add example for context propagation in a server with goroutines.

Signed-off-by: Daniel Strobusch <[email protected]>

examples/features/context/README.md

@@ -0,0 +1,12 @@
+# Context
+
+This example shows how servers can process requests in separate goroutines and
+handle context cancellation.
+
+```
+go run server/main.go
+```
+
+```
+go run client/main.go
+```

examples/features/context/client/main.go

@@ -0,0 +1,161 @@
+/*
+ *
+ * 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 client demonstrates how to cancel in-flight RPCs by canceling the
+// context passed to the RPC.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/credentials/insecure"
+	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 cancelStream() {
+	fmt.Println("sending two messages and then canceling")
+	conn, err := grpc.NewClient(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	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("canceling context")
+	cancel()
+}
+
+func closeConnection() {
+	fmt.Println("sending two messages and then closing connection")
+	conn, err := grpc.NewClient(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer func() {
+		fmt.Println("closing connection")
+		conn.Close()
+	}()
+
+	c := pb.NewEchoClient(conn)
+
+	stream, err := c.BidirectionalStreamingEcho(context.Background())
+	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)
+}
+
+func timout() {
+	fmt.Println("sending two messages and then waiting for timeout")
+	conn, err := grpc.NewClient(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
+	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(), 1*time.Second)
+	defer cancel()
+
+	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)
+	}
+
+	recvMessage(stream, codes.OK)
+	recvMessage(stream, codes.OK)
+
+	fmt.Println("waiting for timeout")
+	<-ctx.Done()
+}
+
+func main() {
+	flag.Parse()
+
+	// simulate some client behaviors which terminate with different reasons
+	cancelStream()
+	closeConnection()
+	timout()
+}

examples/features/context/server/main.go

@@ -0,0 +1,96 @@
+/*
+ *
+ * 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 handle canceled contexts when a client
+// cancels an in-flight RPC.
+package main
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+
+	"golang.org/x/net/http2"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/internal/transport"
+
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+)
+
+var port = flag.Int("port", 50051, "the port to serve on")
+
+type server struct {
+	pb.UnimplementedEchoServer
+}
+
+func workOnMessage(ctx context.Context, msg string) {
+	fmt.Printf("starting work on message: %q\n", msg)
+	i := 0
+	for {
+		if err := ctx.Err(); err != nil {
+			cause := context.Cause(ctx)
+			fmt.Printf("'%v' with cause '%v', message worker for message %q stopping.\n", err, cause, msg)
+			var httpErr *transport.HTTP2CodeError
+			if errors.As(cause, &httpErr) {
+				switch httpErr.Code {
+				case http2.ErrCodeNo:
+					return
+				default:
+					fmt.Printf("unexpected HTTP/2 error: %v", httpErr)
+				}
+			}
+			return
+		}
+		// simulate work on message but don't flood the logs
+		i += 1
+	}
+}
+
+func (s *server) BidirectionalStreamingEcho(stream pb.Echo_BidirectionalStreamingEchoServer) error {
+	ctx := stream.Context()
+	for {
+		recv, err := stream.Recv()
+		if err != nil {
+			fmt.Printf("server: error receiving from stream: %v\n", err)
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		}
+		msg := recv.Message
+		go workOnMessage(ctx, msg)
+		stream.Send(&pb.EchoResponse{Message: msg})
+	}
+}
+
+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)
+}