tests/sshprotoext.py

interfaces: introduce and use a protocol class for the `mpatch` module

See f2832de2a46c for details when this was done for the `bdiff` module.

Two things worth pointing out-

  1) The `cffi` module "inherits" the `pure` implementation of `patchedsize()`
     because of its wildcard import.
  2) It's odd that the `mpatchError` lives in both `pure` and `cext` modules.

I initially thought to move the exception into the new class, and make the
existing class name an alias to the class in the new location, but the exception
is created in C code by the `cext` module, so that won't work.  I don't think a
protocol class is approriate, because there's nothing special about the class to
distinguish from any other `Exception`.  Fortunately, nobody is catching this
exception in core, so we can kick the can down the road.

# sshprotoext.py - Extension to test behavior of SSH 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 extension replaces the SSH server started via `hg serve --stdio`.
# The server behaves differently depending on environment variables.


from mercurial import (
    error,
    extensions,
    registrar,
    sshpeer,
    wireprotoserver,
    wireprotov1server,
)

configtable = {}
configitem = registrar.configitem(configtable)

configitem(b'sshpeer', b'mode', default=None)
configitem(b'sshpeer', b'handshake-mode', default=None)


class bannerserver(wireprotoserver.sshserver):
    """Server that sends a banner to stdout."""

    def serve_forever(self):
        for i in range(10):
            self._ui.fout.write(b'banner: line %d\n' % i)

        super(bannerserver, self).serve_forever()


class prehelloserver(wireprotoserver.sshserver):
    """Tests behavior when connecting to <0.9.1 servers.

    The ``hello`` wire protocol command was introduced in Mercurial
    0.9.1. Modern clients send the ``hello`` command when connecting
    to SSH servers. This mock server tests behavior of the handshake
    when ``hello`` is not supported.
    """

    def serve_forever(self):
        ui = self._ui
        l = ui.fin.readline()
        assert l == b'hello\n'
        # Respond to unknown commands with an empty reply.
        wireprotoserver._sshv1respondbytes(ui.fout, b'')
        l = ui.fin.readline()
        assert l == b'between\n'
        proto = wireprotoserver.sshv1protocolhandler(ui, ui.fin, ui.fout)
        rsp = wireprotov1server.dispatch(self._repo, proto, b'between')
        wireprotoserver._sshv1respondbytes(ui.fout, rsp.data)

        super(prehelloserver, self).serve_forever()


def performhandshake(orig, ui, stdin, stdout, stderr):
    """Wrapped version of sshpeer._performhandshake to send extra commands."""
    mode = ui.config(b'sshpeer', b'handshake-mode')
    if mode == b'pre-no-args':
        ui.debug(b'sending no-args command\n')
        stdin.write(b'no-args\n')
        stdin.flush()
        return orig(ui, stdin, stdout, stderr)
    elif mode == b'pre-multiple-no-args':
        ui.debug(b'sending unknown1 command\n')
        stdin.write(b'unknown1\n')
        ui.debug(b'sending unknown2 command\n')
        stdin.write(b'unknown2\n')
        ui.debug(b'sending unknown3 command\n')
        stdin.write(b'unknown3\n')
        stdin.flush()
        return orig(ui, stdin, stdout, stderr)
    else:
        raise error.ProgrammingError(b'unknown HANDSHAKECOMMANDMODE: %s' % mode)


def extsetup(ui):
    # It's easier for tests to define the server behavior via environment
    # variables than config options. This is because `hg serve --stdio`
    # has to be invoked with a certain form for security reasons and
    # `dummyssh` can't just add `--config` flags to the command line.
    servermode = ui.environ.get(b'SSHSERVERMODE')

    if servermode == b'banner':
        wireprotoserver.sshserver = bannerserver
    elif servermode == b'no-hello':
        wireprotoserver.sshserver = prehelloserver
    elif servermode:
        raise error.ProgrammingError(b'unknown server mode: %s' % servermode)

    peermode = ui.config(b'sshpeer', b'mode')

    if peermode == b'extra-handshake-commands':
        extensions.wrapfunction(sshpeer, '_performhandshake', performhandshake)
    elif peermode:
        raise error.ProgrammingError(b'unknown peer mode: %s' % peermode)