examples: add examples/middleware (#1121)

* examples: add examples/middleware

Co-authored-by: chenzhihui <zhihui_chen@foxmail.com>

examples/middleware/main.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+
+	"github.com/go-kratos/kratos/examples/helloworld/helloworld"
+	"github.com/go-kratos/kratos/v2"
+	"github.com/go-kratos/kratos/v2/middleware"
+	"github.com/go-kratos/kratos/v2/transport/grpc"
+	"github.com/go-kratos/kratos/v2/transport/http"
+)
+
+type server struct {
+	helloworld.UnimplementedGreeterServer
+}
+
+func (s *server) SayHello(ctx context.Context, in *helloworld.HelloRequest) (*helloworld.HelloReply, error) {
+	return &helloworld.HelloReply{Message: "hello"}, nil
+}
+
+func authMiddleware(handler middleware.Handler) middleware.Handler {
+	return func(ctx context.Context, req interface{}) (reply interface{}, err error) {
+		log.Println("auth middleware in", req)
+		reply, err = handler(ctx, req)
+		fmt.Println("auth middleware out", reply)
+		return
+	}
+}
+
+func loggingMiddleware(handler middleware.Handler) middleware.Handler {
+	return func(ctx context.Context, req interface{}) (reply interface{}, err error) {
+		fmt.Println("logging middleware in", req)
+		reply, err = handler(ctx, req)
+		fmt.Println("logging middleware out", reply)
+		return
+	}
+}
+
+func main() {
+	httpSrv := http.NewServer(
+		http.Address(":8000"),
+		http.Middleware(
+			loggingMiddleware,
+			authMiddleware,
+		),
+	)
+	grpcSrv := grpc.NewServer(
+		grpc.Address(":9000"),
+		grpc.Middleware(
+			loggingMiddleware,
+			authMiddleware,
+		),
+	)
+	s := &server{}
+	helloworld.RegisterGreeterServer(grpcSrv, s)
+	helloworld.RegisterGreeterHTTPServer(httpSrv, s)
+	app := kratos.New(
+		kratos.Name("helloworld"),
+		kratos.Server(
+			httpSrv,
+			grpcSrv,
+		),
+	)
+	if err := app.Run(); err != nil {
+		log.Fatal(err)
+	}
+}