test/xds: remove redundant server when using stubserver in tests (#7846)

examples/features/gracefulstop/server/main.go

@@ -0,0 +1,87 @@
+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Binary server demonstrates how to gracefully stop a gRPC server.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"sync"
+	"sync/atomic"
+
+	"google.golang.org/grpc"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+)
+
+var (
+	port           = flag.Int("port", 50052, "port number")
+	streamMessages int32
+	mu             sync.Mutex
+	streamCh       chan struct{} // to signal if server streaming started
+)
+
+type server struct {
+	pb.UnimplementedEchoServer
+}
+
+// ServerStreamingEcho implements the EchoService.ServerStreamingEcho method.
+// It receives an EchoRequest and sends back a stream of EchoResponses until an
+// error occurs or the stream is closed.
+func (s *server) ServerStreamingEcho(_ *pb.EchoRequest, stream pb.Echo_ServerStreamingEchoServer) error {
+	// Signal streaming start to initiate graceful stop which should wait until
+	// server streaming finishes.
+	streamCh <- struct{}{}
+
+	for {
+		atomic.AddInt32(&streamMessages, 1)
+
+		mu.Lock()
+		if err := stream.Send(&pb.EchoResponse{Message: fmt.Sprintf("Messages Sent: %d", streamMessages)}); err != nil {
+			log.Printf("Stream is sending data: %v. Stop Streaming", err)
+			return err
+		}
+		mu.Unlock()
+	}
+}
+
+func main() {
+	streamCh = make(chan struct{})
+	flag.Parse()
+
+	address := fmt.Sprintf(":%v", *port)
+	lis, err := net.Listen("tcp", address)
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+
+	s := grpc.NewServer()
+	pb.RegisterEchoServer(s, &server{})
+
+	go func() {
+		<-streamCh // wait until server streaming starts
+		log.Println("Initiating graceful shutdown...")
+		s.GracefulStop() // gracefully stop server after in-flight server streaming rpc finishes
+		log.Println("Server stopped gracefully.")
+	}()
+
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}