examples: add keepalive example

examples/features/keepalive/README.md

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+# Keepalive
+
+This example illustrates how to set up client-side keepalive pings and
+server-side keepalive ping enforcement and connection idleness settings.  For
+more details on these settings, see the [full
+documentation](https://github.com/grpc/grpc-go/tree/master/Documentation/keepalive.md).
+
+
+```
+go run server/main.go
+```
+
+```
+GODEBUG=http2debug=2 go run client/main.go
+```

examples/features/keepalive/client/main.go

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+/*
+ *
+ * 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 client is an example client.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"time"
+
+	"google.golang.org/grpc"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/keepalive"
+)
+
+var addr = flag.String("addr", "localhost:50052", "the address to connect to")
+
+var kacp = keepalive.ClientParameters{
+	Time:                10 * time.Second, // send pings every 10 seconds if there is no activity
+	Timeout:             time.Second,      // wait 1 second for ping ack before considering the connection dead
+	PermitWithoutStream: true,             // send pings even without active streams
+}
+
+func main() {
+	flag.Parse()
+
+	conn, err := grpc.Dial(*addr, grpc.WithInsecure(), grpc.WithKeepaliveParams(kacp))
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer conn.Close()
+
+	c := pb.NewEchoClient(conn)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Minute)
+	defer cancel()
+	fmt.Println("Performing unary request")
+	res, err := c.UnaryEcho(ctx, &pb.EchoRequest{Message: "keepalive demo"})
+	if err != nil {
+		log.Fatal("unexpected error from UnaryEcho: %v", err)
+	}
+	fmt.Println("RPC response:", res)
+	select {} // Block forever; run with GODEBUG=http2debug=2 to observe ping frames and GOAWAYs due to idleness.
+}

examples/features/keepalive/server/main.go

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+/*
+ *
+ * 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"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/keepalive"
+	"google.golang.org/grpc/status"
+)
+
+var port = flag.Int("port", 50052, "port number")
+
+var kaep = keepalive.EnforcementPolicy{
+	MinTime:             5 * time.Second, // If a client pings more than once every 5 seconds, terminate the connection
+	PermitWithoutStream: true,            // Allow pings even when there are no active streams
+}
+
+var kasp = keepalive.ServerParameters{
+	MaxConnectionIdle:     15 * time.Second, // If a client is idle for 10 seconds, send a GOAWAY
+	MaxConnectionAge:      30 * time.Second, // If any connection is alive for more than 30 seconds, send a GOAWAY
+	MaxConnectionAgeGrace: 5 * time.Second,  // Allow 5 seconds for pending RPCs to complete before forcibly closing connections
+	Time:                  5 * time.Second,  // Ping the client if it is idle for 5 seconds to ensure the connection is still active
+	Timeout:               1 * time.Second,  // Wait 1 second for the ping ack before assuming the connection is dead
+}
+
+// server implements EchoServer.
+type server struct{}
+
+func (s *server) UnaryEcho(ctx context.Context, req *pb.EchoRequest) (*pb.EchoResponse, error) {
+	return &pb.EchoResponse{Message: req.Message}, nil
+}
+
+func (s *server) ServerStreamingEcho(req *pb.EchoRequest, stream pb.Echo_ServerStreamingEchoServer) error {
+	return status.Error(codes.Unimplemented, "RPC unimplemented")
+}
+
+func (s *server) ClientStreamingEcho(stream pb.Echo_ClientStreamingEchoServer) error {
+	return status.Error(codes.Unimplemented, "RPC unimplemented")
+}
+
+func (s *server) 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)
+	}
+
+	s := grpc.NewServer(grpc.KeepaliveEnforcementPolicy(kaep), grpc.KeepaliveParams(kasp))
+	pb.RegisterEchoServer(s, &server{})
+
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}