mp3_streamer.go

package main

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"net/http"
	"os"
	"os/signal"

	"github.com/bobertlo/go-mpg123/mpg123"
	"github.com/gordonklaus/portaudio"
)

const sampleRate = 44100
const seconds = 2

func main() {

	if len(os.Args) < 2 {
		fmt.Println("missing required argument:  input file name")
		return
	}
	fmt.Println("Playing.  Press Ctrl-C to stop.")

	sig := make(chan os.Signal, 1)
	signal.Notify(sig, os.Interrupt, os.Kill)

	// create mpg123 decoder instance
	decoder, err := mpg123.NewDecoder("")
	chk(err)

	fileName := os.Args[1]
	chk(decoder.Open(fileName))
	defer decoder.Close()

	// get audio format information
	rate, channels, _ := decoder.GetFormat()

	// make sure output format does not change
	decoder.FormatNone()
	decoder.Format(rate, channels, mpg123.ENC_SIGNED_16)

	portaudio.Initialize()
	defer portaudio.Terminate()
	buffer := make([]float32, rate*seconds)
	stream, err := portaudio.OpenDefaultStream(
		1, 0, float64(rate), len(buffer), func(in []float32) {
			for i := range buffer {
				buffer[i] = in[i]
			}
		})
	chk(err)
	chk(stream.Start())
	defer stream.Close()

	go func() {
		for {
			audio := make([]byte, 2*len(buffer))
			_, err = decoder.Read(audio)
			if err == mpg123.EOF {
				break
			}
			chk(err)

			chk(binary.Read(bytes.NewBuffer(audio), binary.LittleEndian, buffer))
			chk(stream.Write())
			select {
			case <-sig:
				return
			default:
			}
		}
	}()

	http.HandleFunc("/audio", handleAudioStream)
	http.ListenAndServe(":8080", nil)

}

func handleAudioStream(w http.ResponseWriter, r *http.Request) {
	flusher, ok := w.(http.Flusher)
	if !ok {
		panic("expected http.ResponseWriter to be an http.Flusher")
	}

	w.Header().Set("Connection", "Keep-Alive")
	w.Header().Set("Access-Control-Allow-Origin", "*")
	w.Header().Set("X-Content-Type-Options", "nosniff")
	w.Header().Set("Transfer-Encoding", "chunked")
	w.Header().Set("Content-Type", "audio/wave")
	for true {
		binary.Write(w, binary.BigEndian, &buffer)
		flusher.Flush() // Trigger "chunked" encoding and send a chunk...
		return
	}
}

func chk(err error) {
	if err != nil {
		panic(err)
	}
}