))
            self._request_start_time = time.time()
            if 'hpssdetail' in debug.debug_flags:
                mutter('hpss body content: %s', body)
        self._write_args(args)
        bytes = self._encode_bulk_data(body)
        self._request.accept_bytes(bytes)
        self._request.finished_writing()
        self._last_verb = args[0]

    def call_with_body_readv_array(self, args, body):
        """Make a remote call with a readv array.

        The body is encoded with one line per readv offset pair. The numbers in
        each pair are separated by a comma, and no trailing \n is emitted.
        """
        if 'hpss' in debug.debug_flags:
            mutter('hpss call w/readv: %s', repr(args)[1:-1])
            if getattr(self._request._medium, '_path', None) is not None:
                mutter('                  (to %s)', self._request._medium._path)
            self._request_start_time = time.time()
        self._write_args(args)
        readv_bytes = self._serialise_offsets(body)
        bytes = self._encode_bulk_data(readv_bytes)
        self._request.accept_bytes(bytes)
        self._request.finished_writing()
        if 'hpss' in debug.debug_flags:
            mutter('              %d bytes in readv request', len(readv_bytes))
        self._last_verb = args[0]

    def call_with_body_stream(self, args, stream):
        # Protocols v1 and v2 don't support body streams.  So it's safe to
        # assume that a v1/v2 server doesn't support whatever method we're
        # trying to call with a body stream.
        self._request.finished_writing()
        self._request.finished_reading()
        raise errors.UnknownSmartMethod(args[0])

    def cancel_read_body(self):
        """After expecting a body, a response code may indicate one otherwise.

        This method lets the domain client inform the protocol that no body
        will be transmitted. This is a terminal method: after calling it the
        protocol is not able to be used further.
        """
        self._request.finished_reading()

    def _read_response_tuple(self):
        result = self._recv_tuple()
        if 'hpss' in debug.debug_flags:
            if self._request_start_time is not None:
                mutter('   result:   %6.3fs  %s',
                       time.time() - self._request_start_time,
                       repr(result)[1:-1])
                self._request_start_time = None
            else:
                mutter('   result:   %s', repr(result)[1:-1])
        return result

    def read_response_tuple(self, expect_body=False):
        """Read a response tuple from the wire.

        This should only be called once.
        """
        result = self._read_response_tuple()
        self._response_is_unknown_method(result)
        self._raise_args_if_error(result)
        if not expect_body:
            self._request.finished_reading()
        return result

    def _raise_args_if_error(self, result_tuple):
        # Later protocol versions have an explicit flag in the protocol to say
        # if an error response is "failed" or not.  In version 1 we don't have
        # that luxury.  So here is a complete list of errors that can be
        # returned in response to existing version 1 smart requests.  Responses
        # starting with these codes are always "failed" responses.
        v1_error_codes = [
            'norepository',
            'NoSuchFile',
            'FileExists',
            'DirectoryNotEmpty',
            'ShortReadvError',
            'UnicodeEncodeError',
            'UnicodeDecodeError',
            'ReadOnlyError',
            'nobranch',
            'NoSuchRevision',
            'nosuchrevision',
            'LockContention',
            'UnlockableTransport',
            'LockFailed',
            'TokenMismatch',
            'ReadError',
            'PermissionDenied',
            ]
        if result_tuple[0] in v1_error_codes:
            self._request.finished_reading()
            raise errors.ErrorFromSmartServer(result_tuple)

    def _response_is_unknown_method(self, result_tuple):
        """Raise UnexpectedSmartServerResponse if the response is an 'unknonwn
        method' response to the request.

        :param response: The response from a smart client call_expecting_body
            call.
        :param verb: The verb used in that call.
        :raises: UnexpectedSmartServerResponse
        """
        if (result_tuple == ('error', "Generic bzr smart protocol error: "
                "bad request '%s'" % self._last_verb) or
              result_tuple == ('error', "Generic bzr smart protocol error: "
                "bad request u'%s'" % self._last_verb)):
            # The response will have no body, so we've finished reading.
            self._request.finished_reading()
            raise errors.UnknownSmartMethod(self._last_verb)

    def read_body_bytes(self, count=-1):
        """Read bytes from the body, decoding into a byte stream.

        We read all bytes at once to ensure we've checked the trailer for
        errors, and then feed the buffer back as read_body_bytes is called.
        """
        if self._body_buffer is not None:
            return self._body_buffer.read(count)
        _body_decoder = LengthPrefixedBodyDecoder()

        while not _body_decoder.finished_reading:
            bytes = self._request.read_bytes(_body_decoder.next_read_size())
            if bytes == '':
                # end of file encountered reading from server
                raise errors.ConnectionReset(
                    "Connection lost while reading response body.")
            _body_decoder.accept_bytes(bytes)
        self._request.finished_reading()
        self._body_buffer = StringIO(_body_decoder.read_pending_data())
        # XXX: TODO check the trailer result.
        if 'hpss' in debug.debug_flags:
            mutter('              %d body bytes read',
                   len(self._body_buffer.getvalue()))
        return self._body_buffer.read(count)

    def _recv_tuple(self):
        """Receive a tuple from the medium request."""
        return _decode_tuple(self._request.read_line())

    def query_version(self):
        """Return protocol version number of the server."""
        self.call('hello')
        resp = self.read_response_tuple()
        if resp == ('ok', '1'):
            return 1
        elif resp == ('ok', '2'):
            return 2
        else:
            raise errors.SmartProtocolError("bad response %r" % (resp,))

    def _write_args(self, args):
        self._write_protocol_version()
        bytes = _encode_tuple(args)
        self._request.accept_bytes(bytes)

    def _write_protocol_version(self):
        """Write any prefixes this protocol requires.

        Version one doesn't send protocol versions.
        """


class SmartClientRequestProtocolTwo(SmartClientRequestProtocolOne):
    """Version two of the client side of the smart protocol.

    This prefixes the request with the value of REQUEST_VERSION_TWO.
    """

    response_marker = RESPONSE_VERSION_TWO
    request_marker = REQUEST_VERSION_TWO

    def read_response_tuple(self, expect_body=False):
        """Read a response tuple from the wire.

        This should only be called once.
        """
        version = self._request.read_line()
        if version != self.response_marker:
            self._request.finished_reading()
            raise errors.UnexpectedProtocolVersionMarker(version)
        response_status = self._request.read_line()
        result = SmartClientRequestProtocolOne._read_response_tuple(self)
        self._response_is_unknown_method(result)
        if response_status == 'success\n':
            self.response_status = True
            if not expect_body:
                self._request.finished_reading()
            return result
        elif response_status == 'failed\n':
            self.response_status = False
            self._request.finished_reading()
            raise errors.ErrorFromSmartServer(result)
        else:
            raise errors.SmartProtocolError(
                'bad protocol status %r' % response_status)

    def _write_protocol_version(self):
        """Write any prefixes this protocol requires.

        Version two sends the value of REQUEST_VERSION_TWO.
        """
        self._request.accept_bytes(self.request_marker)

    def read_streamed_body(self):
        """Read bytes from the body, decoding into a byte stream.
        """
        # Read no more than 64k at a time so that we don't risk error 10055 (no
        # buffer space available) on Windows.
        _body_decoder = ChunkedBodyDecoder()
        while not _body_decoder.finished_reading:
            bytes = self._request.read_bytes(_body_decoder.next_read_size())
            if bytes == '':
                # end of file encountered reading from server
                raise errors.ConnectionReset(
                    "Connection lost while reading streamed body.")
            _body_decoder.accept_bytes(bytes)
            for body_bytes in iter(_body_decoder.read_next_chunk, None):
                if 'hpss' in debug.debug_flags and type(body_bytes) is str:
                    mutter('              %d byte chunk read',
                           len(body_bytes))
                yield body_bytes
        self._request.finished_reading()


def build_server_protocol_three(backing_transport, write_func,
                                root_client_path):
    request_handler = request.SmartServerRequestHandler(
        backing_transport, commands=request.request_handlers,
        root_client_path=root_client_path)
    responder = ProtocolThreeResponder(write_func)
    message_handler = message.ConventionalRequestHandler(request_handler, responder)
    return ProtocolThreeDecoder(message_handler)


class ProtocolThreeDecoder(_StatefulDecoder):

    response_marker = RESPONSE_VERSION_THREE
    request_marker = REQUEST_VERSION_THREE

    def __init__(self, message_handler, expect_version_marker=False):
        _StatefulDecoder.__init__(self)
        self._has_dispatched = False
        # Initial state
        if expect_version_marker:
            self.state_accept = self._state_accept_expecting_protocol_version
            # We're expecting at least the protocol version marker + some
            # headers.
            self._number_needed_bytes = len(MESSAGE_VERSION_THREE) + 4
        else:
            self.state_accept = self._state_accept_expecting_headers
            self._number_needed_bytes = 4
        self.decoding_failed = False
        self.request_handler = self.message_handler = message_handler

    def accept_bytes(self, bytes):
        self._number_needed_bytes = None
        try:
            _StatefulDecoder.accept_bytes(self, bytes)
        except KeyboardInterrupt:
            raise
        except errors.SmartMessageHandlerError, exception:
            # We do *not* set self.decoding_failed here.  The message handler
            # has raised an error, but the decoder is still able to parse bytes
            # and determine when this message ends.
            if not isinstance(exception.exc_value, errors.UnknownSmartMethod):
                log_exception_quietly()
            self.message_handler.protocol_error(exception.exc_value)
            # The state machine is ready to continue decoding, but the
            # exception has interrupted the loop that runs the state machine.
            # So we call accept_bytes again to restart it.
            self.accept_bytes('')
        except Exception, exception:
            # The decoder itself has raised an exception.  We cannot continue
            # decoding.
            self.decoding_failed = True
            if isinstance(exception, errors.UnexpectedProtocolVersionMarker):
                # This happens during normal operation when the client tries a
                # protocol version the server doesn't understand, so no need to
                # log a traceback every time.
                # Note that this can only happen when
                # expect_version_marker=True, which is only the case on the
                # client side.
                pass
            else:
                log_exception_quietly()
            self.message_handler.protocol_error(exception)

    def _extract_length_prefixed_bytes(self):
        if self._in_buffer_len < 4:
            # A length prefix by itself is 4 bytes, and we don't even have that
            # many yet.
            raise _NeedMoreBytes(4)
        (length,) = struct.unpack('!L', self._get_in_bytes(4))
        end_of_bytes = 4 + length
        if self._in_buffer_len < end_of_bytes:
            # We haven't yet read as many bytes as the length-prefix says there
            # are.
            raise _NeedMoreBytes(end_of_bytes)
        # Extract the bytes from the buffer.
        in_buf = self._get_in_buffer()
        bytes = in_buf[4:end_of_bytes]
        self._set_in_buffer(in_buf[end_of_bytes:])
        return bytes

    def _extract_prefixed_bencoded_data(self):
        prefixed_bytes = self._extract_length_prefixed_bytes()
        try:
            decoded = bdecode_as_tuple(prefixed_bytes)
        except ValueError:
            raise errors.SmartProtocolError(
                'Bytes %r not bencoded' % (prefixed_bytes,))
        return decoded

    def _extract_single_byte(self):
        if self._in_buffer_len == 0:
            # The buffer is empty
            raise _NeedMoreBytes(1)
        in_buf = self._get_in_buffer()
        one_byte = in_buf[0]
        self._set_in_buffer(in_buf[1:])
        return one_byte

    def _state_accept_expecting_protocol_version(self):
        needed_bytes = len(MESSAGE_VERSION_THREE) - self._in_buffer_len
        in_buf = self._get_in_buffer()
        if needed_bytes > 0:
            # We don't have enough bytes to check if the protocol version
            # marker is right.  But we can check if it is already wrong by
            # checking that the start of MESSAGE_VERSION_THREE matches what
            # we've read so far.
            # [In fact, if the remote end isn't bzr we might never receive
            # len(MESSAGE_VERSION_THREE) bytes.  So if the bytes we have so far
            # are wrong then we should just raise immediately rather than
            # stall.]
            if not MESSAGE_VERSION_THREE.startswith(in_buf):
                # We have enough bytes to know the protocol version is wrong
                raise errors.UnexpectedProtocolVersionMarker(in_buf)
            raise _NeedMoreBytes(len(MESSAGE_VERSION_THREE))
        if not in_buf.startswith(MESSAGE_VERSION_THREE):
            raise errors.UnexpectedProtocolVersionMarker(in_buf)
        self._set_in_buffer(in_buf[len(MESSAGE_VERSION_THREE):])
        self.state_accept = self._state_accept_expecting_headers

    def _state_accept_expecting_headers(self):
        decoded = self._extract_prefixed_bencoded_data()
        if type(decoded) is not dict:
            raise errors.SmartProtocolError(
                'Header object %r is not a dict' % (decoded,))
        self.state_accept = self._state_accept_expecting_message_part
        try:
            self.message_handler.headers_received(decoded)
        except:
            raise errors.SmartMessageHandlerError(sys.exc_info())

    def _state_accept_expecting_message_part(self):
        message_part_kind = self._extract_single_byte()
        if message_part_kind == 'o':
            self.state_accept = self._state_accept_expecting_one_byte
        elif message_part_kind == 's':
            self.state_accept = self._state_accept_expecting_structure
        elif message_part_kind == 'b':
            self.state_accept = self._state_accept_expecting_bytes
        elif message_part_kind == 'e':
            self.done()
        else:
            raise errors.SmartProtocolError(
                'Bad message kind byte: %r' % (message_part_kind,))

    def _state_accept_expecting_one_byte(self):
        byte = self._extract_single_byte()
        self.state_accept = self._state_accept_expecting_message_part
        try:
            self.message_handler.byte_part_received(byte)
        except:
            raise errors.SmartMessageHandlerError(sys.exc_info())

    def _state_accept_expecting_bytes(self):
        # XXX: this should not buffer whole message part, but instead deliver
        # the bytes as they arrive.
        prefixed_bytes = self._extract_length_prefixed_bytes()
        self.state_accept = self._state_accept_expecting_message_part
        try:
            self.message_handler.bytes_part_received(prefixed_bytes)
        except:
            raise errors.SmartMessageHandlerError(sys.exc_info())

    def _state_accept_expecting_structure(self):
        structure = self._extract_prefixed_bencoded_data()
        self.state_accept = self._state_accept_expecting_message_part
        try:
            self.message_handler.structure_part_received(structure)
        except:
            raise errors.SmartMessageHandlerError(sys.exc_info())

    def done(self):
        self.unused_data = self._get_in_buffer()
        self._set_in_buffer(None)
        self.state_accept = self._state_accept_reading_unused
        try:
            self.message_handler.end_received()
        except:
            raise errors.SmartMessageHandlerError(sys.exc_info())

    def _state_accept_reading_unused(self):
        self.unused_data += self._get_in_buffer()
        self._set_in_buffer(None)

    def next_read_size(self):
        if self.state_accept == self._state_accept_reading_unused:
            return 0
        elif self.decoding_failed:
            # An exception occured while processing this message, probably from
            # self.message_handler.  We're not sure that this state machine is
            # in a consistent state, so just signal that we're done (i.e. give
            # up).
            return 0
        else:
            if self._number_needed_bytes is not None:
                return self._number_needed_bytes - self._in_buffer_len
            else:
                raise AssertionError("don't know how many bytes are expected!")


class _ProtocolThreeEncoder(object):

    response_marker = request_marker = MESSAGE_VERSION_THREE

    def __init__(self, write_func):
        self._buf = []
        self._real_write_func = write_func

    def _write_func(self, bytes):
        self._buf.append(bytes)
        if len(self._buf) > 100:
            self.flush()

    def flush(self):
        if self._buf:
            self._real_write_func(''.join(self._buf))
            del self._buf[:]

    def _serialise_offsets(self, offsets):
        """Serialise a readv offset list."""
        txt = []
        for start, length in offsets:
            txt.append('%d,%d' % (start, length))
        return '\n'.join(txt)

    def _write_protocol_version(self):
        self._write_func(MESSAGE_VERSION_THREE)

    def _write_prefixed_bencode(self, structure):
        bytes = bencode(structure)
        self._write_func(struct.pack('!L', len(bytes)))
        self._write_func(bytes)

    def _write_headers(self, headers):
        self._write_prefixed_bencode(headers)

    def _write_structure(self, args):
        self._write_func('s')
        utf8_args = []
        for arg in args:
            if type(arg) is unicode:
                utf8_args.append(arg.encode('utf8'))
            else:
                utf8_args.append(arg)
        self._write_prefixed_bencode(utf8_args)

    def _write_end(self):
        self._write_func('e')
        self.flush()

    def _write_prefixed_body(self, bytes):
        self._write_func('b')
        self._write_func(struct.pack('!L', len(bytes)))
        self._write_func(bytes)

    def _write_chunked_body_start(self):
        self._write_func('oC')

    def _write_error_status(self):
        self._write_func('oE')

    def _write_success_status(self):
        self._write_func('oS')


class ProtocolThreeResponder(_ProtocolThreeEncoder):

    def __init__(self, write_func):
        _ProtocolThreeEncoder.__init__(self, write_func)
        self.response_sent = False
        self._headers = {'Software version': bzrlib.__version__}

    def send_error(self, exception):
        if self.response_sent:
            raise AssertionError(
                "send_error(%s) called, but response already sent."
                % (exception,))
        if isinstance(exception, errors.UnknownSmartMethod):
            failure = request.FailedSmartServerResponse(
                ('UnknownMethod', exception.verb))
            self.send_response(failure)
            return
        self.response_sent = True
        self._write_protocol_version()
        self._write_headers(self._headers)
        self._write_error_status()
        self._write_structure(('error', str(exception)))
        self._write_end()

    def send_response(self, response):
        if self.response_sent:
            raise AssertionError(
                "send_response(%r) called, but response already sent."
                % (response,))
        self.response_sent = True
        self._write_protocol_version()
        self._write_headers(self._headers)
        if response.is_successful():
            self._write_success_status()
        else:
            self._write_error_status()
        self._write_structure(response.args)
        if response.body is not None:
            self._write_prefixed_body(response.body)
        elif response.body_stream is not None:
            for exc_info, chunk in _iter_with_errors(response.body_stream):
                if exc_info is not None:
                    self._write_error_status()
                    error_struct = request._translate_error(exc_info[1])
                    self._write_structure(error_struct)
                    break
                else:
                    if isinstance(chunk, request.FailedSmartServerResponse):
                        self._write_error_status()
                        self._write_structure(chunk.args)
                        break
                    self._write_prefixed_body(chunk)
        self._write_end()


def _iter_with_errors(iterable):
    """Handle errors from iterable.next().

    Use like::

        for exc_info, value in _iter_with_errors(iterable):
            ...

    This is a safer alternative to::

        try:
            for value in iterable:
               ...
        except:
            ...

    Because the latter will catch errors from the for-loop body, not just
    iterable.next()

    If an error occurs, exc_info will be a exc_info tuple, and the generator
    will terminate.  Otherwise exc_info will be None, and value will be the
    value from iterable.next().  Note that KeyboardInterrupt and SystemExit
    will not be itercepted.
    """
    iterator = iter(iterable)
    while True:
        try:
            yield None, iterator.next()
        except StopIteration:
            return
        except (KeyboardInterrupt, SystemExit):
            raise
        except Exception:
            mutter('_iter_with_errors caught error')
            log_exception_quietly()
            yield sys.exc_info(), None
            return


class ProtocolThreeRequester(_ProtocolThreeEncoder, Requester):

    def __init__(self, medium_request):
        _ProtocolThreeEncoder.__init__(self, medium_request.accept_bytes)
        self._medium_request = medium_request
        self._headers = {}

    def set_headers(self, headers):
        self._headers = headers.copy()

    def call(self, *args):
        if 'hpss' in debug.debug_flags:
            mutter('hpss call:   %s', repr(args)[1:-1])
            base = getattr(self._medium_request._medium, 'base', None)
            if base is not None:
                mutter('             (to %s)', base)
            self._request_start_time = time.time()
        self._write_protocol_version()
        self._write_headers(self._headers)
        self._write_structure(args)
        self._write_end()
        self._medium_request.finished_writing()

    def call_with_body_bytes(self, args, body):
        """Make a remote call of args with body bytes 'body'.

        After calling this, call read_response_tuple to find the result out.
        """
        if 'hpss' in debug.debug_flags:
            mutter('hpss call w/body: %s (%r...)', repr(args)[1:-1], body[:20])
            path = getattr(self._medium_request._medium, '_path', None)
            if path is not None:
                mutter('                  (to %s)', path)
            mutter('              %d bytes', len(body))
            self._request_start_time = time.time()
        self._write_protocol_version()
        self._write_headers(self._headers)
        self._write_structure(args)
        self._write_prefixed_body(body)
        self._write_end()
        self._medium_request.finished_writing()

    def call_with_body_readv_array(self, args, body):
        """Make a remote call with a readv array.

        The body is encoded with one line per readv offset pair. The numbers in
        each pair are separated by a comma, and no trailing \n is emitted.
        """
        if 'hpss' in debug.debug_flags:
            mutter('hpss call w/readv: %s', repr(args)[1:-1])
            path = getattr(self._medium_request._medium, '_path', None)
            if path is not None:
                mutter('                  (to %s)', path)
            self._request_start_time = time.time()
        self._write_protocol_version()
        self._write_headers(self._headers)
        self._write_structure(args)
        readv_bytes = self._serialise_offsets(body)
        if 'hpss' in debug.debug_flags:
            mutter('              %d bytes in readv request', len(readv_bytes))
        self._write_prefixed_body(readv_bytes)
        self._write_end()
        self._medium_request.finished_writing()

    def call_with_body_stream(self, args, stream):
        if 'hpss' in debug.debug_flags:
            mutter('hpss call w/body stream: %r', args)
            path = getattr(self._medium_request._medium, '_path', None)
            if path is not None:
                mutter('                  (to %s)', path)
            self._request_start_time = time.time()
        self._write_protocol_version()
        self._write_headers(self._headers)
        self._write_structure(args)
        # TODO: notice if the server has sent an early error reply before we
        #       have finished sending the stream.  We would notice at the end
        #       anyway, but if the medium can deliver it early then it's good
        #       to short-circuit the whole request...
        for exc_info, part in _iter_with_errors(stream):
            if exc_info is not None:
                # Iterating the stream failed.  Cleanly abort the request.
                self._write_error_status()
                # Currently the client unconditionally sends ('error',) as the
                # error args.
                self._write_structure(('error',))
                self._write_end()
                self._medium_request.finished_writing()
                raise exc_info[0], exc_info[1], exc_info[2]
            else:
                self._write_prefixed_body(part)
                self.flush()
        self._write_end()
        self._medium_request.finished_writing()