TCP port forward through HTTP CONNECT PROXY

main.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"net/http"
	"net/url"
)

func handleConnection(clientConn net.Conn, proxyURL *url.URL, targetAddress string) {
	defer clientConn.Close()
	proxyConn, err := net.Dial("tcp", proxyURL.Host)
	if err != nil {
		fmt.Printf("Failed to connect to proxy: %v\n", err)
		return
	}
	defer proxyConn.Close()

	connectReq := &http.Request{
		Method: http.MethodConnect,
		URL:    &url.URL{Opaque: targetAddress},
		Host:   targetAddress,
		Header: make(http.Header),
	}
	err = connectReq.Write(proxyConn)
	if err != nil {
		fmt.Printf("Failed to write CONNECT request: %v\n", err)
		return
	}

	resp, err := http.ReadResponse(bufio.NewReader(proxyConn), connectReq)
	if err != nil {
		fmt.Printf("Failed to read CONNECT response: %v\n", err)
		return
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := ioutil.ReadAll(resp.Body)
		fmt.Printf("Proxy CONNECT response status: %v\n%s\n", resp.Status, body)
		return
	}

	go io.Copy(proxyConn, clientConn)
	io.Copy(clientConn, proxyConn)
}

func main() {
	listenAddr := "0.0.0.0:8088"
	proxyURL, err := url.Parse("http://squid-host:3128")
	if err != nil {
		fmt.Printf("Failed to parse proxy URL: %v\n", err)
		return
	}
	targetAddress := "target-mysql-host:3306"
	listener, err := net.Listen("tcp", listenAddr)
	if err != nil {
		fmt.Printf("Failed to start listener: %v\n", err)
		return
	}
	defer listener.Close()

	fmt.Printf("Listening on %s\n", listenAddr)
	for {
		clientConn, err := listener.Accept()
		if err != nil {
			fmt.Printf("Failed to accept connection: %v\n", err)
			continue
		}

		go handleConnection(clientConn, proxyURL, targetAddress)
	}
}

Or simply

socat TCP-LISTEN:8088,reuseaddr,fork PROXY:squid-host:target-mysql-host:3306,proxyport=3128