example: cancellation (#2525)

examples/features/cancellation/README.md

@@ -0,0 +1,13 @@
+# Cancellation
+
+This example shows how clients can cancel in-flight RPCs by canceling the
+context passed to the RPC call.  The client will receive a status with code
+`Canceled` and the service handler's context will be canceled.
+
+```
+go run server/main.go
+```
+
+```
+go run client/main.go
+```

examples/features/cancellation/client/main.go

@@ -0,0 +1,94 @@
+/*
+ *
+ * Copyright 2018 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"
+	"google.golang.org/grpc/codes"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/status"
+)
+
+var addr = flag.String("addr", "localhost:50051", "the address to connect to")
+
+func sendMessage(stream pb.Echo_BidirectionalStreamingEchoClient, msg string) error {
+	fmt.Printf("sending message %q\n", msg)
+	return stream.Send(&pb.EchoRequest{Message: msg})
+}
+
+func recvMessage(stream pb.Echo_BidirectionalStreamingEchoClient, wantErrCode codes.Code) {
+	res, err := stream.Recv()
+	if status.Code(err) != wantErrCode {
+		log.Fatalf("stream.Recv() = %v, %v; want _, status.Code(err)=%v", res, err, wantErrCode)
+	}
+	if err != nil {
+		fmt.Printf("stream.Recv() returned expected error %v\n", err)
+		return
+	}
+	fmt.Printf("received message %q\n", res.GetMessage())
+}
+
+func main() {
+	flag.Parse()
+
+	// Set up a connection to the server.
+	conn, err := grpc.Dial(*addr, grpc.WithInsecure())
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer conn.Close()
+
+	c := pb.NewEchoClient(conn)
+
+	// Initiate the stream with a context that supports cancellation.
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	stream, err := c.BidirectionalStreamingEcho(ctx)
+	if err != nil {
+		log.Fatalf("error creating stream: %v", err)
+	}
+
+	// Send some test messages.
+	if err := sendMessage(stream, "hello"); err != nil {
+		log.Fatalf("error sending on stream: %v", err)
+	}
+	if err := sendMessage(stream, "world"); err != nil {
+		log.Fatalf("error sending on stream: %v", err)
+	}
+
+	// Ensure the RPC is working.
+	recvMessage(stream, codes.OK)
+	recvMessage(stream, codes.OK)
+
+	fmt.Println("cancelling context")
+	cancel()
+
+	// This Send may or may not return an error, depending on whether the
+	// monitored context detects cancellation before the call is made.
+	sendMessage(stream, "closed")
+
+	// This Recv should never succeed.
+	recvMessage(stream, codes.Canceled)
+}

examples/features/cancellation/server/main.go

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+/*
+ *
+ * Copyright 2018 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"
+	"io"
+	"log"
+	"net"
+
+	"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", 50051, "the port to serve on")
+
+type server struct{}
+
+func (s *server) UnaryEcho(ctx context.Context, in *pb.EchoRequest) (*pb.EchoResponse, error) {
+	return nil, status.Error(codes.Unimplemented, "not implemented")
+}
+
+func (s *server) ServerStreamingEcho(in *pb.EchoRequest, stream pb.Echo_ServerStreamingEchoServer) error {
+	return status.Error(codes.Unimplemented, "not implemented")
+}
+
+func (s *server) ClientStreamingEcho(stream pb.Echo_ClientStreamingEchoServer) error {
+	return status.Error(codes.Unimplemented, "not implemented")
+}
+
+func (s *server) BidirectionalStreamingEcho(stream pb.Echo_BidirectionalStreamingEchoServer) error {
+	for {
+		in, err := stream.Recv()
+		if err != nil {
+			fmt.Printf("server: error receiving from stream: %v\n", err)
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+		fmt.Printf("echoing message %q\n", in.Message)
+		stream.Send(&pb.EchoResponse{Message: in.Message})
+	}
+}
+
+func main() {
+	flag.Parse()
+
+	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+	fmt.Printf("server listening at port %v\n", lis.Addr())
+	s := grpc.NewServer()
+	pb.RegisterEchoServer(s, &server{})
+	s.Serve(lis)
+}