Add soundbox.toLinkLocal()

To communicate with soundbox devices it is required to convert the known
device MAC address (printed on the case) to an IPv6 link-local address.

1 files changed, 19 insertions, 0 deletions

diff --git a/ipv6.go b/ipv6.go
new file mode 100644
index 0000000..355e233
--- /dev/null
+++ b/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")
+	}
+}