Implement UDP socket server and add package installation check utility

cmd/udpsocket/main.go

@@ -0,0 +1,58 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"packets/configs"
+	"packets/internal/consts"
+	"path/filepath"
+	"strings"
+)
+
+func CheckDownloaded(filename string) bool {
+
+	cfg, err := configs.GetConfigTOML()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	_, err = os.Stat(filepath.Join(cfg.Config.Cache_d, filename))
+	return err == nil
+}
+
+func main() {
+	pid := os.Getpid()
+	if err := os.WriteFile(filepath.Join(consts.DefaultLinux_d, "udp.pid"), []byte(fmt.Sprint(pid)), 0664); err != nil {
+		fmt.Println("error saving subprocess pid", err)
+	}
+	cfg, err := configs.GetConfigTOML()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	addr := net.UDPAddr{IP: net.IPv4zero, Port: 1333}
+	conn, err := net.ListenUDP("udp", &addr)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer conn.Close()
+	buf := make([]byte, 1500)
+
+	for {
+		n, remote, err := conn.ReadFromUDP(buf)
+		if err != nil {
+			log.Println("error creating udp socket", err)
+		}
+		msg := string(buf[:n])
+		if !strings.HasPrefix(msg, "Q:") {
+			continue
+		}
+		filename := strings.TrimPrefix(msg, "Q:")
+		if CheckDownloaded(filename) {
+			reply := fmt.Sprintf("H:%s:%d", filename, cfg.Config.HttpPort)
+			conn.WriteToUDP([]byte(reply), remote)
+		}
+	}
+}