mercurial/commandserver.py

git: skeleton of a new extension to _directly_ operate on git repos

This is based in part of work I did years ago in hgit, but it's mostly
new code since I'm using pygit2 instead of dulwich and the hg storage
interfaces have improved. Some cleanup of old hgit code by Pulkit,
which I greatly appreciate.

test-git-interop.t does not cover a whole lot of cases, but it
passes. It includes status, diff, making a new commit, and `hg annotate`
working on the git repository.

This is _not_ (yet) production quality code: this is an
experiment. Known technical debt lurking in this implementation:

 * Writing bookmarks just totally ignores transactions.
 * The way progress is threaded down into the gitstore is awful.
 * Ideally we'd find a way to incrementally reindex DAGs. I'm not sure
   how to do that efficiently, so we might need a "known only fast-forwards"
   mode on the DAG indexer for use on `hg commit` and friends.
 * We don't even _try_ to do anything reasonable for `hg pull` or `hg push`.
 * Mercurial need an interface for the changelog type.

Tests currently require git 2.24 as far as I'm aware: `git status` has
some changed output that I didn't try and handle in a compatible way.

This patch has produced some interesting cleanups, most recently on
the manifest type. I expect continuing down this road will produce
other meritorious cleanups throughout our code.

Differential Revision: https://phab.mercurial-scm.org/D6734

# commandserver.py - communicate with Mercurial's API over a pipe
#
#  Copyright 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 gc
import os
import random
import signal
import socket
import struct
import traceback

try:
    import selectors

    selectors.BaseSelector
except ImportError:
    from .thirdparty import selectors2 as selectors

from .i18n import _
from .pycompat import getattr
from . import (
    encoding,
    error,
    loggingutil,
    pycompat,
    repocache,
    util,
    vfs as vfsmod,
)
from .utils import (
    cborutil,
    procutil,
)


class channeledoutput(object):
    """
    Write data to out in the following format:

    data length (unsigned int),
    data
    """

    def __init__(self, out, channel):
        self.out = out
        self.channel = channel

    @property
    def name(self):
        return b'<%c-channel>' % self.channel

    def write(self, data):
        if not data:
            return
        # single write() to guarantee the same atomicity as the underlying file
        self.out.write(struct.pack(b'>cI', self.channel, len(data)) + data)
        self.out.flush()

    def __getattr__(self, attr):
        if attr in ('isatty', 'fileno', 'tell', 'seek'):
            raise AttributeError(attr)
        return getattr(self.out, attr)


class channeledmessage(object):
    """
    Write encoded message and metadata to out in the following format:

    data length (unsigned int),
    encoded message and metadata, as a flat key-value dict.

    Each message should have 'type' attribute. Messages of unknown type
    should be ignored.
    """

    # teach ui that write() can take **opts
    structured = True

    def __init__(self, out, channel, encodename, encodefn):
        self._cout = channeledoutput(out, channel)
        self.encoding = encodename
        self._encodefn = encodefn

    def write(self, data, **opts):
        opts = pycompat.byteskwargs(opts)
        if data is not None:
            opts[b'data'] = data
        self._cout.write(self._encodefn(opts))

    def __getattr__(self, attr):
        return getattr(self._cout, attr)


class channeledinput(object):
    """
    Read data from in_.

    Requests for input are written to out in the following format:
    channel identifier - 'I' for plain input, 'L' line based (1 byte)
    how many bytes to send at most (unsigned int),

    The client replies with:
    data length (unsigned int), 0 meaning EOF
    data
    """

    maxchunksize = 4 * 1024

    def __init__(self, in_, out, channel):
        self.in_ = in_
        self.out = out
        self.channel = channel

    @property
    def name(self):
        return b'<%c-channel>' % self.channel

    def read(self, size=-1):
        if size < 0:
            # if we need to consume all the clients input, ask for 4k chunks
            # so the pipe doesn't fill up risking a deadlock
            size = self.maxchunksize
            s = self._read(size, self.channel)
            buf = s
            while s:
                s = self._read(size, self.channel)
                buf += s

            return buf
        else:
            return self._read(size, self.channel)

    def _read(self, size, channel):
        if not size:
            return b''
        assert size > 0

        # tell the client we need at most size bytes
        self.out.write(struct.pack(b'>cI', channel, size))
        self.out.flush()

        length = self.in_.read(4)
        length = struct.unpack(b'>I', length)[0]
        if not length:
            return b''
        else:
            return self.in_.read(length)

    def readline(self, size=-1):
        if size < 0:
            size = self.maxchunksize
            s = self._read(size, b'L')
            buf = s
            # keep asking for more until there's either no more or
            # we got a full line
            while s and not s.endswith(b'\n'):
                s = self._read(size, b'L')
                buf += s

            return buf
        else:
            return self._read(size, b'L')

    def __iter__(self):
        return self

    def next(self):
        l = self.readline()
        if not l:
            raise StopIteration
        return l

    __next__ = next

    def __getattr__(self, attr):
        if attr in ('isatty', 'fileno', 'tell', 'seek'):
            raise AttributeError(attr)
        return getattr(self.in_, attr)


_messageencoders = {
    b'cbor': lambda v: b''.join(cborutil.streamencode(v)),
}


def _selectmessageencoder(ui):
    # experimental config: cmdserver.message-encodings
    encnames = ui.configlist(b'cmdserver', b'message-encodings')
    for n in encnames:
        f = _messageencoders.get(n)
        if f:
            return n, f
    raise error.Abort(
        b'no supported message encodings: %s' % b' '.join(encnames)
    )


class server(object):
    """
    Listens for commands on fin, runs them and writes the output on a channel
    based stream to fout.
    """

    def __init__(self, ui, repo, fin, fout, prereposetups=None):
        self.cwd = encoding.getcwd()

        if repo:
            # the ui here is really the repo ui so take its baseui so we don't
            # end up with its local configuration
            self.ui = repo.baseui
            self.repo = repo
            self.repoui = repo.ui
        else:
            self.ui = ui
            self.repo = self.repoui = None
        self._prereposetups = prereposetups

        self.cdebug = channeledoutput(fout, b'd')
        self.cerr = channeledoutput(fout, b'e')
        self.cout = channeledoutput(fout, b'o')
        self.cin = channeledinput(fin, fout, b'I')
        self.cresult = channeledoutput(fout, b'r')

        if self.ui.config(b'cmdserver', b'log') == b'-':
            # switch log stream of server's ui to the 'd' (debug) channel
            # (don't touch repo.ui as its lifetime is longer than the server)
            self.ui = self.ui.copy()
            setuplogging(self.ui, repo=None, fp=self.cdebug)

        # TODO: add this to help/config.txt when stabilized
        # ``channel``
        #   Use separate channel for structured output. (Command-server only)
        self.cmsg = None
        if ui.config(b'ui', b'message-output') == b'channel':
            encname, encfn = _selectmessageencoder(ui)
            self.cmsg = channeledmessage(fout, b'm', encname, encfn)

        self.client = fin

    def cleanup(self):
        """release and restore resources taken during server session"""

    def _read(self, size):
        if not size:
            return b''

        data = self.client.read(size)

        # is the other end closed?
        if not data:
            raise EOFError

        return data

    def _readstr(self):
        """read a string from the channel

        format:
        data length (uint32), data
        """
        length = struct.unpack(b'>I', self._read(4))[0]
        if not length:
            return b''
        return self._read(length)

    def _readlist(self):
        """read a list of NULL separated strings from the channel"""
        s = self._readstr()
        if s:
            return s.split(b'\0')
        else:
            return []

    def runcommand(self):
        """ reads a list of \0 terminated arguments, executes
        and writes the return code to the result channel """
        from . import dispatch  # avoid cycle

        args = self._readlist()

        # copy the uis so changes (e.g. --config or --verbose) don't
        # persist between requests
        copiedui = self.ui.copy()
        uis = [copiedui]
        if self.repo:
            self.repo.baseui = copiedui
            # clone ui without using ui.copy because this is protected
            repoui = self.repoui.__class__(self.repoui)
            repoui.copy = copiedui.copy  # redo copy protection
            uis.append(repoui)
            self.repo.ui = self.repo.dirstate._ui = repoui
            self.repo.invalidateall()

        for ui in uis:
            ui.resetstate()
            # any kind of interaction must use server channels, but chg may
            # replace channels by fully functional tty files. so nontty is
            # enforced only if cin is a channel.
            if not util.safehasattr(self.cin, b'fileno'):
                ui.setconfig(b'ui', b'nontty', b'true', b'commandserver')

        req = dispatch.request(
            args[:],
            copiedui,
            self.repo,
            self.cin,
            self.cout,
            self.cerr,
            self.cmsg,
            prereposetups=self._prereposetups,
        )

        try:
            ret = dispatch.dispatch(req) & 255
            self.cresult.write(struct.pack(b'>i', int(ret)))
        finally:
            # restore old cwd
            if b'--cwd' in args:
                os.chdir(self.cwd)

    def getencoding(self):
        """ writes the current encoding to the result channel """
        self.cresult.write(encoding.encoding)

    def serveone(self):
        cmd = self.client.readline()[:-1]
        if cmd:
            handler = self.capabilities.get(cmd)
            if handler:
                handler(self)
            else:
                # clients are expected to check what commands are supported by
                # looking at the servers capabilities
                raise error.Abort(_(b'unknown command %s') % cmd)

        return cmd != b''

    capabilities = {b'runcommand': runcommand, b'getencoding': getencoding}

    def serve(self):
        hellomsg = b'capabilities: ' + b' '.join(sorted(self.capabilities))
        hellomsg += b'\n'
        hellomsg += b'encoding: ' + encoding.encoding
        hellomsg += b'\n'
        if self.cmsg:
            hellomsg += b'message-encoding: %s\n' % self.cmsg.encoding
        hellomsg += b'pid: %d' % procutil.getpid()
        if util.safehasattr(os, b'getpgid'):
            hellomsg += b'\n'
            hellomsg += b'pgid: %d' % os.getpgid(0)

        # write the hello msg in -one- chunk
        self.cout.write(hellomsg)

        try:
            while self.serveone():
                pass
        except EOFError:
            # we'll get here if the client disconnected while we were reading
            # its request
            return 1

        return 0


def setuplogging(ui, repo=None, fp=None):
    """Set up server logging facility

    If cmdserver.log is '-', log messages will be sent to the given fp.
    It should be the 'd' channel while a client is connected, and otherwise
    is the stderr of the server process.
    """
    # developer config: cmdserver.log
    logpath = ui.config(b'cmdserver', b'log')
    if not logpath:
        return
    # developer config: cmdserver.track-log
    tracked = set(ui.configlist(b'cmdserver', b'track-log'))

    if logpath == b'-' and fp:
        logger = loggingutil.fileobjectlogger(fp, tracked)
    elif logpath == b'-':
        logger = loggingutil.fileobjectlogger(ui.ferr, tracked)
    else:
        logpath = os.path.abspath(util.expandpath(logpath))
        # developer config: cmdserver.max-log-files
        maxfiles = ui.configint(b'cmdserver', b'max-log-files')
        # developer config: cmdserver.max-log-size
        maxsize = ui.configbytes(b'cmdserver', b'max-log-size')
        vfs = vfsmod.vfs(os.path.dirname(logpath))
        logger = loggingutil.filelogger(
            vfs,
            os.path.basename(logpath),
            tracked,
            maxfiles=maxfiles,
            maxsize=maxsize,
        )

    targetuis = {ui}
    if repo:
        targetuis.add(repo.baseui)
        targetuis.add(repo.ui)
    for u in targetuis:
        u.setlogger(b'cmdserver', logger)


class pipeservice(object):
    def __init__(self, ui, repo, opts):
        self.ui = ui
        self.repo = repo

    def init(self):
        pass

    def run(self):
        ui = self.ui
        # redirect stdio to null device so that broken extensions or in-process
        # hooks will never cause corruption of channel protocol.
        with ui.protectedfinout() as (fin, fout):
            sv = server(ui, self.repo, fin, fout)
            try:
                return sv.serve()
            finally:
                sv.cleanup()


def _initworkerprocess():
    # use a different process group from the master process, in order to:
    # 1. make the current process group no longer "orphaned" (because the
    #    parent of this process is in a different process group while
    #    remains in a same session)
    #    according to POSIX 2.2.2.52, orphaned process group will ignore
    #    terminal-generated stop signals like SIGTSTP (Ctrl+Z), which will
    #    cause trouble for things like ncurses.
    # 2. the client can use kill(-pgid, sig) to simulate terminal-generated
    #    SIGINT (Ctrl+C) and process-exit-generated SIGHUP. our child
    #    processes like ssh will be killed properly, without affecting
    #    unrelated processes.
    os.setpgid(0, 0)
    # change random state otherwise forked request handlers would have a
    # same state inherited from parent.
    random.seed()


def _serverequest(ui, repo, conn, createcmdserver, prereposetups):
    fin = conn.makefile('rb')
    fout = conn.makefile('wb')
    sv = None
    try:
        sv = createcmdserver(repo, conn, fin, fout, prereposetups)
        try:
            sv.serve()
        # handle exceptions that may be raised by command server. most of
        # known exceptions are caught by dispatch.
        except error.Abort as inst:
            ui.error(_(b'abort: %s\n') % inst)
        except IOError as inst:
            if inst.errno != errno.EPIPE:
                raise
        except KeyboardInterrupt:
            pass
        finally:
            sv.cleanup()
    except:  # re-raises
        # also write traceback to error channel. otherwise client cannot
        # see it because it is written to server's stderr by default.
        if sv:
            cerr = sv.cerr
        else:
            cerr = channeledoutput(fout, b'e')
        cerr.write(encoding.strtolocal(traceback.format_exc()))
        raise
    finally:
        fin.close()
        try:
            fout.close()  # implicit flush() may cause another EPIPE
        except IOError as inst:
            if inst.errno != errno.EPIPE:
                raise


class unixservicehandler(object):
    """Set of pluggable operations for unix-mode services

    Almost all methods except for createcmdserver() are called in the main
    process. You can't pass mutable resource back from createcmdserver().
    """

    pollinterval = None

    def __init__(self, ui):
        self.ui = ui

    def bindsocket(self, sock, address):
        util.bindunixsocket(sock, address)
        sock.listen(socket.SOMAXCONN)
        self.ui.status(_(b'listening at %s\n') % address)
        self.ui.flush()  # avoid buffering of status message

    def unlinksocket(self, address):
        os.unlink(address)

    def shouldexit(self):
        """True if server should shut down; checked per pollinterval"""
        return False

    def newconnection(self):
        """Called when main process notices new connection"""

    def createcmdserver(self, repo, conn, fin, fout, prereposetups):
        """Create new command server instance; called in the process that
        serves for the current connection"""
        return server(self.ui, repo, fin, fout, prereposetups)


class unixforkingservice(object):
    """
    Listens on unix domain socket and forks server per connection
    """

    def __init__(self, ui, repo, opts, handler=None):
        self.ui = ui
        self.repo = repo
        self.address = opts[b'address']
        if not util.safehasattr(socket, b'AF_UNIX'):
            raise error.Abort(_(b'unsupported platform'))
        if not self.address:
            raise error.Abort(_(b'no socket path specified with --address'))
        self._servicehandler = handler or unixservicehandler(ui)
        self._sock = None
        self._mainipc = None
        self._workeripc = None
        self._oldsigchldhandler = None
        self._workerpids = set()  # updated by signal handler; do not iterate
        self._socketunlinked = None
        # experimental config: cmdserver.max-repo-cache
        maxlen = ui.configint(b'cmdserver', b'max-repo-cache')
        if maxlen < 0:
            raise error.Abort(_(b'negative max-repo-cache size not allowed'))
        self._repoloader = repocache.repoloader(ui, maxlen)
        # attempt to avoid crash in CoreFoundation when using chg after fix in
        # a89381e04c58
        if pycompat.isdarwin:
            procutil.gui()

    def init(self):
        self._sock = socket.socket(socket.AF_UNIX)
        # IPC channel from many workers to one main process; this is actually
        # a uni-directional pipe, but is backed by a DGRAM socket so each
        # message can be easily separated.
        o = socket.socketpair(socket.AF_UNIX, socket.SOCK_DGRAM)
        self._mainipc, self._workeripc = o
        self._servicehandler.bindsocket(self._sock, self.address)
        if util.safehasattr(procutil, b'unblocksignal'):
            procutil.unblocksignal(signal.SIGCHLD)
        o = signal.signal(signal.SIGCHLD, self._sigchldhandler)
        self._oldsigchldhandler = o
        self._socketunlinked = False
        self._repoloader.start()

    def _unlinksocket(self):
        if not self._socketunlinked:
            self._servicehandler.unlinksocket(self.address)
            self._socketunlinked = True

    def _cleanup(self):
        signal.signal(signal.SIGCHLD, self._oldsigchldhandler)
        self._sock.close()
        self._mainipc.close()
        self._workeripc.close()
        self._unlinksocket()
        self._repoloader.stop()
        # don't kill child processes as they have active clients, just wait
        self._reapworkers(0)

    def run(self):
        try:
            self._mainloop()
        finally:
            self._cleanup()

    def _mainloop(self):
        exiting = False
        h = self._servicehandler
        selector = selectors.DefaultSelector()
        selector.register(
            self._sock, selectors.EVENT_READ, self._acceptnewconnection
        )
        selector.register(
            self._mainipc, selectors.EVENT_READ, self._handlemainipc
        )
        while True:
            if not exiting and h.shouldexit():
                # clients can no longer connect() to the domain socket, so
                # we stop queuing new requests.
                # for requests that are queued (connect()-ed, but haven't been
                # accept()-ed), handle them before exit. otherwise, clients
                # waiting for recv() will receive ECONNRESET.
                self._unlinksocket()
                exiting = True
            try:
                events = selector.select(timeout=h.pollinterval)
            except OSError as inst:
                # selectors2 raises ETIMEDOUT if timeout exceeded while
                # handling signal interrupt. That's probably wrong, but
                # we can easily get around it.
                if inst.errno != errno.ETIMEDOUT:
                    raise
                events = []
            if not events:
                # only exit if we completed all queued requests
                if exiting:
                    break
                continue
            for key, _mask in events:
                key.data(key.fileobj, selector)
        selector.close()

    def _acceptnewconnection(self, sock, selector):
        h = self._servicehandler
        try:
            conn, _addr = sock.accept()
        except socket.error as inst:
            if inst.args[0] == errno.EINTR:
                return
            raise

        # Future improvement: On Python 3.7, maybe gc.freeze() can be used
        # to prevent COW memory from being touched by GC.
        # https://instagram-engineering.com/
        #   copy-on-write-friendly-python-garbage-collection-ad6ed5233ddf
        pid = os.fork()
        if pid:
            try:
                self.ui.log(
                    b'cmdserver', b'forked worker process (pid=%d)\n', pid
                )
                self._workerpids.add(pid)
                h.newconnection()
            finally:
                conn.close()  # release handle in parent process
        else:
            try:
                selector.close()
                sock.close()
                self._mainipc.close()
                self._runworker(conn)
                conn.close()
                self._workeripc.close()
                os._exit(0)
            except:  # never return, hence no re-raises
                try:
                    self.ui.traceback(force=True)
                finally:
                    os._exit(255)

    def _handlemainipc(self, sock, selector):
        """Process messages sent from a worker"""
        try:
            path = sock.recv(32768)  # large enough to receive path
        except socket.error as inst:
            if inst.args[0] == errno.EINTR:
                return
            raise
        self._repoloader.load(path)

    def _sigchldhandler(self, signal, frame):
        self._reapworkers(os.WNOHANG)

    def _reapworkers(self, options):
        while self._workerpids:
            try:
                pid, _status = os.waitpid(-1, options)
            except OSError as inst:
                if inst.errno == errno.EINTR:
                    continue
                if inst.errno != errno.ECHILD:
                    raise
                # no child processes at all (reaped by other waitpid()?)
                self._workerpids.clear()
                return
            if pid == 0:
                # no waitable child processes
                return
            self.ui.log(b'cmdserver', b'worker process exited (pid=%d)\n', pid)
            self._workerpids.discard(pid)

    def _runworker(self, conn):
        signal.signal(signal.SIGCHLD, self._oldsigchldhandler)
        _initworkerprocess()
        h = self._servicehandler
        try:
            _serverequest(
                self.ui,
                self.repo,
                conn,
                h.createcmdserver,
                prereposetups=[self._reposetup],
            )
        finally:
            gc.collect()  # trigger __del__ since worker process uses os._exit

    def _reposetup(self, ui, repo):
        if not repo.local():
            return

        class unixcmdserverrepo(repo.__class__):
            def close(self):
                super(unixcmdserverrepo, self).close()
                try:
                    self._cmdserveripc.send(self.root)
                except socket.error:
                    self.ui.log(
                        b'cmdserver', b'failed to send repo root to master\n'
                    )

        repo.__class__ = unixcmdserverrepo
        repo._cmdserveripc = self._workeripc

        cachedrepo = self._repoloader.get(repo.root)
        if cachedrepo is None:
            return
        repo.ui.log(b'repocache', b'repo from cache: %s\n', repo.root)
        repocache.copycache(cachedrepo, repo)