protect against reentrant closing

broker/src/tunneldigger_broker/tunnel.py

@@ -79,6 +79,7 @@ def __init__(self, broker, address, endpoint, uuid, tunnel_id, remote_tunnel_id,
         self.created_time = None
         self.keepalive_seqno = 0
         self.error_count = 0
+        self.closing = False
 
         # Initialize PMTU values.
         self.automatic_pmtu = pmtu_fixed == 0
@@ -260,6 +261,11 @@ def close(self, reason=protocol.ERROR_REASON_UNDEFINED):
         :param reason: Reason code for the tunnel being closed
         """
 
+        if self.closing:
+            # While closing we send messages, and that can fail and we can recursively end up here again.
+            return
+        self.closing = True
+
         logger.info("{}: Closing after {} seconds (reason=0x{:x})".format(self.name, int(time.time() - self.created_time), reason))
 
         # Run pre-down hook.