wireprotoserver: move SSH server operation to a standalone function

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

--- a/mercurial/wireprotoserver.py	Wed Feb 14 17:35:13 2018 -0700
+++ b/mercurial/wireprotoserver.py	Thu Feb 08 15:09:59 2018 -0800
@@ -409,6 +409,56 @@
         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
@@ -423,36 +473,6 @@
         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 != ''

--- a/tests/sshprotoext.py	Wed Feb 14 17:35:13 2018 -0700
+++ b/tests/sshprotoext.py	Thu Feb 08 15:09:59 2018 -0800
@@ -48,7 +48,9 @@
         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()
@@ -72,8 +74,10 @@
         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)

--- a/tests/test-sshserver.py	Wed Feb 14 17:35:13 2018 -0700
+++ b/tests/test-sshserver.py	Thu Feb 08 15:09:59 2018 -0800
@@ -23,8 +23,11 @@
 
     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)