gserver/handler.go

package main

import (
	"fmt"
	auth "github.com/abbot/go-http-auth"
	"io"
	"log"
	"net"
	"net/http"
	"strings"
	"time"
)

// handler process the proxy request first(if enabled)
// and route the request to the registered http.Handler
type handler struct {
	handler      http.Handler
	enableProxy  bool
	enableAuth   bool
	authMethod   *auth.DigestAuth
	localDomains []string
}

var defaultTransport http.RoundTripper = &http.Transport{
	//DialContext:         dialContext,
	MaxIdleConns:          50,
	IdleConnTimeout:       30 * time.Second,
	MaxIdleConnsPerHost:   3,
	DisableKeepAlives:     true,
	ResponseHeaderTimeout: 2 * time.Second,
}

// ServeHTTP implements the http.Handler interface
func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// http/1.1 local request
	if r.ProtoMajor == 1 && r.RequestURI[0] == '/' {
		if h.handler != nil {
			h.handler.ServeHTTP(w, r)
		} else {
			http.DefaultServeMux.ServeHTTP(w, r)
		}
		return
	}

	// http/2.0 local request
	if r.ProtoMajor == 2 && h.isLocalRequest(r) {
		if h.handler != nil {
			h.handler.ServeHTTP(w, r)
		} else {
			http.DefaultServeMux.ServeHTTP(w, r)
		}
		return
	}

	// proxy request

	if !h.enableProxy {
		w.WriteHeader(http.StatusNotFound)
		fmt.Fprintf(w, "<h1>404 Not Found</h1>")
		return
	}

	if h.enableAuth {
		u, _ := h.authMethod.CheckAuth(r)
		if u == "" {
			h.authMethod.RequireAuth(w, r)
			return
		}
	}

	if r.Method == http.MethodConnect {
		// CONNECT request
		h.handleCONNECT(w, r)
	} else {
		// GET, POST, PUT, ....
		h.handleHTTP(w, r)
	}
}

func (h *handler) handleHTTP(w http.ResponseWriter, r *http.Request) {

	var resp *http.Response
	var err error

	r.Header.Del("proxy-connection")

	if r.ProtoMajor == 2 {
		r.URL.Scheme = "http"
		r.URL.Host = r.Host
		r.RequestURI = r.URL.String()
		if r.Method != http.MethodPost && r.Method != http.MethodPut {
			r.ContentLength = 0
			r.Body.Close()
			r.Body = nil
		}
	}

	resp, err = defaultTransport.RoundTrip(r)
	if err != nil {
		log.Printf("RoundTrip: %s", err)
		w.Header().Set("Content-Type", "text/plain")
		w.WriteHeader(http.StatusServiceUnavailable)
		fmt.Fprintf(w, "%s", err)
		return
	}

	defer resp.Body.Close()

	hdr := w.Header()

	resp.Header.Del("connection")

	for k, v := range resp.Header {
		for _, v1 := range v {
			hdr.Add(k, v1)
		}
	}

	w.WriteHeader(resp.StatusCode)
	io.Copy(w, resp.Body)
}

type flushWriter struct {
	w io.Writer
}

func (fw flushWriter) Write(buf []byte) (int, error) {
	n, err := fw.w.Write(buf)
	fw.w.(http.Flusher).Flush()
	return n, err
}

func (h *handler) handleCONNECT(w http.ResponseWriter, r *http.Request) {
	host := r.RequestURI

	if r.ProtoMajor == 2 {
		host = r.URL.Host
	}

	if !strings.Contains(host, ":") {
		host = fmt.Sprintf("%s:443", host)
	}

	var conn net.Conn
	var err error

	conn, err = net.Dial("tcp", host)
	if err != nil {
		log.Printf("net.dial: %s", err)
		w.Header().Set("Content-Type", "text/plain")
		w.WriteHeader(http.StatusServiceUnavailable)
		fmt.Fprintf(w, "dial to %s failed: %s", host, err)
		return
	}

	if r.ProtoMajor == 1 {
		// HTTP/1.1
		hj, _ := w.(http.Hijacker)
		conn1, _, _ := hj.Hijack()

		fmt.Fprintf(conn1, "%s 200 connection established\r\n\r\n", r.Proto)

		pipeAndClose(conn, conn1)
		return
	}

	// HTTP/2.0

	defer conn.Close()

	w.WriteHeader(http.StatusOK)
	w.(http.Flusher).Flush()

	ch := make(chan int, 2)
	go func() {
		io.Copy(conn, r.Body)
		ch <- 1
	}()

	go func() {
		io.Copy(flushWriter{w}, conn)
		ch <- 1
	}()

	<-ch
}

// isLocalRequest determine the http2 request is local path request
// or the proxy request
func (h *handler) isLocalRequest(r *http.Request) bool {
	if !h.enableProxy {
		return true
	}

	if len(h.localDomains) == 0 {
		return true
	}

	host := r.Host
	if h1, _, err := net.SplitHostPort(r.Host); err == nil {
		host = h1
	}

	for _, s := range h.localDomains {
		if strings.HasSuffix(host, s) {
			return true
		}
	}

	return false
}

func pipeAndClose(r1, r2 io.ReadWriteCloser) {
	defer r1.Close()
	defer r2.Close()

	ch := make(chan int, 2)
	go func() {
		io.Copy(r1, r2)
		ch <- 1
	}()

	go func() {
		io.Copy(r2, r1)
		ch <- 1
	}()

	<-ch
}