server: OPEN/CLOSE on crowded mailbox should provoke "crowded" error

The Mailbox object throws CrowdedError, but WebSocketRendezvous wasn't
handling it specifically. The server responded by dropping the connection and
logging an "Unhandled Error", so the client would reconnect and then get the
same error again and again.

This changes WebSocketRendezvous to handle CrowdedError by sending a
"crowded" error response. The client should react to this by giving up on the
connection entirely, and not reconnecting.

src/wormhole/server/rendezvous_websocket.py

@@ -231,8 +231,11 @@ class WebSocketRendezvous(websocket.WebSocketServerProtocol):
         mailbox_id = msg["mailbox"]
         assert isinstance(mailbox_id, type(""))
         self._mailbox_id = mailbox_id
+        try:
             self._mailbox = self._app.open_mailbox(mailbox_id, self._side,
                                                    server_rx)
+        except CrowdedError:
+            raise Error("crowded")
         def _send(sm):
             self.send("message", side=sm.side, phase=sm.phase,
                       body=sm.body, server_rx=sm.server_rx, id=sm.msg_id)
@@ -268,8 +271,11 @@ class WebSocketRendezvous(websocket.WebSocketServerProtocol):
                 raise Error("close without mailbox must follow open")
             mailbox_id = self._mailbox_id
         if not self._mailbox:
+            try:
                 self._mailbox = self._app.open_mailbox(mailbox_id, self._side,
                                                        server_rx)
+            except CrowdedError:
+                raise Error("crowded")
         if self._listening:
             self._mailbox.remove_listener(self)
             self._listening = False

src/wormhole/test/test_server.py

@@ -892,6 +892,22 @@ class WebSocketAPI(_Util, ServerBase, unittest.TestCase):
         self.assertEqual(err["type"], "error")
         self.assertEqual(err["error"], "only one open per connection")
 
+    @inlineCallbacks
+    def test_open_crowded(self):
+        c1 = yield self.make_client()
+        yield c1.next_non_ack()
+        c1.send("bind", appid="appid", side="side")
+        app = self._rendezvous.get_app("appid")
+
+        mbid = app.claim_nameplate("np1", "side1", 0)
+        app.claim_nameplate("np1", "side2", 0)
+
+        # the third open will signal crowding
+        c1.send("open", mailbox=mbid)
+        err = yield c1.next_non_ack()
+        self.assertEqual(err["type"], "error")
+        self.assertEqual(err["error"], "crowded")
+
     @inlineCallbacks
     def test_add(self):
         c1 = yield self.make_client()
@@ -991,6 +1007,22 @@ class WebSocketAPI(_Util, ServerBase, unittest.TestCase):
         self.assertEqual(err["type"], "error")
         self.assertEqual(err["error"], "open and close must use same mailbox")
 
+    @inlineCallbacks
+    def test_close_crowded(self):
+        c1 = yield self.make_client()
+        yield c1.next_non_ack()
+        c1.send("bind", appid="appid", side="side")
+        app = self._rendezvous.get_app("appid")
+
+        mbid = app.claim_nameplate("np1", "side1", 0)
+        app.claim_nameplate("np1", "side2", 0)
+
+        # a close that allocates a third side will signal crowding
+        c1.send("close", mailbox=mbid)
+        err = yield c1.next_non_ack()
+        self.assertEqual(err["type"], "error")
+        self.assertEqual(err["error"], "crowded")
+
 
     @inlineCallbacks
     def test_disconnect(self):