Refactor code structure for improved readability and maintainability

symcon-collector/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:20-alpine
+FROM node:22-alpine
 
 WORKDIR /app
 
@@ -7,4 +7,4 @@ RUN npm install
 
 COPY src ./src
 
-CMD ["npm", "start"]
+CMD ["npm", "start"]

symcon-collector/package.json

@@ -4,7 +4,8 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "start": "node src/index.js"
+    "start": "node src/index.js",
+    "check": "node --check src/index.js"
   },
   "dependencies": {
     "mysql2": "^3.12.0"

symcon-collector/src/index.js

@@ -7,6 +7,7 @@ const maxConcurrency = Math.max(1, Math.min(16, Number(process.env.SYMCON_MAX_CO
 const sourcePollState = new Map();
 const valueCache = new Map();
 let polling = false;
+let lastKnownGoodStore = { sources: [], datapoints: [] };
 
 const db = mysql.createPool({
   host: process.env.DB_HOST || "mariadb",
@@ -67,17 +68,18 @@ async function updateWorkerState(source, status, error = "") {
 
 function readStore() {
   if (!existsSync(sourcesFile)) {
-    return { sources: [], datapoints: [] };
+    return structuredClone(lastKnownGoodStore);
   }
   try {
     const store = JSON.parse(readFileSync(sourcesFile, "utf8"));
-    return {
+    lastKnownGoodStore = {
       sources: Array.isArray(store.sources) ? store.sources : [],
       datapoints: Array.isArray(store.datapoints) ? store.datapoints : [],
     };
+    return structuredClone(lastKnownGoodStore);
   } catch (error) {
-    console.warn("Quellenkonfiguration konnte nicht gelesen werden:", error.message);
-    return { sources: [], datapoints: [] };
+    console.warn("Quellenkonfiguration konnte nicht gelesen werden, letzter gültiger Stand wird verwendet:", error.message);
+    return structuredClone(lastKnownGoodStore);
   }
 }
 
@@ -262,4 +264,4 @@ setInterval(() => pollDueSources().catch((error) => console.error("IP-Symcon Pol
 ensureWorkerStateTable()
   .then(() => pollDueSources())
   .catch((error) => console.error("IP-Symcon Start-Polling fehlgeschlagen:", error.message));
-console.log(`SE LTD Symcon Collector gestartet (Intervall-Prüfung ${pollTickMs} ms, Parallelität ${maxConcurrency}).`);
+console.log(`SE LTD Symcon Collector gestartet (Intervall-Prüfung ${pollTickMs} ms, Parallelität ${maxConcurrency}).`);