annotate mercurial/wireprotov2peer.py @ 37719:a656cba08a04

wireprotov2: move response handling out of httppeer

And fix some bugs while we're here.

The code for processing response data from the unified framing
protocol is mostly peer agnostic. The peer-specific bits are the
configuration of the client reactor and how I/O is performed. I
initially implemented things in httppeer for expediency.

This commit establishes a module for holding the peer API level
code for the framing based protocol. Inside this module we have
a class to help coordinate higher-level activities, such as managing
response object.

The client handler bits could be rolled into clientreactor. However,
I want clientreactor to be sans I/O and I want it to only be
concerned with protocol-level details, not higher-level concepts
like how protocol events are converted into peer API concepts. I
want clientreactor to receive a frame and then tell the caller what
should probably be done about it. If we start putting things like
future resolution into clientreactor, we'll constrain how the protocol
can be used (e.g. by requiring futures).

The new code is loosely based on what was in httppeer before. I
changed things a bit around response handling. We now buffer the
entire response "body" and then handle it as one atomic unit. This
fixed a bug around decoding CBOR data that spanned multiple frames.
I also fixed an off-by-one bug where we failed to read a single byte
CBOR value at the end of the stream. That's why tests have changed.

The new state of httppeer is much cleaner. It is largely agnostic
about framing protocol implementation details. That's how it should
be: the framing protocol is designed to be largely transport
agnostic. We want peers merely putting bytes on the wire and telling
the framing protocol where to read response data from.

There's still a bit of work to be done here, especially for
representing responses. But at least we're a step closer to having a
higher-level peer interface that can be plugged into the SSH peer
someday.

I initially added this class to wireprotoframing. However, we'll
eventually need version 2 specific functions to convert CBOR responses
into data structures expected by the code calling commands. This
needs to live somewhere. Since that code would be shared across peers,
we need a common module. We have wireprotov1peer for the equivalent
version 1 code. So I decided to establish wireprotov2peer.

Differential Revision: https://phab.mercurial-scm.org/D3379

# wireprotov2peer.py - client side code for wire protocol version 2
#
# 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.

from __future__ import absolute_import

from .i18n import _
from .thirdparty import (
    cbor,
)
from . import (
    error,
    util,
    wireprotoframing,
)

class clienthandler(object):
    """Object to handle higher-level client activities.

    The ``clientreactor`` is used to hold low-level state about the frame-based
    protocol, such as which requests and streams are active. This type is used
    for higher-level operations, such as reading frames from a socket, exposing
    and managing a higher-level primitive for representing command responses,
    etc. This class is what peers should probably use to bridge wire activity
    with the higher-level peer API.
    """

    def __init__(self, ui, clientreactor):
        self._ui = ui
        self._reactor = clientreactor
        self._requests = {}
        self._futures = {}
        self._responses = {}

    def callcommand(self, command, args, f):
        """Register a request to call a command.

        Returns an iterable of frames that should be sent over the wire.
        """
        request, action, meta = self._reactor.callcommand(command, args)

        if action != 'noop':
            raise error.ProgrammingError('%s not yet supported' % action)

        rid = request.requestid
        self._requests[rid] = request
        self._futures[rid] = f
        self._responses[rid] = {
            'cbor': False,
            'b': util.bytesio(),
        }

        return iter(())

    def flushcommands(self):
        """Flush all queued commands.

        Returns an iterable of frames that should be sent over the wire.
        """
        action, meta = self._reactor.flushcommands()

        if action != 'sendframes':
            raise error.ProgrammingError('%s not yet supported' % action)

        return meta['framegen']

    def readframe(self, fh):
        """Attempt to read and process a frame.

        Returns None if no frame was read. Presumably this means EOF.
        """
        frame = wireprotoframing.readframe(fh)
        if frame is None:
            # TODO tell reactor?
            return

        self._ui.note(_('received %r\n') % frame)
        self._processframe(frame)

        return True

    def _processframe(self, frame):
        """Process a single read frame."""

        action, meta = self._reactor.onframerecv(frame)

        if action == 'error':
            e = error.RepoError(meta['message'])

            if frame.requestid in self._futures:
                self._futures[frame.requestid].set_exception(e)
            else:
                raise e

        if frame.requestid not in self._requests:
            raise error.ProgrammingError(
                'received frame for unknown request; this is either a bug in '
                'the clientreactor not screening for this or this instance was '
                'never told about this request: %r' % frame)

        response = self._responses[frame.requestid]

        if action == 'responsedata':
            response['b'].write(meta['data'])

            if meta['cbor']:
                response['cbor'] = True

            if meta['eos']:
                if meta['cbor']:
                    # If CBOR, decode every object.
                    b = response['b']

                    size = b.tell()
                    b.seek(0)

                    decoder = cbor.CBORDecoder(b)

                    result = []
                    while b.tell() < size:
                        result.append(decoder.decode())
                else:
                    result = [response['b'].getvalue()]

                self._futures[frame.requestid].set_result(result)

                del self._requests[frame.requestid]
                del self._futures[frame.requestid]

        else:
            raise error.ProgrammingError(
                'unhandled action from clientreactor: %s' % action)