Use Go code for output network stream

Calling the external program `ffmpeg` should be avoided completely in
the future to make soundbox-go a pure Go code base. `ffmpeg` provides
the following functionality to soundbox-go:

- web radio input stream transport
- re-encoding of the audio stream
- output stream transport to soundbox devices

The last part should be replaced with this commit as a first step.

1 files changed, 68 insertions, 16 deletions

diff --git a/soundbox/stream.go b/soundbox/stream.go
index 4b08840..0d6fe5f 100644
--- a/soundbox/stream.go
+++ b/soundbox/stream.go
@@ -2,15 +2,22 @@ package soundbox
 
 import (
 	"context"
+	"errors"
 	"fmt"
-	"os/exec"
+	"io"
 	"net"
+	"os/exec"
+	"time"
 )
 
 // streamingPort is the default network port a soundbox is listening to for
 // incoming audio stream data.
 const streamingPort = 5316
 
+const bufferSize = 20
+
+const writeTimeout = 1 * time.Second
+
 // StreamURLContext streams audio from a given URL to one or multiple soundbox
 // devices. The devices are referenced via their MAC addresses given by the
 // targets argument. The ctx argument is passed to cancel the streaming.
@@ -20,29 +27,74 @@ func StreamURLContext(ctx context.Context, url string, targets []net.HardwareAdd
 		return err
 	}
 
+	ips := make([]net.IP, 0)
+	for _, target := range targets {
+		ip, err := toLinkLocal(target)
+		if err != nil {
+			return err
+		}
+		ips = append(ips, ip)
+	}
+
+	conns := make([]net.Conn, 0)
+	for _, ip := range ips {
+		var d net.Dialer
+		conn, err := d.DialContext(
+			ctx,
+			"tcp6",
+			fmt.Sprintf("[%s%%%s]:%d", ip, iface.Name, streamingPort),
+		)
+		if err != nil {
+			return err
+		}
+		conns = append(conns, conn)
+	}
+	defer func() {
+		for _, conn := range conns {
+			conn.Close()
+		}
+	}()
+
 	args := []string{
 		"-re",
 		"-i",
 		url,
+		"-acodec",
+		"flac",
+		"-f",
+		"ogg",
+		"-",
 	}
 
-	for _, target := range targets {
-		ip, err := toLinkLocal(target)
+	cmd := exec.CommandContext(ctx, "ffmpeg", args...)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+
+	err = cmd.Start()
+	if err != nil {
+		return err
+	}
+
+	for {
+		buffer := make([]byte, bufferSize)
+		i, err := stdout.Read(buffer)
 		if err != nil {
-			return err
+			if errors.Is(err, io.EOF) {
+				break
+			} else {
+				return err
+			}
+		}
+		for _, conn := range conns {
+			conn.SetDeadline(time.Now().Add(writeTimeout))
+			_, err = conn.Write(buffer[:i])
+			if err != nil {
+				return err
+			}
 		}
-
-		args = append(args, "-acodec")
-		args = append(args, "flac")
-		args = append(args, "-f")
-		args = append(args, "ogg")
-		args = append(args, fmt.Sprintf(
-			"tcp://[%s%%%s]:%d",
-			ip,
-			iface.Name,
-			streamingPort,
-		))
 	}
 
-	return exec.CommandContext(ctx, "ffmpeg", args...).Run()
+	return cmd.Wait()
 }