Port Forwarding
To create a port forwarding program in Go, you need to create a few files: main.go for the main logic and optionally, a forwarder.go file for the port forwarding functionality. Here is a step-by-step guide:
Step 1: Initialize the Go Module
First, create a new directory for your project and initialize the Go module.
mkdir portforwarding
cd portforwarding
go mod init github.com/username/portforwarding
Step 2: Create the forwarder.go File
Create a forwarder/forwarder.go file to handle the port forwarding functionality.
// forwarder.go
package forwarder
import (
"io"
"log"
"net"
)
// forward handles the forwarding of data between the client and the target server.
func forward(src net.Conn, dst net.Conn) {
defer src.Close()
defer dst.Close()
io.Copy(src, dst)
}
// handleConnection handles the incoming client connection and forwards data to the target server.
func handleConnection(clientConn net.Conn, target string) {
defer clientConn.Close()
serverConn, err := net.Dial("tcp", target)
if err != nil {
log.Printf("Failed to connect to target server: %v", err)
return
}
defer serverConn.Close()
go forward(clientConn, serverConn)
forward(serverConn, clientConn)
}
// StartForwarder starts the port forwarder on the specified port and forwards traffic to the target server.
func StartForwarder(listenPort, target string) error {
listener, err := net.Listen("tcp", ":"+listenPort)
if err != nil {
return err
}
defer listener.Close()
log.Printf("Port forwarder started on port %s, forwarding to %s", listenPort, target)
for {
clientConn, err := listener.Accept()
if err != nil {
log.Printf("Failed to accept connection: %v", err)
continue
}
go handleConnection(clientConn, target)
}
}
Step 3: Create the main.go File
Create a main.go file to use the port forwarding functionality.
// main.go
package main
import (
"fmt"
"log"
"os"
"github.com/username/portforwarding/forwarder"
)
func main() {
if len(os.Args) != 3 {
fmt.Println("Usage: portforwarding <listen_port> <target>")
os.Exit(1)
}
listenPort := os.Args[1]
target := os.Args[2]
fmt.Printf("Starting port forwarder on port %s, forwarding to %s...\n", listenPort, target)
if err := forwarder.StartForwarder(listenPort, target); err != nil {
log.Fatalf("Port forwarder failed: %v", err)
}
}
Step 4: Run the Program
Run the program using the go run command.
go run main.go 8080 example.com:80
This will start the port forwarder on port 8080 and forward traffic to example.com on port 80.
Last modified: 08 January 2025