annotate mercurial/branchmap.py @ 37051:40206e227412

wireproto: define and implement protocol for issuing requests

The existing HTTP and SSH wire protocols suffer from a host of flaws
and shortcomings. I've been wanting to rewrite the protocol for a while
now. Supporting partial clone - which will require new wire protocol
commands and capabilities - and other advanced server functionality
will be much easier if we start from a clean slate and don't have
to be constrained by limitations of the existing wire protocol.

This commit starts to introduce a new data exchange format for
use over the wire protocol.

The new protocol is built on top of "frames," which are atomic
units of metadata + data. Frames will make it easier to implement
proxies and other mechanisms that want to inspect data without
having to maintain state. The existing frame metadata is very
minimal and it will evolve heavily. (We will eventually support
things like concurrent requests, out-of-order responses,
compression, side-channels for status updates, etc. Some of
these will require additions to the frame header.)

Another benefit of frames is that all reads are of a fixed size.
A reader works by consuming a frame header, extracting the payload
length, then reading that many bytes. No lookahead, buffering, or
memory reallocations are needed.

The new protocol attempts to be transport agnostic. I want all that's
required to use the new protocol to be a pair of unidirectional,
half-duplex pipes. (Yes, we will eventually make use of full-duplex
pipes, but that's for another commit.) Notably, when the SSH
transport switches to this new protocol, stderr will be unused.
This is by design: the lack of stderr on HTTP harms protocol
behavior there. By shoehorning everything into a pair of pipes,
we can have more consistent behavior across transports.

We currently only define the client side parts of the new protocol,
specifically the bits for requesting that a command run. This keeps
the new code and feature small and somewhat easy to review.

We add support to `hg debugwireproto` for writing frames into
HTTP request bodies. Our tests that issue commands to the new
HTTP endpoint have been updated to transmit frames. The server
bits haven't been touched to consume the frames yet. This will
occur in the next commit...

Astute readers may notice that the command name is transmitted in
both the HTTP request URL and the command request frame. This is
partially a kludge from me initially implementing the frame-based
protocol for SSH first. But it is also a feature: I intend to
eventually support issuing multiple commands per HTTP request. This
will allow us to replace the abomination that is the "batch" wire
protocol command with a protocol-level mechanism for performing
multi-dispatch. Because I want the frame-based protocol to be
as similar as possible across transports, I'd rather we (redundantly)
include the command name in the frame than differ behavior between
transports that have out-of-band routing information (like HTTP)
readily available.

Differential Revision: https://phab.mercurial-scm.org/D2851

# branchmap.py - logic to computes, maintain and stores branchmap for local repo
#
# 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 struct

from .node import (
    bin,
    hex,
    nullid,
    nullrev,
)
from . import (
    encoding,
    error,
    pycompat,
    scmutil,
    util,
)

calcsize = struct.calcsize
pack_into = struct.pack_into
unpack_from = struct.unpack_from

def _filename(repo):
    """name of a branchcache file for a given repo or repoview"""
    filename = "branch2"
    if repo.filtername:
        filename = '%s-%s' % (filename, repo.filtername)
    return filename

def read(repo):
    try:
        f = repo.cachevfs(_filename(repo))
        lines = f.read().split('\n')
        f.close()
    except (IOError, OSError):
        return None

    try:
        cachekey = lines.pop(0).split(" ", 2)
        last, lrev = cachekey[:2]
        last, lrev = bin(last), int(lrev)
        filteredhash = None
        if len(cachekey) > 2:
            filteredhash = bin(cachekey[2])
        partial = branchcache(tipnode=last, tiprev=lrev,
                              filteredhash=filteredhash)
        if not partial.validfor(repo):
            # invalidate the cache
            raise ValueError(r'tip differs')
        cl = repo.changelog
        for l in lines:
            if not l:
                continue
            node, state, label = l.split(" ", 2)
            if state not in 'oc':
                raise ValueError(r'invalid branch state')
            label = encoding.tolocal(label.strip())
            node = bin(node)
            if not cl.hasnode(node):
                raise ValueError(
                    r'node %s does not exist' % pycompat.sysstr(hex(node)))
            partial.setdefault(label, []).append(node)
            if state == 'c':
                partial._closednodes.add(node)
    except Exception as inst:
        if repo.ui.debugflag:
            msg = 'invalid branchheads cache'
            if repo.filtername is not None:
                msg += ' (%s)' % repo.filtername
            msg += ': %s\n'
            repo.ui.debug(msg % pycompat.bytestr(inst))
        partial = None
    return partial

### Nearest subset relation
# Nearest subset of filter X is a filter Y so that:
# * Y is included in X,
# * X - Y is as small as possible.
# This create and ordering used for branchmap purpose.
# the ordering may be partial
subsettable = {None: 'visible',
               'visible-hidden': 'visible',
               'visible': 'served',
               'served': 'immutable',
               'immutable': 'base'}

def updatecache(repo):
    cl = repo.changelog
    filtername = repo.filtername
    partial = repo._branchcaches.get(filtername)

    revs = []
    if partial is None or not partial.validfor(repo):
        partial = read(repo)
        if partial is None:
            subsetname = subsettable.get(filtername)
            if subsetname is None:
                partial = branchcache()
            else:
                subset = repo.filtered(subsetname)
                partial = subset.branchmap().copy()
                extrarevs = subset.changelog.filteredrevs - cl.filteredrevs
                revs.extend(r for  r in extrarevs if r <= partial.tiprev)
    revs.extend(cl.revs(start=partial.tiprev + 1))
    if revs:
        partial.update(repo, revs)
        partial.write(repo)

    assert partial.validfor(repo), filtername
    repo._branchcaches[repo.filtername] = partial

def replacecache(repo, bm):
    """Replace the branchmap cache for a repo with a branch mapping.

    This is likely only called during clone with a branch map from a remote.
    """
    rbheads = []
    closed = []
    for bheads in bm.itervalues():
        rbheads.extend(bheads)
        for h in bheads:
            r = repo.changelog.rev(h)
            b, c = repo.changelog.branchinfo(r)
            if c:
                closed.append(h)

    if rbheads:
        rtiprev = max((int(repo.changelog.rev(node))
                for node in rbheads))
        cache = branchcache(bm,
                            repo[rtiprev].node(),
                            rtiprev,
                            closednodes=closed)

        # Try to stick it as low as possible
        # filter above served are unlikely to be fetch from a clone
        for candidate in ('base', 'immutable', 'served'):
            rview = repo.filtered(candidate)
            if cache.validfor(rview):
                repo._branchcaches[candidate] = cache
                cache.write(rview)
                break

class branchcache(dict):
    """A dict like object that hold branches heads cache.

    This cache is used to avoid costly computations to determine all the
    branch heads of a repo.

    The cache is serialized on disk in the following format:

    <tip hex node> <tip rev number> [optional filtered repo hex hash]
    <branch head hex node> <open/closed state> <branch name>
    <branch head hex node> <open/closed state> <branch name>
    ...

    The first line is used to check if the cache is still valid. If the
    branch cache is for a filtered repo view, an optional third hash is
    included that hashes the hashes of all filtered revisions.

    The open/closed state is represented by a single letter 'o' or 'c'.
    This field can be used to avoid changelog reads when determining if a
    branch head closes a branch or not.
    """

    def __init__(self, entries=(), tipnode=nullid, tiprev=nullrev,
                 filteredhash=None, closednodes=None):
        super(branchcache, self).__init__(entries)
        self.tipnode = tipnode
        self.tiprev = tiprev
        self.filteredhash = filteredhash
        # closednodes is a set of nodes that close their branch. If the branch
        # cache has been updated, it may contain nodes that are no longer
        # heads.
        if closednodes is None:
            self._closednodes = set()
        else:
            self._closednodes = closednodes

    def validfor(self, repo):
        """Is the cache content valid regarding a repo

        - False when cached tipnode is unknown or if we detect a strip.
        - True when cache is up to date or a subset of current repo."""
        try:
            return ((self.tipnode == repo.changelog.node(self.tiprev))
                    and (self.filteredhash == \
                         scmutil.filteredhash(repo, self.tiprev)))
        except IndexError:
            return False

    def _branchtip(self, heads):
        '''Return tuple with last open head in heads and false,
        otherwise return last closed head and true.'''
        tip = heads[-1]
        closed = True
        for h in reversed(heads):
            if h not in self._closednodes:
                tip = h
                closed = False
                break
        return tip, closed

    def branchtip(self, branch):
        '''Return the tipmost open head on branch head, otherwise return the
        tipmost closed head on branch.
        Raise KeyError for unknown branch.'''
        return self._branchtip(self[branch])[0]

    def iteropen(self, nodes):
        return (n for n in nodes if n not in self._closednodes)

    def branchheads(self, branch, closed=False):
        heads = self[branch]
        if not closed:
            heads = list(self.iteropen(heads))
        return heads

    def iterbranches(self):
        for bn, heads in self.iteritems():
            yield (bn, heads) + self._branchtip(heads)

    def copy(self):
        """return an deep copy of the branchcache object"""
        return branchcache(self, self.tipnode, self.tiprev, self.filteredhash,
                           self._closednodes)

    def write(self, repo):
        try:
            f = repo.cachevfs(_filename(repo), "w", atomictemp=True)
            cachekey = [hex(self.tipnode), '%d' % self.tiprev]
            if self.filteredhash is not None:
                cachekey.append(hex(self.filteredhash))
            f.write(" ".join(cachekey) + '\n')
            nodecount = 0
            for label, nodes in sorted(self.iteritems()):
                for node in nodes:
                    nodecount += 1
                    if node in self._closednodes:
                        state = 'c'
                    else:
                        state = 'o'
                    f.write("%s %s %s\n" % (hex(node), state,
                                            encoding.fromlocal(label)))
            f.close()
            repo.ui.log('branchcache',
                        'wrote %s branch cache with %d labels and %d nodes\n',
                        repo.filtername, len(self), nodecount)
        except (IOError, OSError, error.Abort) as inst:
            # Abort may be raised by read only opener, so log and continue
            repo.ui.debug("couldn't write branch cache: %s\n" %
                          util.forcebytestr(inst))

    def update(self, repo, revgen):
        """Given a branchhead cache, self, that may have extra nodes or be
        missing heads, and a generator of nodes that are strictly a superset of
        heads missing, this function updates self to be correct.
        """
        starttime = util.timer()
        cl = repo.changelog
        # collect new branch entries
        newbranches = {}
        getbranchinfo = repo.revbranchcache().branchinfo
        for r in revgen:
            branch, closesbranch = getbranchinfo(r)
            newbranches.setdefault(branch, []).append(r)
            if closesbranch:
                self._closednodes.add(cl.node(r))

        # fetch current topological heads to speed up filtering
        topoheads = set(cl.headrevs())

        # if older branchheads are reachable from new ones, they aren't
        # really branchheads. Note checking parents is insufficient:
        # 1 (branch a) -> 2 (branch b) -> 3 (branch a)
        for branch, newheadrevs in newbranches.iteritems():
            bheads = self.setdefault(branch, [])
            bheadset = set(cl.rev(node) for node in bheads)

            # This have been tested True on all internal usage of this function.
            # run it again in case of doubt
            # assert not (set(bheadrevs) & set(newheadrevs))
            newheadrevs.sort()
            bheadset.update(newheadrevs)

            # This prunes out two kinds of heads - heads that are superseded by
            # a head in newheadrevs, and newheadrevs that are not heads because
            # an existing head is their descendant.
            uncertain = bheadset - topoheads
            if uncertain:
                floorrev = min(uncertain)
                ancestors = set(cl.ancestors(newheadrevs, floorrev))
                bheadset -= ancestors
            bheadrevs = sorted(bheadset)
            self[branch] = [cl.node(rev) for rev in bheadrevs]
            tiprev = bheadrevs[-1]
            if tiprev > self.tiprev:
                self.tipnode = cl.node(tiprev)
                self.tiprev = tiprev

        if not self.validfor(repo):
            # cache key are not valid anymore
            self.tipnode = nullid
            self.tiprev = nullrev
            for heads in self.values():
                tiprev = max(cl.rev(node) for node in heads)
                if tiprev > self.tiprev:
                    self.tipnode = cl.node(tiprev)
                    self.tiprev = tiprev
        self.filteredhash = scmutil.filteredhash(repo, self.tiprev)

        duration = util.timer() - starttime
        repo.ui.log('branchcache', 'updated %s branch cache in %.4f seconds\n',
                    repo.filtername, duration)

# Revision branch info cache

_rbcversion = '-v1'
_rbcnames = 'rbc-names' + _rbcversion
_rbcrevs = 'rbc-revs' + _rbcversion
# [4 byte hash prefix][4 byte branch name number with sign bit indicating open]
_rbcrecfmt = '>4sI'
_rbcrecsize = calcsize(_rbcrecfmt)
_rbcnodelen = 4
_rbcbranchidxmask = 0x7fffffff
_rbccloseflag = 0x80000000

class revbranchcache(object):
    """Persistent cache, mapping from revision number to branch name and close.
    This is a low level cache, independent of filtering.

    Branch names are stored in rbc-names in internal encoding separated by 0.
    rbc-names is append-only, and each branch name is only stored once and will
    thus have a unique index.

    The branch info for each revision is stored in rbc-revs as constant size
    records. The whole file is read into memory, but it is only 'parsed' on
    demand. The file is usually append-only but will be truncated if repo
    modification is detected.
    The record for each revision contains the first 4 bytes of the
    corresponding node hash, and the record is only used if it still matches.
    Even a completely trashed rbc-revs fill thus still give the right result
    while converging towards full recovery ... assuming no incorrectly matching
    node hashes.
    The record also contains 4 bytes where 31 bits contains the index of the
    branch and the last bit indicate that it is a branch close commit.
    The usage pattern for rbc-revs is thus somewhat similar to 00changelog.i
    and will grow with it but be 1/8th of its size.
    """

    def __init__(self, repo, readonly=True):
        assert repo.filtername is None
        self._repo = repo
        self._names = [] # branch names in local encoding with static index
        self._rbcrevs = bytearray()
        self._rbcsnameslen = 0 # length of names read at _rbcsnameslen
        try:
            bndata = repo.cachevfs.read(_rbcnames)
            self._rbcsnameslen = len(bndata) # for verification before writing
            if bndata:
                self._names = [encoding.tolocal(bn)
                               for bn in bndata.split('\0')]
        except (IOError, OSError):
            if readonly:
                # don't try to use cache - fall back to the slow path
                self.branchinfo = self._branchinfo

        if self._names:
            try:
                data = repo.cachevfs.read(_rbcrevs)
                self._rbcrevs[:] = data
            except (IOError, OSError) as inst:
                repo.ui.debug("couldn't read revision branch cache: %s\n" %
                              util.forcebytestr(inst))
        # remember number of good records on disk
        self._rbcrevslen = min(len(self._rbcrevs) // _rbcrecsize,
                               len(repo.changelog))
        if self._rbcrevslen == 0:
            self._names = []
        self._rbcnamescount = len(self._names) # number of names read at
                                               # _rbcsnameslen
        self._namesreverse = dict((b, r) for r, b in enumerate(self._names))

    def _clear(self):
        self._rbcsnameslen = 0
        del self._names[:]
        self._rbcnamescount = 0
        self._namesreverse.clear()
        self._rbcrevslen = len(self._repo.changelog)
        self._rbcrevs = bytearray(self._rbcrevslen * _rbcrecsize)

    def branchinfo(self, rev):
        """Return branch name and close flag for rev, using and updating
        persistent cache."""
        changelog = self._repo.changelog
        rbcrevidx = rev * _rbcrecsize

        # avoid negative index, changelog.read(nullrev) is fast without cache
        if rev == nullrev:
            return changelog.branchinfo(rev)

        # if requested rev isn't allocated, grow and cache the rev info
        if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
            return self._branchinfo(rev)

        # fast path: extract data from cache, use it if node is matching
        reponode = changelog.node(rev)[:_rbcnodelen]
        cachenode, branchidx = unpack_from(
            _rbcrecfmt, util.buffer(self._rbcrevs), rbcrevidx)
        close = bool(branchidx & _rbccloseflag)
        if close:
            branchidx &= _rbcbranchidxmask
        if cachenode == '\0\0\0\0':
            pass
        elif cachenode == reponode:
            try:
                return self._names[branchidx], close
            except IndexError:
                # recover from invalid reference to unknown branch
                self._repo.ui.debug("referenced branch names not found"
                    " - rebuilding revision branch cache from scratch\n")
                self._clear()
        else:
            # rev/node map has changed, invalidate the cache from here up
            self._repo.ui.debug("history modification detected - truncating "
                "revision branch cache to revision %d\n" % rev)
            truncate = rbcrevidx + _rbcrecsize
            del self._rbcrevs[truncate:]
            self._rbcrevslen = min(self._rbcrevslen, truncate)

        # fall back to slow path and make sure it will be written to disk
        return self._branchinfo(rev)

    def _branchinfo(self, rev):
        """Retrieve branch info from changelog and update _rbcrevs"""
        changelog = self._repo.changelog
        b, close = changelog.branchinfo(rev)
        if b in self._namesreverse:
            branchidx = self._namesreverse[b]
        else:
            branchidx = len(self._names)
            self._names.append(b)
            self._namesreverse[b] = branchidx
        reponode = changelog.node(rev)
        if close:
            branchidx |= _rbccloseflag
        self._setcachedata(rev, reponode, branchidx)
        return b, close

    def setdata(self, branch, rev, node, close):
        """add new data information to the cache"""
        if branch in self._namesreverse:
            branchidx = self._namesreverse[branch]
        else:
            branchidx = len(self._names)
            self._names.append(branch)
            self._namesreverse[branch] = branchidx
        if close:
            branchidx |= _rbccloseflag
        self._setcachedata(rev, node, branchidx)
        # If no cache data were readable (non exists, bad permission, etc)
        # the cache was bypassing itself by setting:
        #
        #   self.branchinfo = self._branchinfo
        #
        # Since we now have data in the cache, we need to drop this bypassing.
        if 'branchinfo' in vars(self):
            del self.branchinfo

    def _setcachedata(self, rev, node, branchidx):
        """Writes the node's branch data to the in-memory cache data."""
        if rev == nullrev:
            return
        rbcrevidx = rev * _rbcrecsize
        if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
            self._rbcrevs.extend('\0' *
                                 (len(self._repo.changelog) * _rbcrecsize -
                                  len(self._rbcrevs)))
        pack_into(_rbcrecfmt, self._rbcrevs, rbcrevidx, node, branchidx)
        self._rbcrevslen = min(self._rbcrevslen, rev)

        tr = self._repo.currenttransaction()
        if tr:
            tr.addfinalize('write-revbranchcache', self.write)

    def write(self, tr=None):
        """Save branch cache if it is dirty."""
        repo = self._repo
        wlock = None
        step = ''
        try:
            if self._rbcnamescount < len(self._names):
                step = ' names'
                wlock = repo.wlock(wait=False)
                if self._rbcnamescount != 0:
                    f = repo.cachevfs.open(_rbcnames, 'ab')
                    if f.tell() == self._rbcsnameslen:
                        f.write('\0')
                    else:
                        f.close()
                        repo.ui.debug("%s changed - rewriting it\n" % _rbcnames)
                        self._rbcnamescount = 0
                        self._rbcrevslen = 0
                if self._rbcnamescount == 0:
                    # before rewriting names, make sure references are removed
                    repo.cachevfs.unlinkpath(_rbcrevs, ignoremissing=True)
                    f = repo.cachevfs.open(_rbcnames, 'wb')
                f.write('\0'.join(encoding.fromlocal(b)
                                  for b in self._names[self._rbcnamescount:]))
                self._rbcsnameslen = f.tell()
                f.close()
                self._rbcnamescount = len(self._names)

            start = self._rbcrevslen * _rbcrecsize
            if start != len(self._rbcrevs):
                step = ''
                if wlock is None:
                    wlock = repo.wlock(wait=False)
                revs = min(len(repo.changelog),
                           len(self._rbcrevs) // _rbcrecsize)
                f = repo.cachevfs.open(_rbcrevs, 'ab')
                if f.tell() != start:
                    repo.ui.debug("truncating cache/%s to %d\n"
                                  % (_rbcrevs, start))
                    f.seek(start)
                    if f.tell() != start:
                        start = 0
                        f.seek(start)
                    f.truncate()
                end = revs * _rbcrecsize
                f.write(self._rbcrevs[start:end])
                f.close()
                self._rbcrevslen = revs
        except (IOError, OSError, error.Abort, error.LockError) as inst:
            repo.ui.debug("couldn't write revision branch cache%s: %s\n"
                          % (step, util.forcebytestr(inst)))
        finally:
            if wlock is not None:
                wlock.release()