view mercurial/peer.py @ 37485:0b7475ea38cf

wireproto: port heads command to wire protocol v2

After much thought and consideration, wire protocol version 2's
commands will be defined in different functions from the existing
commands. This will make it easier to implement these commands
because it won't require shoehorning things like response formatting
and argument declaration into the same APIs.

For example, wire protocol version 1 requires that commands declare
a fixed and ordered list of argument names. It isn't really possible
to insert new arguments or have optional arguments without
breaking backwards compatibility. Wire protocol version 2, however,
uses CBOR maps for passing arguments. So arguments a) can be
optional b) can be added without BC c) can be strongly typed.

This commit starts our trek towards reimplementing the wire protocol
for version 2 with the heads command. It is pretty similar to the
existing heads command. One added feature is it can be told to
operate on only public phase changesets. This is useful for
making discovery faster when a repo has tens of thousands of
draft phase heads (such as Mozilla's "try" repository).

The HTTPv2 server-side protocol has had its `getargs()` implementation
updated to reflect that arguments are a map and not a list.

Differential Revision: https://phab.mercurial-scm.org/D3179

# peer.py - repository base classes for mercurial
#
# Copyright 2005, 2006 Matt Mackall <[e-mail]>
# Copyright 2006 Vadim Gelfer <[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 . import (
    error,
    pycompat,
    util,
)

# abstract batching support

class future(object):
    '''placeholder for a value to be set later'''
    def set(self, value):
        if util.safehasattr(self, 'value'):
            raise error.RepoError("future is already set")
        self.value = value

class batcher(object):
    '''base class for batches of commands submittable in a single request

    All methods invoked on instances of this class are simply queued and
    return a a future for the result. Once you call submit(), all the queued
    calls are performed and the results set in their respective futures.
    '''
    def __init__(self):
        self.calls = []
    def __getattr__(self, name):
        def call(*args, **opts):
            resref = future()
            # Please don't invent non-ascii method names, or you will
            # give core hg a very sad time.
            self.calls.append((name.encode('ascii'), args, opts, resref,))
            return resref
        return call
    def submit(self):
        raise NotImplementedError()

class iterbatcher(batcher):

    def submit(self):
        raise NotImplementedError()

    def results(self):
        raise NotImplementedError()

class localiterbatcher(iterbatcher):
    def __init__(self, local):
        super(iterbatcher, self).__init__()
        self.local = local

    def submit(self):
        # submit for a local iter batcher is a noop
        pass

    def results(self):
        for name, args, opts, resref in self.calls:
            resref.set(getattr(self.local, name)(*args, **opts))
            yield resref.value

def batchable(f):
    '''annotation for batchable methods

    Such methods must implement a coroutine as follows:

    @batchable
    def sample(self, one, two=None):
        # Build list of encoded arguments suitable for your wire protocol:
        encargs = [('one', encode(one),), ('two', encode(two),)]
        # Create future for injection of encoded result:
        encresref = future()
        # Return encoded arguments and future:
        yield encargs, encresref
        # Assuming the future to be filled with the result from the batched
        # request now. Decode it:
        yield decode(encresref.value)

    The decorator returns a function which wraps this coroutine as a plain
    method, but adds the original method as an attribute called "batchable",
    which is used by remotebatch to split the call into separate encoding and
    decoding phases.
    '''
    def plain(*args, **opts):
        batchable = f(*args, **opts)
        encargsorres, encresref = next(batchable)
        if not encresref:
            return encargsorres # a local result in this case
        self = args[0]
        cmd = pycompat.bytesurl(f.__name__)  # ensure cmd is ascii bytestr
        encresref.set(self._submitone(cmd, encargsorres))
        return next(batchable)
    setattr(plain, 'batchable', f)
    return plain