lil-connect-proxy.go

package main

import (
        "io"
        "log"
        "net"
        "net/http"
        "os"
)

func main() {
        log.Fatal(http.ListenAndServe("10.2.0.1:8123", http.HandlerFunc(handle)))
}

func handle(w http.ResponseWriter, r *http.Request) {
        if r.Method == "CONNECT" {
                log.Printf("CONNECT RequestURI = %q", r.RequestURI)

                var d net.Dialer
                c, err := d.DialContext(r.Context(), "tcp", r.RequestURI)
                if err != nil {
                        http.Error(w, err.Error(), http.StatusBadGateway)
                        return
                }
                defer c.Close()

                conn, _, err := w.(http.Hijacker).Hijack()
                if err != nil {
                        panic(err)
                }
                defer conn.Close()
                io.WriteString(conn, "HTTP/1.1 200 OK\r\n\r\n")

                errc := make(chan error, 1)
                go func() {
                        _, err := io.Copy(c, conn)
                        errc <- err
                }()
                go func() {
                        _, err := io.Copy(conn, c)
                        errc <- err
                }()
                <-errc
        }
        r.Write(os.Stderr)
}