Allow application services to have an optional 'url'

If 'url' is not specified, they will not be pushed for events or queries. This
is useful for bots who simply wish to reserve large chunks of user/alias
namespace, and don't care about being pushed for events.

synapse/appservice/api.py

@@ -67,6 +67,8 @@ class ApplicationServiceApi(SimpleHttpClient):
 
     @defer.inlineCallbacks
     def query_user(self, service, user_id):
+        if service.url == "":
+            defer.returnValue(False)
         uri = service.url + ("/users/%s" % urllib.quote(user_id))
         response = None
         try:
@@ -86,6 +88,8 @@ class ApplicationServiceApi(SimpleHttpClient):
 
     @defer.inlineCallbacks
     def query_alias(self, service, alias):
+        if service.url == "":
+            defer.returnValue(False)
         uri = service.url + ("/rooms/%s" % urllib.quote(alias))
         response = None
         try:
@@ -113,6 +117,8 @@ class ApplicationServiceApi(SimpleHttpClient):
             raise ValueError(
                 "Unrecognised 'kind' argument %r to query_3pe()", kind
             )
+        if service.url == "":
+            defer.returnValue([])
 
         uri = "%s%s/thirdparty/%s/%s" % (
             service.url,
@@ -145,6 +151,8 @@ class ApplicationServiceApi(SimpleHttpClient):
             defer.returnValue([])
 
     def get_3pe_protocol(self, service, protocol):
+        if service.url == "":
+            defer.returnValue({})
         @defer.inlineCallbacks
         def _get():
             uri = "%s%s/thirdparty/protocol/%s" % (
@@ -166,6 +174,9 @@ class ApplicationServiceApi(SimpleHttpClient):
 
     @defer.inlineCallbacks
     def push_bulk(self, service, events, txn_id=None):
+        if service.url == "":
+            defer.returnValue(True)
+
         events = self._serialize(events)
 
         if txn_id is None:

synapse/config/appservice.py

@@ -132,6 +132,12 @@ def _load_appservice(hostname, as_info, config_filename):
         for p in protocols:
             if not isinstance(p, str):
                 raise KeyError("Bad value for 'protocols' item")
+
+    if as_info["url"] == "":
+        logger.info(
+            "(%s) Explicitly empty 'url' provided. This application service will not receive events or queries.",
+            config_filename,
+        )
     return ApplicationService(
         token=as_info["as_token"],
         url=as_info["url"],