basic functions

go.mod

@@ -0,0 +1,5 @@
+module goproxy
+
+go 1.22.5
+
+require github.com/yosuke-furukawa/json5 v0.1.1 // indirect

go.sum

@@ -0,0 +1,2 @@
+github.com/yosuke-furukawa/json5 v0.1.1 h1:0F9mNwTvOuDNH243hoPqvf+dxa5QsKnZzU20uNsh3ZI=
+github.com/yosuke-furukawa/json5 v0.1.1/go.mod h1:sw49aWDqNdRJ6DYUtIQiaA3xyj2IL9tjeNYmX2ixwcU=

main.go

@@ -0,0 +1,167 @@
+package main
+
+import (
+	"io"
+	"io/ioutil"
+	"log"
+	"net"
+	"os"
+	"strings"
+
+	"github.com/yosuke-furukawa/json5/encoding/json5"
+)
+
+type ProxyConfig struct {
+	Proxy []Proxy `json:"proxy"`
+}
+
+type Proxy struct {
+	Local  string `json:"local,omitempty"`
+	Remote string `json:"remote"`
+	Type   string `json:"type,omitempty"` // "tcp", "udp", or "both"
+}
+
+func handleTCPConnection(src net.Conn, targetAddr string) {
+	defer src.Close()
+
+	dst, err := net.Dial("tcp", targetAddr)
+	if err != nil {
+		log.Printf("Unable to connect to target: %v\n", err)
+		return
+	}
+	defer dst.Close()
+
+	done := make(chan struct{})
+
+	go func() {
+		io.Copy(dst, src)
+		done <- struct{}{}
+	}()
+
+	go func() {
+		io.Copy(src, dst)
+		done <- struct{}{}
+	}()
+
+	<-done
+}
+
+func startTCPProxy(localAddr, targetAddr string) {
+	listener, err := net.Listen("tcp", localAddr)
+	if err != nil {
+		log.Fatalf("Unable to listen on %s: %v\n", localAddr, err)
+	}
+	defer listener.Close()
+
+	log.Printf("Listening on %s (TCP), forwarding to %s\n", localAddr, targetAddr)
+
+	for {
+		conn, err := listener.Accept()
+		if err != nil {
+			log.Printf("Failed to accept connection: %v\n", err)
+			continue
+		}
+
+		go handleTCPConnection(conn, targetAddr)
+	}
+}
+
+func startUDPProxy(localAddr, targetAddr string) {
+	localConn, err := net.ListenPacket("udp", localAddr)
+	if err != nil {
+		log.Fatalf("Unable to listen on %s: %v\n", localAddr, err)
+	}
+	defer localConn.Close()
+
+	remoteAddr, err := net.ResolveUDPAddr("udp", targetAddr)
+	if err != nil {
+		log.Fatalf("Unable to resolve target address: %v\n", err)
+	}
+
+	buf := make([]byte, 4096)
+
+	log.Printf("Listening on %s (UDP), forwarding to %s\n", localAddr, targetAddr)
+
+	for {
+		n, addr, err := localConn.ReadFrom(buf)
+		if err != nil {
+			log.Printf("Failed to read from connection: %v\n", err)
+			continue
+		}
+
+		go func(data []byte, addr net.Addr) {
+			remoteConn, err := net.DialUDP("udp", nil, remoteAddr)
+			if err != nil {
+				log.Printf("Unable to connect to target: %v\n", err)
+				return
+			}
+			defer remoteConn.Close()
+
+			_, err = remoteConn.Write(data)
+			if err != nil {
+				log.Printf("Failed to write to target: %v\n", err)
+				return
+			}
+
+			n, _, err := remoteConn.ReadFrom(data)
+			if err != nil {
+				log.Printf("Failed to read from target: %v\n", err)
+				return
+			}
+
+			_, err = localConn.WriteTo(data[:n], addr)
+			if err != nil {
+				log.Printf("Failed to write back to source: %v\n", err)
+			}
+		}(buf[:n], addr)
+	}
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		log.Fatalf("Usage: %s <config-file>", os.Args[0])
+	}
+
+	configFile := os.Args[1]
+
+	configData, err := ioutil.ReadFile(configFile)
+	if err != nil {
+		log.Fatalf("Failed to read config file: %v\n", err)
+	}
+
+	var config ProxyConfig
+	if err := json5.Unmarshal(configData, &config); err != nil {
+		log.Fatalf("Failed to parse config file: %v\n", err)
+	}
+
+	for _, proxy := range config.Proxy {
+		// Default type to "both" if not provided
+		if proxy.Type == "" {
+			proxy.Type = "both"
+		}
+
+		// Default local to the port of remote if not provided
+		if proxy.Local == "" {
+			parts := strings.Split(proxy.Remote, ":")
+			if len(parts) == 2 {
+				proxy.Local = ":" + parts[1]
+			} else {
+				log.Fatalf("Invalid remote address format: %s\n", proxy.Remote)
+			}
+		}
+
+		switch proxy.Type {
+		case "tcp":
+			go startTCPProxy(proxy.Local, proxy.Remote)
+		case "udp":
+			go startUDPProxy(proxy.Local, proxy.Remote)
+		case "both":
+			go startTCPProxy(proxy.Local, proxy.Remote)
+			go startUDPProxy(proxy.Local, proxy.Remote)
+		default:
+			log.Printf("Unknown proxy type: %s\n", proxy.Type)
+		}
+	}
+
+	select {}
+}