add traffic limiter plugin

limiter/traffic/example/http/main.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+)
+
+var (
+	port = flag.Int("port", 8000, "The server port")
+)
+
+type limiterRequest struct {
+	Network string `json:"network"`
+	Addr    string `json:"addr"`
+	Client  string `json:"client"`
+	Src     string `json:"src"`
+}
+
+type limiterResponse struct {
+	In  int64 `json:"in"`
+	Out int64 `json:"out"`
+}
+
+func main() {
+	flag.Parse()
+	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+	log.Printf("server listening at %v", lis.Addr())
+
+	http.HandleFunc("/limiter", func(w http.ResponseWriter, r *http.Request) {
+		req := limiterRequest{}
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			log.Println(err)
+			w.WriteHeader(http.StatusBadRequest)
+			return
+		}
+
+		resp := limiterResponse{
+			In:  1024 * 1024, // 1MB
+			Out: 512 * 1024,  // 512KB
+		}
+
+		log.Printf("limiter: client=%s src=%s network=%s, addr=%s", req.Client, req.Src, req.Network, req.Addr)
+
+		json.NewEncoder(w).Encode(resp)
+	})
+
+	if err := http.Serve(lis, nil); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}