client hijack demo

Change-Id: I68d16b4a26bffe98b3c73feda130bfa4addf9436
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/clienthijackdemo/clienthijackdemo.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"bufio"
+	"context"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httptrace"
+	"os"
+	"runtime"
+	"strings"
+	"time"
+)
+
+var listen = flag.String("listen", ":8070", "listen")
+
+func main() {
+	flag.Parse()
+	log.Printf("%v; listening on %v ...", runtime.Version(), *listen)
+	go client()
+	log.Fatal(http.ListenAndServe(*listen, http.HandlerFunc(serve)))
+}
+
+func client() {
+	time.Sleep(200 * time.Millisecond)
+
+	tr := &http.Transport{
+		DisableKeepAlives: true,
+	}
+	connc := make(chan net.Conn, 1)
+	ctx := httptrace.WithClientTrace(context.Background(), &httptrace.ClientTrace{
+		GotConn: func(ci httptrace.GotConnInfo) {
+			log.Printf("gotconn: %+v", ci)
+			connc <- ci.Conn
+		},
+	})
+	req, _ := http.NewRequestWithContext(ctx, "POST", "http://localhost:8070", nil)
+	req.Header.Set("Connection", "upgrade")
+	req.Header.Set("Upgrade", "tailscale")
+	_, err := tr.RoundTrip(req)
+	if err != nil {
+		log.Printf("Failed: %v", err)
+		return
+	}
+	//log.Printf("client got: %+v", res)
+	//log.Printf("body type is %T", res.Body)
+
+	conn := <-connc
+	log.Printf("Conn was %T", conn)
+	go func() {
+		for {
+			time.Sleep(time.Second)
+			fmt.Fprintf(conn, "it is %v\n", time.Now())
+		}
+	}()
+	_, err = io.Copy(os.Stdout, conn) // res.Body)
+	log.Printf("Copy from conn: %v", err)
+}
+
+func serve(w http.ResponseWriter, r *http.Request) {
+	log.Printf("server got: %+v", r)
+	proto := r.Header.Get("Upgrade")
+	if proto != "tailscale" {
+		http.Error(w, "want tailscale", 400)
+		return
+	}
+
+	conn, brw, err := w.(http.Hijacker).Hijack()
+	if err != nil {
+		panic(err)
+	}
+	defer conn.Close()
+
+	io.WriteString(conn, "HTTP/1.0 101 Switch Protocols\r\nContent-Length: 1234\r\nConnection: upgrade\r\nUpgrade: tailscale\r\n\r\n")
+	/*w.Header().Set("Upgrade", "tailscale")
+	w.Header().Set("Content-Length", "1") // bug workaround
+	w.WriteHeader(101)
+	w.(http.Flusher).Flush()
+	*/
+
+	defer log.Printf("ending serve")
+
+	io.WriteString(conn, "hi.\n")
+
+	bs := bufio.NewScanner(brw)
+	for bs.Scan() {
+		fmt.Fprintln(conn, strings.TrimSpace(bs.Text()))
+	}
+	log.Printf("Scan: %v", bs.Err())
+}