Change module name and restructure contentv0.1.2

The repository names for soundbox are named as below:

- app: soundbox-app
- Go library module: soundbox-go
- Device: soundbox

The Go module names were:

- app: xengineering.eu/soundbox/app
- Go library module: xengineering.eu/soundbox

This does not make clear which module is related to which repository
since the names are different. Thus it should be changed to:

- app: xengineering.eu/soundbox-app
- Go library module: xengineering.eu/soundbox-go

The import statement for the library is then:

    import "xengineering.eu/soundbox-go/soundbox"

This is a bit longer but it keeps the property that the library is
referenced inside the code by the simple name `soundbox`.

5 files changed, 163 insertions, 0 deletions

diff --git a/soundbox/interfaces.go b/soundbox/interfaces.go
new file mode 100644
index 0000000..2854b1a
--- /dev/null
+++ b/soundbox/interfaces.go
@@ -0,0 +1,39 @@
+package soundbox
+
+import (
+	"fmt"
+	"net"
+)
+
+// getInterface is a function guessing which interface should be used for
+// soundbox streaming. This is required since soundbox relies on communication
+// via IPv6 link-local addresses which require a specified interface to allow
+// communication. This function returns the first interface it finds which is
+// up and has a link-local address assigned.
+func getInterface() (net.Interface, error) {
+	all, err := net.Interfaces()
+	if err != nil {
+		return net.Interface{}, err
+	}
+
+	for _, iface := range all {
+		if iface.Flags & net.FlagUp == 0 {
+			continue
+		}
+		addresses, err := iface.Addrs()
+		if err != nil {
+			return net.Interface{}, err
+		}
+		for _, addr := range addresses {
+			ip, _, err := net.ParseCIDR(addr.String())
+			if err != nil {
+				return net.Interface{}, err
+			}
+			if ip.IsLinkLocalUnicast() {
+				return iface, nil
+			}
+		}
+	}
+
+	return net.Interface{}, fmt.Errorf("No interface found for soundbox streaming")
+}
diff --git a/soundbox/ipv6.go b/soundbox/ipv6.go
new file mode 100644
index 0000000..355e233
--- /dev/null
+++ b/soundbox/ipv6.go
@@ -0,0 +1,19 @@
+package soundbox
+
+import (
+	"fmt"
+	"net"
+)
+
+// toLinkLocal converts a MAC address to the corresponding IPv6 link-local
+// address.
+func toLinkLocal(ha net.HardwareAddr) (net.IP, error) {
+	switch len(ha) {
+	case 6:
+		ip := net.IP{0xfe, 0x80, 0, 0, 0, 0, 0, 0,
+			ha[0] ^ 0b10, ha[1], ha[2], 0xff, 0xfe, ha[3], ha[4], ha[5]}
+		return ip, nil
+	default:
+		return nil, fmt.Errorf("Only IEEE 802 MAC-48 addresses supported")
+	}
+}
diff --git a/soundbox/ipv6_test.go b/soundbox/ipv6_test.go
new file mode 100644
index 0000000..93ac489
--- /dev/null
+++ b/soundbox/ipv6_test.go
@@ -0,0 +1,19 @@
+package soundbox
+
+import (
+	"net"
+	"reflect"
+	"testing"
+)
+
+func TestToLinkLocal(t *testing.T) {
+	input := net.HardwareAddr{0xab, 0xcd, 0xef, 0x12, 0x34, 0x56}
+	expected := net.IP{0xfe, 0x80, 0, 0, 0, 0, 0, 0, 0xa9, 0xcd, 0xef, 0xff, 0xfe, 0x12, 0x34, 0x56}
+	computed, err := toLinkLocal(input)
+	if err != nil {
+		t.Fatalf("Failed to call toLinkLocal(): %v", err)
+	}
+	if !reflect.DeepEqual(computed, expected) {
+		t.Fatalf("Computed IPv6 link-local address %v did not match expectation %v", computed, expected)
+	}
+}
diff --git a/soundbox/stream.go b/soundbox/stream.go
new file mode 100644
index 0000000..cc8fcea
--- /dev/null
+++ b/soundbox/stream.go
@@ -0,0 +1,48 @@
+package soundbox
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"net"
+)
+
+// streamingPort is the default network port a soundbox is listening to for
+// incoming audio stream data.
+const streamingPort = 5316
+
+// 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.
+func StreamURLContext(ctx context.Context, url string, targets []net.HardwareAddr) error {
+	iface, err := getInterface()
+	if err != nil {
+		return err
+	}
+
+	cmd := []string{
+		"-re",
+		"-i",
+		url,
+	}
+
+	for _, target := range targets {
+		ip, err := toLinkLocal(target)
+		if err != nil {
+			return err
+		}
+
+		cmd = append(cmd, "-acodec")
+		cmd = append(cmd, "flac")
+		cmd = append(cmd, "-f")
+		cmd = append(cmd, "ogg")
+		cmd = append(cmd, fmt.Sprintf(
+			"tcp://[%s%%%s]:%d",
+			ip,
+			iface.Name,
+			streamingPort,
+		))
+	}
+
+	return exec.CommandContext(ctx, "ffmpeg", cmd...).Run()
+}
diff --git a/soundbox/stream_test.go b/soundbox/stream_test.go
new file mode 100644
index 0000000..41907ad
--- /dev/null
+++ b/soundbox/stream_test.go
@@ -0,0 +1,38 @@
+package soundbox_test
+
+import (
+	"context"
+	"log"
+	"net"
+	"time"
+
+	"xengineering.eu/soundbox-go/soundbox"
+)
+
+func ExampleStreamURLContext() {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	// all soundboxes are referenced by their MAC address
+	soundboxes := []net.HardwareAddr{
+		{0x00, 0x00, 0x5E, 0x00, 0x53, 0x01},
+		{0x00, 0x00, 0x5E, 0x00, 0x53, 0x02},
+		{0x00, 0x00, 0x5E, 0x00, 0x53, 0x03},
+	}
+
+	// currently only web radio is supported
+	url := "https://example.org/radio.mp3"
+
+	// start streaming
+	go func() {
+		err := soundbox.StreamURLContext(ctx, url, soundboxes)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	// let it play for some time
+	time.Sleep(time.Minute)
+
+	// stop it
+	cancel()
+}