# 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  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 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.util.bencode import bdecode, 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 1.3)\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)


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.dispatch_command(req_args[0], req_args[1:])
                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):
        self.count = count


class _StatefulDecoder(object):

    def __init__(self):
        self.finished_reading = False
        self.unused_data = ''
        self.bytes_left = None
        self._number_needed_bytes = None

    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
        current_state = self.state_accept
        self._number_needed_bytes = None
        try:
            self.state_accept(bytes)
            while current_state != self.state_accept:
                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._in_buffer = ''
        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 == '':
                # 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') - len(self._in_buffer))
        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):
        pos = self._in_buffer.find('\n')
        if pos == -1:
            # We haven't read a complete line yet, so there's nothing to do.
            raise _NeedMoreBytes(1)
        line = self._in_buffer[:pos]
        # Trim the prefix (including '\n' delimiter) from the _in_buffer.
        self._in_buffer = self._in_buffer[pos+1:]
        return line

    def _finished(self):
        self.unused_data = self._in_buffer
        self._in_buffer = None
        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, bytes):
        self._in_buffer += bytes
        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, bytes):
        self._in_buffer += bytes
        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, bytes):
        self._in_buffer += bytes
        in_buffer_len = len(self._in_buffer)
        self.chunk_in_progress += self._in_buffer[:self.bytes_left]
        self._in_buffer = self._in_buffer[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, bytes):
        self.unused_data += bytes


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._in_buffer = ''
        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, bytes):
        self._in_buffer += bytes
        pos = self._in_buffer.find('\n')
        if pos == -1:
            return
        self.bytes_left = int(self._in_buffer[:pos])
        self._in_buffer = self._in_buffer[pos+1:]
        self.bytes_left -= len(self._in_buffer)
        self.state_accept = self._state_accept_reading_body
        self.state_read = self._state_read_in_buffer

    def _state_accept_reading_body(self, bytes):
        self._in_buffer += bytes
        self.bytes_left -= len(bytes)
        if self.bytes_left <= 0:
            # Finished with body
            if self.bytes_left != 0:
                self._trailer_buffer = self._in_buffer[self.bytes_left:]
                self._in_buffer = self._in_buffer[:self.bytes_left]
            self.bytes_left = None
            self.state_accept = self._state_accept_reading_trailer
        
    def _state_accept_reading_trailer(self, bytes):
        self._trailer_buffer += bytes
        # 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, bytes):
        self.unused_data += bytes

    def _state_read_no_data(self):
        return ''

    def _state_read_in_buffer(self):
        result = self._in_buffer
        self._in_buffer = ''
        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

    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 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):
        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()

        # Read no more than 64k at a time so that we don't risk error 10055 (no
        # buffer space available) on Windows.
        max_read = 64 * 1024
        while not _body_decoder.finished_reading:
            bytes_wanted = min(_body_decoder.next_read_size(), max_read)
            bytes = self._request.read_bytes(bytes_wanted)
            _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._recv_line())

    def _recv_line(self):
        """Read an entire line from the medium request."""
        line = ''
        while not line or line[-1] != '\n':
            # TODO: this is inefficient - but tuples are short.
            new_char = self._request.read_bytes(1)
            if new_char == '':
                # end of file encountered reading from server
                raise errors.ConnectionReset(
                    "please check connectivity and permissions",
                    "(and try -Dhpss if further diagnosis is required)")
            line += new_char
        return 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
        elif resp == ('ok', '3'):
            return 3
        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:
            raise errors.SmartProtocolError('bad protocol marker %r' % version)
        response_status = self._recv_line()
        result = SmartClientRequestProtocolOne._read_response_tuple(self)
        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.
        max_read = 64 * 1024
        _body_decoder = ChunkedBodyDecoder()
        while not _body_decoder.finished_reading:
            bytes_wanted = min(_body_decoder.next_read_size(), max_read)
            bytes = self._request.read_bytes(bytes_wanted)
            _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):
        _StatefulDecoder.__init__(self)
        self.has_dispatched = False
        # Initial state
        self._in_buffer = ''
        self._number_needed_bytes = 4
        self.state_accept = self._state_accept_expecting_headers
        self.errored = 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 Exception, exception:
            log_exception_quietly()
            self.message_handler.protocol_error(exception)
            self.errored = True

    def _extract_length_prefixed_bytes(self):
        if len(self._in_buffer) < 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._in_buffer[:4])
        end_of_bytes = 4 + length
        if len(self._in_buffer) < 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.
        bytes = self._in_buffer[4:end_of_bytes]
        self._in_buffer = self._in_buffer[end_of_bytes:]
        return bytes

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

    def _extract_single_byte(self):
        if self._in_buffer == '':
            # The buffer is empty
            raise _NeedMoreBytes(1)
        one_byte = self._in_buffer[0]
        self._in_buffer = self._in_buffer[1:]
        return one_byte

    def _state_accept_expecting_headers(self, bytes):
        self._in_buffer += bytes
        decoded = self._extract_prefixed_bencoded_data()
        if type(decoded) is not dict:
            raise errors.SmartProtocolError(
                'Header object %r is not a dict' % (decoded,))
        self.message_handler.headers_received(decoded)
        self.state_accept = self._state_accept_expecting_message_part
    
    def _state_accept_expecting_message_part(self, bytes):
        self._in_buffer += bytes
        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, bytes):
        self._in_buffer += bytes
        byte = self._extract_single_byte()
        self.message_handler.byte_part_received(byte)
        self.state_accept = self._state_accept_expecting_message_part

    def _state_accept_expecting_bytes(self, bytes):
        # XXX: this should not buffer whole message part, but instead deliver
        # the bytes as they arrive.
        self._in_buffer += bytes
        prefixed_bytes = self._extract_length_prefixed_bytes()
        self.message_handler.bytes_part_received(prefixed_bytes)
        self.state_accept = self._state_accept_expecting_message_part

    def _state_accept_expecting_structure(self, bytes):
        self._in_buffer += bytes
        structure = self._extract_prefixed_bencoded_data()
        self.message_handler.structure_part_received(structure)
        self.state_accept = self._state_accept_expecting_message_part

    def done(self):
        self.unused_data = self._in_buffer
        self._in_buffer = None
        self.state_accept = self._state_accept_reading_unused
        self.message_handler.end_received()

    def _state_accept_reading_unused(self, bytes):
        self.unused_data += bytes

    def next_read_size(self):
        if self.state_accept == self._state_accept_reading_unused:
            return 0
        elif self.errored:
            # 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 - len(self._in_buffer)
            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._write_func = write_func

    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=None):
        if headers is None:
            headers = {'Software version': bzrlib.__version__}
        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')

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

    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

    def send_error(self, exception):
        assert not self.response_sent
        if isinstance(exception, errors.UnknownSmartMethod):
            failure = request.FailedSmartServerResponse(
                ('UnknownMethod', exception.verb))
            self.send_response(failure)
            return
        self.response_sent = True
        self._write_headers()
        self._write_error_status()
        self._write_structure(('error', str(exception)))
        self._write_end()

    def send_response(self, response):
        assert not self.response_sent
        self.response_sent = True
        self._write_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 chunk in response.body_stream:
                self._write_prefixed_body(chunk)
        self._write_end()
        

class ProtocolThreeRequester(_ProtocolThreeEncoder, Requester):

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

    def call(self, *args, **kw):
        # XXX: ideally, signature would be call(self, *args, headers=None), but
        # python doesn't allow that.  So, we fake it.
        headers = None
        if 'headers' in kw:
            headers = kw.pop('headers')
        if kw != {}:
            raise TypeError('Unexpected keyword arguments: %r' % (kw,))
        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(headers)
        self._write_structure(args)
        self._write_end()
        self._medium_request.finished_writing()

    def call_with_body_bytes(self, args, body, headers=None):
        """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(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, headers=None):
        """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(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()