Add all BENNC message types with unit tests

src/messages/keepalive.ts

@@ -0,0 +1,16 @@
+import { MessageTypes } from '../common'
+import { numberToUint16BE } from '../utilities/number'
+import { packOutgoingPacket } from './packet'
+
+const MESSAGE_TYPE = numberToUint16BE(MessageTypes.Keepalive)
+
+/**
+ * Create an outgoing keepalive (0x0005) packet.
+ * @returns An outgoing keepalive (0x0005) packet.
+ */
+export function packKeepaliveMessage (): Buffer {
+  return packOutgoingPacket({
+    messageType: MESSAGE_TYPE,
+    data: Buffer.alloc(0)
+  })
+}