--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/sshprotoext.py	Sun Feb 04 14:02:41 2018 -0800
@@ -0,0 +1,108 @@
+# sshprotoext.py - Extension to test behavior of SSH protocol
+#
+# Copyright 2018 Gregory Szorc <gregory.szorc@gmail.com>
+#
+# 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,
+    registrar,
+    sshpeer,
+    wireproto,
+    wireprotoserver,
+)
+
+configtable = {}
+configitem = registrar.configitem(configtable)
+
+configitem('sshpeer', 'mode', default=None)
+configitem('sshpeer', '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.
+        self._sendresponse(b'')
+        l = self._fin.readline()
+        assert l == b'between\n'
+        rsp = wireproto.dispatch(self._repo, self, b'between')
+        self._handlers[rsp.__class__](self, rsp)
+
+        super(prehelloserver, self).serve_forever()
+
+class extrahandshakecommandspeer(sshpeer.sshpeer):
+    """An ssh peer that sends extra commands as part of initial handshake."""
+    # There isn't a good hook point. So we wrap _callstream() and inject
+    # logic when the peer says "hello".
+    def _callstream(self, cmd, **args):
+        if cmd != b'hello':
+            return super(extrahandshakecommandspeer, self)._callstream(cmd,
+                                                                       **args)
+
+        mode = self._ui.config(b'sshpeer', b'handshake-mode')
+        if mode == b'pre-no-args':
+            self._callstream(b'no-args')
+            return super(extrahandshakecommandspeer, self)._callstream(
+                cmd, **args)
+        elif mode == b'pre-multiple-no-args':
+            self._callstream(b'unknown1')
+            self._callstream(b'unknown2')
+            self._callstream(b'unknown3')
+            return super(extrahandshakecommandspeer, self)._callstream(
+                cmd, **args)
+        else:
+            raise error.ProgrammingError(b'unknown HANDSHAKECOMMANDMODE: %s' %
+                                         mode)
+
+def registercommands():
+    def dummycommand(repo, proto):
+        raise error.ProgrammingError('this should never be called')
+
+    wireproto.wireprotocommand(b'no-args', b'')(dummycommand)
+    wireproto.wireprotocommand(b'unknown1', b'')(dummycommand)
+    wireproto.wireprotocommand(b'unknown2', b'')(dummycommand)
+    wireproto.wireprotocommand(b'unknown3', b'')(dummycommand)
+
+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:
+        raise error.ProgrammingError(b'unknown server mode: %s' % servermode)
+
+    peermode = ui.config(b'sshpeer', b'mode')
+
+    if peermode == b'extra-handshake-commands':
+        sshpeer.sshpeer = extrahandshakecommandspeer
+        registercommands()
+    elif peermode:
+        raise error.ProgrammingError(b'unknown peer mode: %s' % peermode)