mercurial/wireprototypes.py

debugcommands: add debugwireproto command

We currently don't have a low-level mechanism for sending
arbitrary wire protocol commands. Having a generic and robust
mechanism for sending wire protocol commands, examining wire
data, etc would make it vastly easier to test the wire protocol
and debug server operation. This is a problem I've wanted a
solution for numerous times, especially recently as I've been
hacking on a new version of the wire protocol.

This commit establishes a `hg debugwireproto` command for sending
data to a peer.

The command invents a mini language for specifying actions to take.
This will enable a lot of flexibility for issuing commands and testing
variations for how commands are sent.

Right now, we only support low-level raw sends and receives. These
are probably the least valuable commands to intended users of this
command. But they are the most useful commands to implement to
bootstrap the feature (I've chosen to reimplement test-ssh-proto.t
using this command to prove its usefulness).

My eventual goal of `hg debugwireproto` is to allow calling wire
protocol commands with a human-friendly interface. Essentially,
people can type in a command name and arguments and
`hg debugwireproto` will figure out how to send that on the wire.
I'd love to eventually be able to save the server's raw response
to a file. This would allow us to e.g. call "getbundle" wire
protocol commands easily.

test-ssh-proto.t has been updated to use the new command in lieu
of piping directly to a server process. As part of the transition,
test behavior improved. Before, we piped all request data to the
server at once. Now, we have explicit control over the ordering of
operations. e.g. we can send one command, receive its response,
then send another command. This will allow us to more robustly
test race conditions, buffering behavior, etc.

There were some subtle changes in test behavior. For example,
previous behavior would often send trailing newlines to the server.
The new mechanism doesn't treat literal newlines specially and
requires newlines be escaped in the payload.

Because the new logging code is very low level, it is easy to
introduce race conditions in tests. For example, the number of bytes
returned by a read() may vary depending on load. This is why tests
make heavy use of "readline" for consuming data: the result of
that operation should be deterministic and not subject to race
conditions. There are still some uses of "readavailable." However,
those are only for reading from stderr. I was able to reproduce
timing issues with my system under load when using "readavailable"
globally. But if I "readline" to grab stdout, "readavailable"
appears to work deterministically for stderr. I think this is
because the server writes to stderr first. As long as the OS
delivers writes to pipes in the same order they were made, this
should work. If there are timing issues, we can introduce a
mechanism to readline from stderr.

Differential Revision: https://phab.mercurial-scm.org/D2392

# 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

import abc

class bytesresponse(object):
    """A wire protocol response consisting of raw bytes."""
    def __init__(self, data):
        self.data = data

class ooberror(object):
    """wireproto reply: failure of a batch of operation

    Something failed during a batch call. The error message is stored in
    `self.message`.
    """
    def __init__(self, message):
        self.message = message

class pushres(object):
    """wireproto reply: success with simple integer return

    The call was successful and returned an integer contained in `self.res`.
    """
    def __init__(self, res, output):
        self.res = res
        self.output = output

class pusherr(object):
    """wireproto reply: failure

    The call failed. The `self.res` attribute contains the error message.
    """
    def __init__(self, res, output):
        self.res = res
        self.output = output

class streamres(object):
    """wireproto reply: binary stream

    The call was successful and the result is a stream.

    Accepts a generator containing chunks of data to be sent to the client.

    ``prefer_uncompressed`` indicates that the data is expected to be
    uncompressable and that the stream should therefore use the ``none``
    engine.
    """
    def __init__(self, gen=None, prefer_uncompressed=False):
        self.gen = gen
        self.prefer_uncompressed = prefer_uncompressed

class streamreslegacy(object):
    """wireproto reply: uncompressed binary stream

    The call was successful and the result is a stream.

    Accepts a generator containing chunks of data to be sent to the client.

    Like ``streamres``, but sends an uncompressed data for "version 1" clients
    using the application/mercurial-0.1 media type.
    """
    def __init__(self, gen=None):
        self.gen = gen

class baseprotocolhandler(object):
    """Abstract base class for wire protocol handlers.

    A wire protocol handler serves as an interface between protocol command
    handlers and the wire protocol transport layer. Protocol handlers provide
    methods to read command arguments, redirect stdio for the duration of
    the request, handle response types, etc.
    """

    __metaclass__ = abc.ABCMeta

    @abc.abstractproperty
    def name(self):
        """The name of the protocol implementation.

        Used for uniquely identifying the transport type.
        """

    @abc.abstractmethod
    def getargs(self, args):
        """return the value for arguments in <args>

        returns a list of values (same order as <args>)"""

    @abc.abstractmethod
    def forwardpayload(self, fp):
        """Read the raw payload and forward to a file.

        The payload is read in full before the function returns.
        """

    @abc.abstractmethod
    def mayberedirectstdio(self):
        """Context manager to possibly redirect stdio.

        The context manager yields a file-object like object that receives
        stdout and stderr output when the context manager is active. Or it
        yields ``None`` if no I/O redirection occurs.

        The intent of this context manager is to capture stdio output
        so it may be sent in the response. Some transports support streaming
        stdio to the client in real time. For these transports, stdio output
        won't be captured.
        """

    @abc.abstractmethod
    def client(self):
        """Returns a string representation of this client (as bytes)."""