make kestrel a tak server, so that it can send and receive pois as cots data

test/helpers/fakeAtakClient.js

@@ -0,0 +1,54 @@
+/**
+ * Build a TAK Protocol stream frame: 0xBF, varint payload length, payload.
+ * @param {string|Buffer} payload - UTF-8 payload (e.g. CoT XML)
+ * @returns {Buffer} TAK stream frame buffer.
+ */
+export function buildTakFrame(payload) {
+  const buf = Buffer.isBuffer(payload) ? payload : Buffer.from(payload, 'utf8')
+  let n = buf.length
+  const varint = []
+  while (true) {
+    const byte = n & 0x7F
+    n >>>= 7
+    if (n === 0) {
+      varint.push(byte)
+      break
+    }
+    varint.push(byte | 0x80)
+  }
+  return Buffer.concat([Buffer.from([0xBF]), Buffer.from(varint), buf])
+}
+
+/**
+ * Build CoT XML for a position update (event + point + optional contact).
+ * @param {object} opts - Position options
+ * @param {string} opts.uid - Entity UID
+ * @param {number} opts.lat - Latitude
+ * @param {number} opts.lon - Longitude
+ * @param {string} [opts.callsign] - Optional callsign
+ * @param {string} [opts.type] - Optional event type (default a-f-G)
+ * @returns {string} CoT XML string.
+ */
+export function buildPositionCotXml({ uid, lat, lon, callsign, type = 'a-f-G' }) {
+  const contact = callsign ? `<detail><contact callsign="${escapeXml(callsign)}"/></detail>` : ''
+  return `<event uid="${escapeXml(uid)}" type="${escapeXml(type)}"><point lat="${lat}" lon="${lon}"/>${contact}</event>`
+}
+
+/**
+ * Build CoT XML for auth (username/password).
+ * @param {object} opts - Auth options
+ * @param {string} opts.username - Username
+ * @param {string} opts.password - Password
+ * @returns {string} CoT XML string.
+ */
+export function buildAuthCotXml({ username, password }) {
+  return `<event><detail><auth username="${escapeXml(username)}" password="${escapeXml(password)}"/></detail></event>`
+}
+
+function escapeXml(s) {
+  return String(s)
+    .replace(/&/g, '&amp;')
+    .replace(/</g, '&lt;')
+    .replace(/>/g, '&gt;')
+    .replace(/"/g, '&quot;')
+}