fix: modules losing data after HTTP 304 responses (#4180)

When a server responds with 304 (nothing changed since last fetch), the
response has no body. Several modules were trying to parse that empty
body anyway - which either cleared their cached data or threw an
exception. The result: a blank calendar, empty newsfeed, or missing
weather data after the next refresh cycle.

This was reported in the forum:
https://forum.magicmirror.builders/topic/20250/calendar-events-broadcasting-nothing-showing

The bug was "introduced" by #4120, which correctly started forwarding
304s to consumers - but not all were ready for it.

### Fix

Skip parsing on 304 and keep the existing data as-is:

- **calendar** - re-broadcasts cached events
- **newsfeed** - re-broadcasts cached items
- **buienradar, openmeteo, weatherflow, weathergov** - return early
before calling `response.json()`

Author: KristjanESPERANTO

defaultmodules/calendar/calendarfetcher.js

@@ -51,6 +51,13 @@ class CalendarFetcher {
 	 */
 	async #handleResponse (response) {
 		try {
+			// 304 Not Modified has no body: keep previously fetched events and just re-broadcast them.
+			if (response.status === 304) {
+				this.lastFetch = Date.now();
+				this.broadcastEvents();
+				return;
+			}
+
 			const responseData = await response.text();
 			const parsed = await ical.async.parseICS(responseData);
 

defaultmodules/newsfeed/newsfeedfetcher.js

@@ -68,6 +68,12 @@ class NewsfeedFetcher {
 	 * @param {Response} response - The fetch Response object
 	 */
 	async #handleResponse (response) {
+		// 304 Not Modified has no body: keep previously fetched items and re-broadcast them.
+		if (response.status === 304) {
+			this.broadcastItems();
+			return;
+		}
+
 		this.items = [];
 		const parser = new FeedMe();
 

defaultmodules/weather/providers/buienradar.js

@@ -111,6 +111,7 @@ class BuienradarProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				const data = await response.json();
 				this.#handleResponse(data);

defaultmodules/weather/providers/envcanada.js

@@ -69,6 +69,7 @@ class EnvCanadaProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				// Check if hour changed - restart fetcher with new URL
 				const newHour = new Date().toISOString().substring(11, 13);

defaultmodules/weather/providers/openmeteo.js

@@ -172,6 +172,7 @@ class OpenMeteoProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				const data = await response.json();
 				this.#handleResponse(data);

defaultmodules/weather/providers/openweathermap.js

@@ -73,6 +73,7 @@ class OpenWeatherMapProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				const data = await response.json();
 				this.#handleResponse(data);

defaultmodules/weather/providers/pirateweather.js

@@ -52,6 +52,7 @@ class PirateweatherProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				const data = await response.json();
 				this.#handleResponse(data);

defaultmodules/weather/providers/smhi.js

@@ -95,6 +95,7 @@ class SMHIProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				const data = await response.json();
 				this.#handleResponse(data);

defaultmodules/weather/providers/ukmetofficedatahub.js

@@ -64,6 +64,7 @@ class UkMetOfficeDataHubProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				const data = await response.json();
 				this.#handleResponse(data);

defaultmodules/weather/providers/weatherflow.js

@@ -74,6 +74,7 @@ class WeatherFlowProvider {
 		});
 
 		this.fetcher.on("response", async (response) => {
+			if (response.status === 304) return;
 			try {
 				const data = await response.json();
 				const processed = this.#processData(data);