diff mercurial/wireprotoframing.py @ 37057:2ec1fb9de638

wireproto: add request IDs to frames

One of my primary goals with the new wire protocol is to make
operations faster and enable both client and server-side
operations to scale to multiple CPU cores.

One of the ways we make server interactions faster is by reducing
the number of round trips to that server.

With the existing wire protocol, the "batch" command facilitates
executing multiple commands from a single request payload. The way
it works is the requests for multiple commands are serialized. The
server executes those commands sequentially then serializes all
their results. As an optimization for reducing round trips, this
is very effective. The technical implementation, however, is pretty
bad and suffers from a number of deficiencies. For example, it
creates a new place where authorization to run a command must be
checked. (The lack of this checking in older Mercurial releases
was CVE-2018-1000132.)

The principles behind the "batch" command are sound. However, the
execution is not. Therefore, I want to ditch "batch" in the
new wire protocol and have protocol level support for issuing
multiple requests in a single round trip.

This commit introduces support in the frame-based wire protocol to
facilitate this. We do this by adding a "request ID" to each frame.
If a server sees frames associated with different "request IDs," it
handles them as separate requests. All of this happening possibly
as part of the same message from client to server (the same request
body in the case of HTTP).

We /could/ model the exchange the way pipelined HTTP requests do,
where the server processes requests in order they are issued and
received. But this artifically constrains scalability. A better
model is to allow multi-requests to be executed concurrently and
for responses to be sent and handled concurrently. So the
specification explicitly allows this. There is some work to be done
around specifying dependencies between multi-requests. We take
the easy road for now and punt on this problem, declaring that
if order is important, clients must not issue the request until
responses to dependent requests have been received.

This commit focuses on the boilerplate of implementing the request
ID. The server reactor still can't manage multiple, in-flight
request IDs. This will be addressed in a subsequent commit.

Because the wire semantics have changed, we bump the version of the
media type.

Differential Revision: https://phab.mercurial-scm.org/D2869

--- a/mercurial/wireprotoframing.py	Wed Mar 14 14:01:16 2018 -0700
+++ b/mercurial/wireprotoframing.py	Wed Mar 14 16:51:34 2018 -0700
@@ -19,7 +19,7 @@
     util,
 )
 
-FRAME_HEADER_SIZE = 4
+FRAME_HEADER_SIZE = 6
 DEFAULT_MAX_FRAME_SIZE = 32768
 
 FRAME_TYPE_COMMAND_NAME = 0x01
@@ -89,28 +89,43 @@
 
 ARGUMENT_FRAME_HEADER = struct.Struct(r'<HH')
 
-def makeframe(frametype, frameflags, payload):
+def makeframe(requestid, frametype, frameflags, 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
+    # 4 bits type
+    # 4 bits flags
+
     l = struct.pack(r'<I', len(payload))
     frame[0:3] = l[0:3]
-    frame[3] = (frametype << 4) | frameflags
-    frame[4:] = payload
+    struct.pack_into(r'<H', frame, 3, requestid)
+    frame[5] = (frametype << 4) | frameflags
+    frame[6:] = payload
 
     return frame
 
 def makeframefromhumanstring(s):
-    """Given a string of the form: <type> <flags> <payload>, creates a frame.
+    """Create a frame from a human readable string
+
+    Strings have the form:
+
+        <request-id> <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 is an integer.
+
     Frame type and flags can be specified by integer or named constant.
+
     Flags can be delimited by `|` to bitwise OR them together.
     """
-    frametype, frameflags, payload = s.split(b' ', 2)
+    requestid, frametype, frameflags, payload = s.split(b' ', 3)
+
+    requestid = int(requestid)
 
     if frametype in FRAME_TYPES:
         frametype = FRAME_TYPES[frametype]
@@ -127,7 +142,7 @@
 
     payload = util.unescapestr(payload)
 
-    return makeframe(frametype, finalflags, payload)
+    return makeframe(requestid, frametype, finalflags, payload)
 
 def parseheader(data):
     """Parse a unified framing protocol frame header from a buffer.
@@ -140,12 +155,13 @@
     # 4 bits frame flags
     # ... payload
     framelength = data[0] + 256 * data[1] + 16384 * data[2]
-    typeflags = data[3]
+    requestid = struct.unpack_from(r'<H', data, 3)[0]
+    typeflags = data[5]
 
     frametype = (typeflags & 0xf0) >> 4
     frameflags = typeflags & 0x0f
 
-    return frametype, frameflags, framelength
+    return requestid, frametype, frameflags, framelength
 
 def readframe(fh):
     """Read a unified framing protocol frame from a file object.
@@ -165,16 +181,16 @@
         raise error.Abort(_('received incomplete frame: got %d bytes: %s') %
                           (readcount, header))
 
-    frametype, frameflags, framelength = parseheader(header)
+    requestid, frametype, frameflags, framelength = parseheader(header)
 
     payload = fh.read(framelength)
     if len(payload) != framelength:
         raise error.Abort(_('frame length error: expected %d; got %d') %
                           (framelength, len(payload)))
 
-    return frametype, frameflags, payload
+    return requestid, frametype, frameflags, payload
 
-def createcommandframes(cmd, args, datafh=None):
+def createcommandframes(requestid, cmd, args, datafh=None):
     """Create frames necessary to transmit a request to run a command.
 
     This is a generator of bytearrays. Each item represents a frame
@@ -189,7 +205,7 @@
     if not flags:
         flags |= FLAG_COMMAND_NAME_EOS
 
-    yield makeframe(FRAME_TYPE_COMMAND_NAME, flags, cmd)
+    yield makeframe(requestid, FRAME_TYPE_COMMAND_NAME, flags, cmd)
 
     for i, k in enumerate(sorted(args)):
         v = args[k]
@@ -205,7 +221,7 @@
         payload[offset:offset + len(v)] = v
 
         flags = FLAG_COMMAND_ARGUMENT_EOA if last else 0
-        yield makeframe(FRAME_TYPE_COMMAND_ARGUMENT, flags, payload)
+        yield makeframe(requestid, FRAME_TYPE_COMMAND_ARGUMENT, flags, payload)
 
     if datafh:
         while True:
@@ -219,12 +235,12 @@
                 assert datafh.read(1) == b''
                 done = True
 
-            yield makeframe(FRAME_TYPE_COMMAND_DATA, flags, data)
+            yield makeframe(requestid, FRAME_TYPE_COMMAND_DATA, flags, data)
 
             if done:
                 break
 
-def createbytesresponseframesfrombytes(data,
+def createbytesresponseframesfrombytes(requestid, data,
                                        maxframesize=DEFAULT_MAX_FRAME_SIZE):
     """Create a raw frame to send a bytes response from static bytes input.
 
@@ -233,7 +249,7 @@
 
     # Simple case of a single frame.
     if len(data) <= maxframesize:
-        yield makeframe(FRAME_TYPE_BYTES_RESPONSE,
+        yield makeframe(requestid, FRAME_TYPE_BYTES_RESPONSE,
                         FLAG_BYTES_RESPONSE_EOS, data)
         return
 
@@ -248,12 +264,12 @@
         else:
             flags = FLAG_BYTES_RESPONSE_CONTINUATION
 
-        yield makeframe(FRAME_TYPE_BYTES_RESPONSE, flags, chunk)
+        yield makeframe(requestid, FRAME_TYPE_BYTES_RESPONSE, flags, chunk)
 
         if done:
             break
 
-def createerrorframe(msg, protocol=False, application=False):
+def createerrorframe(requestid, msg, protocol=False, application=False):
     # TODO properly handle frame size limits.
     assert len(msg) <= DEFAULT_MAX_FRAME_SIZE
 
@@ -263,7 +279,7 @@
     if application:
         flags |= FLAG_ERROR_RESPONSE_APPLICATION
 
-    yield makeframe(FRAME_TYPE_ERROR_RESPONSE, flags, msg)
+    yield makeframe(requestid, FRAME_TYPE_ERROR_RESPONSE, flags, msg)
 
 class serverreactor(object):
     """Holds state of a server handling frame-based protocol requests.
@@ -326,6 +342,7 @@
         self._deferoutput = deferoutput
         self._state = 'idle'
         self._bufferedframegens = []
+        self._activerequestid = None
         self._activecommand = None
         self._activeargs = None
         self._activedata = None
@@ -334,7 +351,7 @@
         self._activeargname = None
         self._activeargchunks = None
 
-    def onframerecv(self, frametype, frameflags, payload):
+    def onframerecv(self, requestid, frametype, frameflags, payload):
         """Process a frame that has been received off the wire.
 
         Returns a dict with an ``action`` key that details what action,
@@ -351,14 +368,14 @@
         if not meth:
             raise error.ProgrammingError('unhandled state: %s' % self._state)
 
-        return meth(frametype, frameflags, payload)
+        return meth(requestid, frametype, frameflags, payload)
 
-    def onbytesresponseready(self, data):
+    def onbytesresponseready(self, requestid, data):
         """Signal that a bytes response is ready to be sent to the client.
 
         The raw bytes response is passed as an argument.
         """
-        framegen = createbytesresponseframesfrombytes(data)
+        framegen = createbytesresponseframesfrombytes(requestid, data)
 
         if self._deferoutput:
             self._bufferedframegens.append(framegen)
@@ -387,9 +404,9 @@
             'framegen': makegen(),
         }
 
-    def onapplicationerror(self, msg):
+    def onapplicationerror(self, requestid, msg):
         return 'sendframes', {
-            'framegen': createerrorframe(msg, application=True),
+            'framegen': createerrorframe(requestid, msg, application=True),
         }
 
     def _makeerrorresult(self, msg):
@@ -399,6 +416,7 @@
 
     def _makeruncommandresult(self):
         return 'runcommand', {
+            'requestid': self._activerequestid,
             'command': self._activecommand,
             'args': self._activeargs,
             'data': self._activedata.getvalue() if self._activedata else None,
@@ -409,7 +427,7 @@
             'state': self._state,
         }
 
-    def _onframeidle(self, frametype, frameflags, payload):
+    def _onframeidle(self, requestid, frametype, frameflags, payload):
         # The only frame type that should be received in this state is a
         # command request.
         if frametype != FRAME_TYPE_COMMAND_NAME:
@@ -417,6 +435,7 @@
             return self._makeerrorresult(
                 _('expected command frame; got %d') % frametype)
 
+        self._activerequestid = requestid
         self._activecommand = payload
         self._activeargs = {}
         self._activedata = None
@@ -439,7 +458,7 @@
             return self._makeerrorresult(_('missing frame flags on '
                                            'command frame'))
 
-    def _onframereceivingargs(self, frametype, frameflags, payload):
+    def _onframereceivingargs(self, requestid, frametype, frameflags, payload):
         if frametype != FRAME_TYPE_COMMAND_ARGUMENT:
             self._state = 'errored'
             return self._makeerrorresult(_('expected command argument '
@@ -492,7 +511,7 @@
         else:
             return self._makewantframeresult()
 
-    def _onframereceivingdata(self, frametype, frameflags, payload):
+    def _onframereceivingdata(self, requestid, frametype, frameflags, payload):
         if frametype != FRAME_TYPE_COMMAND_DATA:
             self._state = 'errored'
             return self._makeerrorresult(_('expected command data frame; '
@@ -512,5 +531,5 @@
             return self._makeerrorresult(_('command data frame without '
                                            'flags'))
 
-    def _onframeerrored(self, frametype, frameflags, payload):
+    def _onframeerrored(self, requestid, frametype, frameflags, payload):
         return self._makeerrorresult(_('server already errored'))