wireproto: show unknown id and flags in repr(frame)

Perhaps we'll want it for debugging.

mercurial/wireprotoframing.py

@@ -1,867 +1,870
 # wireprotoframing.py - unified framing protocol for wire protocol
 #
 # Copyright 2018 Gregory Szorc <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 # This file contains functionality to support the unified frame-based wire
 # protocol. For details about the protocol, see
 # `hg help internals.wireprotocol`.
 
 from __future__ import absolute_import
 
 import struct
 
 from .i18n import _
 from .thirdparty import (
     attr,
     cbor,
 )
 from . import (
     error,
     util,
 )
 from .utils import (
     stringutil,
 )
 
 FRAME_HEADER_SIZE = 8
 DEFAULT_MAX_FRAME_SIZE = 32768
 
 STREAM_FLAG_BEGIN_STREAM = 0x01
 STREAM_FLAG_END_STREAM = 0x02
 STREAM_FLAG_ENCODING_APPLIED = 0x04
 
 STREAM_FLAGS = {
     b'stream-begin': STREAM_FLAG_BEGIN_STREAM,
     b'stream-end': STREAM_FLAG_END_STREAM,
     b'encoded': STREAM_FLAG_ENCODING_APPLIED,
 }
 
 FRAME_TYPE_COMMAND_REQUEST = 0x01
 FRAME_TYPE_COMMAND_DATA = 0x03
 FRAME_TYPE_BYTES_RESPONSE = 0x04
 FRAME_TYPE_ERROR_RESPONSE = 0x05
 FRAME_TYPE_TEXT_OUTPUT = 0x06
 FRAME_TYPE_PROGRESS = 0x07
 FRAME_TYPE_STREAM_SETTINGS = 0x08
 
 FRAME_TYPES = {
     b'command-request': FRAME_TYPE_COMMAND_REQUEST,
     b'command-data': FRAME_TYPE_COMMAND_DATA,
     b'bytes-response': FRAME_TYPE_BYTES_RESPONSE,
     b'error-response': FRAME_TYPE_ERROR_RESPONSE,
     b'text-output': FRAME_TYPE_TEXT_OUTPUT,
     b'progress': FRAME_TYPE_PROGRESS,
     b'stream-settings': FRAME_TYPE_STREAM_SETTINGS,
 }
 
 FLAG_COMMAND_REQUEST_NEW = 0x01
 FLAG_COMMAND_REQUEST_CONTINUATION = 0x02
 FLAG_COMMAND_REQUEST_MORE_FRAMES = 0x04
 FLAG_COMMAND_REQUEST_EXPECT_DATA = 0x08
 
 FLAGS_COMMAND_REQUEST = {
     b'new': FLAG_COMMAND_REQUEST_NEW,
     b'continuation': FLAG_COMMAND_REQUEST_CONTINUATION,
     b'more': FLAG_COMMAND_REQUEST_MORE_FRAMES,
     b'have-data': FLAG_COMMAND_REQUEST_EXPECT_DATA,
 }
 
 FLAG_COMMAND_DATA_CONTINUATION = 0x01
 FLAG_COMMAND_DATA_EOS = 0x02
 
 FLAGS_COMMAND_DATA = {
     b'continuation': FLAG_COMMAND_DATA_CONTINUATION,
     b'eos': FLAG_COMMAND_DATA_EOS,
 }
 
 FLAG_BYTES_RESPONSE_CONTINUATION = 0x01
 FLAG_BYTES_RESPONSE_EOS = 0x02
 FLAG_BYTES_RESPONSE_CBOR = 0x04
 
 FLAGS_BYTES_RESPONSE = {
     b'continuation': FLAG_BYTES_RESPONSE_CONTINUATION,
     b'eos': FLAG_BYTES_RESPONSE_EOS,
     b'cbor': FLAG_BYTES_RESPONSE_CBOR,
 }
 
 FLAG_ERROR_RESPONSE_PROTOCOL = 0x01
 FLAG_ERROR_RESPONSE_APPLICATION = 0x02
 
 FLAGS_ERROR_RESPONSE = {
     b'protocol': FLAG_ERROR_RESPONSE_PROTOCOL,
     b'application': FLAG_ERROR_RESPONSE_APPLICATION,
 }
 
 # Maps frame types to their available flags.
 FRAME_TYPE_FLAGS = {
     FRAME_TYPE_COMMAND_REQUEST: FLAGS_COMMAND_REQUEST,
     FRAME_TYPE_COMMAND_DATA: FLAGS_COMMAND_DATA,
     FRAME_TYPE_BYTES_RESPONSE: FLAGS_BYTES_RESPONSE,
     FRAME_TYPE_ERROR_RESPONSE: FLAGS_ERROR_RESPONSE,
     FRAME_TYPE_TEXT_OUTPUT: {},
     FRAME_TYPE_PROGRESS: {},
     FRAME_TYPE_STREAM_SETTINGS: {},
 }
 
 ARGUMENT_RECORD_HEADER = struct.Struct(r'<HH')
 
 def humanflags(mapping, value):
     """Convert a numeric flags value to a human value, using a mapping table."""
+    namemap = {v: k for k, v in mapping.iteritems()}
     flags = []
-    for val, name in sorted({v: k for k, v in mapping.iteritems()}.iteritems()):
+    val = 1
+    while value >= val:
         if value & val:
-            flags.append(name)
+            flags.append(namemap.get(val, '<unknown 0x%02x>' % val))
+        val <<= 1
 
     return b'|'.join(flags)
 
 @attr.s(slots=True)
 class frameheader(object):
     """Represents the data in a frame header."""
 
     length = attr.ib()
     requestid = attr.ib()
     streamid = attr.ib()
     streamflags = attr.ib()
     typeid = attr.ib()
     flags = attr.ib()
 
 @attr.s(slots=True, repr=False)
 class frame(object):
     """Represents a parsed frame."""
 
     requestid = attr.ib()
     streamid = attr.ib()
     streamflags = attr.ib()
     typeid = attr.ib()
     flags = attr.ib()
     payload = attr.ib()
 
     def __repr__(self):
-        typename = '<unknown>'
+        typename = '<unknown 0x%02x>' % self.typeid
         for name, value in FRAME_TYPES.iteritems():
             if value == self.typeid:
                 typename = name
                 break
 
         return ('frame(size=%d; request=%d; stream=%d; streamflags=%s; '
                 'type=%s; flags=%s)' % (
             len(self.payload), self.requestid, self.streamid,
             humanflags(STREAM_FLAGS, self.streamflags), typename,
             humanflags(FRAME_TYPE_FLAGS.get(self.typeid, {}), self.flags)))
 
 def makeframe(requestid, streamid, streamflags, typeid, flags, payload):
     """Assemble a frame into a byte array."""
     # TODO assert size of payload.
     frame = bytearray(FRAME_HEADER_SIZE + len(payload))
 
     # 24 bits length
     # 16 bits request id
     # 8 bits stream id
     # 8 bits stream flags
     # 4 bits type
     # 4 bits flags
 
     l = struct.pack(r'<I', len(payload))
     frame[0:3] = l[0:3]
     struct.pack_into(r'<HBB', frame, 3, requestid, streamid, streamflags)
     frame[7] = (typeid << 4) | flags
     frame[8:] = payload
 
     return frame
 
 def makeframefromhumanstring(s):
     """Create a frame from a human readable string
 
     DANGER: NOT SAFE TO USE WITH UNTRUSTED INPUT BECAUSE OF POTENTIAL
     eval() USAGE. DO NOT USE IN CORE.
 
     Strings have the form:
 
         <request-id> <stream-id> <stream-flags> <type> <flags> <payload>
 
     This can be used by user-facing applications and tests for creating
     frames easily without having to type out a bunch of constants.
 
     Request ID and stream IDs are integers.
 
     Stream flags, frame type, and flags can be specified by integer or
     named constant.
 
     Flags can be delimited by `|` to bitwise OR them together.
 
     If the payload begins with ``cbor:``, the following string will be
     evaluated as Python code and the resulting object will be fed into
     a CBOR encoder. Otherwise, the payload is interpreted as a Python
     byte string literal.
     """
     fields = s.split(b' ', 5)
     requestid, streamid, streamflags, frametype, frameflags, payload = fields
 
     requestid = int(requestid)
     streamid = int(streamid)
 
     finalstreamflags = 0
     for flag in streamflags.split(b'|'):
         if flag in STREAM_FLAGS:
             finalstreamflags |= STREAM_FLAGS[flag]
         else:
             finalstreamflags |= int(flag)
 
     if frametype in FRAME_TYPES:
         frametype = FRAME_TYPES[frametype]
     else:
         frametype = int(frametype)
 
     finalflags = 0
     validflags = FRAME_TYPE_FLAGS[frametype]
     for flag in frameflags.split(b'|'):
         if flag in validflags:
             finalflags |= validflags[flag]
         else:
             finalflags |= int(flag)
 
     if payload.startswith(b'cbor:'):
         payload = cbor.dumps(stringutil.evalpython(payload[5:]), canonical=True)
 
     else:
         payload = stringutil.unescapestr(payload)
 
     return makeframe(requestid=requestid, streamid=streamid,
                      streamflags=finalstreamflags, typeid=frametype,
                      flags=finalflags, payload=payload)
 
 def parseheader(data):
     """Parse a unified framing protocol frame header from a buffer.
 
     The header is expected to be in the buffer at offset 0 and the
     buffer is expected to be large enough to hold a full header.
     """
     # 24 bits payload length (little endian)
     # 16 bits request ID
     # 8 bits stream ID
     # 8 bits stream flags
     # 4 bits frame type
     # 4 bits frame flags
     # ... payload
     framelength = data[0] + 256 * data[1] + 16384 * data[2]
     requestid, streamid, streamflags = struct.unpack_from(r'<HBB', data, 3)
     typeflags = data[7]
 
     frametype = (typeflags & 0xf0) >> 4
     frameflags = typeflags & 0x0f
 
     return frameheader(framelength, requestid, streamid, streamflags,
                        frametype, frameflags)
 
 def readframe(fh):
     """Read a unified framing protocol frame from a file object.
 
     Returns a 3-tuple of (type, flags, payload) for the decoded frame or
     None if no frame is available. May raise if a malformed frame is
     seen.
     """
     header = bytearray(FRAME_HEADER_SIZE)
 
     readcount = fh.readinto(header)
 
     if readcount == 0:
         return None
 
     if readcount != FRAME_HEADER_SIZE:
         raise error.Abort(_('received incomplete frame: got %d bytes: %s') %
                           (readcount, header))
 
     h = parseheader(header)
 
     payload = fh.read(h.length)
     if len(payload) != h.length:
         raise error.Abort(_('frame length error: expected %d; got %d') %
                           (h.length, len(payload)))
 
     return frame(h.requestid, h.streamid, h.streamflags, h.typeid, h.flags,
                  payload)
 
 def createcommandframes(stream, requestid, cmd, args, datafh=None,
                         maxframesize=DEFAULT_MAX_FRAME_SIZE):
     """Create frames necessary to transmit a request to run a command.
 
     This is a generator of bytearrays. Each item represents a frame
     ready to be sent over the wire to a peer.
     """
     data = {b'name': cmd}
     if args:
         data[b'args'] = args
 
     data = cbor.dumps(data, canonical=True)
 
     offset = 0
 
     while True:
         flags = 0
 
         # Must set new or continuation flag.
         if not offset:
             flags |= FLAG_COMMAND_REQUEST_NEW
         else:
             flags |= FLAG_COMMAND_REQUEST_CONTINUATION
 
         # Data frames is set on all frames.
         if datafh:
             flags |= FLAG_COMMAND_REQUEST_EXPECT_DATA
 
         payload = data[offset:offset + maxframesize]
         offset += len(payload)
 
         if len(payload) == maxframesize and offset < len(data):
             flags |= FLAG_COMMAND_REQUEST_MORE_FRAMES
 
         yield stream.makeframe(requestid=requestid,
                                typeid=FRAME_TYPE_COMMAND_REQUEST,
                                flags=flags,
                                payload=payload)
 
         if not (flags & FLAG_COMMAND_REQUEST_MORE_FRAMES):
             break
 
     if datafh:
         while True:
             data = datafh.read(DEFAULT_MAX_FRAME_SIZE)
 
             done = False
             if len(data) == DEFAULT_MAX_FRAME_SIZE:
                 flags = FLAG_COMMAND_DATA_CONTINUATION
             else:
                 flags = FLAG_COMMAND_DATA_EOS
                 assert datafh.read(1) == b''
                 done = True
 
             yield stream.makeframe(requestid=requestid,
                                    typeid=FRAME_TYPE_COMMAND_DATA,
                                    flags=flags,
                                    payload=data)
 
             if done:
                 break
 
 def createbytesresponseframesfrombytes(stream, requestid, data,
                                        maxframesize=DEFAULT_MAX_FRAME_SIZE):
     """Create a raw frame to send a bytes response from static bytes input.
 
     Returns a generator of bytearrays.
     """
 
     # Simple case of a single frame.
     if len(data) <= maxframesize:
         yield stream.makeframe(requestid=requestid,
                                typeid=FRAME_TYPE_BYTES_RESPONSE,
                                flags=FLAG_BYTES_RESPONSE_EOS,
                                payload=data)
         return
 
     offset = 0
     while True:
         chunk = data[offset:offset + maxframesize]
         offset += len(chunk)
         done = offset == len(data)
 
         if done:
             flags = FLAG_BYTES_RESPONSE_EOS
         else:
             flags = FLAG_BYTES_RESPONSE_CONTINUATION
 
         yield stream.makeframe(requestid=requestid,
                                typeid=FRAME_TYPE_BYTES_RESPONSE,
                                flags=flags,
                                payload=chunk)
 
         if done:
             break
 
 def createerrorframe(stream, requestid, msg, protocol=False, application=False):
     # TODO properly handle frame size limits.
     assert len(msg) <= DEFAULT_MAX_FRAME_SIZE
 
     flags = 0
     if protocol:
         flags |= FLAG_ERROR_RESPONSE_PROTOCOL
     if application:
         flags |= FLAG_ERROR_RESPONSE_APPLICATION
 
     yield stream.makeframe(requestid=requestid,
                            typeid=FRAME_TYPE_ERROR_RESPONSE,
                            flags=flags,
                            payload=msg)
 
 def createtextoutputframe(stream, requestid, atoms,
                           maxframesize=DEFAULT_MAX_FRAME_SIZE):
     """Create a text output frame to render text to people.
 
     ``atoms`` is a 3-tuple of (formatting string, args, labels).
 
     The formatting string contains ``%s`` tokens to be replaced by the
     corresponding indexed entry in ``args``. ``labels`` is an iterable of
     formatters to be applied at rendering time. In terms of the ``ui``
     class, each atom corresponds to a ``ui.write()``.
     """
     atomdicts = []
 
     for (formatting, args, labels) in atoms:
         # TODO look for localstr, other types here?
 
         if not isinstance(formatting, bytes):
             raise ValueError('must use bytes formatting strings')
         for arg in args:
             if not isinstance(arg, bytes):
                 raise ValueError('must use bytes for arguments')
         for label in labels:
             if not isinstance(label, bytes):
                 raise ValueError('must use bytes for labels')
 
         # Formatting string must be ASCII.
         formatting = formatting.decode(r'ascii', r'replace').encode(r'ascii')
 
         # Arguments must be UTF-8.
         args = [a.decode(r'utf-8', r'replace').encode(r'utf-8') for a in args]
 
         # Labels must be ASCII.
         labels = [l.decode(r'ascii', r'strict').encode(r'ascii')
                   for l in labels]
 
         atom = {b'msg': formatting}
         if args:
             atom[b'args'] = args
         if labels:
             atom[b'labels'] = labels
 
         atomdicts.append(atom)
 
     payload = cbor.dumps(atomdicts, canonical=True)
 
     if len(payload) > maxframesize:
         raise ValueError('cannot encode data in a single frame')
 
     yield stream.makeframe(requestid=requestid,
                            typeid=FRAME_TYPE_TEXT_OUTPUT,
                            flags=0,
                            payload=payload)
 
 class stream(object):
     """Represents a logical unidirectional series of frames."""
 
     def __init__(self, streamid, active=False):
         self.streamid = streamid
         self._active = False
 
     def makeframe(self, requestid, typeid, flags, payload):
         """Create a frame to be sent out over this stream.
 
         Only returns the frame instance. Does not actually send it.
         """
         streamflags = 0
         if not self._active:
             streamflags |= STREAM_FLAG_BEGIN_STREAM
             self._active = True
 
         return makeframe(requestid, self.streamid, streamflags, typeid, flags,
                          payload)
 
 def ensureserverstream(stream):
     if stream.streamid % 2:
         raise error.ProgrammingError('server should only write to even '
                                      'numbered streams; %d is not even' %
                                      stream.streamid)
 
 class serverreactor(object):
     """Holds state of a server handling frame-based protocol requests.
 
     This class is the "brain" of the unified frame-based protocol server
     component. While the protocol is stateless from the perspective of
     requests/commands, something needs to track which frames have been
     received, what frames to expect, etc. This class is that thing.
 
     Instances are modeled as a state machine of sorts. Instances are also
     reactionary to external events. The point of this class is to encapsulate
     the state of the connection and the exchange of frames, not to perform
     work. Instead, callers tell this class when something occurs, like a
     frame arriving. If that activity is worthy of a follow-up action (say
     *run a command*), the return value of that handler will say so.
 
     I/O and CPU intensive operations are purposefully delegated outside of
     this class.
 
     Consumers are expected to tell instances when events occur. They do so by
     calling the various ``on*`` methods. These methods return a 2-tuple
     describing any follow-up action(s) to take. The first element is the
     name of an action to perform. The second is a data structure (usually
     a dict) specific to that action that contains more information. e.g.
     if the server wants to send frames back to the client, the data structure
     will contain a reference to those frames.
 
     Valid actions that consumers can be instructed to take are:
 
     sendframes
        Indicates that frames should be sent to the client. The ``framegen``
        key contains a generator of frames that should be sent. The server
        assumes that all frames are sent to the client.
 
     error
        Indicates that an error occurred. Consumer should probably abort.
 
     runcommand
        Indicates that the consumer should run a wire protocol command. Details
        of the command to run are given in the data structure.
 
     wantframe
        Indicates that nothing of interest happened and the server is waiting on
        more frames from the client before anything interesting can be done.
 
     noop
        Indicates no additional action is required.
 
     Known Issues
     ------------
 
     There are no limits to the number of partially received commands or their
     size. A malicious client could stream command request data and exhaust the
     server's memory.
 
     Partially received commands are not acted upon when end of input is
     reached. Should the server error if it receives a partial request?
     Should the client send a message to abort a partially transmitted request
     to facilitate graceful shutdown?
 
     Active requests that haven't been responded to aren't tracked. This means
     that if we receive a command and instruct its dispatch, another command
     with its request ID can come in over the wire and there will be a race
     between who responds to what.
     """
 
     def __init__(self, deferoutput=False):
         """Construct a new server reactor.
 
         ``deferoutput`` can be used to indicate that no output frames should be
         instructed to be sent until input has been exhausted. In this mode,
         events that would normally generate output frames (such as a command
         response being ready) will instead defer instructing the consumer to
         send those frames. This is useful for half-duplex transports where the
         sender cannot receive until all data has been transmitted.
         """
         self._deferoutput = deferoutput
         self._state = 'idle'
         self._nextoutgoingstreamid = 2
         self._bufferedframegens = []
         # stream id -> stream instance for all active streams from the client.
         self._incomingstreams = {}
         self._outgoingstreams = {}
         # request id -> dict of commands that are actively being received.
         self._receivingcommands = {}
         # Request IDs that have been received and are actively being processed.
         # Once all output for a request has been sent, it is removed from this
         # set.
         self._activecommands = set()
 
     def onframerecv(self, frame):
         """Process a frame that has been received off the wire.
 
         Returns a dict with an ``action`` key that details what action,
         if any, the consumer should take next.
         """
         if not frame.streamid % 2:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('received frame with even numbered stream ID: %d') %
                   frame.streamid)
 
         if frame.streamid not in self._incomingstreams:
             if not frame.streamflags & STREAM_FLAG_BEGIN_STREAM:
                 self._state = 'errored'
                 return self._makeerrorresult(
                     _('received frame on unknown inactive stream without '
                       'beginning of stream flag set'))
 
             self._incomingstreams[frame.streamid] = stream(frame.streamid)
 
         if frame.streamflags & STREAM_FLAG_ENCODING_APPLIED:
             # TODO handle decoding frames
             self._state = 'errored'
             raise error.ProgrammingError('support for decoding stream payloads '
                                          'not yet implemented')
 
         if frame.streamflags & STREAM_FLAG_END_STREAM:
             del self._incomingstreams[frame.streamid]
 
         handlers = {
             'idle': self._onframeidle,
             'command-receiving': self._onframecommandreceiving,
             'errored': self._onframeerrored,
         }
 
         meth = handlers.get(self._state)
         if not meth:
             raise error.ProgrammingError('unhandled state: %s' % self._state)
 
         return meth(frame)
 
     def onbytesresponseready(self, stream, requestid, data):
         """Signal that a bytes response is ready to be sent to the client.
 
         The raw bytes response is passed as an argument.
         """
         ensureserverstream(stream)
 
         def sendframes():
             for frame in createbytesresponseframesfrombytes(stream, requestid,
                                                             data):
                 yield frame
 
             self._activecommands.remove(requestid)
 
         result = sendframes()
 
         if self._deferoutput:
             self._bufferedframegens.append(result)
             return 'noop', {}
         else:
             return 'sendframes', {
                 'framegen': result,
             }
 
     def oninputeof(self):
         """Signals that end of input has been received.
 
         No more frames will be received. All pending activity should be
         completed.
         """
         # TODO should we do anything about in-flight commands?
 
         if not self._deferoutput or not self._bufferedframegens:
             return 'noop', {}
 
         # If we buffered all our responses, emit those.
         def makegen():
             for gen in self._bufferedframegens:
                 for frame in gen:
                     yield frame
 
         return 'sendframes', {
             'framegen': makegen(),
         }
 
     def onapplicationerror(self, stream, requestid, msg):
         ensureserverstream(stream)
 
         return 'sendframes', {
             'framegen': createerrorframe(stream, requestid, msg,
                                          application=True),
         }
 
     def makeoutputstream(self):
         """Create a stream to be used for sending data to the client."""
         streamid = self._nextoutgoingstreamid
         self._nextoutgoingstreamid += 2
 
         s = stream(streamid)
         self._outgoingstreams[streamid] = s
 
         return s
 
     def _makeerrorresult(self, msg):
         return 'error', {
             'message': msg,
         }
 
     def _makeruncommandresult(self, requestid):
         entry = self._receivingcommands[requestid]
 
         if not entry['requestdone']:
             self._state = 'errored'
             raise error.ProgrammingError('should not be called without '
                                          'requestdone set')
 
         del self._receivingcommands[requestid]
 
         if self._receivingcommands:
             self._state = 'command-receiving'
         else:
             self._state = 'idle'
 
         # Decode the payloads as CBOR.
         entry['payload'].seek(0)
         request = cbor.load(entry['payload'])
 
         if b'name' not in request:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('command request missing "name" field'))
 
         if b'args' not in request:
             request[b'args'] = {}
 
         assert requestid not in self._activecommands
         self._activecommands.add(requestid)
 
         return 'runcommand', {
             'requestid': requestid,
             'command': request[b'name'],
             'args': request[b'args'],
             'data': entry['data'].getvalue() if entry['data'] else None,
         }
 
     def _makewantframeresult(self):
         return 'wantframe', {
             'state': self._state,
         }
 
     def _validatecommandrequestframe(self, frame):
         new = frame.flags & FLAG_COMMAND_REQUEST_NEW
         continuation = frame.flags & FLAG_COMMAND_REQUEST_CONTINUATION
 
         if new and continuation:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('received command request frame with both new and '
                   'continuation flags set'))
 
         if not new and not continuation:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('received command request frame with neither new nor '
                   'continuation flags set'))
 
     def _onframeidle(self, frame):
         # The only frame type that should be received in this state is a
         # command request.
         if frame.typeid != FRAME_TYPE_COMMAND_REQUEST:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('expected command request frame; got %d') % frame.typeid)
 
         res = self._validatecommandrequestframe(frame)
         if res:
             return res
 
         if frame.requestid in self._receivingcommands:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('request with ID %d already received') % frame.requestid)
 
         if frame.requestid in self._activecommands:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('request with ID %d is already active') % frame.requestid)
 
         new = frame.flags & FLAG_COMMAND_REQUEST_NEW
         moreframes = frame.flags & FLAG_COMMAND_REQUEST_MORE_FRAMES
         expectingdata = frame.flags & FLAG_COMMAND_REQUEST_EXPECT_DATA
 
         if not new:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('received command request frame without new flag set'))
 
         payload = util.bytesio()
         payload.write(frame.payload)
 
         self._receivingcommands[frame.requestid] = {
             'payload': payload,
             'data': None,
             'requestdone': not moreframes,
             'expectingdata': bool(expectingdata),
         }
 
         # This is the final frame for this request. Dispatch it.
         if not moreframes and not expectingdata:
             return self._makeruncommandresult(frame.requestid)
 
         assert moreframes or expectingdata
         self._state = 'command-receiving'
         return self._makewantframeresult()
 
     def _onframecommandreceiving(self, frame):
         if frame.typeid == FRAME_TYPE_COMMAND_REQUEST:
             # Process new command requests as such.
             if frame.flags & FLAG_COMMAND_REQUEST_NEW:
                 return self._onframeidle(frame)
 
             res = self._validatecommandrequestframe(frame)
             if res:
                 return res
 
         # All other frames should be related to a command that is currently
         # receiving but is not active.
         if frame.requestid in self._activecommands:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('received frame for request that is still active: %d') %
                 frame.requestid)
 
         if frame.requestid not in self._receivingcommands:
             self._state = 'errored'
             return self._makeerrorresult(
                 _('received frame for request that is not receiving: %d') %
                   frame.requestid)
 
         entry = self._receivingcommands[frame.requestid]
 
         if frame.typeid == FRAME_TYPE_COMMAND_REQUEST:
             moreframes = frame.flags & FLAG_COMMAND_REQUEST_MORE_FRAMES
             expectingdata = bool(frame.flags & FLAG_COMMAND_REQUEST_EXPECT_DATA)
 
             if entry['requestdone']:
                 self._state = 'errored'
                 return self._makeerrorresult(
                     _('received command request frame when request frames '
                       'were supposedly done'))
 
             if expectingdata != entry['expectingdata']:
                 self._state = 'errored'
                 return self._makeerrorresult(
                     _('mismatch between expect data flag and previous frame'))
 
             entry['payload'].write(frame.payload)
 
             if not moreframes:
                 entry['requestdone'] = True
 
             if not moreframes and not expectingdata:
                 return self._makeruncommandresult(frame.requestid)
 
             return self._makewantframeresult()
 
         elif frame.typeid == FRAME_TYPE_COMMAND_DATA:
             if not entry['expectingdata']:
                 self._state = 'errored'
                 return self._makeerrorresult(_(
                     'received command data frame for request that is not '
                     'expecting data: %d') % frame.requestid)
 
             if entry['data'] is None:
                 entry['data'] = util.bytesio()
 
             return self._handlecommanddataframe(frame, entry)
         else:
             self._state = 'errored'
             return self._makeerrorresult(_(
                 'received unexpected frame type: %d') % frame.typeid)
 
     def _handlecommanddataframe(self, frame, entry):
         assert frame.typeid == FRAME_TYPE_COMMAND_DATA
 
         # TODO support streaming data instead of buffering it.
         entry['data'].write(frame.payload)
 
         if frame.flags & FLAG_COMMAND_DATA_CONTINUATION:
             return self._makewantframeresult()
         elif frame.flags & FLAG_COMMAND_DATA_EOS:
             entry['data'].seek(0)
             return self._makeruncommandresult(frame.requestid)
         else:
             self._state = 'errored'
             return self._makeerrorresult(_('command data frame without '
                                            'flags'))
 
     def _onframeerrored(self, frame):
         return self._makeerrorresult(_('server already errored'))