Cache ADSB/AIS calls

server/src/ais.mjs

@@ -8,6 +8,10 @@ const SENDER_TYPE = {
 	12: 'AtoN', 13: 'SART/EPIRB'
 };
 
+let aisCache = null;
+let aisCacheTs = 0;
+const AIS_TTL = 1000;
+
 function decodeMsgTypes(raw) {
 	const types = [];
 	for (let i = 0; i < 32; i++) {
@@ -38,6 +42,7 @@ function decodeFlags(flags) {
 }
 
 export async function getAIS() {
+	if (aisCache && Date.now() - aisCacheTs < AIS_TTL) return aisCache;
 	const {ADSB_URL} = cfg();
 	if (!ADSB_URL) return {data: []};
 	const r = await fetch(`${ADSB_URL}:9990/api/ships_array.json`);
@@ -45,7 +50,7 @@ export async function getAIS() {
 
 	const staticMap = new Map(staticRows.map(row => [row[0], row]));
 
-	return dynamic.map(row => {
+	aisCache = dynamic.map(row => {
 		const [mmsi, lat, lon, distance, bearing, heading,
 			cog, speed, status, rrsi, ppm, count, msg_type,
 			last_signal, last_group, group_mask, flags, altitude,
@@ -79,4 +84,6 @@ export async function getAIS() {
 			status
 		};
 	});
+	aisCacheTs = Date.now();
+	return aisCache;
 }