add grpc example (#1401)

use grpc helloworld example.

examples/grpc/gin/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	pb "github.com/gin-gonic/gin/examples/grpc/pb"
+	"google.golang.org/grpc"
+)
+
+func main() {
+	// Set up a connection to the server.
+	conn, err := grpc.Dial("localhost:50051", grpc.WithInsecure())
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer conn.Close()
+	client := pb.NewGreeterClient(conn)
+
+	// Set up a http setver.
+	r := gin.Default()
+	r.GET("/rest/n/:name", func(c *gin.Context) {
+		name := c.Param("name")
+
+		// Contact the server and print out its response.
+		req := &pb.HelloRequest{Name: name}
+		res, err := client.SayHello(g, req)
+		if err != nil {
+			c.JSON(http.StatusInternalServerError, gin.H{
+				"error": err.Error(),
+			})
+			return
+		}
+
+		c.JSON(http.StatusOK, gin.H{
+			"result": fmt.Sprint(res.Message),
+		})
+	})
+
+	// Run http server
+	if err := r.Run(":8052"); err != nil {
+		log.Fatalf("could not run server: %v", err)
+	}
+}