RST case

case.go

package main

import (
	"bufio"
	"fmt"
	//	"io/ioutil"
	"log"
	"net"
	"os"
	"reflect"
)

func GetFD(l net.Listener) (uintptr, string) {
	v := reflect.ValueOf(l).Elem().FieldByName("fd").Elem()
	fd := uintptr(v.FieldByName("sysfd").Int())
	addr := l.Addr()
	name := fmt.Sprintf("%s:%s->", addr.Network(), addr.String())
	return fd, name
}

func CloneListener(l net.Listener) (net.Listener, error) {
	fd, fdName := GetFD(l)
	return net.FileListener(os.NewFile(fd, fdName))
}

func serve(l net.Listener) {
	for {
		c, err := l.Accept()
		if err != nil {
			log.Printf("Listener exiting: err: %s", err)
			return
		}
		log.Printf("Listener accepted connection")
		out := ""
		scanner := bufio.NewScanner(c)
		for scanner.Scan() {
			out += scanner.Text()
			// our null handler doesn't send a body, so we know the request is
			// done when we reach the blank line after the headers
			if scanner.Text() == "" {
				break
			}
		}
		log.Printf("Client read: %s", out)
		c.Write([]byte("Hello, world!\n"))
		c.Close()
	}
}

func send(addr string) (string, error) {
	conn, err := net.Dial("tcp", addr)
	if err != nil {
		return "", fmt.Errorf("failed to dial, error: %s", err)
	}
	defer conn.Close()
	_, err = conn.Write([]byte("GET / HTTP/1.1\nHost: localhost:8000\n\n"))
	if err != nil {
		return "", fmt.Errorf("failed to write, error: %s", err)
	}
	log.Printf("Scanner read the response, reading headers")
	out := ""
	scanner := bufio.NewScanner(conn)
	for scanner.Scan() {
		out += scanner.Text()
		// our null handler doesn't send a body, so we know the request is
		// done when we reach the blank line after the headers
		if scanner.Text() == "" {
			break
		}
	}

	return out, scanner.Err()
}

func withClone() {
	addr := "127.0.0.1:48879"
	l, err := net.Listen("tcp", addr)
	if err != nil {
		log.Fatalln(err)
	}
	log.Println("listening on", l.Addr())

	go serve(l)

	l2, err := CloneListener(l)
	if err != nil {
		log.Fatalln(err)
	}

	go serve(l2)

	if err := l.Close(); err != nil {
		log.Fatalln(err)
	}

	out, err := send(addr)
	log.Printf("Client got response: %s, error: %s", out, err)
}

func withoutClone() {
	addr := "127.0.0.1:48879"
	l, err := net.Listen("tcp", addr)
	if err != nil {
		log.Fatalln(err)
	}
	log.Println("listening on", l.Addr())

	go serve(l)

	out, err := send(addr)
	log.Printf("Client got response: %s, error: %s", out, err)

	if err := l.Close(); err != nil {
		log.Fatalln(err)
	}
}

func main() {
	withClone()
}