wireprotoserver: move SSH server operation to a standalone function

The server-side processing logic will soon get a bit more complicated
in order to handle protocol switches. We will use a state machine
to help make the transitions clearer.

To prepare for this, we move SSH server operation into a standalone
function. We structure it as a very simple state machine. It only
has two states for now, with one state containing the bulk of the
logic. But things will evolve shortly.

Differential Revision: https://phab.mercurial-scm.org/D2203

mercurial/wireprotoserver.py

@@ -1,458 +1,478 b''
 # Copyright 21 May 2005 - (c) 2005 Jake Edge <[e-mail]>
 # 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 abc
 import contextlib
 import struct
 import sys
 
 from .i18n import _
 from . import (
     encoding,
     error,
     hook,
     pycompat,
     util,
     wireproto,
     wireprototypes,
 )
 
 stringio = util.stringio
 
 urlerr = util.urlerr
 urlreq = util.urlreq
 
 HTTP_OK = 200
 
 HGTYPE = 'application/mercurial-0.1'
 HGTYPE2 = 'application/mercurial-0.2'
 HGERRTYPE = 'application/hg-error'
 
 # Names of the SSH protocol implementations.
 SSHV1 = 'ssh-v1'
 # This is advertised over the wire. Incremental the counter at the end
 # to reflect BC breakages.
 SSHV2 = 'exp-ssh-v2-0001'
 
 class baseprotocolhandler(object):
     """Abstract base class for wire protocol handlers.
 
     A wire protocol handler serves as an interface between protocol command
     handlers and the wire protocol transport layer. Protocol handlers provide
     methods to read command arguments, redirect stdio for the duration of
     the request, handle response types, etc.
     """
 
     __metaclass__ = abc.ABCMeta
 
     @abc.abstractproperty
     def name(self):
         """The name of the protocol implementation.
 
         Used for uniquely identifying the transport type.
         """
 
     @abc.abstractmethod
     def getargs(self, args):
         """return the value for arguments in <args>
 
         returns a list of values (same order as <args>)"""
 
     @abc.abstractmethod
     def forwardpayload(self, fp):
         """Read the raw payload and forward to a file.
 
         The payload is read in full before the function returns.
         """
 
     @abc.abstractmethod
     def mayberedirectstdio(self):
         """Context manager to possibly redirect stdio.
 
         The context manager yields a file-object like object that receives
         stdout and stderr output when the context manager is active. Or it
         yields ``None`` if no I/O redirection occurs.
 
         The intent of this context manager is to capture stdio output
         so it may be sent in the response. Some transports support streaming
         stdio to the client in real time. For these transports, stdio output
         won't be captured.
         """
 
     @abc.abstractmethod
     def client(self):
         """Returns a string representation of this client (as bytes)."""
 
 def decodevaluefromheaders(req, headerprefix):
     """Decode a long value from multiple HTTP request headers.
 
     Returns the value as a bytes, not a str.
     """
     chunks = []
     i = 1
     prefix = headerprefix.upper().replace(r'-', r'_')
     while True:
         v = req.env.get(r'HTTP_%s_%d' % (prefix, i))
         if v is None:
             break
         chunks.append(pycompat.bytesurl(v))
         i += 1
 
     return ''.join(chunks)
 
 class webproto(baseprotocolhandler):
     def __init__(self, req, ui):
         self._req = req
         self._ui = ui
 
     @property
     def name(self):
         return 'http'
 
     def getargs(self, args):
         knownargs = self._args()
         data = {}
         keys = args.split()
         for k in keys:
             if k == '*':
                 star = {}
                 for key in knownargs.keys():
                     if key != 'cmd' and key not in keys:
                         star[key] = knownargs[key][0]
                 data['*'] = star
             else:
                 data[k] = knownargs[k][0]
         return [data[k] for k in keys]
 
     def _args(self):
         args = util.rapply(pycompat.bytesurl, self._req.form.copy())
         postlen = int(self._req.env.get(r'HTTP_X_HGARGS_POST', 0))
         if postlen:
             args.update(urlreq.parseqs(
                 self._req.read(postlen), keep_blank_values=True))
             return args
 
         argvalue = decodevaluefromheaders(self._req, r'X-HgArg')
         args.update(urlreq.parseqs(argvalue, keep_blank_values=True))
         return args
 
     def forwardpayload(self, fp):
         length = int(self._req.env[r'CONTENT_LENGTH'])
         # If httppostargs is used, we need to read Content-Length
         # minus the amount that was consumed by args.
         length -= int(self._req.env.get(r'HTTP_X_HGARGS_POST', 0))
         for s in util.filechunkiter(self._req, limit=length):
             fp.write(s)
 
     @contextlib.contextmanager
     def mayberedirectstdio(self):
         oldout = self._ui.fout
         olderr = self._ui.ferr
 
         out = util.stringio()
 
         try:
             self._ui.fout = out
             self._ui.ferr = out
             yield out
         finally:
             self._ui.fout = oldout
             self._ui.ferr = olderr
 
     def client(self):
         return 'remote:%s:%s:%s' % (
             self._req.env.get('wsgi.url_scheme') or 'http',
             urlreq.quote(self._req.env.get('REMOTE_HOST', '')),
             urlreq.quote(self._req.env.get('REMOTE_USER', '')))
 
 def iscmd(cmd):
     return cmd in wireproto.commands
 
 def parsehttprequest(repo, req, query):
     """Parse the HTTP request for a wire protocol request.
 
     If the current request appears to be a wire protocol request, this
     function returns a dict with details about that request, including
     an ``abstractprotocolserver`` instance suitable for handling the
     request. Otherwise, ``None`` is returned.
 
     ``req`` is a ``wsgirequest`` instance.
     """
     # HTTP version 1 wire protocol requests are denoted by a "cmd" query
     # string parameter. If it isn't present, this isn't a wire protocol
     # request.
     if r'cmd' not in req.form:
         return None
 
     cmd = pycompat.sysbytes(req.form[r'cmd'][0])
 
     # The "cmd" request parameter is used by both the wire protocol and hgweb.
     # While not all wire protocol commands are available for all transports,
     # if we see a "cmd" value that resembles a known wire protocol command, we
     # route it to a protocol handler. This is better than routing possible
     # wire protocol requests to hgweb because it prevents hgweb from using
     # known wire protocol commands and it is less confusing for machine
     # clients.
     if cmd not in wireproto.commands:
         return None
 
     proto = webproto(req, repo.ui)
 
     return {
         'cmd': cmd,
         'proto': proto,
         'dispatch': lambda: _callhttp(repo, req, proto, cmd),
         'handleerror': lambda ex: _handlehttperror(ex, req, cmd),
     }
 
 def _httpresponsetype(ui, req, prefer_uncompressed):
     """Determine the appropriate response type and compression settings.
 
     Returns a tuple of (mediatype, compengine, engineopts).
     """
     # Determine the response media type and compression engine based
     # on the request parameters.
     protocaps = decodevaluefromheaders(req, r'X-HgProto').split(' ')
 
     if '0.2' in protocaps:
         # All clients are expected to support uncompressed data.
         if prefer_uncompressed:
             return HGTYPE2, util._noopengine(), {}
 
         # Default as defined by wire protocol spec.
         compformats = ['zlib', 'none']
         for cap in protocaps:
             if cap.startswith('comp='):
                 compformats = cap[5:].split(',')
                 break
 
         # Now find an agreed upon compression format.
         for engine in wireproto.supportedcompengines(ui, util.SERVERROLE):
             if engine.wireprotosupport().name in compformats:
                 opts = {}
                 level = ui.configint('server', '%slevel' % engine.name())
                 if level is not None:
                     opts['level'] = level
 
                 return HGTYPE2, engine, opts
 
         # No mutually supported compression format. Fall back to the
         # legacy protocol.
 
     # Don't allow untrusted settings because disabling compression or
     # setting a very high compression level could lead to flooding
     # the server's network or CPU.
     opts = {'level': ui.configint('server', 'zliblevel')}
     return HGTYPE, util.compengines['zlib'], opts
 
 def _callhttp(repo, req, proto, cmd):
     def genversion2(gen, engine, engineopts):
         # application/mercurial-0.2 always sends a payload header
         # identifying the compression engine.
         name = engine.wireprotosupport().name
         assert 0 < len(name) < 256
         yield struct.pack('B', len(name))
         yield name
 
         for chunk in gen:
             yield chunk
 
     rsp = wireproto.dispatch(repo, proto, cmd)
 
     if not wireproto.commands.commandavailable(cmd, proto):
         req.respond(HTTP_OK, HGERRTYPE,
                     body=_('requested wire protocol command is not available '
                            'over HTTP'))
         return []
 
     if isinstance(rsp, bytes):
         req.respond(HTTP_OK, HGTYPE, body=rsp)
         return []
     elif isinstance(rsp, wireprototypes.bytesresponse):
         req.respond(HTTP_OK, HGTYPE, body=rsp.data)
         return []
     elif isinstance(rsp, wireprototypes.streamreslegacy):
         gen = rsp.gen
         req.respond(HTTP_OK, HGTYPE)
         return gen
     elif isinstance(rsp, wireprototypes.streamres):
         gen = rsp.gen
 
         # This code for compression should not be streamres specific. It
         # is here because we only compress streamres at the moment.
         mediatype, engine, engineopts = _httpresponsetype(
             repo.ui, req, rsp.prefer_uncompressed)
         gen = engine.compressstream(gen, engineopts)
 
         if mediatype == HGTYPE2:
             gen = genversion2(gen, engine, engineopts)
 
         req.respond(HTTP_OK, mediatype)
         return gen
     elif isinstance(rsp, wireprototypes.pushres):
         rsp = '%d\n%s' % (rsp.res, rsp.output)
         req.respond(HTTP_OK, HGTYPE, body=rsp)
         return []
     elif isinstance(rsp, wireprototypes.pusherr):
         # This is the httplib workaround documented in _handlehttperror().
         req.drain()
 
         rsp = '0\n%s\n' % rsp.res
         req.respond(HTTP_OK, HGTYPE, body=rsp)
         return []
     elif isinstance(rsp, wireprototypes.ooberror):
         rsp = rsp.message
         req.respond(HTTP_OK, HGERRTYPE, body=rsp)
         return []
     raise error.ProgrammingError('hgweb.protocol internal failure', rsp)
 
 def _handlehttperror(e, req, cmd):
     """Called when an ErrorResponse is raised during HTTP request processing."""
 
     # Clients using Python's httplib are stateful: the HTTP client
     # won't process an HTTP response until all request data is
     # sent to the server. The intent of this code is to ensure
     # we always read HTTP request data from the client, thus
     # ensuring httplib transitions to a state that allows it to read
     # the HTTP response. In other words, it helps prevent deadlocks
     # on clients using httplib.
 
     if (req.env[r'REQUEST_METHOD'] == r'POST' and
         # But not if Expect: 100-continue is being used.
         (req.env.get('HTTP_EXPECT',
                      '').lower() != '100-continue') or
         # Or the non-httplib HTTP library is being advertised by
         # the client.
         req.env.get('X-HgHttp2', '')):
         req.drain()
     else:
         req.headers.append((r'Connection', r'Close'))
 
     # TODO This response body assumes the failed command was
     # "unbundle." That assumption is not always valid.
     req.respond(e, HGTYPE, body='0\n%s\n' % e)
 
     return ''
 
 def _sshv1respondbytes(fout, value):
     """Send a bytes response for protocol version 1."""
     fout.write('%d\n' % len(value))
     fout.write(value)
     fout.flush()
 
 def _sshv1respondstream(fout, source):
     write = fout.write
     for chunk in source.gen:
         write(chunk)
     fout.flush()
 
 def _sshv1respondooberror(fout, ferr, rsp):
     ferr.write(b'%s\n-\n' % rsp)
     ferr.flush()
     fout.write(b'\n')
     fout.flush()
 
 class sshv1protocolhandler(baseprotocolhandler):
     """Handler for requests services via version 1 of SSH protocol."""
     def __init__(self, ui, fin, fout):
         self._ui = ui
         self._fin = fin
         self._fout = fout
 
     @property
     def name(self):
         return SSHV1
 
     def getargs(self, args):
         data = {}
         keys = args.split()
         for n in xrange(len(keys)):
             argline = self._fin.readline()[:-1]
             arg, l = argline.split()
             if arg not in keys:
                 raise error.Abort(_("unexpected parameter %r") % arg)
             if arg == '*':
                 star = {}
                 for k in xrange(int(l)):
                     argline = self._fin.readline()[:-1]
                     arg, l = argline.split()
                     val = self._fin.read(int(l))
                     star[arg] = val
                 data['*'] = star
             else:
                 val = self._fin.read(int(l))
                 data[arg] = val
         return [data[k] for k in keys]
 
     def forwardpayload(self, fpout):
         # The file is in the form:
         #
         # <chunk size>\n<chunk>
         # ...
         # 0\n
         _sshv1respondbytes(self._fout, b'')
         count = int(self._fin.readline())
         while count:
             fpout.write(self._fin.read(count))
             count = int(self._fin.readline())
 
     @contextlib.contextmanager
     def mayberedirectstdio(self):
         yield None
 
     def client(self):
         client = encoding.environ.get('SSH_CLIENT', '').split(' ', 1)[0]
         return 'remote:ssh:' + client
 
+def _runsshserver(ui, repo, fin, fout):
+    state = 'protov1-serving'
+    proto = sshv1protocolhandler(ui, fin, fout)
+
+    while True:
+        if state == 'protov1-serving':
+            # Commands are issued on new lines.
+            request = fin.readline()[:-1]
+
+            # Empty lines signal to terminate the connection.
+            if not request:
+                state = 'shutdown'
+                continue
+
+            available = wireproto.commands.commandavailable(request, proto)
+
+            # This command isn't available. Send an empty response and go
+            # back to waiting for a new command.
+            if not available:
+                _sshv1respondbytes(fout, b'')
+                continue
+
+            rsp = wireproto.dispatch(repo, proto, request)
+
+            if isinstance(rsp, bytes):
+                _sshv1respondbytes(fout, rsp)
+            elif isinstance(rsp, wireprototypes.bytesresponse):
+                _sshv1respondbytes(fout, rsp.data)
+            elif isinstance(rsp, wireprototypes.streamres):
+                _sshv1respondstream(fout, rsp)
+            elif isinstance(rsp, wireprototypes.streamreslegacy):
+                _sshv1respondstream(fout, rsp)
+            elif isinstance(rsp, wireprototypes.pushres):
+                _sshv1respondbytes(fout, b'')
+                _sshv1respondbytes(fout, b'%d' % rsp.res)
+            elif isinstance(rsp, wireprototypes.pusherr):
+                _sshv1respondbytes(fout, rsp.res)
+            elif isinstance(rsp, wireprototypes.ooberror):
+                _sshv1respondooberror(fout, ui.ferr, rsp.message)
+            else:
+                raise error.ProgrammingError('unhandled response type from '
+                                             'wire protocol command: %s' % rsp)
+
+        elif state == 'shutdown':
+            break
+
+        else:
+            raise error.ProgrammingError('unhandled ssh server state: %s' %
+                                         state)
+
 class sshserver(object):
     def __init__(self, ui, repo):
         self._ui = ui
         self._repo = repo
         self._fin = ui.fin
         self._fout = ui.fout
 
         hook.redirect(True)
         ui.fout = repo.ui.fout = ui.ferr
 
         # Prevent insertion/deletion of CRs
         util.setbinary(self._fin)
         util.setbinary(self._fout)
 
-        self._proto = sshv1protocolhandler(self._ui, self._fin, self._fout)
-
     def serve_forever(self):
-        while self.serve_one():
-            pass
+        _runsshserver(self._ui, self._repo, self._fin, self._fout)
         sys.exit(0)
-
-    def serve_one(self):
-        cmd = self._fin.readline()[:-1]
-        if cmd and wireproto.commands.commandavailable(cmd, self._proto):
-            rsp = wireproto.dispatch(self._repo, self._proto, cmd)
-
-            if isinstance(rsp, bytes):
-                _sshv1respondbytes(self._fout, rsp)
-            elif isinstance(rsp, wireprototypes.bytesresponse):
-                _sshv1respondbytes(self._fout, rsp.data)
-            elif isinstance(rsp, wireprototypes.streamres):
-                _sshv1respondstream(self._fout, rsp)
-            elif isinstance(rsp, wireprototypes.streamreslegacy):
-                _sshv1respondstream(self._fout, rsp)
-            elif isinstance(rsp, wireprototypes.pushres):
-                _sshv1respondbytes(self._fout, b'')
-                _sshv1respondbytes(self._fout, b'%d' % rsp.res)
-            elif isinstance(rsp, wireprototypes.pusherr):
-                _sshv1respondbytes(self._fout, rsp.res)
-            elif isinstance(rsp, wireprototypes.ooberror):
-                _sshv1respondooberror(self._fout, self._ui.ferr, rsp.message)
-            else:
-                raise error.ProgrammingError('unhandled response type from '
-                                             'wire protocol command: %s' % rsp)
-        elif cmd:
-            _sshv1respondbytes(self._fout, b'')
-        return cmd != ''

tests/sshprotoext.py

@@ -1,127 +1,131 b''
 # sshprotoext.py - Extension to test behavior of SSH protocol
 #
 # Copyright 2018 Gregory Szorc <[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.
 
 # This extension replaces the SSH server started via `hg serve --stdio`.
 # The server behaves differently depending on environment variables.
 
 from __future__ import absolute_import
 
 from mercurial import (
     error,
     extensions,
     registrar,
     sshpeer,
     wireproto,
     wireprotoserver,
 )
 
 configtable = {}
 configitem = registrar.configitem(configtable)
 
 configitem(b'sshpeer', b'mode', default=None)
 configitem(b'sshpeer', b'handshake-mode', default=None)
 
 class bannerserver(wireprotoserver.sshserver):
     """Server that sends a banner to stdout."""
     def serve_forever(self):
         for i in range(10):
             self._fout.write(b'banner: line %d\n' % i)
 
         super(bannerserver, self).serve_forever()
 
 class prehelloserver(wireprotoserver.sshserver):
     """Tests behavior when connecting to <0.9.1 servers.
 
     The ``hello`` wire protocol command was introduced in Mercurial
     0.9.1. Modern clients send the ``hello`` command when connecting
     to SSH servers. This mock server tests behavior of the handshake
     when ``hello`` is not supported.
     """
     def serve_forever(self):
         l = self._fin.readline()
         assert l == b'hello\n'
         # Respond to unknown commands with an empty reply.
         wireprotoserver._sshv1respondbytes(self._fout, b'')
         l = self._fin.readline()
         assert l == b'between\n'
-        rsp = wireproto.dispatch(self._repo, self._proto, b'between')
+        proto = wireprotoserver.sshv1protocolhandler(self._ui, self._fin,
+                                                     self._fout)
+        rsp = wireproto.dispatch(self._repo, proto, b'between')
         wireprotoserver._sshv1respondbytes(self._fout, rsp.data)
 
         super(prehelloserver, self).serve_forever()
 
 class upgradev2server(wireprotoserver.sshserver):
     """Tests behavior for clients that issue upgrade to version 2."""
     def serve_forever(self):
         name = wireprotoserver.SSHV2
         l = self._fin.readline()
         assert l.startswith(b'upgrade ')
         token, caps = l[:-1].split(b' ')[1:]
         assert caps == b'proto=%s' % name
 
         # Filter hello and between requests.
         l = self._fin.readline()
         assert l == b'hello\n'
         l = self._fin.readline()
         assert l == b'between\n'
         l = self._fin.readline()
         assert l == b'pairs 81\n'
         self._fin.read(81)
 
         # Send the upgrade response.
+        proto = wireprotoserver.sshv1protocolhandler(self._ui, self._fin,
+                                                     self._fout)
         self._fout.write(b'upgraded %s %s\n' % (token, name))
-        servercaps = wireproto.capabilities(self._repo, self._proto)
+        servercaps = wireproto.capabilities(self._repo, proto)
         rsp = b'capabilities: %s' % servercaps.data
         self._fout.write(b'%d\n' % len(rsp))
         self._fout.write(rsp)
         self._fout.write(b'\n')
         self._fout.flush()
 
         super(upgradev2server, self).serve_forever()
 
 def performhandshake(orig, ui, stdin, stdout, stderr):
     """Wrapped version of sshpeer._performhandshake to send extra commands."""
     mode = ui.config(b'sshpeer', b'handshake-mode')
     if mode == b'pre-no-args':
         ui.debug(b'sending no-args command\n')
         stdin.write(b'no-args\n')
         stdin.flush()
         return orig(ui, stdin, stdout, stderr)
     elif mode == b'pre-multiple-no-args':
         ui.debug(b'sending unknown1 command\n')
         stdin.write(b'unknown1\n')
         ui.debug(b'sending unknown2 command\n')
         stdin.write(b'unknown2\n')
         ui.debug(b'sending unknown3 command\n')
         stdin.write(b'unknown3\n')
         stdin.flush()
         return orig(ui, stdin, stdout, stderr)
     else:
         raise error.ProgrammingError(b'unknown HANDSHAKECOMMANDMODE: %s' %
                                      mode)
 
 def extsetup(ui):
     # It's easier for tests to define the server behavior via environment
     # variables than config options. This is because `hg serve --stdio`
     # has to be invoked with a certain form for security reasons and
     # `dummyssh` can't just add `--config` flags to the command line.
     servermode = ui.environ.get(b'SSHSERVERMODE')
 
     if servermode == b'banner':
         wireprotoserver.sshserver = bannerserver
     elif servermode == b'no-hello':
         wireprotoserver.sshserver = prehelloserver
     elif servermode == b'upgradev2':
         wireprotoserver.sshserver = upgradev2server
     elif servermode:
         raise error.ProgrammingError(b'unknown server mode: %s' % servermode)
 
     peermode = ui.config(b'sshpeer', b'mode')
 
     if peermode == b'extra-handshake-commands':
         extensions.wrapfunction(sshpeer, '_performhandshake', performhandshake)
     elif peermode:
         raise error.ProgrammingError(b'unknown peer mode: %s' % peermode)

tests/test-sshserver.py

@@ -1,47 +1,50 b''
 from __future__ import absolute_import, print_function
 
 import io
 import unittest
 
 import silenttestrunner
 
 from mercurial import (
     util,
     wireproto,
     wireprotoserver,
 )
 
 class SSHServerGetArgsTests(unittest.TestCase):
     def testparseknown(self):
         tests = [
             (b'* 0\nnodes 0\n', [b'', {}]),
             (b'* 0\nnodes 40\n1111111111111111111111111111111111111111\n',
              [b'1111111111111111111111111111111111111111', {}]),
         ]
         for input, expected in tests:
             self.assertparse(b'known', input, expected)
 
     def assertparse(self, cmd, input, expected):
         server = mockserver(input)
+        proto = wireprotoserver.sshv1protocolhandler(server._ui,
+                                                     server._fin,
+                                                     server._fout)
         _func, spec = wireproto.commands[cmd]
-        self.assertEqual(server._proto.getargs(spec), expected)
+        self.assertEqual(proto.getargs(spec), expected)
 
 def mockserver(inbytes):
     ui = mockui(inbytes)
     repo = mockrepo(ui)
     return wireprotoserver.sshserver(ui, repo)
 
 class mockrepo(object):
     def __init__(self, ui):
         self.ui = ui
 
 class mockui(object):
     def __init__(self, inbytes):
         self.fin = io.BytesIO(inbytes)
         self.fout = io.BytesIO()
         self.ferr = io.BytesIO()
 
 if __name__ == '__main__':
     # Don't call into msvcrt to set BytesIO to binary mode
     util.setbinary = lambda fp: True
     silenttestrunner.main(__name__)