bugfix: Fix #908 by setting the correct state after the event (#913)

* bugfix: Fix #908 by setting the correct state after the event

Previously, this would only happen if the state already existed
previously!

* Structured logging

federationapi/routing/send.go

@@ -116,6 +116,7 @@ func (t *txnReq) processTransaction() (*gomatrixserverlib.RespSend, error) {
 			results[e.EventID()] = gomatrixserverlib.PDUResult{
 				Error: err.Error(),
 			}
+			util.GetLogger(t.context).WithError(err).WithField("event_id", e.EventID()).Warn("Failed to process incoming federation event, skipping it.")
 		} else {
 			results[e.EventID()] = gomatrixserverlib.PDUResult{}
 		}

roomserver/state/v1/state.go

@@ -366,11 +366,16 @@ func (v StateResolutionV1) loadStateAfterEventsForNumericTuples(
 			// update that key in the result.
 			// If the requested event wasn't a state event then the state after
 			// it is the same as the state before it.
+			set := false
 			for i := range result {
 				if result[i].StateKeyTuple == prevState.StateKeyTuple {
 					result[i] = prevState.StateEntry
+					set = true
 				}
 			}
+			if !set { // no previous state exists for this event: add new state
+				result = append(result, prevState.StateEntry)
+			}
 		}
 		return result, nil
 	}