Fix lint failures in Complement tests (#19855)

Running `scripts-dev/lint.sh` locally revealed a failure, so here are the fixes that the linter
applied + a manual change to address an issue that couldn't be
auto-fixed.

Author: AndrewFerr

.github/workflows/tests.yml

@@ -60,9 +60,10 @@ jobs:
               - 'poetry.lock'
               - 'docker/**'
               - '.ci/**'
-              - 'scripts-dev/complement.sh'
               - '.github/workflows/tests.yml'
+              - 'scripts-dev/complement.sh'
               - '.github/workflows/complement_tests.yml'
+              - 'complement/**'
 
             linting:
               - 'synapse/**'

changelog.d/19855.bugfix

@@ -0,0 +1 @@
+Provide remote servers a way to find out about an event created during the remote join handshake. Contributed by @FrenchGithubUser and @jason-famedly @ Famedly.

complement/tests/federation_room_join_test.go

@@ -68,53 +68,56 @@ func TestEventBetweenMakeJoinAndSendJoinIsNotLost(t *testing.T) {
 	// Complement server is not fully in the room until send_join completes, so
 	// we can't use HandleTransactionRequests (which requires the room in
 	// srv.rooms). Instead we parse the raw transaction body ourselves.
-	srv.Mux().Handle("/_matrix/federation/v1/send/{transactionID}", http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
-		body, err := io.ReadAll(req.Body)
-		must.NotError(t, "failed to read request body in /send handler: %v", err)
-		txn := gjson.ParseBytes(body)
-		txn.Get("pdus").ForEach(func(_, pdu gjson.Result) bool {
-			eventID := pdu.Get("event_id").String()
-			eventType := pdu.Get("type").String()
-			t.Logf("Received PDU via /send: type=%s id=%s", eventType, eventID)
-
-			// messageEventID is set after make_join but before send_join.
-			// Transactions can arrive before that window, so skip PDUs that
-			// arrive before we know which event to look for.
-			msgID, _ := messageEventID.Load().(string)
-			if msgID == "" {
-				return true
-			}
+	srv.Mux().
+		Handle("/_matrix/federation/v1/send/{transactionID}", http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+			body, err := io.ReadAll(req.Body)
+			must.NotError(t, "failed to read request body in /send handler: %v", err)
+			txn := gjson.ParseBytes(body)
+			txn.Get("pdus").ForEach(func(_, pdu gjson.Result) bool {
+				eventID := pdu.Get("event_id").String()
+				eventType := pdu.Get("type").String()
+				t.Logf("Received PDU via /send: type=%s id=%s", eventType, eventID)
+
+				// messageEventID is set after make_join but before send_join.
+				// Transactions can arrive before that window, so skip PDUs that
+				// arrive before we know which event to look for.
+				msgID, _ := messageEventID.Load().(string)
+				if msgID == "" {
+					return true
+				}
 
-			// Check if this IS the message event (server pushed it directly).
-			if eventID == msgID {
-				messageDiscoverableWaiter.Finish()
-				return true
-			}
-
-			// Check if this event's prev_events directly reference the message (e.g. a dummy
-			// event tying the two forward extremities together). If so, the joining server
-			// can backfill from that event and will discover the message.
-			//
-			// XXX: We only check one level of prev_events: if the reference is deeper in the
-			// DAG, it's valid and the joining server can still reach the message through
-			// backfill but our checks don't account for that yet (feel free to edit this
-			// assertion if you run into this)
-			pdu.Get("prev_events").ForEach(func(_, prevEvent gjson.Result) bool {
-				if prevEvent.String() == msgID {
+				// Check if this IS the message event (server pushed it directly).
+				if eventID == msgID {
 					messageDiscoverableWaiter.Finish()
-					return false
+					return true
 				}
+
+				// Check if this event's prev_events directly reference the message (e.g. a dummy
+				// event tying the two forward extremities together). If so, the joining server
+				// can backfill from that event and will discover the message.
+				//
+				// XXX: We only check one level of prev_events: if the reference is deeper in the
+				// DAG, it's valid and the joining server can still reach the message through
+				// backfill but our checks don't account for that yet (feel free to edit this
+				// assertion if you run into this)
+				pdu.Get("prev_events").ForEach(func(_, prevEvent gjson.Result) bool {
+					if prevEvent.String() == msgID {
+						messageDiscoverableWaiter.Finish()
+						return false
+					}
+					return true
+				})
+
 				return true
 			})
-
-			return true
-		})
-		w.WriteHeader(200)
-		// Respond with an empty PDU error map, which is the federation /send
-		// success response format: each key would be a PDU ID whose processing
-		// failed; an empty object means all PDUs were accepted.
-		w.Write([]byte(`{"pdus":{}}`))
-	})).Methods("PUT")
+			w.WriteHeader(200)
+			// Respond with an empty PDU error map, which is the federation /send
+			// success response format: each key would be a PDU ID whose processing
+			// failed; an empty object means all PDUs were accepted.
+			_, err = w.Write([]byte(`{"pdus":{}}`))
+			must.NotError(t, "failed to write response body in /send handler: %v", err)
+		})).
+		Methods("PUT")
 
 	cancel := srv.Listen()
 	defer cancel()