chgserver: implement validate command

validate will load the repo config and check if the server has up-to-date
config to continue serve the client. In case it does not, the server will
send instructions to the client about what to do next, including to retry
with a different address or to unlink an outdated socket file to stop an
old server.

hgext/chgserver.py

@@ -1,634 +1,665
 # chgserver.py - command server extension for cHg
 #
 # Copyright 2011 Yuya Nishihara <[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.
 
 """command server extension for cHg (EXPERIMENTAL)
 
 'S' channel (read/write)
     propagate ui.system() request to client
 
 'attachio' command
     attach client's stdio passed by sendmsg()
 
 'chdir' command
     change current directory
 
 'getpager' command
     checks if pager is enabled and which pager should be executed
 
 'setenv' command
     replace os.environ completely
 
 'setumask' command
     set umask
 
+'validate' command
+    reload the config and check if the server is up to date
+
 'SIGHUP' signal
     reload configuration files
 
 Config
 ------
 
 ::
 
   [chgserver]
   idletimeout = 3600 # seconds, after which an idle server will exit
   skiphash = False   # whether to skip config or env change checks
 """
 
 from __future__ import absolute_import
 
 import SocketServer
 import errno
 import inspect
 import os
 import re
 import signal
 import struct
 import sys
 import threading
 import time
 import traceback
 
 from mercurial.i18n import _
 
 from mercurial import (
     cmdutil,
     commands,
     commandserver,
     dispatch,
     error,
     extensions,
     osutil,
     util,
 )
 
 # Note for extension authors: ONLY specify testedwith = 'internal' for
 # extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
 # be specifying the version(s) of Mercurial they are tested with, or
 # leave the attribute unspecified.
 testedwith = 'internal'
 
 _log = commandserver.log
 
 def _hashlist(items):
     """return sha1 hexdigest for a list"""
     return util.sha1(str(items)).hexdigest()
 
 # sensitive config sections affecting confighash
 _configsections = ['extensions']
 
 # sensitive environment variables affecting confighash
 _envre = re.compile(r'''\A(?:
                     CHGHG
                     |HG.*
                     |LANG(?:UAGE)?
                     |LC_.*
                     |LD_.*
                     |PATH
                     |PYTHON.*
                     |TERM(?:INFO)?
                     |TZ
                     )\Z''', re.X)
 
 def _confighash(ui):
     """return a quick hash for detecting config/env changes
 
     confighash is the hash of sensitive config items and environment variables.
 
     for chgserver, it is designed that once confighash changes, the server is
     not qualified to serve its client and should redirect the client to a new
     server. different from mtimehash, confighash change will not mark the
     server outdated and exit since the user can have different configs at the
     same time.
     """
     sectionitems = []
     for section in _configsections:
         sectionitems.append(ui.configitems(section))
     sectionhash = _hashlist(sectionitems)
     envitems = [(k, v) for k, v in os.environ.iteritems() if _envre.match(k)]
     envhash = _hashlist(sorted(envitems))
     return sectionhash[:6] + envhash[:6]
 
 def _getmtimepaths(ui):
     """get a list of paths that should be checked to detect change
 
     The list will include:
     - extensions (will not cover all files for complex extensions)
     - mercurial/__version__.py
     - python binary
     """
     modules = [m for n, m in extensions.extensions(ui)]
     try:
         from mercurial import __version__
         modules.append(__version__)
     except ImportError:
         pass
     files = [sys.executable]
     for m in modules:
         try:
             files.append(inspect.getabsfile(m))
         except TypeError:
             pass
     return sorted(set(files))
 
 def _mtimehash(paths):
     """return a quick hash for detecting file changes
 
     mtimehash calls stat on given paths and calculate a hash based on size and
     mtime of each file. mtimehash does not read file content because reading is
     expensive. therefore it's not 100% reliable for detecting content changes.
     it's possible to return different hashes for same file contents.
     it's also possible to return a same hash for different file contents for
     some carefully crafted situation.
 
     for chgserver, it is designed that once mtimehash changes, the server is
     considered outdated immediately and should no longer provide service.
     """
     def trystat(path):
         try:
             st = os.stat(path)
             return (st.st_mtime, st.st_size)
         except OSError:
             # could be ENOENT, EPERM etc. not fatal in any case
             pass
     return _hashlist(map(trystat, paths))[:12]
 
 class hashstate(object):
     """a structure storing confighash, mtimehash, paths used for mtimehash"""
     def __init__(self, confighash, mtimehash, mtimepaths):
         self.confighash = confighash
         self.mtimehash = mtimehash
         self.mtimepaths = mtimepaths
 
     @staticmethod
     def fromui(ui, mtimepaths=None):
         if mtimepaths is None:
             mtimepaths = _getmtimepaths(ui)
         confighash = _confighash(ui)
         mtimehash = _mtimehash(mtimepaths)
         _log('confighash = %s mtimehash = %s\n' % (confighash, mtimehash))
         return hashstate(confighash, mtimehash, mtimepaths)
 
 # copied from hgext/pager.py:uisetup()
 def _setuppagercmd(ui, options, cmd):
     if not ui.formatted():
         return
 
     p = ui.config("pager", "pager", os.environ.get("PAGER"))
     usepager = False
     always = util.parsebool(options['pager'])
     auto = options['pager'] == 'auto'
 
     if not p:
         pass
     elif always:
         usepager = True
     elif not auto:
         usepager = False
     else:
         attended = ['annotate', 'cat', 'diff', 'export', 'glog', 'log', 'qdiff']
         attend = ui.configlist('pager', 'attend', attended)
         ignore = ui.configlist('pager', 'ignore')
         cmds, _ = cmdutil.findcmd(cmd, commands.table)
 
         for cmd in cmds:
             var = 'attend-%s' % cmd
             if ui.config('pager', var):
                 usepager = ui.configbool('pager', var)
                 break
             if (cmd in attend or
                 (cmd not in ignore and not attend)):
                 usepager = True
                 break
 
     if usepager:
         ui.setconfig('ui', 'formatted', ui.formatted(), 'pager')
         ui.setconfig('ui', 'interactive', False, 'pager')
         return p
 
 _envvarre = re.compile(r'\$[a-zA-Z_]+')
 
 def _clearenvaliases(cmdtable):
     """Remove stale command aliases referencing env vars; variable expansion
     is done at dispatch.addaliases()"""
     for name, tab in cmdtable.items():
         cmddef = tab[0]
         if (isinstance(cmddef, dispatch.cmdalias) and
             not cmddef.definition.startswith('!') and  # shell alias
             _envvarre.search(cmddef.definition)):
             del cmdtable[name]
 
 def _newchgui(srcui, csystem):
     class chgui(srcui.__class__):
         def __init__(self, src=None):
             super(chgui, self).__init__(src)
             if src:
                 self._csystem = getattr(src, '_csystem', csystem)
             else:
                 self._csystem = csystem
 
         def system(self, cmd, environ=None, cwd=None, onerr=None,
                    errprefix=None):
             # copied from mercurial/util.py:system()
             self.flush()
             def py2shell(val):
                 if val is None or val is False:
                     return '0'
                 if val is True:
                     return '1'
                 return str(val)
             env = os.environ.copy()
             if environ:
                 env.update((k, py2shell(v)) for k, v in environ.iteritems())
             env['HG'] = util.hgexecutable()
             rc = self._csystem(cmd, env, cwd)
             if rc and onerr:
                 errmsg = '%s %s' % (os.path.basename(cmd.split(None, 1)[0]),
                                     util.explainexit(rc)[0])
                 if errprefix:
                     errmsg = '%s: %s' % (errprefix, errmsg)
                 raise onerr(errmsg)
             return rc
 
     return chgui(srcui)
 
 def _renewui(srcui, args=None):
     if not args:
         args = []
 
     newui = srcui.__class__()
     for a in ['fin', 'fout', 'ferr', 'environ']:
         setattr(newui, a, getattr(srcui, a))
     if util.safehasattr(srcui, '_csystem'):
         newui._csystem = srcui._csystem
 
     # load wd and repo config, copied from dispatch.py
     cwds = dispatch._earlygetopt(['--cwd'], args)
     cwd = cwds and os.path.realpath(cwds[-1]) or None
     rpath = dispatch._earlygetopt(["-R", "--repository", "--repo"], args)
     path, newui = dispatch._getlocal(newui, rpath, wd=cwd)
 
     # internal config: extensions.chgserver
     # copy it. it can only be overrided from command line.
     newui.setconfig('extensions', 'chgserver',
                     srcui.config('extensions', 'chgserver'), '--config')
 
     # command line args
     dispatch._parseconfig(newui, dispatch._earlygetopt(['--config'], args))
 
     # stolen from tortoisehg.util.copydynamicconfig()
     for section, name, value in srcui.walkconfig():
         source = srcui.configsource(section, name)
         if ':' in source or source == '--config':
             # path:line or command line
             continue
         if source == 'none':
             # ui.configsource returns 'none' by default
             source = ''
         newui.setconfig(section, name, value, source)
     return newui
 
 class channeledsystem(object):
     """Propagate ui.system() request in the following format:
 
     payload length (unsigned int),
     cmd, '\0',
     cwd, '\0',
     envkey, '=', val, '\0',
     ...
     envkey, '=', val
 
     and waits:
 
     exitcode length (unsigned int),
     exitcode (int)
     """
     def __init__(self, in_, out, channel):
         self.in_ = in_
         self.out = out
         self.channel = channel
 
     def __call__(self, cmd, environ, cwd):
         args = [util.quotecommand(cmd), cwd or '.']
         args.extend('%s=%s' % (k, v) for k, v in environ.iteritems())
         data = '\0'.join(args)
         self.out.write(struct.pack('>cI', self.channel, len(data)))
         self.out.write(data)
         self.out.flush()
 
         length = self.in_.read(4)
         length, = struct.unpack('>I', length)
         if length != 4:
             raise error.Abort(_('invalid response'))
         rc, = struct.unpack('>i', self.in_.read(4))
         return rc
 
 _iochannels = [
     # server.ch, ui.fp, mode
     ('cin', 'fin', 'rb'),
     ('cout', 'fout', 'wb'),
     ('cerr', 'ferr', 'wb'),
 ]
 
 class chgcmdserver(commandserver.server):
     def __init__(self, ui, repo, fin, fout, sock, hashstate, baseaddress):
         super(chgcmdserver, self).__init__(
             _newchgui(ui, channeledsystem(fin, fout, 'S')), repo, fin, fout)
         self.clientsock = sock
         self._oldios = []  # original (self.ch, ui.fp, fd) before "attachio"
         self.hashstate = hashstate
         self.baseaddress = baseaddress
+        if hashstate is not None:
+            self.capabilities = self.capabilities.copy()
+            self.capabilities['validate'] = chgcmdserver.validate
 
     def cleanup(self):
         # dispatch._runcatch() does not flush outputs if exception is not
         # handled by dispatch._dispatch()
         self.ui.flush()
         self._restoreio()
 
     def attachio(self):
         """Attach to client's stdio passed via unix domain socket; all
         channels except cresult will no longer be used
         """
         # tell client to sendmsg() with 1-byte payload, which makes it
         # distinctive from "attachio\n" command consumed by client.read()
         self.clientsock.sendall(struct.pack('>cI', 'I', 1))
         clientfds = osutil.recvfds(self.clientsock.fileno())
         _log('received fds: %r\n' % clientfds)
 
         ui = self.ui
         ui.flush()
         first = self._saveio()
         for fd, (cn, fn, mode) in zip(clientfds, _iochannels):
             assert fd > 0
             fp = getattr(ui, fn)
             os.dup2(fd, fp.fileno())
             os.close(fd)
             if not first:
                 continue
             # reset buffering mode when client is first attached. as we want
             # to see output immediately on pager, the mode stays unchanged
             # when client re-attached. ferr is unchanged because it should
             # be unbuffered no matter if it is a tty or not.
             if fn == 'ferr':
                 newfp = fp
             else:
                 # make it line buffered explicitly because the default is
                 # decided on first write(), where fout could be a pager.
                 if fp.isatty():
                     bufsize = 1  # line buffered
                 else:
                     bufsize = -1  # system default
                 newfp = os.fdopen(fp.fileno(), mode, bufsize)
                 setattr(ui, fn, newfp)
             setattr(self, cn, newfp)
 
         self.cresult.write(struct.pack('>i', len(clientfds)))
 
     def _saveio(self):
         if self._oldios:
             return False
         ui = self.ui
         for cn, fn, _mode in _iochannels:
             ch = getattr(self, cn)
             fp = getattr(ui, fn)
             fd = os.dup(fp.fileno())
             self._oldios.append((ch, fp, fd))
         return True
 
     def _restoreio(self):
         ui = self.ui
         for (ch, fp, fd), (cn, fn, _mode) in zip(self._oldios, _iochannels):
             newfp = getattr(ui, fn)
             # close newfp while it's associated with client; otherwise it
             # would be closed when newfp is deleted
             if newfp is not fp:
                 newfp.close()
             # restore original fd: fp is open again
             os.dup2(fd, fp.fileno())
             os.close(fd)
             setattr(self, cn, ch)
             setattr(ui, fn, fp)
         del self._oldios[:]
 
+    def validate(self):
+        """Reload the config and check if the server is up to date
+
+        Read a list of '\0' separated arguments.
+        Write a non-empty list of '\0' separated instruction strings or '\0'
+        if the list is empty.
+        An instruction string could be either:
+            - "unlink $path", the client should unlink the path to stop the
+              outdated server.
+            - "redirect $path", the client should try to connect to another
+              server instead.
+        """
+        args = self._readlist()
+        self.ui = _renewui(self.ui, args)
+        newhash = hashstate.fromui(self.ui, self.hashstate.mtimepaths)
+        insts = []
+        if newhash.mtimehash != self.hashstate.mtimehash:
+            addr = _hashaddress(self.baseaddress, self.hashstate.confighash)
+            insts.append('unlink %s' % addr)
+        if newhash.confighash != self.hashstate.confighash:
+            addr = _hashaddress(self.baseaddress, newhash.confighash)
+            insts.append('redirect %s' % addr)
+        _log('validate: %s\n' % insts)
+        self.cresult.write('\0'.join(insts) or '\0')
+
     def chdir(self):
         """Change current directory
 
         Note that the behavior of --cwd option is bit different from this.
         It does not affect --config parameter.
         """
         path = self._readstr()
         if not path:
             return
         _log('chdir to %r\n' % path)
         os.chdir(path)
 
     def setumask(self):
         """Change umask"""
         mask = struct.unpack('>I', self._read(4))[0]
         _log('setumask %r\n' % mask)
         os.umask(mask)
 
     def getpager(self):
         """Read cmdargs and write pager command to r-channel if enabled
 
         If pager isn't enabled, this writes '\0' because channeledoutput
         does not allow to write empty data.
         """
         args = self._readlist()
         try:
             cmd, _func, args, options, _cmdoptions = dispatch._parse(self.ui,
                                                                      args)
         except (error.Abort, error.AmbiguousCommand, error.CommandError,
                 error.UnknownCommand):
             cmd = None
             options = {}
         if not cmd or 'pager' not in options:
             self.cresult.write('\0')
             return
 
         pagercmd = _setuppagercmd(self.ui, options, cmd)
         if pagercmd:
             self.cresult.write(pagercmd)
         else:
             self.cresult.write('\0')
 
     def setenv(self):
         """Clear and update os.environ
 
         Note that not all variables can make an effect on the running process.
         """
         l = self._readlist()
         try:
             newenv = dict(s.split('=', 1) for s in l)
         except ValueError:
             raise ValueError('unexpected value in setenv request')
 
         diffkeys = set(k for k in set(os.environ.keys() + newenv.keys())
                        if os.environ.get(k) != newenv.get(k))
         _log('change env: %r\n' % sorted(diffkeys))
 
         os.environ.clear()
         os.environ.update(newenv)
 
         if set(['HGPLAIN', 'HGPLAINEXCEPT']) & diffkeys:
             # reload config so that ui.plain() takes effect
             self.ui = _renewui(self.ui)
 
         _clearenvaliases(commands.table)
 
     capabilities = commandserver.server.capabilities.copy()
     capabilities.update({'attachio': attachio,
                          'chdir': chdir,
                          'getpager': getpager,
                          'setenv': setenv,
                          'setumask': setumask})
 
 # copied from mercurial/commandserver.py
 class _requesthandler(SocketServer.StreamRequestHandler):
     def handle(self):
         # use a different process group from the master process, making this
         # process pass kernel "is_current_pgrp_orphaned" check so signals like
         # SIGTSTP, SIGTTIN, SIGTTOU are not ignored.
         os.setpgid(0, 0)
         ui = self.server.ui
         repo = self.server.repo
         sv = chgcmdserver(ui, repo, self.rfile, self.wfile, self.connection,
                           self.server.hashstate, self.server.baseaddress)
         try:
             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.warn(_('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.
             traceback.print_exc(file=sv.cerr)
             raise
 
 def _tempaddress(address):
     return '%s.%d.tmp' % (address, os.getpid())
 
 def _hashaddress(address, hashstr):
     return '%s-%s' % (address, hashstr)
 
 class AutoExitMixIn:  # use old-style to comply with SocketServer design
     lastactive = time.time()
     idletimeout = 3600  # default 1 hour
 
     def startautoexitthread(self):
         # note: the auto-exit check here is cheap enough to not use a thread,
         # be done in serve_forever. however SocketServer is hook-unfriendly,
         # you simply cannot hook serve_forever without copying a lot of code.
         # besides, serve_forever's docstring suggests using thread.
         thread = threading.Thread(target=self._autoexitloop)
         thread.daemon = True
         thread.start()
 
     def _autoexitloop(self, interval=1):
         while True:
             time.sleep(interval)
             if not self.issocketowner():
                 _log('%s is not owned, exiting.\n' % self.server_address)
                 break
             if time.time() - self.lastactive > self.idletimeout:
                 _log('being idle too long. exiting.\n')
                 break
         self.shutdown()
 
     def process_request(self, request, address):
         self.lastactive = time.time()
         return SocketServer.ForkingMixIn.process_request(
             self, request, address)
 
     def server_bind(self):
         # use a unique temp address so we can stat the file and do ownership
         # check later
         tempaddress = _tempaddress(self.server_address)
         self.socket.bind(tempaddress)
         self._socketstat = os.stat(tempaddress)
         # rename will replace the old socket file if exists atomically. the
         # old server will detect ownership change and exit.
         util.rename(tempaddress, self.server_address)
 
     def issocketowner(self):
         try:
             stat = os.stat(self.server_address)
             return (stat.st_ino == self._socketstat.st_ino and
                     stat.st_mtime == self._socketstat.st_mtime)
         except OSError:
             return False
 
     def unlinksocketfile(self):
         if not self.issocketowner():
             return
         # it is possible to have a race condition here that we may
         # remove another server's socket file. but that's okay
         # since that server will detect and exit automatically and
         # the client will start a new server on demand.
         try:
             os.unlink(self.server_address)
         except OSError as exc:
             if exc.errno != errno.ENOENT:
                 raise
 
 class chgunixservice(commandserver.unixservice):
     def init(self):
         signal.signal(signal.SIGHUP, self._reloadconfig)
         self._inithashstate()
         class cls(AutoExitMixIn, SocketServer.ForkingMixIn,
                   SocketServer.UnixStreamServer):
             ui = self.ui
             repo = self.repo
             hashstate = self.hashstate
             baseaddress = self.baseaddress
         self.server = cls(self.address, _requesthandler)
         self.server.idletimeout = self.ui.configint(
             'chgserver', 'idletimeout', self.server.idletimeout)
         self.server.startautoexitthread()
         self._createsymlink()
         # avoid writing "listening at" message to stdout before attachio
         # request, which calls setvbuf()
 
     def _inithashstate(self):
         self.baseaddress = self.address
         if self.ui.configbool('chgserver', 'skiphash', False):
             self.hashstate = None
             return
         self.hashstate = hashstate.fromui(self.ui)
         self.address = _hashaddress(self.address, self.hashstate.confighash)
 
     def _createsymlink(self):
         if self.baseaddress == self.address:
             return
         tempaddress = _tempaddress(self.baseaddress)
         os.symlink(os.path.basename(self.address), tempaddress)
         util.rename(tempaddress, self.baseaddress)
 
     def _reloadconfig(self, signum, frame):
         self.ui = self.server.ui = _renewui(self.ui)
 
     def run(self):
         try:
             self.server.serve_forever()
         finally:
             self.server.unlinksocketfile()
 
 def uisetup(ui):
     commandserver._servicemap['chgunix'] = chgunixservice
 
     # CHGINTERNALMARK is temporarily set by chg client to detect if chg will
     # start another chg. drop it to avoid possible side effects.
     if 'CHGINTERNALMARK' in os.environ:
         del os.environ['CHGINTERNALMARK']