mercurial/wireprotov2peer.py

windows: add a method to convert Unix style command lines to Windows style

This started as a copy/paste of `os.path.expandvars()`, but limited to a given
dictionary of variables, converting `foo = foo + bar` to `foo += bar`, and
adding 'b' string prefixes.  Then code was added to make sure that a value being
substituted in wouldn't itself be expanded by cmd.exe.  But that left
inconsistent results between `$var1` and `%var1%` when its value was '%foo%'-
since neither were touched, `$var1` wouldn't expand but `%var1%` would.  So
instead, this just converts the Unix style to Windows style (if the variable
exists, because Windows will leave `%missing%` as-is), and lets cmd.exe do its
thing.

I then dropped the %% -> % conversion (because Windows doesn't do this), and
added the ability to escape the '$' with '\'.  The escape character is dropped,
for consistency with shell handling.

After everything seemed stable and working, running the whole test suite flagged
a problem near the end of test-bookmarks.t:1069.  The problem is cmd.exe won't
pass empty variables to its child, so defined but empty variables are now
skipped.  I can't think of anything better, and it seems like a pre-existing
violation of the documentation, which calls out that HG_OLDNODE is empty on
bookmark creation.

Future additions could potentially be replacing strong quotes with double quotes
(cmd.exe doesn't know what to do with the former), escaping a double quote, and
some tilde expansion via os.path.expanduser().  I've got some doubts about
replacing the strong quotes in case sh.exe is run, but it seems like the right
thing to do the vast majority of the time.  The original form of this was
discussed about a year ago[1].

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-July/100735.html

# 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 (
    encoding,
    error,
    util,
    wireprotoframing,
)

def formatrichmessage(atoms):
    """Format an encoded message from the framing protocol."""

    chunks = []

    for atom in atoms:
        msg = _(atom[b'msg'])

        if b'args' in atom:
            msg = msg % atom[b'args']

        chunks.append(msg)

    return b''.join(chunks)

class commandresponse(object):
    """Represents the response to a command request."""

    def __init__(self, requestid, command):
        self.requestid = requestid
        self.command = command

        self.b = util.bytesio()

    def cborobjects(self):
        """Obtain decoded CBOR objects from this response."""
        size = self.b.tell()
        self.b.seek(0)

        decoder = cbor.CBORDecoder(self.b)

        while self.b.tell() < size:
            yield decoder.decode()

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] = commandresponse(rid, command)

        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['eos']:
                # If the command has a decoder, resolve the future to the
                # decoded value. Otherwise resolve to the rich response object.
                decoder = COMMAND_DECODERS.get(response.command)

                # TODO consider always resolving the overall status map.
                if decoder:
                    objs = response.cborobjects()

                    overall = next(objs)

                    if overall['status'] == 'ok':
                        self._futures[frame.requestid].set_result(decoder(objs))
                    else:
                        e = error.RepoError(
                            formatrichmessage(overall['error']['message']))
                        self._futures[frame.requestid].set_exception(e)
                else:
                    self._futures[frame.requestid].set_result(response)

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

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

def decodebranchmap(objs):
    # Response should be a single CBOR map of branch name to array of nodes.
    bm = next(objs)

    return {encoding.tolocal(k): v for k, v in bm.items()}

def decodeheads(objs):
    # Array of node bytestrings.
    return next(objs)

def decodeknown(objs):
    # Bytestring where each byte is a 0 or 1.
    raw = next(objs)

    return [True if c == '1' else False for c in raw]

def decodelistkeys(objs):
    # Map with bytestring keys and values.
    return next(objs)

def decodelookup(objs):
    return next(objs)

def decodepushkey(objs):
    return next(objs)

COMMAND_DECODERS = {
    'branchmap': decodebranchmap,
    'heads': decodeheads,
    'known': decodeknown,
    'listkeys': decodelistkeys,
    'lookup': decodelookup,
    'pushkey': decodepushkey,
}