Toy HTTP-over-stdio thing

rwlisten.go

package main

import (
	"fmt"
	"io"
	"net"
	"net/http"
	"os"
	"time"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
		fmt.Fprintln(w, "Hello, world")
	})

	listener := newRWListener(os.Stdin, os.Stdout)
	http.Serve(listener, nil)
}

// rwListener implements net.Listener on top of the given reader/writer
// pair. Only a single "connection" can be open at a given time - once
// Accept() has returned a connection, further calls to Accept() will block
// until that connection has been closed or the listener is closed.
type rwListener struct {
	r     io.Reader
	w     io.Writer
	stop  chan struct{}
	avail chan struct{}
}

func newRWListener(r io.Reader, w io.Writer) *rwListener {
	l := &rwListener{
		r:     r,
		w:     w,
		stop:  make(chan struct{}),
		avail: make(chan struct{}, 1),
	}
	l.avail <- struct{}{}
	return l
}

func (l *rwListener) Accept() (net.Conn, error) {
	select {
	case <-l.avail:
		return &rwConn{
			r:      l.r,
			w:      l.w,
			closed: l.avail,
		}, nil

	case <-l.stop:
		return nil, fmt.Errorf("closed")
	}
}

func (l *rwListener) Addr() net.Addr {
	return &rwAddr{}
}

func (l *rwListener) Close() error {
	close(l.stop)
	return nil
}

// rwConn is a net.Conn for a reader/writer pair. A send to the closed chan
// will happen when Close() is called.
type rwConn struct {
	r      io.Reader
	w      io.Writer
	closed chan struct{}
}

func (c rwConn) RemoteAddr() net.Addr {
	return rwAddr{}
}

func (c rwConn) LocalAddr() net.Addr {
	return rwAddr{}
}

func (c rwConn) Close() error {
	c.closed <- struct{}{}
	return nil
}

func (c rwConn) Read(data []byte) (int, error) {
	return c.r.Read(data)
}

func (c rwConn) Write(data []byte) (int, error) {
	return c.w.Write(data)
}

func (c rwConn) SetReadDeadline(t time.Time) error  { return nil }
func (c rwConn) SetWriteDeadline(t time.Time) error { return nil }
func (c rwConn) SetDeadline(t time.Time) error      { return nil }

// rwAddr is a net.Addr for r/w connections
type rwAddr struct{}

func (rwAddr) String() string {
	return "-"
}

func (rwAddr) Network() string {
	return "rw"
}