init

main.go

@@ -0,0 +1,182 @@
+package main
+
+import (
+	"bufio"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+	"strings"
+	"time"
+)
+
+func getEnvDefault(name, def string) string {
+	v := os.Getenv(name)
+	if v != "" {
+		return v
+	}
+	return def
+}
+
+func parseProxy() *url.URL {
+	raw := strings.TrimPrefix(strings.TrimSpace(os.Getenv("PROXY")), "http://")
+	if raw == "" {
+		log.Fatal("missing PROXY (format: login:password@ip:port)")
+	}
+
+	creds, hostPort, ok := strings.Cut(raw, "@")
+	if !ok {
+		log.Fatal("expected login:password@ip:port")
+	}
+
+	login, password, ok := strings.Cut(creds, ":")
+	if !ok || strings.TrimSpace(login) == "" || strings.TrimSpace(password) == "" {
+		log.Fatal("expected login:password before @")
+	}
+
+	hostPort = strings.TrimSpace(hostPort)
+	if _, _, err := net.SplitHostPort(hostPort); err != nil {
+		log.Fatalf("invalid ip:port: %v", err)
+	}
+
+	return &url.URL{Scheme: "http", User: url.UserPassword(login, password), Host: hostPort}
+}
+
+func proxyHandler(transport *http.Transport, upstream *url.URL) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/health" {
+			w.Write([]byte("ok"))
+			return
+		}
+
+		if r.Method == http.MethodConnect {
+			handleTunneling(w, r, upstream)
+			return
+		}
+
+		handleHTTP(w, r, transport)
+	}
+}
+
+func handleHTTP(w http.ResponseWriter, r *http.Request, transport *http.Transport) {
+	target := r.URL
+	if !target.IsAbs() {
+		target = &(*r.URL)
+		target.Scheme = "http"
+		target.Host = r.Host
+	}
+
+	outReq, err := http.NewRequestWithContext(r.Context(), r.Method, target.String(), r.Body)
+	if err != nil {
+		http.Error(w, "bad request", http.StatusBadRequest)
+		return
+	}
+	outReq.Header = r.Header.Clone()
+	outReq.RequestURI = ""
+
+	resp, err := transport.RoundTrip(outReq)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	}
+	defer resp.Body.Close()
+
+	copyHeader(w.Header(), resp.Header)
+	w.WriteHeader(resp.StatusCode)
+	_, _ = io.Copy(w, resp.Body)
+}
+
+func handleTunneling(w http.ResponseWriter, r *http.Request, upstream *url.URL) {
+	targetAddr := r.Host
+	if _, _, err := net.SplitHostPort(targetAddr); err != nil {
+		targetAddr = net.JoinHostPort(targetAddr, "443")
+	}
+
+	upstreamConn, err := net.DialTimeout("tcp", upstream.Host, 10*time.Second)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	}
+
+	if _, err := fmt.Fprintf(
+		upstreamConn,
+		"CONNECT %s HTTP/1.1\r\nHost: %s\r\nProxy-Authorization: %s\r\n\r\n",
+		targetAddr,
+		targetAddr,
+		basicAuthHeader(upstream.User),
+	); err != nil {
+		_ = upstreamConn.Close()
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	}
+
+	br := bufio.NewReader(upstreamConn)
+	resp, err := http.ReadResponse(br, &http.Request{Method: http.MethodConnect})
+	if err != nil {
+		_ = upstreamConn.Close()
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	}
+	if resp.StatusCode != http.StatusOK {
+		_ = resp.Body.Close()
+		_ = upstreamConn.Close()
+		http.Error(w, resp.Status, http.StatusBadGateway)
+		return
+	}
+	_ = resp.Body.Close()
+
+	hijacker, ok := w.(http.Hijacker)
+	if !ok {
+		_ = upstreamConn.Close()
+		http.Error(w, "hijacking not supported", http.StatusInternalServerError)
+		return
+	}
+
+	clientConn, _, err := hijacker.Hijack()
+	if err != nil {
+		_ = upstreamConn.Close()
+		return
+	}
+
+	_, _ = clientConn.Write([]byte("HTTP/1.1 200 Connection Established\r\n\r\n"))
+
+	go transfer(upstreamConn, clientConn)
+	go transfer(clientConn, upstreamConn)
+}
+
+func basicAuthHeader(user *url.Userinfo) string {
+	if user == nil {
+		return ""
+	}
+	password, _ := user.Password()
+	token := base64.StdEncoding.EncodeToString([]byte(user.Username() + ":" + password))
+	return "Basic " + token
+}
+
+func transfer(dst io.WriteCloser, src io.ReadCloser) {
+	defer dst.Close()
+	defer src.Close()
+	_, _ = io.Copy(dst, src)
+}
+
+func copyHeader(dst, src http.Header) {
+	for k, vv := range src {
+		for _, v := range vv {
+			dst.Add(k, v)
+		}
+	}
+}
+
+func main() {
+	listenAddr := ":" + getEnvDefault("PORT", "80")
+	upstream := parseProxy()
+
+	transport := &http.Transport{Proxy: http.ProxyURL(upstream)}
+
+	log.Printf("Proxy running on %s -> http://%s@%s", listenAddr, upstream.User.Username(), upstream.Host)
+	log.Fatal(http.ListenAndServe(listenAddr, proxyHandler(transport, upstream)))
+}