gistfile1.txt

package main

import (
        "os"
        "strconv"
        "syscall"
        "fmt"
        "net"
        "net/http"
)

const (
        listenFdsStart = 3
)

func fcntl(fd int, cmd int, arg int) (val int, errno int) {
        r0, _, e1 := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(cmd), uintptr(arg))
        val = int(r0)
        errno = int(e1)
        return
}

func ListenFds() []*os.File {
        pid, err := strconv.Atoi(os.Getenv("LISTEN_PID"))
        if err != nil || pid != os.Getpid() {
                return nil
        }
        nfds, err := strconv.Atoi(os.Getenv("LISTEN_FDS"))
        if err != nil || nfds == 0 {
                return nil
        }
        files := []*os.File(nil)
        for fd := listenFdsStart; fd < listenFdsStart+nfds; fd++ {
                flags, errno := fcntl(fd, syscall.F_GETFD, 0)
                if errno != 0 {
                        return nil
                }
                if flags&syscall.FD_CLOEXEC != 0 {
                        continue
                }
                syscall.CloseOnExec(fd)
                files = append(files, os.NewFile(uintptr(fd), ""))
        }
        return files
}

func fooHandler(w http.ResponseWriter, r *http.Request) {
  fmt.Println("served", r.URL)
	w.Header().Set("Content-Type", "text/plain")
	fmt.Fprintf(w, "Hello World, %s\n", r.Host)
}

func main() {
	fmt.Println("starting up")
	listen_fds := ListenFds()

	for fd_i := range listen_fds {
		l, err := net.FileListener(listen_fds[fd_i])
		if err != nil {
			// handle error
			fmt.Println("got err", err)
		}

		http.HandleFunc("/foo", fooHandler)
		http.Serve(l, nil)
	}
}