frame

server/src/services/roverSnapshotService/poller.js

@@ -8,6 +8,8 @@ const logger = require('../../globals/logger').child('roverSnapshot');
 
 const SNAPSHOT_DIR = process.env.ROVER_SNAPSHOT_DIR || '/var/lib/rover-snapshots';
 const POLL_INTERVAL_MS = 300;
+const FORCE_REREAD_STALE_MS = 2000;
+const STALE_WARN_MS = 10000;
 
 const roverState = new Map();
 const events = new EventEmitter();
@@ -26,19 +28,46 @@ function getSnapshotPath(id) {
 
 function createRoverSnapshotPoller({ roverManager }) {
   async function fetchSnapshot(id) {
-    const state = roverState.get(id);
+    const prev = roverState.get(id);
-    if (state?.fetching) return;
+    if (prev?.fetching) return;
     markState(id, { fetching: true });
     try {
       const filePath = getSnapshotPath(id);
       const stats = await fs.stat(filePath);
-      if (state?.mtimeMs && stats.mtimeMs <= state.mtimeMs) return;
+      const now = Date.now();
+      const staleAgeMs = prev?.ts ? now - prev.ts : 0;
+      const mtimeUnchanged = Boolean(prev?.mtimeMs && stats.mtimeMs <= prev.mtimeMs);
+      const shouldForceRead = mtimeUnchanged && staleAgeMs >= FORCE_REREAD_STALE_MS;
+      if (mtimeUnchanged && !shouldForceRead) return;
+
       const buffer = await fs.readFile(filePath);
-      const ts = stats.mtimeMs || Date.now();
+      const ts = stats.mtimeMs || now;
-      markState(id, { frame: buffer, ts, error: null, failures: 0, mtimeMs: stats.mtimeMs });
+      const prevFrame = prev?.frame || null;
-      events.emit('frame', { id, buffer, ts });
+      const changed =
+        !prevFrame ||
+        prevFrame.length !== buffer.length ||
+        !prevFrame.equals(buffer) ||
+        !mtimeUnchanged;
+      const nextState = markState(id, {
+        frame: changed ? buffer : prevFrame,
+        ts: changed ? ts : prev?.ts || ts,
+        error: null,
+        failures: 0,
+        mtimeMs: stats.mtimeMs,
+      });
+      if (changed) {
+        events.emit('frame', { id, buffer, ts: nextState.ts });
+      } else if (staleAgeMs >= STALE_WARN_MS) {
+        logger.warn('Snapshot appears stale', {
+          id,
+          snapshotDir: SNAPSHOT_DIR,
+          path: filePath,
+          ageMs: staleAgeMs,
+          mtimeMs: stats.mtimeMs,
+        });
+      }
     } catch (err) {
-      const failures = (state?.failures || 0) + 1;
+      const failures = (prev?.failures || 0) + 1;
       const message = err.code === 'ENOENT' ? 'Snapshot missing' : err.message;
       markState(id, { error: message, failures });
       events.emit('status', { id, error: message });
@@ -64,6 +93,11 @@ function createRoverSnapshotPoller({ roverManager }) {
 
   function startAll() {
     stopAll();
+    logger.info('Starting rover snapshot polling', {
+      snapshotDir: SNAPSHOT_DIR,
+      intervalMs: POLL_INTERVAL_MS,
+      forceRereadStaleMs: FORCE_REREAD_STALE_MS,
+    });
     pollTimer = setInterval(() => {
       const roster = roverManager.getRoster();
       const activeIds = new Set(roster.map((entry) => String(entry.id)));