examples: add client/server to be used for xds examples (#3362)

examples/features/xds/README.md

@@ -0,0 +1,37 @@
+# gRPC xDS example
+
+xDS is the protocol initially used by Envoy, that is evolving into a universal
+data plan API for service mesh.
+
+The xDS example is a Hello World client/server capable of being configured with
+the XDS management protocol. Out-of-the-box it behaves the same as [our other
+hello world
+example](https://github.com/grpc/grpc-go/tree/master/examples/helloworld). The
+server replies with responses including its hostname.
+
+**Note** that xDS support is incomplete and experimental, with limited
+compatibility.
+
+## xDS environment setup
+
+This example doesn't include instuctions to setup xDS environment. Please
+refer to documentation specific for your xDS management server.
+
+The client also needs a bootstrap file. See [gRFC
+A27](https://github.com/grpc/proposal/pull/170/files#diff-05ea4a5894abbc0261b006741220598cR100)
+for the bootstrap format.
+
+## The client
+
+The client application needs to import the xDS package to install the resolver and balancers:
+
+```go
+_ "google.golang.org/grpc/xds/experimental" // To install the xds resolvers and balancers.
+```
+
+Then, use `xds-experimental` target scheme for the ClientConn.
+
+```
+$ export GRPC_XDS_BOOTSTRAP=/path/to/bootstrap.json
+$ go run client/main.go "xDS world" xds-experimental:///target_service
+```

examples/features/xds/client/main.go

@@ -0,0 +1,97 @@
+// +build go1.11
+
+/*
+ *
+ * Copyright 2020 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.
+ *
+ */
+
+// Package main implements a client for Greeter service.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"time"
+
+	"google.golang.org/grpc"
+	pb "google.golang.org/grpc/examples/helloworld/helloworld"
+
+	_ "google.golang.org/grpc/xds/experimental" // To install the xds resolvers and balancers.
+)
+
+const (
+	defaultTarget = "localhost:50051"
+	defaultName   = "world"
+)
+
+var help = flag.Bool("help", false, "Print usage information")
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), `
+Usage: client [name [target]]
+
+  name
+        The name you wish to be greeted by. Defaults to %q
+  target
+        The URI of the server, e.g. "xds-experimental:///helloworld-service". Defaults to %q
+`, defaultName, defaultTarget)
+
+		flag.PrintDefaults()
+	}
+}
+
+func main() {
+	flag.Parse()
+	if *help {
+		flag.Usage()
+		return
+	}
+	args := flag.Args()
+
+	if len(args) > 2 {
+		flag.Usage()
+		return
+	}
+
+	name := defaultName
+	if len(args) > 0 {
+		name = args[0]
+	}
+
+	target := defaultTarget
+	if len(args) > 1 {
+		target = args[1]
+	}
+
+	// Set up a connection to the server.
+	conn, err := grpc.Dial(target, grpc.WithInsecure())
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer conn.Close()
+	c := pb.NewGreeterClient(conn)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	r, err := c.SayHello(ctx, &pb.HelloRequest{Name: name})
+	if err != nil {
+		log.Fatalf("could not greet: %v", err)
+	}
+	log.Printf("Greeting: %s", r.GetMessage())
+}

examples/features/xds/server/main.go

@@ -0,0 +1,129 @@
+// +build go1.11
+
+/*
+ *
+ * Copyright 2020 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.
+ *
+ */
+
+// Package main starts Greeter service that will response with the hostname.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"math/rand"
+	"net"
+	"os"
+	"strconv"
+	"time"
+
+	"google.golang.org/grpc"
+	pb "google.golang.org/grpc/examples/helloworld/helloworld"
+)
+
+var help = flag.Bool("help", false, "Print usage information")
+
+const (
+	defaultPort = 50051
+)
+
+// server is used to implement helloworld.GreeterServer.
+type server struct {
+	pb.UnimplementedGreeterServer
+
+	serverName string
+}
+
+func newServer(serverName string) *server {
+	return &server{
+		serverName: serverName,
+	}
+}
+
+// SayHello implements helloworld.GreeterServer
+func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
+	log.Printf("Received: %v", in.GetName())
+	return &pb.HelloReply{Message: "Hello " + in.GetName() + ", from " + s.serverName}, nil
+}
+
+func determineHostname() string {
+	hostname, err := os.Hostname()
+	if err != nil {
+		log.Printf("Failed to get hostname: %v, will generate one", err)
+		rand.Seed(time.Now().UnixNano())
+		return fmt.Sprintf("generated-%03d", rand.Int()%100)
+	}
+	return hostname
+}
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), `
+Usage: server [port [hostname]]
+
+  port
+        The listen port. Defaults to %d
+  hostname
+        The name clients will see in greet responses. Defaults to the machine's hostname
+`, defaultPort)
+
+		flag.PrintDefaults()
+	}
+}
+
+func main() {
+	flag.Parse()
+	if *help {
+		flag.Usage()
+		return
+	}
+	args := flag.Args()
+
+	if len(args) > 2 {
+		flag.Usage()
+		return
+	}
+
+	port := defaultPort
+	if len(args) > 0 {
+		var err error
+		port, err = strconv.Atoi(args[0])
+		if err != nil {
+			log.Printf("Invalid port number: %v", err)
+			flag.Usage()
+			return
+		}
+	}
+
+	var hostname string
+	if len(args) > 1 {
+		hostname = args[1]
+	}
+	if hostname == "" {
+		hostname = determineHostname()
+	}
+
+	lis, err := net.Listen("tcp", fmt.Sprintf("localhost:%d", port))
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+	s := grpc.NewServer()
+	pb.RegisterGreeterServer(s, newServer(hostname))
+	log.Printf("serving on %s, hostname %s", lis.Addr(), hostname)
+	s.Serve(lis)
+}