feat(layers): GNSS interference layer from ADS-B NIC/NACp integrity

Bins airborne ADS-B v1/v2 aircraft that report degraded navigation
integrity (NIC < 7, NACp < 8, or readsb's GPS-loss flag) into 0.5 degree
cells over a rolling 30-minute window, coloured with the gpsjam.org
bands. Keyless: reads the capped adsb.lol point snapshot around the view
through /api/gnss-integrity, which returns integrity fields only, caches
60 s per whole-degree anchor, backs off on upstream 429 and serves the
last snapshot on failure. Adds scripts/qa-gnss.mjs.

Built by the Hex project (Crew Leo Agile dev team).

Co-Authored-By: Claude <[email protected]>

src/data/dataCredits.js

@@ -104,7 +104,7 @@ export const DATA_CREDITS = [
   {
     key: 'adsblol',
     html:
-      'Military flights, aircraft traces & bounded regional flight fallback: ' +
+      'Military flights, aircraft traces, bounded regional flight fallback & GNSS interference: ' +
       '<a href="https://adsb.lol" target="_blank" rel="noopener">adsb.lol</a> ' +
       '(ODbL 1.0)',
   },

src/data/gnssIntegrityProxy.test.mjs

@@ -0,0 +1,183 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  gnssIntegrityAnchor,
+  gnssIntegrityProxy,
+} from '../../server/providers/gnssIntegrity.js';
+
+const snapshot = {
+  now: 1,
+  ac: [
+    {
+      hex: '4ca7b5',
+      type: 'adsb_icao',
+      version: 2,
+      alt_baro: 36000,
+      lat: 50.1,
+      lon: 19.9,
+      nic: 0,
+      nac_p: 0,
+      seen_pos: 1,
+      flight: 'RYR1AB  ',
+      r: 'EI-ABC',
+    },
+    { hex: '000001', type: 'mlat', lat: 50, lon: 20, nic: 0, nac_p: 0 },
+  ],
+};
+
+function install(options = {}, hook = 'configureServer') {
+  let handler;
+  const plugin = gnssIntegrityProxy(options);
+  assert.equal(plugin.name, 'gnss-integrity');
+  plugin[hook]({
+    middlewares: {
+      use(path, callback) {
+        assert.equal(path, '/api/gnss-integrity');
+        handler = callback;
+      },
+    },
+  });
+  return async (url = '/?lat=50&lon=20', method = 'GET', peer = 'local') => {
+    const res = {
+      writeHead(status, headers) {
+        this.status = status;
+        this.headers = headers;
+      },
+      end(body) {
+        this.body = JSON.parse(body);
+      },
+    };
+    await handler({ url, method, socket: { remoteAddress: peer } }, res);
+    return res;
+  };
+}
+
+test('anchors snap to whole degrees and reject missing or out-of-range values', () => {
+  assert.deepEqual(gnssIntegrityAnchor('/?lat=50.44&lon=19.51'), {
+    lat: 50,
+    lon: 20,
+  });
+  assert.equal(gnssIntegrityAnchor('/?lat=91&lon=0'), null);
+  assert.equal(gnssIntegrityAnchor('/?lat=0&lon=-181'), null);
+  assert.equal(gnssIntegrityAnchor('/?lat=0'), null);
+  assert.equal(gnssIntegrityAnchor('/?lat=abc&lon=1'), null);
+});
+
+for (const hook of ['configureServer', 'configurePreviewServer']) {
+  test(`${hook}: fetches the fixed adsb.lol origin and returns only integrity facts`, async () => {
+    const calls = [];
+    const request = install(
+      {
+        now: () => 1234,
+        fetchImpl: async (url, options) => {
+          calls.push(url);
+          assert.ok(options.signal instanceof AbortSignal);
+          assert.equal(options.redirect, 'error');
+          return Response.json(snapshot);
+        },
+      },
+      hook,
+    );
+    const res = await request(
+      '/?lat=50.2&lon=19.8&url=https://invalid.example',
+    );
+    assert.equal(res.status, 200);
+    assert.deepEqual(calls, ['https://api.adsb.lol/v2/lat/50/lon/20/dist/250']);
+    assert.deepEqual(res.body, {
+      fetchedAt: 1234,
+      anchor: { lat: 50, lon: 20 },
+      radiusNm: 250,
+      rows: [
+        {
+          hex: '4ca7b5',
+          lat: 50.1,
+          lon: 19.9,
+          nic: 0,
+          nacp: 0,
+          gpsLost: false,
+          degraded: true,
+        },
+      ],
+    });
+    assert.equal(res.headers['Cache-Control'], 'no-store');
+  });
+}
+
+test('snapshots are cached per anchor and concurrent reads share one upstream call', async () => {
+  let clock = 0;
+  let calls = 0;
+  const request = install({
+    now: () => clock,
+    fetchImpl: async () => {
+      calls += 1;
+      return Response.json(snapshot);
+    },
+  });
+  await Promise.all([request(), request('/?lat=50.3&lon=20.2')]);
+  assert.equal(calls, 1);
+  clock = 59_000;
+  await request();
+  assert.equal(calls, 1);
+  clock = 61_000;
+  await request();
+  assert.equal(calls, 2);
+  await request('/?lat=10&lon=10');
+  assert.equal(calls, 3);
+});
+
+test('an upstream failure serves the last snapshot as stale, else 502', async () => {
+  let clock = 0;
+  let fail = false;
+  const request = install({
+    now: () => clock,
+    fetchImpl: async () =>
+      fail ? new Response('down', { status: 503 }) : Response.json(snapshot),
+  });
+  await request();
+  fail = true;
+  clock = 120_000;
+  const stale = await request();
+  assert.equal(stale.status, 200);
+  assert.equal(stale.body.stale, true);
+  assert.equal(stale.headers['X-Data-Stale'], 'true');
+  const missing = await request('/?lat=-10&lon=-10');
+  assert.equal(missing.status, 502);
+  assert.deepEqual(missing.body, { error: 'gnss_integrity_unavailable' });
+});
+
+test('an upstream 429 starts a cooldown with no further upstream calls', async () => {
+  let clock = 0;
+  let calls = 0;
+  const request = install({
+    now: () => clock,
+    fetchImpl: async () => {
+      calls += 1;
+      return new Response('slow down', {
+        status: 429,
+        headers: { 'retry-after': '120' },
+      });
+    },
+  });
+  assert.equal((await request()).status, 502);
+  const cooling = await request('/?lat=1&lon=1');
+  assert.equal(cooling.status, 429);
+  assert.equal(calls, 1);
+  clock = 121_000;
+  await request('/?lat=2&lon=2');
+  assert.equal(calls, 2);
+});
+
+test('the route rejects other methods, paths, bad anchors, a malformed feed and floods', async () => {
+  const request = install({
+    fetchImpl: async () => Response.json({ nope: true }),
+  });
+  assert.equal((await request('/', 'POST')).status, 405);
+  assert.equal((await request('/other?lat=1&lon=1')).status, 404);
+  assert.equal((await request('/?lat=1')).status, 400);
+  assert.equal((await request('/?lat=1&lon=1')).status, 502);
+  let limited = 0;
+  for (let i = 0; i < 40; i += 1)
+    if ((await request('/?lat=1&lon=1', 'GET', 'flood')).status === 429)
+      limited += 1;
+  assert.ok(limited > 0);
+});

src/data/layerState.js

@@ -607,6 +607,11 @@ export const LAYER_STATE_REGISTRY = Object.freeze([
     disposition: 'enabled+options',
     optionOwner: 'flights',
   }),
+  Object.freeze({
+    id: 'gnss-interference',
+    token: '0',
+    disposition: 'enabled-only',
+  }),
   Object.freeze({ id: 'local-dams', token: 'q', disposition: 'enabled-only' }),
   Object.freeze({
     id: 'local-datacenters',

src/data/layerState.test.mjs

@@ -2639,6 +2639,23 @@ test('the recent-imagery split is share-link only: never stored locally, and a s
   );
 });
 
+test('GNSS interference uses digit 0 without colliding with other digit tokens', () => {
+  const decoded = decodeLayerStateParams(new URLSearchParams('v=2&l=0.2.1'));
+  assert.deepEqual(decoded.enabledLayerIds, [
+    'fire-perimeters',
+    'gnss-interference',
+    'recent-imagery',
+  ]);
+  assert.equal(
+    LAYER_STATE_REGISTRY.find(({ id }) => id === 'gnss-interference').token,
+    '0',
+  );
+  assert.deepEqual(
+    decodeLayerStateParams(new URLSearchParams(encode(decoded))),
+    decoded,
+  );
+});
+
 test('fire perimeters uses digit 2 without colliding with wind or recent imagery', () => {
   const decoded = decodeLayerStateParams(new URLSearchParams('v=2&l=2.k.1'));
   assert.deepEqual(decoded.enabledLayerIds, [

src/data/layerStateTokenLedger.test.mjs

@@ -131,7 +131,7 @@ test('reservation ledger is complete, pinned, and rejects duplicate or malformed
   assert.equal(Object.keys(LAYER_STATE_TOKEN_RESERVATIONS).length, 29);
   assert.deepEqual(
     { ...LAYER_STATE_TOKEN_RESERVATIONS },
-    { ...LEGACY_LAYER_STATE_TOKENS, 'street-level': '0' },
+    { ...LEGACY_LAYER_STATE_TOKENS, 'street-level': '0', 'gnss-interference': '0' },
   );
   assert.throws(
     () => parseLayerStateTokenReservations(reservationRows.slice(1)),

src/data/layerStateTokenReservations.json

@@ -9,6 +9,7 @@
   ["earthquakes", "e"],
   ["fire-perimeters", "2"],
   ["flights", "f"],
+  ["gnss-interference", "0"],
   ["local-dams", "q"],
   ["local-datacenters", "d"],
   ["local-firms", "w"],