examples: Add audio_network example

Signed-off-by: Lilis Iskandar <lilis@veand.co>

examples/audio_network/audio_network.go

@@ -0,0 +1,92 @@
+package main
+
+// typedef unsigned char Uint8;
+// void AudioCallback(void *userdata, Uint8 *stream, int len);
+import "C"
+import (
+	"io/ioutil"
+	"log"
+	"net/http"
+	"reflect"
+	"unsafe"
+
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+const (
+	sampleHz = 48000
+)
+
+var (
+	audioData []byte
+)
+
+//export AudioCallback
+func AudioCallback(userdata unsafe.Pointer, stream *C.Uint8, length C.int) {
+	n := int(length)
+	hdr := reflect.SliceHeader{Data: uintptr(unsafe.Pointer(stream)), Len: n, Cap: n}
+	buf := *(*[]C.Uint8)(unsafe.Pointer(&hdr))
+
+	if len(audioData) == 0 {
+		for i := 0; i < n; i++ {
+			buf[i] = 0
+		}
+	} else {
+		for i := 0; i < n; i++ {
+			if i >= len(audioData) {
+				break
+			}
+
+			buf[i] = C.Uint8(audioData[i])
+		}
+
+		if n <= len(audioData) {
+			// Remove processed audio data
+			audioData = audioData[n:]
+		} else {
+			// Clear audio data
+			audioData = audioData[len(audioData):]
+		}
+	}
+}
+
+// Handle audio data that is sent through HTTP
+// Must be stereo unsigned 8-bit audio data at 48000Hz to play correctly
+func audioHandler(w http.ResponseWriter, r *http.Request) {
+	data, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+
+	audioData = append(audioData, data...)
+
+	w.WriteHeader(http.StatusOK)
+}
+
+func main() {
+	if err := sdl.Init(sdl.INIT_AUDIO); err != nil {
+		log.Println(err)
+		return
+	}
+	defer sdl.Quit()
+
+	spec := &sdl.AudioSpec{
+		Freq:     sampleHz,
+		Format:   sdl.AUDIO_U8,
+		Channels: 2,
+		Samples:  sampleHz,
+		Callback: sdl.AudioCallback(C.AudioCallback),
+	}
+	if err := sdl.OpenAudio(spec, nil); err != nil {
+		log.Println(err)
+		return
+	}
+	defer sdl.CloseAudio()
+
+	sdl.PauseAudio(false)
+
+	http.HandleFunc("/audio", audioHandler)
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}
+