aerialcombat · May 12, 2024 19:28 · aerialcombat · May 12, 2024
diff --git a/goproxy.go b/goproxy.go
 package main

 import (
 	"flag"
 	"io"
 	"log"
 	"net"
 	"net/http"
 	"strings"
 )

 // hopHeaders are headers that should be removed when sent to the backend.
 var hopHeaders = []string{
 	"Connection",
 	"Keep-Alive",
 	"Proxy-Authenticate",
 	"Proxy-Authorization",
 	"Te", // TE as per canonicalization
 	"Trailers",
 	"Transfer-Encoding",
 	"Upgrade",
 }

 // Proxy represents the proxy handler.
 type Proxy struct{}

 // NewProxy creates a new instance of a Proxy.
 func NewProxy() *Proxy {
 	return &Proxy{}
 }

 // ServeHTTP handles HTTP requests to the proxy.
 func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	log.Printf("%s %s %s", r.RemoteAddr, r.Method, r.URL)

 	if r.Method == "CONNECT" {
 		p.handleConnect(w, r)
 	} else {
 		p.forwardRequest(w, r)
 	}
 }

 // handleConnect deals with the CONNECT method by establishing a tunnel.
 func (p *Proxy) handleConnect(w http.ResponseWriter, r *http.Request) {
 	log.Printf("Handling CONNECT method for %s", r.Host)

 	destConn, err := net.Dial("tcp", r.Host)
 	if err != nil {
 		log.Printf("Failed to connect to host %v: %v", r.Host, err)
 		http.Error(w, "Failed to connect to target host", http.StatusInternalServerError)
 		return
 	}

 	hijacker, ok := w.(http.Hijacker)
 	if !ok {
 		http.Error(w, "HTTP Server does not support hijacking", http.StatusInternalServerError)
 		return
 	}

 	clientConn, _, err := hijacker.Hijack()
 	if err != nil {
 		http.Error(w, "Hijacking failed", http.StatusInternalServerError)
 		return
 	}

 	clientConn.Write([]byte("HTTP/1.1 200 Connection Established\r\n\r\n"))

 	go transfer(destConn, clientConn)
 	go transfer(clientConn, destConn)
 }

 // forwardRequest forwards an HTTP request to the destination server.
 func (p *Proxy) forwardRequest(w http.ResponseWriter, r *http.Request) {
 	delHopHeaders(r.Header)
 	appendHostToXForwardHeader(r.Header, clientIP(r))

 	client := &http.Client{}
 	r.RequestURI = ""

 	resp, err := client.Do(r)
 	if err != nil {
 		log.Printf("Error forwarding request: %v", err)
 		http.Error(w, "Server Error", http.StatusInternalServerError)
 		return
 	}
 	defer resp.Body.Close()

 	copyResponse(w, resp)
 }

 // copyResponse copies the response from the destination server to the client.
 func copyResponse(w http.ResponseWriter, resp *http.Response) {
 	delHopHeaders(resp.Header)
 	copyHeader(w.Header(), resp.Header)
 	w.WriteHeader(resp.StatusCode)
 	io.Copy(w, resp.Body)
 }

 // transfer relays data between source and destination.
 func transfer(destination, source net.Conn) {
 	defer destination.Close()
 	defer source.Close()
 	io.Copy(destination, source)
 }

 // clientIP extracts the client IP address from the request.
 func clientIP(r *http.Request) string {
 	if clientIP, _, err := net.SplitHostPort(r.RemoteAddr); err == nil {
 		return clientIP
 	}
 	return "unknown"
 }

 // appendHostToXForwardHeader appends the host to the X-Forwarded-For header.
 func appendHostToXForwardHeader(header http.Header, host string) {
 	if prior, ok := header["X-Forwarded-For"]; ok {
 		host = strings.Join(prior, ", ") + ", " + host
 	}
 	header.Set("X-Forwarded-For", host)
 }

 // copyHeader copies headers from source to destination, except hop-by-hop headers.
 func copyHeader(dst, src http.Header) {
 	for k, vv := range src {
 		for _, v := range vv {
 			dst.Add(k, v)
 		}
 	}
 }

 // delHopHeaders deletes hop-by-hop headers.
 func delHopHeaders(header http.Header) {
 	for _, h := range hopHeaders {
 		header.Del(h)
 	}
 }

 func main() {
 	addr := flag.String("addr", "localhost:8080", "The address of the application.")
 	flag.Parse()

 	proxy := NewProxy()

 	log.Printf("Starting proxy server on %s", *addr)
 	if err := http.ListenAndServe(*addr, proxy); err != nil {
 		log.Fatalf("ListenAndServe: %v", err)
 	}
 }
	package main

	import (
	"flag"
	"io"
	"log"
	"net"
	"net/http"
	"strings"
	)

	// hopHeaders are headers that should be removed when sent to the backend.
	var hopHeaders = []string{
	"Connection",
	"Keep-Alive",
	"Proxy-Authenticate",
	"Proxy-Authorization",
	"Te", // TE as per canonicalization
	"Trailers",
	"Transfer-Encoding",
	"Upgrade",
	}

	// Proxy represents the proxy handler.
	type Proxy struct{}

	// NewProxy creates a new instance of a Proxy.
	func NewProxy() *Proxy {
	return &Proxy{}
	}

	// ServeHTTP handles HTTP requests to the proxy.
	func (p Proxy) ServeHTTP(w http.ResponseWriter, r http.Request) {
	log.Printf("%s %s %s", r.RemoteAddr, r.Method, r.URL)

	if r.Method == "CONNECT" {
	p.handleConnect(w, r)
	} else {
	p.forwardRequest(w, r)
	}
	}

	// handleConnect deals with the CONNECT method by establishing a tunnel.
	func (p Proxy) handleConnect(w http.ResponseWriter, r http.Request) {
	log.Printf("Handling CONNECT method for %s", r.Host)

	destConn, err := net.Dial("tcp", r.Host)
	if err != nil {
	log.Printf("Failed to connect to host %v: %v", r.Host, err)
	http.Error(w, "Failed to connect to target host", http.StatusInternalServerError)
	return
	}

	hijacker, ok := w.(http.Hijacker)
	if !ok {
	http.Error(w, "HTTP Server does not support hijacking", http.StatusInternalServerError)
	return
	}

	clientConn, _, err := hijacker.Hijack()
	if err != nil {
	http.Error(w, "Hijacking failed", http.StatusInternalServerError)
	return
	}

	clientConn.Write([]byte("HTTP/1.1 200 Connection Established\r\n\r\n"))

	go transfer(destConn, clientConn)
	go transfer(clientConn, destConn)
	}

	// forwardRequest forwards an HTTP request to the destination server.
	func (p Proxy) forwardRequest(w http.ResponseWriter, r http.Request) {
	delHopHeaders(r.Header)
	appendHostToXForwardHeader(r.Header, clientIP(r))

	client := &http.Client{}
	r.RequestURI = ""

	resp, err := client.Do(r)
	if err != nil {
	log.Printf("Error forwarding request: %v", err)
	http.Error(w, "Server Error", http.StatusInternalServerError)
	return
	}
	defer resp.Body.Close()

	copyResponse(w, resp)
	}

	// copyResponse copies the response from the destination server to the client.
	func copyResponse(w http.ResponseWriter, resp *http.Response) {
	delHopHeaders(resp.Header)
	copyHeader(w.Header(), resp.Header)
	w.WriteHeader(resp.StatusCode)
	io.Copy(w, resp.Body)
	}

	// transfer relays data between source and destination.
	func transfer(destination, source net.Conn) {
	defer destination.Close()
	defer source.Close()
	io.Copy(destination, source)
	}

	// clientIP extracts the client IP address from the request.
	func clientIP(r *http.Request) string {
	if clientIP, _, err := net.SplitHostPort(r.RemoteAddr); err == nil {
	return clientIP
	}
	return "unknown"
	}

	// appendHostToXForwardHeader appends the host to the X-Forwarded-For header.
	func appendHostToXForwardHeader(header http.Header, host string) {
	if prior, ok := header["X-Forwarded-For"]; ok {
	host = strings.Join(prior, ", ") + ", " + host
	}
	header.Set("X-Forwarded-For", host)
	}

	// copyHeader copies headers from source to destination, except hop-by-hop headers.
	func copyHeader(dst, src http.Header) {
	for k, vv := range src {
	for _, v := range vv {
	dst.Add(k, v)
	}
	}
	}

	// delHopHeaders deletes hop-by-hop headers.
	func delHopHeaders(header http.Header) {
	for _, h := range hopHeaders {
	header.Del(h)
	}
	}

	func main() {
	addr := flag.String("addr", "localhost:8080", "The address of the application.")
	flag.Parse()

	proxy := NewProxy()

	log.Printf("Starting proxy server on %s", *addr)
	if err := http.ListenAndServe(*addr, proxy); err != nil {
	log.Fatalf("ListenAndServe: %v", err)
	}
	}