add traffic limiter plugin

limiter/traffic/example/grpc/main.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+
+	"github.com/go-gost/plugin/limiter/traffic/proto"
+	"google.golang.org/grpc"
+)
+
+var (
+	port = flag.Int("port", 8000, "The server port")
+)
+
+type server struct {
+	proto.UnimplementedLimiterServer
+}
+
+func (s *server) Limit(ctx context.Context, in *proto.LimitRequest) (*proto.LimitReply, error) {
+	reply := &proto.LimitReply{
+		In:  1024 * 1024,
+		Out: 512 * 1024,
+	}
+	log.Printf("limiter: client=%s src=%s network=%s, addr=%s", in.Client, in.Src, in.Network, in.Addr)
+	return reply, nil
+}
+
+func main() {
+	flag.Parse()
+	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
+	if err != nil {
+		log.Fatalf("failed to listen: %v", err)
+	}
+	s := grpc.NewServer()
+	proto.RegisterLimiterServer(s, &server{})
+	log.Printf("server listening at %v", lis.Addr())
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("failed to serve: %v", err)
+	}
+}