Add support for sending failures

synapse/federation/replication.py

@@ -143,6 +143,11 @@ class ReplicationLayer(object):
         self._transaction_queue.enqueue_edu(edu)
         return defer.succeed(None)
 
+    @log_function
+    def send_failure(self, failure, destination):
+        self._transaction_queue.enqueue_failure(failure, destination)
+        return defer.succeed(None)
+
     @log_function
     def make_query(self, destination, query_type, args,
                    retry_on_dns_fail=True):
@@ -558,6 +563,9 @@ class _TransactionQueue(object):
         # destination -> list of tuple(edu, deferred)
         self.pending_edus_by_dest = {}
 
+        # destination -> list of tuple(failure, deferred)
+        self.pending_failures_by_dest = {}
+
         # HACK to get unique tx id
         self._next_txn_id = int(self._clock.time_msec())
 
@@ -610,6 +618,18 @@ class _TransactionQueue(object):
 
         return deferred
 
+    @defer.inlineCallbacks
+    def enqueue_failure(self, failure, destination):
+        deferred = defer.Deferred()
+
+        self.pending_failures_by_dest.setdefault(
+            destination, []
+        ).append(
+            (failure, deferred)
+        )
+
+        yield deferred
+
     @defer.inlineCallbacks
     @log_function
     def _attempt_new_transaction(self, destination):
@@ -619,8 +639,9 @@ class _TransactionQueue(object):
         #  list of (pending_pdu, deferred, order)
         pending_pdus = self.pending_pdus_by_dest.pop(destination, [])
         pending_edus = self.pending_edus_by_dest.pop(destination, [])
+        pending_failures = self.pending_failures_by_dest(destination, [])
 
-        if not pending_pdus and not pending_edus:
+        if not pending_pdus and not pending_edus and not pending_failures:
             return
 
         logger.debug("TX [%s] Attempting new transaction", destination)
@@ -630,7 +651,11 @@ class _TransactionQueue(object):
 
         pdus = [x[0] for x in pending_pdus]
         edus = [x[0] for x in pending_edus]
-        deferreds = [x[1] for x in pending_pdus + pending_edus]
+        failures = [x[0].get_dict() for x in pending_failures]
+        deferreds = [
+            x[1]
+            for x in pending_pdus + pending_edus + pending_failures
+        ]
 
         try:
             self.pending_transactions[destination] = 1
@@ -644,6 +669,7 @@ class _TransactionQueue(object):
                 destination=destination,
                 pdus=pdus,
                 edus=edus,
+                pdu_failures=failures,
             )
 
             self._next_txn_id += 1