1 files changed, 58 insertions, 0 deletions
diff --git a/soundbox/network.go b/soundbox/network.go
new file mode 100644
index 0000000..6e7acea
--- /dev/null
+++ b/soundbox/network.go
@@ -0,0 +1,58 @@
+package soundbox
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+)
+
+const dialTimeoutSeconds = 3
+
+// 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")
+	}
+}
+
+func dialContext(ctx context.Context, ha net.HardwareAddr) (net.Conn, error) {
+	ip, err := toLinkLocal(ha)
+	if err != nil {
+		return nil, err
+	}
+
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	c := make(chan net.Conn)
+	dialContext, cancel := context.WithTimeout(ctx, dialTimeoutSeconds * time.Second)
+	defer cancel()
+	for _, iface := range ifaces {
+		go func() {
+			var d net.Dialer
+			conn, err := d.DialContext(
+				ctx,
+				"tcp6",
+				fmt.Sprintf("[%s%%%s]:%d", ip, iface.Name, streamingPort),
+			)
+			if err == nil {
+				c <- conn
+			}
+		}()
+	}
+	select {
+	case conn := <-c:
+		return conn, nil
+	case <-dialContext.Done():
+		return nil, fmt.Errorf("Could not dial TCP connection to %v on port %d on any interface.", ha, streamingPort)
+	}
+}