wireproto: function for testing if wire protocol command is available

Currently, we perform simple membership testing for whether a wire
command is available. In the future, not all wire protocol commands
will be available on all transports. For example, a legacy transport
may not support newer commands.

In preparation of this, teach the protocol handlers to call into a
function to determine if a wire protocol command is available. That
function currently does membership testing like before, so behavior
should be identical.

In the case of the HTTP server, behavior is a bit wonkier. "cmd" is
used by both the wire protocol and hgweb. We do want the protocol
handler to handle requests for all commands that look like wire
protocol commands, even if they aren't available. Otherwise, the
fallback to hgweb would only confuse automated clients and make it
easier for hgweb to accidentally implement a "cmd" that is identical
to wire protocol commands (since they aren't centrally registered).

Differential Revision: https://phab.mercurial-scm.org/D1999

mercurial/hgweb/hgweb_mod.py

@@ -357,6 +357,14 b' class hgweb(object):'
             query = req.env[r'QUERY_STRING'].partition(r'&')[0]
             query = query.partition(r';')[0]
 
+        # The ``cmd`` request parameter is used by both the wire protocol
+        # and hgweb. We route all known wire protocol commands to the
+        # wire protocol handler, even if the command isn't available for
+        # this transport. That's better for machine clients in the case
+        # of an errant request to an unavailable protocol command. And it
+        # prevents hgweb from accidentally using ``cmd`` values used by
+        # the wire protocol.
+
         # process this if it's a protocol request
         # protocol bits don't need to create any URLs
         # and the clients always use the old URL structure

mercurial/wireproto.py

@@ -691,6 +691,12 b' class commanddict(dict):'
 
         return super(commanddict, self).__setitem__(k, v)
 
+    def commandavailable(self, command, proto):
+        """Determine if a command is available for the requested protocol."""
+        # For now, commands are available for all protocols. So do a simple
+        # membership test.
+        return command in self
+
 commands = commanddict()
 
 def wireprotocommand(name, args=''):

mercurial/wireprotoserver.py

@@ -223,6 +223,13 b' def callhttp(repo, req, cmd):'
             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 []
@@ -351,7 +358,7 b' class sshserver(abstractserverproto):'
 
     def serve_one(self):
         cmd = self._fin.readline()[:-1]
-        if cmd and cmd in wireproto.commands:
+        if cmd and wireproto.commands.commandavailable(cmd, self):
             rsp = wireproto.dispatch(self._repo, self, cmd)
             self._handlers[rsp.__class__](self, rsp)
         elif cmd: