Fix bug where instance descriptor were thrown away after first match

Some users would like to have multiple master services backed by
the same set of instance addresses. This is equivalent to having multiple
unique domains served by one set of load balancers.

There was a bug where OnionBalance would discard a newly received instance
descriptor after finding the first matching instance object. Other master
services would not have their copy of that instance updated. This resulted
in those other instances producing a "No descriptor received for instance"
error.

Thank you to Alec Muffett for reporting this issue.

Resolves #47.

onionbalance/descriptor.py

@@ -255,19 +255,21 @@ def descriptor_received(descriptor_content):
     descriptor_onion_address = util.calc_onion_address(permanent_key)
 
     # Find the HS instance for this descriptor
+    known_descriptor = False
     for service in config.services:
         for instance in service.instances:
             if instance.onion_address == descriptor_onion_address:
-                # Update the descriptor and exit
+                # Update the descriptor
                 instance.update_descriptor(parsed_descriptor)
-                return None
-
-    # No matching service instance was found for the descriptor
-    logger.debug("Received a descriptor for an unknown service:\n%s",
-                 descriptor_content.decode('utf-8'))
-    logger.warning("Received a descriptor with address %s.onion that "
-                   "did not match any configured service instances.",
-                   descriptor_onion_address)
+                known_descriptor = True
+
+    if not known_descriptor:
+        # No matching service instance was found for the descriptor
+        logger.debug("Received a descriptor for an unknown service:\n%s",
+                     descriptor_content.decode('utf-8'))
+        logger.warning("Received a descriptor with address %s.onion that "
+                       "did not match any configured service instances.",
+                       descriptor_onion_address)
 
     return None