Refactor, add HTTP server

.gitignore

@@ -1 +1,2 @@
+*.m4a
 /backend/cache/

backend/main.go

@@ -1,70 +1,41 @@
 package main
 
 import (
-	"bytes"
-	"encoding/binary"
 	"fmt"
 	"io"
 	"log"
+	"net/http"
 	"os"
-	"os/exec"
+	"strings"
-	"strconv"
+	"time"
 
 	"github.com/kkdai/youtube/v2"
 )
 
 const (
-	ItagM4AAudio = 140
+	ContentTypeAudioM4A = "audio/m4a"
-	SizeOfInt16  = 2
+	ItagM4AAudio        = 140
-
+	DefaultHTTPBindAddr = "0.0.0.0:8888"
-	DefaultAudioCodec = "pcm_s16le"
+	DefaultTimeout      = 5 * time.Second
-	DefaultFormat     = "s16le"
-	DefaultSampleRate = 44100
 )
 
-type byteToIntConverter struct {
-	callback func(p []uint16)
-	buf      []uint16
-}
-
-func (w byteToIntConverter) Write(p []byte) (int, error) {
-	if len(p)%2 != 0 {
-		panic("need to handle odd number of bytes")
-	}
-
-	// grow the internal buffer if necessary:
-	exp := len(p) / SizeOfInt16
-	if len(w.buf) < exp {
-		w.buf = append(w.buf, make([]uint16, exp)...)
-
-	}
-	for i := 0; i < len(p); i += SizeOfInt16 {
-		w.buf[i/2] = binary.LittleEndian.Uint16(p[i : i+SizeOfInt16])
-	}
-
-	w.callback(w.buf)
-
-	return len(p), nil
-}
-
 type AudioDownloader struct {
 	videoID  string
 	ytClient youtube.Client
+	reader   io.Reader
 }
 
-func NewAudioDownloader(videoID string) *AudioDownloader {
+func NewAudioDownloader(videoID string) (*AudioDownloader, error) {
-	return &AudioDownloader{videoID: videoID}
+	var (
-}
+		reader   io.Reader
-
+		ytClient youtube.Client
-func (d *AudioDownloader) ReadInts(fn func(p []uint16)) error {
+	)
-	cachePath := fmt.Sprintf("cache/%s.raw", d.videoID)
-
-	var reader io.Reader
 
+	cachePath := fmt.Sprintf("cache/%s.m4a", videoID)
 	fetch := true
+
 	if _, err := os.Stat(cachePath); err == nil {
 		if fptr, err := os.Open(cachePath); err == nil {
-			defer fptr.Close()
 			reader = fptr
 			fetch = false
 		} else {
@@ -75,48 +46,93 @@ func (d *AudioDownloader) ReadInts(fn func(p []uint16)) error {
 	if fetch {
 		log.Println("fetching audio stream from youtube...")
 
-		video, err := d.ytClient.GetVideo(d.videoID)
+		video, err := ytClient.GetVideo(videoID)
 		if err != nil {
-			return fmt.Errorf("error fetching video: %v", err)
+			return nil, fmt.Errorf("error fetching video: %v", err)
 		}
 
 		format := video.Formats.FindByItag(ItagM4AAudio)
-		stream, _, err := d.ytClient.GetStream(video, format)
+		log.Printf("M4A format expected to contain %d bytes", format.ContentLength)
+		stream, _, err := ytClient.GetStream(video, format)
 		if err != nil {
-			return fmt.Errorf("error fetching stream: %v", err)
+			return nil, fmt.Errorf("error fetching stream: %v", err)
 		}
 
+		// TODO: only allow the cached file to be accessed after it has been
+		// successfully downloaded.
 		cacheFile, err := os.Create(cachePath)
 		if err != nil {
-			return fmt.Errorf("error creating cache file: %v", err)
+			return nil, fmt.Errorf("error creating cache file: %v", err)
 		}
 		reader = io.TeeReader(stream, cacheFile)
 	}
 
-	var errOut bytes.Buffer
+	return &AudioDownloader{
-	cmd := exec.Command("ffmpeg", "-i", "-", "-f", DefaultFormat, "-ar", strconv.Itoa(DefaultSampleRate), "-acodec", DefaultAudioCodec, "-")
+		videoID:  videoID,
-	cmd.Stdin = reader
+		ytClient: ytClient,
-	cmd.Stdout = byteToIntConverter{callback: fn}
+		reader:   reader,
-	cmd.Stderr = &errOut
+	}, nil
+}
 
-	if err := cmd.Run(); err != nil {
+func (d *AudioDownloader) Read(p []byte) (int, error) {
-		log.Println(errOut.String())
+	return d.reader.Read(p)
-		return fmt.Errorf("error calling ffmpeg: %v", err)
+}
+
+func (d *AudioDownloader) Close() error {
+	if rc, ok := d.reader.(io.ReadCloser); ok {
+		return rc.Close()
 	}
-
 	return nil
 }
 
-func main() {
+func handleRequest(w http.ResponseWriter, r *http.Request) {
-	videoID := "s_oJYdRlrv0"
+	if r.Method != http.MethodGet {
-	downloader := NewAudioDownloader(videoID)
+		w.WriteHeader(http.StatusMethodNotAllowed)
-	err := downloader.ReadInts(func(p []uint16) {
+		w.Write([]byte("method not allowed"))
-		// log.Printf("ints = %+v", p[0:16])
+		return
-	})
-
-	if err != nil {
-		log.Fatalf("error calling downloader: %v", err)
 	}
 
-	log.Println("done")
+	if !strings.HasPrefix(r.URL.Path, "/api/audio") {
+		w.WriteHeader(http.StatusNotFound)
+		w.Write([]byte("page not found"))
+		return
+	}
+
+	videoID := r.URL.Query().Get("video_id")
+	if videoID == "" {
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte("no video ID provided"))
+		return
+	}
+
+	downloader, err := NewAudioDownloader(videoID)
+	if err != nil {
+		log.Printf("downloader error: %v", err)
+		w.WriteHeader(http.StatusInternalServerError)
+		w.Write([]byte("could not download video"))
+		return
+	}
+	defer downloader.Close()
+
+	w.Header().Add("Content-Type", ContentTypeAudioM4A)
+	w.WriteHeader(http.StatusOK)
+
+	n, err := io.Copy(w, downloader)
+	if err != nil {
+		log.Printf("error writing response: %v", err)
+		return
+	}
+
+	log.Printf("wrote %d bytes for video ID %s", n, videoID)
+}
+
+func main() {
+	srv := http.Server{
+		ReadTimeout:  DefaultTimeout,
+		WriteTimeout: DefaultTimeout,
+		Addr:         DefaultHTTPBindAddr,
+		Handler:      http.HandlerFunc(handleRequest),
+	}
+
+	log.Fatal(srv.ListenAndServe())
 }