mercurial/exchange.py

test: add a push race case where the raced push touch multiple heads

We check case where the raced push update all heads while the racing push
update one of them.

# exchange.py - utility to exchange data between repos.
#
# Copyright 2005-2007 Matt Mackall <[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 errno
import hashlib

from .i18n import _
from .node import (
    hex,
    nullid,
)
from . import (
    bookmarks as bookmod,
    bundle2,
    changegroup,
    discovery,
    error,
    lock as lockmod,
    obsolete,
    phases,
    pushkey,
    scmutil,
    sslutil,
    streamclone,
    url as urlmod,
    util,
)

urlerr = util.urlerr
urlreq = util.urlreq

# Maps bundle version human names to changegroup versions.
_bundlespeccgversions = {'v1': '01',
                         'v2': '02',
                         'packed1': 's1',
                         'bundle2': '02', #legacy
                        }

# Compression engines allowed in version 1. THIS SHOULD NEVER CHANGE.
_bundlespecv1compengines = {'gzip', 'bzip2', 'none'}

def parsebundlespec(repo, spec, strict=True, externalnames=False):
    """Parse a bundle string specification into parts.

    Bundle specifications denote a well-defined bundle/exchange format.
    The content of a given specification should not change over time in
    order to ensure that bundles produced by a newer version of Mercurial are
    readable from an older version.

    The string currently has the form:

       <compression>-<type>[;<parameter0>[;<parameter1>]]

    Where <compression> is one of the supported compression formats
    and <type> is (currently) a version string. A ";" can follow the type and
    all text afterwards is interpreted as URI encoded, ";" delimited key=value
    pairs.

    If ``strict`` is True (the default) <compression> is required. Otherwise,
    it is optional.

    If ``externalnames`` is False (the default), the human-centric names will
    be converted to their internal representation.

    Returns a 3-tuple of (compression, version, parameters). Compression will
    be ``None`` if not in strict mode and a compression isn't defined.

    An ``InvalidBundleSpecification`` is raised when the specification is
    not syntactically well formed.

    An ``UnsupportedBundleSpecification`` is raised when the compression or
    bundle type/version is not recognized.

    Note: this function will likely eventually return a more complex data
    structure, including bundle2 part information.
    """
    def parseparams(s):
        if ';' not in s:
            return s, {}

        params = {}
        version, paramstr = s.split(';', 1)

        for p in paramstr.split(';'):
            if '=' not in p:
                raise error.InvalidBundleSpecification(
                    _('invalid bundle specification: '
                      'missing "=" in parameter: %s') % p)

            key, value = p.split('=', 1)
            key = urlreq.unquote(key)
            value = urlreq.unquote(value)
            params[key] = value

        return version, params


    if strict and '-' not in spec:
        raise error.InvalidBundleSpecification(
                _('invalid bundle specification; '
                  'must be prefixed with compression: %s') % spec)

    if '-' in spec:
        compression, version = spec.split('-', 1)

        if compression not in util.compengines.supportedbundlenames:
            raise error.UnsupportedBundleSpecification(
                    _('%s compression is not supported') % compression)

        version, params = parseparams(version)

        if version not in _bundlespeccgversions:
            raise error.UnsupportedBundleSpecification(
                    _('%s is not a recognized bundle version') % version)
    else:
        # Value could be just the compression or just the version, in which
        # case some defaults are assumed (but only when not in strict mode).
        assert not strict

        spec, params = parseparams(spec)

        if spec in util.compengines.supportedbundlenames:
            compression = spec
            version = 'v1'
            # Generaldelta repos require v2.
            if 'generaldelta' in repo.requirements:
                version = 'v2'
            # Modern compression engines require v2.
            if compression not in _bundlespecv1compengines:
                version = 'v2'
        elif spec in _bundlespeccgversions:
            if spec == 'packed1':
                compression = 'none'
            else:
                compression = 'bzip2'
            version = spec
        else:
            raise error.UnsupportedBundleSpecification(
                    _('%s is not a recognized bundle specification') % spec)

    # Bundle version 1 only supports a known set of compression engines.
    if version == 'v1' and compression not in _bundlespecv1compengines:
        raise error.UnsupportedBundleSpecification(
            _('compression engine %s is not supported on v1 bundles') %
            compression)

    # The specification for packed1 can optionally declare the data formats
    # required to apply it. If we see this metadata, compare against what the
    # repo supports and error if the bundle isn't compatible.
    if version == 'packed1' and 'requirements' in params:
        requirements = set(params['requirements'].split(','))
        missingreqs = requirements - repo.supportedformats
        if missingreqs:
            raise error.UnsupportedBundleSpecification(
                    _('missing support for repository features: %s') %
                      ', '.join(sorted(missingreqs)))

    if not externalnames:
        engine = util.compengines.forbundlename(compression)
        compression = engine.bundletype()[1]
        version = _bundlespeccgversions[version]
    return compression, version, params

def readbundle(ui, fh, fname, vfs=None):
    header = changegroup.readexactly(fh, 4)

    alg = None
    if not fname:
        fname = "stream"
        if not header.startswith('HG') and header.startswith('\0'):
            fh = changegroup.headerlessfixup(fh, header)
            header = "HG10"
            alg = 'UN'
    elif vfs:
        fname = vfs.join(fname)

    magic, version = header[0:2], header[2:4]

    if magic != 'HG':
        raise error.Abort(_('%s: not a Mercurial bundle') % fname)
    if version == '10':
        if alg is None:
            alg = changegroup.readexactly(fh, 2)
        return changegroup.cg1unpacker(fh, alg)
    elif version.startswith('2'):
        return bundle2.getunbundler(ui, fh, magicstring=magic + version)
    elif version == 'S1':
        return streamclone.streamcloneapplier(fh)
    else:
        raise error.Abort(_('%s: unknown bundle version %s') % (fname, version))

def getbundlespec(ui, fh):
    """Infer the bundlespec from a bundle file handle.

    The input file handle is seeked and the original seek position is not
    restored.
    """
    def speccompression(alg):
        try:
            return util.compengines.forbundletype(alg).bundletype()[0]
        except KeyError:
            return None

    b = readbundle(ui, fh, None)
    if isinstance(b, changegroup.cg1unpacker):
        alg = b._type
        if alg == '_truncatedBZ':
            alg = 'BZ'
        comp = speccompression(alg)
        if not comp:
            raise error.Abort(_('unknown compression algorithm: %s') % alg)
        return '%s-v1' % comp
    elif isinstance(b, bundle2.unbundle20):
        if 'Compression' in b.params:
            comp = speccompression(b.params['Compression'])
            if not comp:
                raise error.Abort(_('unknown compression algorithm: %s') % comp)
        else:
            comp = 'none'

        version = None
        for part in b.iterparts():
            if part.type == 'changegroup':
                version = part.params['version']
                if version in ('01', '02'):
                    version = 'v2'
                else:
                    raise error.Abort(_('changegroup version %s does not have '
                                        'a known bundlespec') % version,
                                      hint=_('try upgrading your Mercurial '
                                              'client'))

        if not version:
            raise error.Abort(_('could not identify changegroup version in '
                                'bundle'))

        return '%s-%s' % (comp, version)
    elif isinstance(b, streamclone.streamcloneapplier):
        requirements = streamclone.readbundle1header(fh)[2]
        params = 'requirements=%s' % ','.join(sorted(requirements))
        return 'none-packed1;%s' % urlreq.quote(params)
    else:
        raise error.Abort(_('unknown bundle type: %s') % b)

def _computeoutgoing(repo, heads, common):
    """Computes which revs are outgoing given a set of common
    and a set of heads.

    This is a separate function so extensions can have access to
    the logic.

    Returns a discovery.outgoing object.
    """
    cl = repo.changelog
    if common:
        hasnode = cl.hasnode
        common = [n for n in common if hasnode(n)]
    else:
        common = [nullid]
    if not heads:
        heads = cl.heads()
    return discovery.outgoing(repo, common, heads)

def _forcebundle1(op):
    """return true if a pull/push must use bundle1

    This function is used to allow testing of the older bundle version"""
    ui = op.repo.ui
    forcebundle1 = False
    # The goal is this config is to allow developer to choose the bundle
    # version used during exchanged. This is especially handy during test.
    # Value is a list of bundle version to be picked from, highest version
    # should be used.
    #
    # developer config: devel.legacy.exchange
    exchange = ui.configlist('devel', 'legacy.exchange')
    forcebundle1 = 'bundle2' not in exchange and 'bundle1' in exchange
    return forcebundle1 or not op.remote.capable('bundle2')

class pushoperation(object):
    """A object that represent a single push operation

    Its purpose is to carry push related state and very common operations.

    A new pushoperation should be created at the beginning of each push and
    discarded afterward.
    """

    def __init__(self, repo, remote, force=False, revs=None, newbranch=False,
                 bookmarks=()):
        # repo we push from
        self.repo = repo
        self.ui = repo.ui
        # repo we push to
        self.remote = remote
        # force option provided
        self.force = force
        # revs to be pushed (None is "all")
        self.revs = revs
        # bookmark explicitly pushed
        self.bookmarks = bookmarks
        # allow push of new branch
        self.newbranch = newbranch
        # did a local lock get acquired?
        self.locallocked = None
        # step already performed
        # (used to check what steps have been already performed through bundle2)
        self.stepsdone = set()
        # Integer version of the changegroup push result
        # - None means nothing to push
        # - 0 means HTTP error
        # - 1 means we pushed and remote head count is unchanged *or*
        #   we have outgoing changesets but refused to push
        # - other values as described by addchangegroup()
        self.cgresult = None
        # Boolean value for the bookmark push
        self.bkresult = None
        # discover.outgoing object (contains common and outgoing data)
        self.outgoing = None
        # all remote heads before the push
        self.remoteheads = None
        # testable as a boolean indicating if any nodes are missing locally.
        self.incoming = None
        # phases changes that must be pushed along side the changesets
        self.outdatedphases = None
        # phases changes that must be pushed if changeset push fails
        self.fallbackoutdatedphases = None
        # outgoing obsmarkers
        self.outobsmarkers = set()
        # outgoing bookmarks
        self.outbookmarks = []
        # transaction manager
        self.trmanager = None
        # map { pushkey partid -> callback handling failure}
        # used to handle exception from mandatory pushkey part failure
        self.pkfailcb = {}

    @util.propertycache
    def futureheads(self):
        """future remote heads if the changeset push succeeds"""
        return self.outgoing.missingheads

    @util.propertycache
    def fallbackheads(self):
        """future remote heads if the changeset push fails"""
        if self.revs is None:
            # not target to push, all common are relevant
            return self.outgoing.commonheads
        unfi = self.repo.unfiltered()
        # I want cheads = heads(::missingheads and ::commonheads)
        # (missingheads is revs with secret changeset filtered out)
        #
        # This can be expressed as:
        #     cheads = ( (missingheads and ::commonheads)
        #              + (commonheads and ::missingheads))"
        #              )
        #
        # while trying to push we already computed the following:
        #     common = (::commonheads)
        #     missing = ((commonheads::missingheads) - commonheads)
        #
        # We can pick:
        # * missingheads part of common (::commonheads)
        common = self.outgoing.common
        nm = self.repo.changelog.nodemap
        cheads = [node for node in self.revs if nm[node] in common]
        # and
        # * commonheads parents on missing
        revset = unfi.set('%ln and parents(roots(%ln))',
                         self.outgoing.commonheads,
                         self.outgoing.missing)
        cheads.extend(c.node() for c in revset)
        return cheads

    @property
    def commonheads(self):
        """set of all common heads after changeset bundle push"""
        if self.cgresult:
            return self.futureheads
        else:
            return self.fallbackheads

# mapping of message used when pushing bookmark
bookmsgmap = {'update': (_("updating bookmark %s\n"),
                         _('updating bookmark %s failed!\n')),
              'export': (_("exporting bookmark %s\n"),
                         _('exporting bookmark %s failed!\n')),
              'delete': (_("deleting remote bookmark %s\n"),
                         _('deleting remote bookmark %s failed!\n')),
              }


def push(repo, remote, force=False, revs=None, newbranch=False, bookmarks=(),
         opargs=None):
    '''Push outgoing changesets (limited by revs) from a local
    repository to remote. Return an integer:
      - None means nothing to push
      - 0 means HTTP error
      - 1 means we pushed and remote head count is unchanged *or*
        we have outgoing changesets but refused to push
      - other values as described by addchangegroup()
    '''
    if opargs is None:
        opargs = {}
    pushop = pushoperation(repo, remote, force, revs, newbranch, bookmarks,
                           **opargs)
    if pushop.remote.local():
        missing = (set(pushop.repo.requirements)
                   - pushop.remote.local().supported)
        if missing:
            msg = _("required features are not"
                    " supported in the destination:"
                    " %s") % (', '.join(sorted(missing)))
            raise error.Abort(msg)

    # there are two ways to push to remote repo:
    #
    # addchangegroup assumes local user can lock remote
    # repo (local filesystem, old ssh servers).
    #
    # unbundle assumes local user cannot lock remote repo (new ssh
    # servers, http servers).

    if not pushop.remote.canpush():
        raise error.Abort(_("destination does not support push"))
    # get local lock as we might write phase data
    localwlock = locallock = None
    try:
        # bundle2 push may receive a reply bundle touching bookmarks or other
        # things requiring the wlock. Take it now to ensure proper ordering.
        maypushback = pushop.ui.configbool('experimental', 'bundle2.pushback')
        if (not _forcebundle1(pushop)) and maypushback:
            localwlock = pushop.repo.wlock()
        locallock = pushop.repo.lock()
        pushop.locallocked = True
    except IOError as err:
        pushop.locallocked = False
        if err.errno != errno.EACCES:
            raise
        # source repo cannot be locked.
        # We do not abort the push, but just disable the local phase
        # synchronisation.
        msg = 'cannot lock source repository: %s\n' % err
        pushop.ui.debug(msg)
    try:
        if pushop.locallocked:
            pushop.trmanager = transactionmanager(pushop.repo,
                                                  'push-response',
                                                  pushop.remote.url())
        pushop.repo.checkpush(pushop)
        lock = None
        unbundle = pushop.remote.capable('unbundle')
        if not unbundle:
            lock = pushop.remote.lock()
        try:
            _pushdiscovery(pushop)
            if not _forcebundle1(pushop):
                _pushbundle2(pushop)
            _pushchangeset(pushop)
            _pushsyncphase(pushop)
            _pushobsolete(pushop)
            _pushbookmark(pushop)
        finally:
            if lock is not None:
                lock.release()
        if pushop.trmanager:
            pushop.trmanager.close()
    finally:
        if pushop.trmanager:
            pushop.trmanager.release()
        if locallock is not None:
            locallock.release()
        if localwlock is not None:
            localwlock.release()

    return pushop

# list of steps to perform discovery before push
pushdiscoveryorder = []

# Mapping between step name and function
#
# This exists to help extensions wrap steps if necessary
pushdiscoverymapping = {}

def pushdiscovery(stepname):
    """decorator for function performing discovery before push

    The function is added to the step -> function mapping and appended to the
    list of steps.  Beware that decorated function will be added in order (this
    may matter).

    You can only use this decorator for a new step, if you want to wrap a step
    from an extension, change the pushdiscovery dictionary directly."""
    def dec(func):
        assert stepname not in pushdiscoverymapping
        pushdiscoverymapping[stepname] = func
        pushdiscoveryorder.append(stepname)
        return func
    return dec

def _pushdiscovery(pushop):
    """Run all discovery steps"""
    for stepname in pushdiscoveryorder:
        step = pushdiscoverymapping[stepname]
        step(pushop)

@pushdiscovery('changeset')
def _pushdiscoverychangeset(pushop):
    """discover the changeset that need to be pushed"""
    fci = discovery.findcommonincoming
    commoninc = fci(pushop.repo, pushop.remote, force=pushop.force)
    common, inc, remoteheads = commoninc
    fco = discovery.findcommonoutgoing
    outgoing = fco(pushop.repo, pushop.remote, onlyheads=pushop.revs,
                   commoninc=commoninc, force=pushop.force)
    pushop.outgoing = outgoing
    pushop.remoteheads = remoteheads
    pushop.incoming = inc

@pushdiscovery('phase')
def _pushdiscoveryphase(pushop):
    """discover the phase that needs to be pushed

    (computed for both success and failure case for changesets push)"""
    outgoing = pushop.outgoing
    unfi = pushop.repo.unfiltered()
    remotephases = pushop.remote.listkeys('phases')
    publishing = remotephases.get('publishing', False)
    if (pushop.ui.configbool('ui', '_usedassubrepo', False)
        and remotephases    # server supports phases
        and not pushop.outgoing.missing # no changesets to be pushed
        and publishing):
        # When:
        # - this is a subrepo push
        # - and remote support phase
        # - and no changeset are to be pushed
        # - and remote is publishing
        # We may be in issue 3871 case!
        # We drop the possible phase synchronisation done by
        # courtesy to publish changesets possibly locally draft
        # on the remote.
        remotephases = {'publishing': 'True'}
    ana = phases.analyzeremotephases(pushop.repo,
                                     pushop.fallbackheads,
                                     remotephases)
    pheads, droots = ana
    extracond = ''
    if not publishing:
        extracond = ' and public()'
    revset = 'heads((%%ln::%%ln) %s)' % extracond
    # Get the list of all revs draft on remote by public here.
    # XXX Beware that revset break if droots is not strictly
    # XXX root we may want to ensure it is but it is costly
    fallback = list(unfi.set(revset, droots, pushop.fallbackheads))
    if not outgoing.missing:
        future = fallback
    else:
        # adds changeset we are going to push as draft
        #
        # should not be necessary for publishing server, but because of an
        # issue fixed in xxxxx we have to do it anyway.
        fdroots = list(unfi.set('roots(%ln  + %ln::)',
                       outgoing.missing, droots))
        fdroots = [f.node() for f in fdroots]
        future = list(unfi.set(revset, fdroots, pushop.futureheads))
    pushop.outdatedphases = future
    pushop.fallbackoutdatedphases = fallback

@pushdiscovery('obsmarker')
def _pushdiscoveryobsmarkers(pushop):
    if (obsolete.isenabled(pushop.repo, obsolete.exchangeopt)
        and pushop.repo.obsstore
        and 'obsolete' in pushop.remote.listkeys('namespaces')):
        repo = pushop.repo
        # very naive computation, that can be quite expensive on big repo.
        # However: evolution is currently slow on them anyway.
        nodes = (c.node() for c in repo.set('::%ln', pushop.futureheads))
        pushop.outobsmarkers = pushop.repo.obsstore.relevantmarkers(nodes)

@pushdiscovery('bookmarks')
def _pushdiscoverybookmarks(pushop):
    ui = pushop.ui
    repo = pushop.repo.unfiltered()
    remote = pushop.remote
    ui.debug("checking for updated bookmarks\n")
    ancestors = ()
    if pushop.revs:
        revnums = map(repo.changelog.rev, pushop.revs)
        ancestors = repo.changelog.ancestors(revnums, inclusive=True)
    remotebookmark = remote.listkeys('bookmarks')

    explicit = set([repo._bookmarks.expandname(bookmark)
                    for bookmark in pushop.bookmarks])

    remotebookmark = bookmod.unhexlifybookmarks(remotebookmark)
    comp = bookmod.comparebookmarks(repo, repo._bookmarks, remotebookmark)

    def safehex(x):
        if x is None:
            return x
        return hex(x)

    def hexifycompbookmarks(bookmarks):
        for b, scid, dcid in bookmarks:
            yield b, safehex(scid), safehex(dcid)

    comp = [hexifycompbookmarks(marks) for marks in comp]
    addsrc, adddst, advsrc, advdst, diverge, differ, invalid, same = comp

    for b, scid, dcid in advsrc:
        if b in explicit:
            explicit.remove(b)
        if not ancestors or repo[scid].rev() in ancestors:
            pushop.outbookmarks.append((b, dcid, scid))
    # search added bookmark
    for b, scid, dcid in addsrc:
        if b in explicit:
            explicit.remove(b)
            pushop.outbookmarks.append((b, '', scid))
    # search for overwritten bookmark
    for b, scid, dcid in list(advdst) + list(diverge) + list(differ):
        if b in explicit:
            explicit.remove(b)
            pushop.outbookmarks.append((b, dcid, scid))
    # search for bookmark to delete
    for b, scid, dcid in adddst:
        if b in explicit:
            explicit.remove(b)
            # treat as "deleted locally"
            pushop.outbookmarks.append((b, dcid, ''))
    # identical bookmarks shouldn't get reported
    for b, scid, dcid in same:
        if b in explicit:
            explicit.remove(b)

    if explicit:
        explicit = sorted(explicit)
        # we should probably list all of them
        ui.warn(_('bookmark %s does not exist on the local '
                  'or remote repository!\n') % explicit[0])
        pushop.bkresult = 2

    pushop.outbookmarks.sort()

def _pushcheckoutgoing(pushop):
    outgoing = pushop.outgoing
    unfi = pushop.repo.unfiltered()
    if not outgoing.missing:
        # nothing to push
        scmutil.nochangesfound(unfi.ui, unfi, outgoing.excluded)
        return False
    # something to push
    if not pushop.force:
        # if repo.obsstore == False --> no obsolete
        # then, save the iteration
        if unfi.obsstore:
            # this message are here for 80 char limit reason
            mso = _("push includes obsolete changeset: %s!")
            mst = {"unstable": _("push includes unstable changeset: %s!"),
                   "bumped": _("push includes bumped changeset: %s!"),
                   "divergent": _("push includes divergent changeset: %s!")}
            # If we are to push if there is at least one
            # obsolete or unstable changeset in missing, at
            # least one of the missinghead will be obsolete or
            # unstable. So checking heads only is ok
            for node in outgoing.missingheads:
                ctx = unfi[node]
                if ctx.obsolete():
                    raise error.Abort(mso % ctx)
                elif ctx.troubled():
                    raise error.Abort(mst[ctx.troubles()[0]] % ctx)

        discovery.checkheads(pushop)
    return True

# List of names of steps to perform for an outgoing bundle2, order matters.
b2partsgenorder = []

# Mapping between step name and function
#
# This exists to help extensions wrap steps if necessary
b2partsgenmapping = {}

def b2partsgenerator(stepname, idx=None):
    """decorator for function generating bundle2 part

    The function is added to the step -> function mapping and appended to the
    list of steps.  Beware that decorated functions will be added in order
    (this may matter).

    You can only use this decorator for new steps, if you want to wrap a step
    from an extension, attack the b2partsgenmapping dictionary directly."""
    def dec(func):
        assert stepname not in b2partsgenmapping
        b2partsgenmapping[stepname] = func
        if idx is None:
            b2partsgenorder.append(stepname)
        else:
            b2partsgenorder.insert(idx, stepname)
        return func
    return dec

def _pushb2ctxcheckheads(pushop, bundler):
    """Generate race condition checking parts

    Exists as an independent function to aid extensions
    """
    if not pushop.force:
        bundler.newpart('check:heads', data=iter(pushop.remoteheads))

@b2partsgenerator('changeset')
def _pushb2ctx(pushop, bundler):
    """handle changegroup push through bundle2

    addchangegroup result is stored in the ``pushop.cgresult`` attribute.
    """
    if 'changesets' in pushop.stepsdone:
        return
    pushop.stepsdone.add('changesets')
    # Send known heads to the server for race detection.
    if not _pushcheckoutgoing(pushop):
        return
    pushop.repo.prepushoutgoinghooks(pushop)

    _pushb2ctxcheckheads(pushop, bundler)

    b2caps = bundle2.bundle2caps(pushop.remote)
    version = '01'
    cgversions = b2caps.get('changegroup')
    if cgversions:  # 3.1 and 3.2 ship with an empty value
        cgversions = [v for v in cgversions
                      if v in changegroup.supportedoutgoingversions(
                          pushop.repo)]
        if not cgversions:
            raise ValueError(_('no common changegroup version'))
        version = max(cgversions)
    cg = changegroup.getlocalchangegroupraw(pushop.repo, 'push',
                                            pushop.outgoing,
                                            version=version)
    cgpart = bundler.newpart('changegroup', data=cg)
    if cgversions:
        cgpart.addparam('version', version)
    if 'treemanifest' in pushop.repo.requirements:
        cgpart.addparam('treemanifest', '1')
    def handlereply(op):
        """extract addchangegroup returns from server reply"""
        cgreplies = op.records.getreplies(cgpart.id)
        assert len(cgreplies['changegroup']) == 1
        pushop.cgresult = cgreplies['changegroup'][0]['return']
    return handlereply

@b2partsgenerator('phase')
def _pushb2phases(pushop, bundler):
    """handle phase push through bundle2"""
    if 'phases' in pushop.stepsdone:
        return
    b2caps = bundle2.bundle2caps(pushop.remote)
    if not 'pushkey' in b2caps:
        return
    pushop.stepsdone.add('phases')
    part2node = []

    def handlefailure(pushop, exc):
        targetid = int(exc.partid)
        for partid, node in part2node:
            if partid == targetid:
                raise error.Abort(_('updating %s to public failed') % node)

    enc = pushkey.encode
    for newremotehead in pushop.outdatedphases:
        part = bundler.newpart('pushkey')
        part.addparam('namespace', enc('phases'))
        part.addparam('key', enc(newremotehead.hex()))
        part.addparam('old', enc(str(phases.draft)))
        part.addparam('new', enc(str(phases.public)))
        part2node.append((part.id, newremotehead))
        pushop.pkfailcb[part.id] = handlefailure

    def handlereply(op):
        for partid, node in part2node:
            partrep = op.records.getreplies(partid)
            results = partrep['pushkey']
            assert len(results) <= 1
            msg = None
            if not results:
                msg = _('server ignored update of %s to public!\n') % node
            elif not int(results[0]['return']):
                msg = _('updating %s to public failed!\n') % node
            if msg is not None:
                pushop.ui.warn(msg)
    return handlereply

@b2partsgenerator('obsmarkers')
def _pushb2obsmarkers(pushop, bundler):
    if 'obsmarkers' in pushop.stepsdone:
        return
    remoteversions = bundle2.obsmarkersversion(bundler.capabilities)
    if obsolete.commonversion(remoteversions) is None:
        return
    pushop.stepsdone.add('obsmarkers')
    if pushop.outobsmarkers:
        markers = sorted(pushop.outobsmarkers)
        bundle2.buildobsmarkerspart(bundler, markers)

@b2partsgenerator('bookmarks')
def _pushb2bookmarks(pushop, bundler):
    """handle bookmark push through bundle2"""
    if 'bookmarks' in pushop.stepsdone:
        return
    b2caps = bundle2.bundle2caps(pushop.remote)
    if 'pushkey' not in b2caps:
        return
    pushop.stepsdone.add('bookmarks')
    part2book = []
    enc = pushkey.encode

    def handlefailure(pushop, exc):
        targetid = int(exc.partid)
        for partid, book, action in part2book:
            if partid == targetid:
                raise error.Abort(bookmsgmap[action][1].rstrip() % book)
        # we should not be called for part we did not generated
        assert False

    for book, old, new in pushop.outbookmarks:
        part = bundler.newpart('pushkey')
        part.addparam('namespace', enc('bookmarks'))
        part.addparam('key', enc(book))
        part.addparam('old', enc(old))
        part.addparam('new', enc(new))
        action = 'update'
        if not old:
            action = 'export'
        elif not new:
            action = 'delete'
        part2book.append((part.id, book, action))
        pushop.pkfailcb[part.id] = handlefailure

    def handlereply(op):
        ui = pushop.ui
        for partid, book, action in part2book:
            partrep = op.records.getreplies(partid)
            results = partrep['pushkey']
            assert len(results) <= 1
            if not results:
                pushop.ui.warn(_('server ignored bookmark %s update\n') % book)
            else:
                ret = int(results[0]['return'])
                if ret:
                    ui.status(bookmsgmap[action][0] % book)
                else:
                    ui.warn(bookmsgmap[action][1] % book)
                    if pushop.bkresult is not None:
                        pushop.bkresult = 1
    return handlereply


def _pushbundle2(pushop):
    """push data to the remote using bundle2

    The only currently supported type of data is changegroup but this will
    evolve in the future."""
    bundler = bundle2.bundle20(pushop.ui, bundle2.bundle2caps(pushop.remote))
    pushback = (pushop.trmanager
                and pushop.ui.configbool('experimental', 'bundle2.pushback'))

    # create reply capability
    capsblob = bundle2.encodecaps(bundle2.getrepocaps(pushop.repo,
                                                      allowpushback=pushback))
    bundler.newpart('replycaps', data=capsblob)
    replyhandlers = []
    for partgenname in b2partsgenorder:
        partgen = b2partsgenmapping[partgenname]
        ret = partgen(pushop, bundler)
        if callable(ret):
            replyhandlers.append(ret)
    # do not push if nothing to push
    if bundler.nbparts <= 1:
        return
    stream = util.chunkbuffer(bundler.getchunks())
    try:
        try:
            reply = pushop.remote.unbundle(
                stream, ['force'], pushop.remote.url())
        except error.BundleValueError as exc:
            raise error.Abort(_('missing support for %s') % exc)
        try:
            trgetter = None
            if pushback:
                trgetter = pushop.trmanager.transaction
            op = bundle2.processbundle(pushop.repo, reply, trgetter)
        except error.BundleValueError as exc:
            raise error.Abort(_('missing support for %s') % exc)
        except bundle2.AbortFromPart as exc:
            pushop.ui.status(_('remote: %s\n') % exc)
            if exc.hint is not None:
                pushop.ui.status(_('remote: %s\n') % ('(%s)' % exc.hint))
            raise error.Abort(_('push failed on remote'))
    except error.PushkeyFailed as exc:
        partid = int(exc.partid)
        if partid not in pushop.pkfailcb:
            raise
        pushop.pkfailcb[partid](pushop, exc)
    for rephand in replyhandlers:
        rephand(op)

def _pushchangeset(pushop):
    """Make the actual push of changeset bundle to remote repo"""
    if 'changesets' in pushop.stepsdone:
        return
    pushop.stepsdone.add('changesets')
    if not _pushcheckoutgoing(pushop):
        return
    pushop.repo.prepushoutgoinghooks(pushop)
    outgoing = pushop.outgoing
    unbundle = pushop.remote.capable('unbundle')
    # TODO: get bundlecaps from remote
    bundlecaps = None
    # create a changegroup from local
    if pushop.revs is None and not (outgoing.excluded
                            or pushop.repo.changelog.filteredrevs):
        # push everything,
        # use the fast path, no race possible on push
        bundler = changegroup.cg1packer(pushop.repo, bundlecaps)
        cg = changegroup.getsubset(pushop.repo,
                                   outgoing,
                                   bundler,
                                   'push',
                                   fastpath=True)
    else:
        cg = changegroup.getchangegroup(pushop.repo, 'push', outgoing,
                                        bundlecaps=bundlecaps)

    # apply changegroup to remote
    if unbundle:
        # local repo finds heads on server, finds out what
        # revs it must push. once revs transferred, if server
        # finds it has different heads (someone else won
        # commit/push race), server aborts.
        if pushop.force:
            remoteheads = ['force']
        else:
            remoteheads = pushop.remoteheads
        # ssh: return remote's addchangegroup()
        # http: return remote's addchangegroup() or 0 for error
        pushop.cgresult = pushop.remote.unbundle(cg, remoteheads,
                                            pushop.repo.url())
    else:
        # we return an integer indicating remote head count
        # change
        pushop.cgresult = pushop.remote.addchangegroup(cg, 'push',
                                                       pushop.repo.url())

def _pushsyncphase(pushop):
    """synchronise phase information locally and remotely"""
    cheads = pushop.commonheads
    # even when we don't push, exchanging phase data is useful
    remotephases = pushop.remote.listkeys('phases')
    if (pushop.ui.configbool('ui', '_usedassubrepo', False)
        and remotephases    # server supports phases
        and pushop.cgresult is None # nothing was pushed
        and remotephases.get('publishing', False)):
        # When:
        # - this is a subrepo push
        # - and remote support phase
        # - and no changeset was pushed
        # - and remote is publishing
        # We may be in issue 3871 case!
        # We drop the possible phase synchronisation done by
        # courtesy to publish changesets possibly locally draft
        # on the remote.
        remotephases = {'publishing': 'True'}
    if not remotephases: # old server or public only reply from non-publishing
        _localphasemove(pushop, cheads)
        # don't push any phase data as there is nothing to push
    else:
        ana = phases.analyzeremotephases(pushop.repo, cheads,
                                         remotephases)
        pheads, droots = ana
        ### Apply remote phase on local
        if remotephases.get('publishing', False):
            _localphasemove(pushop, cheads)
        else: # publish = False
            _localphasemove(pushop, pheads)
            _localphasemove(pushop, cheads, phases.draft)
        ### Apply local phase on remote

        if pushop.cgresult:
            if 'phases' in pushop.stepsdone:
                # phases already pushed though bundle2
                return
            outdated = pushop.outdatedphases
        else:
            outdated = pushop.fallbackoutdatedphases

        pushop.stepsdone.add('phases')

        # filter heads already turned public by the push
        outdated = [c for c in outdated if c.node() not in pheads]
        # fallback to independent pushkey command
        for newremotehead in outdated:
            r = pushop.remote.pushkey('phases',
                                      newremotehead.hex(),
                                      str(phases.draft),
                                      str(phases.public))
            if not r:
                pushop.ui.warn(_('updating %s to public failed!\n')
                               % newremotehead)

def _localphasemove(pushop, nodes, phase=phases.public):
    """move <nodes> to <phase> in the local source repo"""
    if pushop.trmanager:
        phases.advanceboundary(pushop.repo,
                               pushop.trmanager.transaction(),
                               phase,
                               nodes)
    else:
        # repo is not locked, do not change any phases!
        # Informs the user that phases should have been moved when
        # applicable.
        actualmoves = [n for n in nodes if phase < pushop.repo[n].phase()]
        phasestr = phases.phasenames[phase]
        if actualmoves:
            pushop.ui.status(_('cannot lock source repo, skipping '
                               'local %s phase update\n') % phasestr)

def _pushobsolete(pushop):
    """utility function to push obsolete markers to a remote"""
    if 'obsmarkers' in pushop.stepsdone:
        return
    repo = pushop.repo
    remote = pushop.remote
    pushop.stepsdone.add('obsmarkers')
    if pushop.outobsmarkers:
        pushop.ui.debug('try to push obsolete markers to remote\n')
        rslts = []
        remotedata = obsolete._pushkeyescape(sorted(pushop.outobsmarkers))
        for key in sorted(remotedata, reverse=True):
            # reverse sort to ensure we end with dump0
            data = remotedata[key]
            rslts.append(remote.pushkey('obsolete', key, '', data))
        if [r for r in rslts if not r]:
            msg = _('failed to push some obsolete markers!\n')
            repo.ui.warn(msg)

def _pushbookmark(pushop):
    """Update bookmark position on remote"""
    if pushop.cgresult == 0 or 'bookmarks' in pushop.stepsdone:
        return
    pushop.stepsdone.add('bookmarks')
    ui = pushop.ui
    remote = pushop.remote

    for b, old, new in pushop.outbookmarks:
        action = 'update'
        if not old:
            action = 'export'
        elif not new:
            action = 'delete'
        if remote.pushkey('bookmarks', b, old, new):
            ui.status(bookmsgmap[action][0] % b)
        else:
            ui.warn(bookmsgmap[action][1] % b)
            # discovery can have set the value form invalid entry
            if pushop.bkresult is not None:
                pushop.bkresult = 1

class pulloperation(object):
    """A object that represent a single pull operation

    It purpose is to carry pull related state and very common operation.

    A new should be created at the beginning of each pull and discarded
    afterward.
    """

    def __init__(self, repo, remote, heads=None, force=False, bookmarks=(),
                 remotebookmarks=None, streamclonerequested=None):
        # repo we pull into
        self.repo = repo
        # repo we pull from
        self.remote = remote
        # revision we try to pull (None is "all")
        self.heads = heads
        # bookmark pulled explicitly
        self.explicitbookmarks = [repo._bookmarks.expandname(bookmark)
                                  for bookmark in bookmarks]
        # do we force pull?
        self.force = force
        # whether a streaming clone was requested
        self.streamclonerequested = streamclonerequested
        # transaction manager
        self.trmanager = None
        # set of common changeset between local and remote before pull
        self.common = None
        # set of pulled head
        self.rheads = None
        # list of missing changeset to fetch remotely
        self.fetch = None
        # remote bookmarks data
        self.remotebookmarks = remotebookmarks
        # result of changegroup pulling (used as return code by pull)
        self.cgresult = None
        # list of step already done
        self.stepsdone = set()
        # Whether we attempted a clone from pre-generated bundles.
        self.clonebundleattempted = False

    @util.propertycache
    def pulledsubset(self):
        """heads of the set of changeset target by the pull"""
        # compute target subset
        if self.heads is None:
            # We pulled every thing possible
            # sync on everything common
            c = set(self.common)
            ret = list(self.common)
            for n in self.rheads:
                if n not in c:
                    ret.append(n)
            return ret
        else:
            # We pulled a specific subset
            # sync on this subset
            return self.heads

    @util.propertycache
    def canusebundle2(self):
        return not _forcebundle1(self)

    @util.propertycache
    def remotebundle2caps(self):
        return bundle2.bundle2caps(self.remote)

    def gettransaction(self):
        # deprecated; talk to trmanager directly
        return self.trmanager.transaction()

class transactionmanager(object):
    """An object to manage the life cycle of a transaction

    It creates the transaction on demand and calls the appropriate hooks when
    closing the transaction."""
    def __init__(self, repo, source, url):
        self.repo = repo
        self.source = source
        self.url = url
        self._tr = None

    def transaction(self):
        """Return an open transaction object, constructing if necessary"""
        if not self._tr:
            trname = '%s\n%s' % (self.source, util.hidepassword(self.url))
            self._tr = self.repo.transaction(trname)
            self._tr.hookargs['source'] = self.source
            self._tr.hookargs['url'] = self.url
        return self._tr

    def close(self):
        """close transaction if created"""
        if self._tr is not None:
            self._tr.close()

    def release(self):
        """release transaction if created"""
        if self._tr is not None:
            self._tr.release()

def pull(repo, remote, heads=None, force=False, bookmarks=(), opargs=None,
         streamclonerequested=None):
    """Fetch repository data from a remote.

    This is the main function used to retrieve data from a remote repository.

    ``repo`` is the local repository to clone into.
    ``remote`` is a peer instance.
    ``heads`` is an iterable of revisions we want to pull. ``None`` (the
    default) means to pull everything from the remote.
    ``bookmarks`` is an iterable of bookmarks requesting to be pulled. By
    default, all remote bookmarks are pulled.
    ``opargs`` are additional keyword arguments to pass to ``pulloperation``
    initialization.
    ``streamclonerequested`` is a boolean indicating whether a "streaming
    clone" is requested. A "streaming clone" is essentially a raw file copy
    of revlogs from the server. This only works when the local repository is
    empty. The default value of ``None`` means to respect the server
    configuration for preferring stream clones.

    Returns the ``pulloperation`` created for this pull.
    """
    if opargs is None:
        opargs = {}
    pullop = pulloperation(repo, remote, heads, force, bookmarks=bookmarks,
                           streamclonerequested=streamclonerequested, **opargs)
    if pullop.remote.local():
        missing = set(pullop.remote.requirements) - pullop.repo.supported
        if missing:
            msg = _("required features are not"
                    " supported in the destination:"
                    " %s") % (', '.join(sorted(missing)))
            raise error.Abort(msg)

    wlock = lock = None
    try:
        wlock = pullop.repo.wlock()
        lock = pullop.repo.lock()
        pullop.trmanager = transactionmanager(repo, 'pull', remote.url())
        streamclone.maybeperformlegacystreamclone(pullop)
        # This should ideally be in _pullbundle2(). However, it needs to run
        # before discovery to avoid extra work.
        _maybeapplyclonebundle(pullop)
        _pulldiscovery(pullop)
        if pullop.canusebundle2:
            _pullbundle2(pullop)
        _pullchangeset(pullop)
        _pullphase(pullop)
        _pullbookmarks(pullop)
        _pullobsolete(pullop)
        pullop.trmanager.close()
    finally:
        lockmod.release(pullop.trmanager, lock, wlock)

    return pullop

# list of steps to perform discovery before pull
pulldiscoveryorder = []

# Mapping between step name and function
#
# This exists to help extensions wrap steps if necessary
pulldiscoverymapping = {}

def pulldiscovery(stepname):
    """decorator for function performing discovery before pull

    The function is added to the step -> function mapping and appended to the
    list of steps.  Beware that decorated function will be added in order (this
    may matter).

    You can only use this decorator for a new step, if you want to wrap a step
    from an extension, change the pulldiscovery dictionary directly."""
    def dec(func):
        assert stepname not in pulldiscoverymapping
        pulldiscoverymapping[stepname] = func
        pulldiscoveryorder.append(stepname)
        return func
    return dec

def _pulldiscovery(pullop):
    """Run all discovery steps"""
    for stepname in pulldiscoveryorder:
        step = pulldiscoverymapping[stepname]
        step(pullop)

@pulldiscovery('b1:bookmarks')
def _pullbookmarkbundle1(pullop):
    """fetch bookmark data in bundle1 case

    If not using bundle2, we have to fetch bookmarks before changeset
    discovery to reduce the chance and impact of race conditions."""
    if pullop.remotebookmarks is not None:
        return
    if pullop.canusebundle2 and 'listkeys' in pullop.remotebundle2caps:
        # all known bundle2 servers now support listkeys, but lets be nice with
        # new implementation.
        return
    pullop.remotebookmarks = pullop.remote.listkeys('bookmarks')


@pulldiscovery('changegroup')
def _pulldiscoverychangegroup(pullop):
    """discovery phase for the pull

    Current handle changeset discovery only, will change handle all discovery
    at some point."""
    tmp = discovery.findcommonincoming(pullop.repo,
                                       pullop.remote,
                                       heads=pullop.heads,
                                       force=pullop.force)
    common, fetch, rheads = tmp
    nm = pullop.repo.unfiltered().changelog.nodemap
    if fetch and rheads:
        # If a remote heads in filtered locally, lets drop it from the unknown
        # remote heads and put in back in common.
        #
        # This is a hackish solution to catch most of "common but locally
        # hidden situation".  We do not performs discovery on unfiltered
        # repository because it end up doing a pathological amount of round
        # trip for w huge amount of changeset we do not care about.
        #
        # If a set of such "common but filtered" changeset exist on the server
        # but are not including a remote heads, we'll not be able to detect it,
        scommon = set(common)
        filteredrheads = []
        for n in rheads:
            if n in nm:
                if n not in scommon:
                    common.append(n)
            else:
                filteredrheads.append(n)
        if not filteredrheads:
            fetch = []
        rheads = filteredrheads
    pullop.common = common
    pullop.fetch = fetch
    pullop.rheads = rheads

def _pullbundle2(pullop):
    """pull data using bundle2

    For now, the only supported data are changegroup."""
    kwargs = {'bundlecaps': caps20to10(pullop.repo)}

    # At the moment we don't do stream clones over bundle2. If that is
    # implemented then here's where the check for that will go.
    streaming = False

    # pulling changegroup
    pullop.stepsdone.add('changegroup')

    kwargs['common'] = pullop.common
    kwargs['heads'] = pullop.heads or pullop.rheads
    kwargs['cg'] = pullop.fetch
    if 'listkeys' in pullop.remotebundle2caps:
        kwargs['listkeys'] = ['phases']
        if pullop.remotebookmarks is None:
            # make sure to always includes bookmark data when migrating
            # `hg incoming --bundle` to using this function.
            kwargs['listkeys'].append('bookmarks')

    # If this is a full pull / clone and the server supports the clone bundles
    # feature, tell the server whether we attempted a clone bundle. The
    # presence of this flag indicates the client supports clone bundles. This
    # will enable the server to treat clients that support clone bundles
    # differently from those that don't.
    if (pullop.remote.capable('clonebundles')
        and pullop.heads is None and list(pullop.common) == [nullid]):
        kwargs['cbattempted'] = pullop.clonebundleattempted

    if streaming:
        pullop.repo.ui.status(_('streaming all changes\n'))
    elif not pullop.fetch:
        pullop.repo.ui.status(_("no changes found\n"))
        pullop.cgresult = 0
    else:
        if pullop.heads is None and list(pullop.common) == [nullid]:
            pullop.repo.ui.status(_("requesting all changes\n"))
    if obsolete.isenabled(pullop.repo, obsolete.exchangeopt):
        remoteversions = bundle2.obsmarkersversion(pullop.remotebundle2caps)
        if obsolete.commonversion(remoteversions) is not None:
            kwargs['obsmarkers'] = True
            pullop.stepsdone.add('obsmarkers')
    _pullbundle2extraprepare(pullop, kwargs)
    bundle = pullop.remote.getbundle('pull', **kwargs)
    try:
        op = bundle2.processbundle(pullop.repo, bundle, pullop.gettransaction)
    except bundle2.AbortFromPart as exc:
        pullop.repo.ui.status(_('remote: abort: %s\n') % exc)
        raise error.Abort(_('pull failed on remote'), hint=exc.hint)
    except error.BundleValueError as exc:
        raise error.Abort(_('missing support for %s') % exc)

    if pullop.fetch:
        results = [cg['return'] for cg in op.records['changegroup']]
        pullop.cgresult = changegroup.combineresults(results)

    # processing phases change
    for namespace, value in op.records['listkeys']:
        if namespace == 'phases':
            _pullapplyphases(pullop, value)

    # processing bookmark update
    for namespace, value in op.records['listkeys']:
        if namespace == 'bookmarks':
            pullop.remotebookmarks = value

    # bookmark data were either already there or pulled in the bundle
    if pullop.remotebookmarks is not None:
        _pullbookmarks(pullop)

def _pullbundle2extraprepare(pullop, kwargs):
    """hook function so that extensions can extend the getbundle call"""
    pass

def _pullchangeset(pullop):
    """pull changeset from unbundle into the local repo"""
    # We delay the open of the transaction as late as possible so we
    # don't open transaction for nothing or you break future useful
    # rollback call
    if 'changegroup' in pullop.stepsdone:
        return
    pullop.stepsdone.add('changegroup')
    if not pullop.fetch:
        pullop.repo.ui.status(_("no changes found\n"))
        pullop.cgresult = 0
        return
    pullop.gettransaction()
    if pullop.heads is None and list(pullop.common) == [nullid]:
        pullop.repo.ui.status(_("requesting all changes\n"))
    elif pullop.heads is None and pullop.remote.capable('changegroupsubset'):
        # issue1320, avoid a race if remote changed after discovery
        pullop.heads = pullop.rheads

    if pullop.remote.capable('getbundle'):
        # TODO: get bundlecaps from remote
        cg = pullop.remote.getbundle('pull', common=pullop.common,
                                     heads=pullop.heads or pullop.rheads)
    elif pullop.heads is None:
        cg = pullop.remote.changegroup(pullop.fetch, 'pull')
    elif not pullop.remote.capable('changegroupsubset'):
        raise error.Abort(_("partial pull cannot be done because "
                           "other repository doesn't support "
                           "changegroupsubset."))
    else:
        cg = pullop.remote.changegroupsubset(pullop.fetch, pullop.heads, 'pull')
    pullop.cgresult = cg.apply(pullop.repo, 'pull', pullop.remote.url())

def _pullphase(pullop):
    # Get remote phases data from remote
    if 'phases' in pullop.stepsdone:
        return
    remotephases = pullop.remote.listkeys('phases')
    _pullapplyphases(pullop, remotephases)

def _pullapplyphases(pullop, remotephases):
    """apply phase movement from observed remote state"""
    if 'phases' in pullop.stepsdone:
        return
    pullop.stepsdone.add('phases')
    publishing = bool(remotephases.get('publishing', False))
    if remotephases and not publishing:
        # remote is new and non-publishing
        pheads, _dr = phases.analyzeremotephases(pullop.repo,
                                                 pullop.pulledsubset,
                                                 remotephases)
        dheads = pullop.pulledsubset
    else:
        # Remote is old or publishing all common changesets
        # should be seen as public
        pheads = pullop.pulledsubset
        dheads = []
    unfi = pullop.repo.unfiltered()
    phase = unfi._phasecache.phase
    rev = unfi.changelog.nodemap.get
    public = phases.public
    draft = phases.draft

    # exclude changesets already public locally and update the others
    pheads = [pn for pn in pheads if phase(unfi, rev(pn)) > public]
    if pheads:
        tr = pullop.gettransaction()
        phases.advanceboundary(pullop.repo, tr, public, pheads)

    # exclude changesets already draft locally and update the others
    dheads = [pn for pn in dheads if phase(unfi, rev(pn)) > draft]
    if dheads:
        tr = pullop.gettransaction()
        phases.advanceboundary(pullop.repo, tr, draft, dheads)

def _pullbookmarks(pullop):
    """process the remote bookmark information to update the local one"""
    if 'bookmarks' in pullop.stepsdone:
        return
    pullop.stepsdone.add('bookmarks')
    repo = pullop.repo
    remotebookmarks = pullop.remotebookmarks
    remotebookmarks = bookmod.unhexlifybookmarks(remotebookmarks)
    bookmod.updatefromremote(repo.ui, repo, remotebookmarks,
                             pullop.remote.url(),
                             pullop.gettransaction,
                             explicit=pullop.explicitbookmarks)

def _pullobsolete(pullop):
    """utility function to pull obsolete markers from a remote

    The `gettransaction` is function that return the pull transaction, creating
    one if necessary. We return the transaction to inform the calling code that
    a new transaction have been created (when applicable).

    Exists mostly to allow overriding for experimentation purpose"""
    if 'obsmarkers' in pullop.stepsdone:
        return
    pullop.stepsdone.add('obsmarkers')
    tr = None
    if obsolete.isenabled(pullop.repo, obsolete.exchangeopt):
        pullop.repo.ui.debug('fetching remote obsolete markers\n')
        remoteobs = pullop.remote.listkeys('obsolete')
        if 'dump0' in remoteobs:
            tr = pullop.gettransaction()
            markers = []
            for key in sorted(remoteobs, reverse=True):
                if key.startswith('dump'):
                    data = util.b85decode(remoteobs[key])
                    version, newmarks = obsolete._readmarkers(data)
                    markers += newmarks
            if markers:
                pullop.repo.obsstore.add(tr, markers)
            pullop.repo.invalidatevolatilesets()
    return tr

def caps20to10(repo):
    """return a set with appropriate options to use bundle20 during getbundle"""
    caps = {'HG20'}
    capsblob = bundle2.encodecaps(bundle2.getrepocaps(repo))
    caps.add('bundle2=' + urlreq.quote(capsblob))
    return caps

# List of names of steps to perform for a bundle2 for getbundle, order matters.
getbundle2partsorder = []

# Mapping between step name and function
#
# This exists to help extensions wrap steps if necessary
getbundle2partsmapping = {}

def getbundle2partsgenerator(stepname, idx=None):
    """decorator for function generating bundle2 part for getbundle

    The function is added to the step -> function mapping and appended to the
    list of steps.  Beware that decorated functions will be added in order
    (this may matter).

    You can only use this decorator for new steps, if you want to wrap a step
    from an extension, attack the getbundle2partsmapping dictionary directly."""
    def dec(func):
        assert stepname not in getbundle2partsmapping
        getbundle2partsmapping[stepname] = func
        if idx is None:
            getbundle2partsorder.append(stepname)
        else:
            getbundle2partsorder.insert(idx, stepname)
        return func
    return dec

def bundle2requested(bundlecaps):
    if bundlecaps is not None:
        return any(cap.startswith('HG2') for cap in bundlecaps)
    return False

def getbundlechunks(repo, source, heads=None, common=None, bundlecaps=None,
                    **kwargs):
    """Return chunks constituting a bundle's raw data.

    Could be a bundle HG10 or a bundle HG20 depending on bundlecaps
    passed.

    Returns an iterator over raw chunks (of varying sizes).
    """
    usebundle2 = bundle2requested(bundlecaps)
    # bundle10 case
    if not usebundle2:
        if bundlecaps and not kwargs.get('cg', True):
            raise ValueError(_('request for bundle10 must include changegroup'))

        if kwargs:
            raise ValueError(_('unsupported getbundle arguments: %s')
                             % ', '.join(sorted(kwargs.keys())))
        outgoing = _computeoutgoing(repo, heads, common)
        bundler = changegroup.getbundler('01', repo, bundlecaps)
        return changegroup.getsubsetraw(repo, outgoing, bundler, source)

    # bundle20 case
    b2caps = {}
    for bcaps in bundlecaps:
        if bcaps.startswith('bundle2='):
            blob = urlreq.unquote(bcaps[len('bundle2='):])
            b2caps.update(bundle2.decodecaps(blob))
    bundler = bundle2.bundle20(repo.ui, b2caps)

    kwargs['heads'] = heads
    kwargs['common'] = common

    for name in getbundle2partsorder:
        func = getbundle2partsmapping[name]
        func(bundler, repo, source, bundlecaps=bundlecaps, b2caps=b2caps,
             **kwargs)

    return bundler.getchunks()

@getbundle2partsgenerator('changegroup')
def _getbundlechangegrouppart(bundler, repo, source, bundlecaps=None,
                              b2caps=None, heads=None, common=None, **kwargs):
    """add a changegroup part to the requested bundle"""
    cg = None
    if kwargs.get('cg', True):
        # build changegroup bundle here.
        version = '01'
        cgversions = b2caps.get('changegroup')
        if cgversions:  # 3.1 and 3.2 ship with an empty value
            cgversions = [v for v in cgversions
                          if v in changegroup.supportedoutgoingversions(repo)]
            if not cgversions:
                raise ValueError(_('no common changegroup version'))
            version = max(cgversions)
        outgoing = _computeoutgoing(repo, heads, common)
        cg = changegroup.getlocalchangegroupraw(repo, source, outgoing,
                                                bundlecaps=bundlecaps,
                                                version=version)

    if cg:
        part = bundler.newpart('changegroup', data=cg)
        if cgversions:
            part.addparam('version', version)
        part.addparam('nbchanges', str(len(outgoing.missing)), mandatory=False)
        if 'treemanifest' in repo.requirements:
            part.addparam('treemanifest', '1')

@getbundle2partsgenerator('listkeys')
def _getbundlelistkeysparts(bundler, repo, source, bundlecaps=None,
                            b2caps=None, **kwargs):
    """add parts containing listkeys namespaces to the requested bundle"""
    listkeys = kwargs.get('listkeys', ())
    for namespace in listkeys:
        part = bundler.newpart('listkeys')
        part.addparam('namespace', namespace)
        keys = repo.listkeys(namespace).items()
        part.data = pushkey.encodekeys(keys)

@getbundle2partsgenerator('obsmarkers')
def _getbundleobsmarkerpart(bundler, repo, source, bundlecaps=None,
                            b2caps=None, heads=None, **kwargs):
    """add an obsolescence markers part to the requested bundle"""
    if kwargs.get('obsmarkers', False):
        if heads is None:
            heads = repo.heads()
        subset = [c.node() for c in repo.set('::%ln', heads)]
        markers = repo.obsstore.relevantmarkers(subset)
        markers = sorted(markers)
        bundle2.buildobsmarkerspart(bundler, markers)

@getbundle2partsgenerator('hgtagsfnodes')
def _getbundletagsfnodes(bundler, repo, source, bundlecaps=None,
                         b2caps=None, heads=None, common=None,
                         **kwargs):
    """Transfer the .hgtags filenodes mapping.

    Only values for heads in this bundle will be transferred.

    The part data consists of pairs of 20 byte changeset node and .hgtags
    filenodes raw values.
    """
    # Don't send unless:
    # - changeset are being exchanged,
    # - the client supports it.
    if not (kwargs.get('cg', True) and 'hgtagsfnodes' in b2caps):
        return

    outgoing = _computeoutgoing(repo, heads, common)
    bundle2.addparttagsfnodescache(repo, bundler, outgoing)

def _getbookmarks(repo, **kwargs):
    """Returns bookmark to node mapping.

    This function is primarily used to generate `bookmarks` bundle2 part.
    It is a separate function in order to make it easy to wrap it
    in extensions. Passing `kwargs` to the function makes it easy to
    add new parameters in extensions.
    """

    return dict(bookmod.listbinbookmarks(repo))

def check_heads(repo, their_heads, context):
    """check if the heads of a repo have been modified

    Used by peer for unbundling.
    """
    heads = repo.heads()
    heads_hash = hashlib.sha1(''.join(sorted(heads))).digest()
    if not (their_heads == ['force'] or their_heads == heads or
            their_heads == ['hashed', heads_hash]):
        # someone else committed/pushed/unbundled while we
        # were transferring data
        raise error.PushRaced('repository changed while %s - '
                              'please try again' % context)

def unbundle(repo, cg, heads, source, url):
    """Apply a bundle to a repo.

    this function makes sure the repo is locked during the application and have
    mechanism to check that no push race occurred between the creation of the
    bundle and its application.

    If the push was raced as PushRaced exception is raised."""
    r = 0
    # need a transaction when processing a bundle2 stream
    # [wlock, lock, tr] - needs to be an array so nested functions can modify it
    lockandtr = [None, None, None]
    recordout = None
    # quick fix for output mismatch with bundle2 in 3.4
    captureoutput = repo.ui.configbool('experimental', 'bundle2-output-capture',
                                       False)
    if url.startswith('remote:http:') or url.startswith('remote:https:'):
        captureoutput = True
    try:
        # note: outside bundle1, 'heads' is expected to be empty and this
        # 'check_heads' call wil be a no-op
        check_heads(repo, heads, 'uploading changes')
        # push can proceed
        if not util.safehasattr(cg, 'params'):
            # legacy case: bundle1 (changegroup 01)
            lockandtr[1] = repo.lock()
            r = cg.apply(repo, source, url)
        else:
            r = None
            try:
                def gettransaction():
                    if not lockandtr[2]:
                        lockandtr[0] = repo.wlock()
                        lockandtr[1] = repo.lock()
                        lockandtr[2] = repo.transaction(source)
                        lockandtr[2].hookargs['source'] = source
                        lockandtr[2].hookargs['url'] = url
                        lockandtr[2].hookargs['bundle2'] = '1'
                    return lockandtr[2]

                # Do greedy locking by default until we're satisfied with lazy
                # locking.
                if not repo.ui.configbool('experimental', 'bundle2lazylocking'):
                    gettransaction()

                op = bundle2.bundleoperation(repo, gettransaction,
                                             captureoutput=captureoutput)
                try:
                    op = bundle2.processbundle(repo, cg, op=op)
                finally:
                    r = op.reply
                    if captureoutput and r is not None:
                        repo.ui.pushbuffer(error=True, subproc=True)
                        def recordout(output):
                            r.newpart('output', data=output, mandatory=False)
                if lockandtr[2] is not None:
                    lockandtr[2].close()
            except BaseException as exc:
                exc.duringunbundle2 = True
                if captureoutput and r is not None:
                    parts = exc._bundle2salvagedoutput = r.salvageoutput()
                    def recordout(output):
                        part = bundle2.bundlepart('output', data=output,
                                                  mandatory=False)
                        parts.append(part)
                raise
    finally:
        lockmod.release(lockandtr[2], lockandtr[1], lockandtr[0])
        if recordout is not None:
            recordout(repo.ui.popbuffer())
    return r

def _maybeapplyclonebundle(pullop):
    """Apply a clone bundle from a remote, if possible."""

    repo = pullop.repo
    remote = pullop.remote

    if not repo.ui.configbool('ui', 'clonebundles', True):
        return

    # Only run if local repo is empty.
    if len(repo):
        return

    if pullop.heads:
        return

    if not remote.capable('clonebundles'):
        return

    res = remote._call('clonebundles')

    # If we call the wire protocol command, that's good enough to record the
    # attempt.
    pullop.clonebundleattempted = True

    entries = parseclonebundlesmanifest(repo, res)
    if not entries:
        repo.ui.note(_('no clone bundles available on remote; '
                       'falling back to regular clone\n'))
        return

    entries = filterclonebundleentries(repo, entries)
    if not entries:
        # There is a thundering herd concern here. However, if a server
        # operator doesn't advertise bundles appropriate for its clients,
        # they deserve what's coming. Furthermore, from a client's
        # perspective, no automatic fallback would mean not being able to
        # clone!
        repo.ui.warn(_('no compatible clone bundles available on server; '
                       'falling back to regular clone\n'))
        repo.ui.warn(_('(you may want to report this to the server '
                       'operator)\n'))
        return

    entries = sortclonebundleentries(repo.ui, entries)

    url = entries[0]['URL']
    repo.ui.status(_('applying clone bundle from %s\n') % url)
    if trypullbundlefromurl(repo.ui, repo, url):
        repo.ui.status(_('finished applying clone bundle\n'))
    # Bundle failed.
    #
    # We abort by default to avoid the thundering herd of
    # clients flooding a server that was expecting expensive
    # clone load to be offloaded.
    elif repo.ui.configbool('ui', 'clonebundlefallback', False):
        repo.ui.warn(_('falling back to normal clone\n'))
    else:
        raise error.Abort(_('error applying bundle'),
                          hint=_('if this error persists, consider contacting '
                                 'the server operator or disable clone '
                                 'bundles via '
                                 '"--config ui.clonebundles=false"'))

def parseclonebundlesmanifest(repo, s):
    """Parses the raw text of a clone bundles manifest.

    Returns a list of dicts. The dicts have a ``URL`` key corresponding
    to the URL and other keys are the attributes for the entry.
    """
    m = []
    for line in s.splitlines():
        fields = line.split()
        if not fields:
            continue
        attrs = {'URL': fields[0]}
        for rawattr in fields[1:]:
            key, value = rawattr.split('=', 1)
            key = urlreq.unquote(key)
            value = urlreq.unquote(value)
            attrs[key] = value

            # Parse BUNDLESPEC into components. This makes client-side
            # preferences easier to specify since you can prefer a single
            # component of the BUNDLESPEC.
            if key == 'BUNDLESPEC':
                try:
                    comp, version, params = parsebundlespec(repo, value,
                                                            externalnames=True)
                    attrs['COMPRESSION'] = comp
                    attrs['VERSION'] = version
                except error.InvalidBundleSpecification:
                    pass
                except error.UnsupportedBundleSpecification:
                    pass

        m.append(attrs)

    return m

def filterclonebundleentries(repo, entries):
    """Remove incompatible clone bundle manifest entries.

    Accepts a list of entries parsed with ``parseclonebundlesmanifest``
    and returns a new list consisting of only the entries that this client
    should be able to apply.

    There is no guarantee we'll be able to apply all returned entries because
    the metadata we use to filter on may be missing or wrong.
    """
    newentries = []
    for entry in entries:
        spec = entry.get('BUNDLESPEC')
        if spec:
            try:
                parsebundlespec(repo, spec, strict=True)
            except error.InvalidBundleSpecification as e:
                repo.ui.debug(str(e) + '\n')
                continue
            except error.UnsupportedBundleSpecification as e:
                repo.ui.debug('filtering %s because unsupported bundle '
                              'spec: %s\n' % (entry['URL'], str(e)))
                continue

        if 'REQUIRESNI' in entry and not sslutil.hassni:
            repo.ui.debug('filtering %s because SNI not supported\n' %
                          entry['URL'])
            continue

        newentries.append(entry)

    return newentries

class clonebundleentry(object):
    """Represents an item in a clone bundles manifest.

    This rich class is needed to support sorting since sorted() in Python 3
    doesn't support ``cmp`` and our comparison is complex enough that ``key=``
    won't work.
    """

    def __init__(self, value, prefers):
        self.value = value
        self.prefers = prefers

    def _cmp(self, other):
        for prefkey, prefvalue in self.prefers:
            avalue = self.value.get(prefkey)
            bvalue = other.value.get(prefkey)

            # Special case for b missing attribute and a matches exactly.
            if avalue is not None and bvalue is None and avalue == prefvalue:
                return -1

            # Special case for a missing attribute and b matches exactly.
            if bvalue is not None and avalue is None and bvalue == prefvalue:
                return 1

            # We can't compare unless attribute present on both.
            if avalue is None or bvalue is None:
                continue

            # Same values should fall back to next attribute.
            if avalue == bvalue:
                continue

            # Exact matches come first.
            if avalue == prefvalue:
                return -1
            if bvalue == prefvalue:
                return 1

            # Fall back to next attribute.
            continue

        # If we got here we couldn't sort by attributes and prefers. Fall
        # back to index order.
        return 0

    def __lt__(self, other):
        return self._cmp(other) < 0

    def __gt__(self, other):
        return self._cmp(other) > 0

    def __eq__(self, other):
        return self._cmp(other) == 0

    def __le__(self, other):
        return self._cmp(other) <= 0

    def __ge__(self, other):
        return self._cmp(other) >= 0

    def __ne__(self, other):
        return self._cmp(other) != 0

def sortclonebundleentries(ui, entries):
    prefers = ui.configlist('ui', 'clonebundleprefers', default=[])
    if not prefers:
        return list(entries)

    prefers = [p.split('=', 1) for p in prefers]

    items = sorted(clonebundleentry(v, prefers) for v in entries)
    return [i.value for i in items]

def trypullbundlefromurl(ui, repo, url):
    """Attempt to apply a bundle from a URL."""
    lock = repo.lock()
    try:
        tr = repo.transaction('bundleurl')
        try:
            try:
                fh = urlmod.open(ui, url)
                cg = readbundle(ui, fh, 'stream')

                if isinstance(cg, bundle2.unbundle20):
                    bundle2.processbundle(repo, cg, lambda: tr)
                elif isinstance(cg, streamclone.streamcloneapplier):
                    cg.apply(repo)
                else:
                    cg.apply(repo, 'clonebundles', url)
                tr.close()
                return True
            except urlerr.httperror as e:
                ui.warn(_('HTTP error fetching bundle: %s\n') % str(e))
            except urlerr.urlerror as e:
                ui.warn(_('error fetching bundle: %s\n') % e.reason[1])

            return False
        finally:
            tr.release()
    finally:
        lock.release()