examples: create an example for enabling and configuring retry (#3028)

examples/features/retry/server/main.go

@@ -0,0 +1,103 @@
+/*
+ *
+ * Copyright 2019 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 is an example server.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"sync"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/status"
+)
+
+var port = flag.Int("port", 50052, "port number")
+
+type failingServer struct {
+	mu sync.Mutex
+
+	reqCounter uint
+	reqModulo  uint
+}
+
+// this method will fail reqModulo - 1 times RPCs and return status code Unavailable,
+// and succeeded RPC on reqModulo times.
+func (s *failingServer) maybeFailRequest() error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.reqCounter++
+	if (s.reqModulo > 0) && (s.reqCounter%s.reqModulo == 0) {
+		return nil
+	}
+
+	return status.Errorf(codes.Unavailable, "maybeFailRequest: failing it")
+}
+
+func (s *failingServer) UnaryEcho(ctx context.Context, req *pb.EchoRequest) (*pb.EchoResponse, error) {
+	if err := s.maybeFailRequest(); err != nil {
+		log.Println("request failed count:", s.reqCounter)
+		return nil, err
+	}
+
+	log.Println("request succeeded count:", s.reqCounter)
+	return &pb.EchoResponse{Message: req.Message}, nil
+}
+
+func (s *failingServer) ServerStreamingEcho(req *pb.EchoRequest, stream pb.Echo_ServerStreamingEchoServer) error {
+	return status.Error(codes.Unimplemented, "RPC unimplemented")
+}
+
+func (s *failingServer) ClientStreamingEcho(stream pb.Echo_ClientStreamingEchoServer) error {
+	return status.Error(codes.Unimplemented, "RPC unimplemented")
+}
+
+func (s *failingServer) BidirectionalStreamingEcho(stream pb.Echo_BidirectionalStreamingEchoServer) error {
+	return status.Error(codes.Unimplemented, "RPC unimplemented")
+}
+
+func main() {
+	flag.Parse()
+
+	address := fmt.Sprintf(":%v", *port)
+	lis, err := net.Listen("tcp", address)
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+	fmt.Println("listen on address", address)
+
+	s := grpc.NewServer()
+
+	// Configure server to pass every fourth RPC;
+	// client is configured to make four attempts.
+	failingservice := &failingServer{
+		reqCounter: 0,
+		reqModulo:  4,
+	}
+
+	pb.RegisterEchoServer(s, failingservice)
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}