Don't cache HEAD requests for local resources

Fixes #125980

Also makes all other types of requests return a 405 since they are not supported

src/vs/workbench/contrib/webview/browser/pre/service-worker.js

@@ -115,6 +115,9 @@ const localhostRequestStore = new RequestStore();
 const notFound = () =>
 	new Response('Not Found', { status: 404, });
 
+const methodNotAllowed = () =>
+	new Response('Method Not Allowed', { status: 405, });
+
 sw.addEventListener('message', async (event) => {
 	switch (event.data.channel) {
 		case 'version':
@@ -170,7 +173,14 @@ sw.addEventListener('message', async (event) => {
 sw.addEventListener('fetch', (event) => {
 	const requestUrl = new URL(event.request.url);
 	if (requestUrl.protocol === 'https:' && requestUrl.hostname.endsWith('.' + resourceBaseAuthority)) {
-		return event.respondWith(processResourceRequest(event, requestUrl));
+		switch (event.request.method) {
+			case 'GET':
+			case 'HEAD':
+				return event.respondWith(processResourceRequest(event, requestUrl));
+
+			default:
+				return event.respondWith(methodNotAllowed());
+		}
 	}
 
 	// See if it's a localhost request
@@ -204,6 +214,8 @@ async function processResourceRequest(event, requestUrl) {
 		return notFound();
 	}
 
+	const shouldTryCaching = (event.request.method === 'GET');
+
 	/**
 	 * @param {ResourceResponse} entry
 	 * @param {Response | undefined} cachedResponse
@@ -235,7 +247,7 @@ async function processResourceRequest(event, requestUrl) {
 			headers
 		});
 
-		if (entry.etag) {
+		if (shouldTryCaching && entry.etag) {
 			caches.open(resourceCacheName).then(cache => {
 				return cache.put(event.request, response);
 			});
@@ -249,8 +261,12 @@ async function processResourceRequest(event, requestUrl) {
 		return notFound();
 	}
 
-	const cache = await caches.open(resourceCacheName);
-	const cached = await cache.match(event.request);
+	/** @type {Response | undefined} */
+	let cached;
+	if (shouldTryCaching) {
+		const cache = await caches.open(resourceCacheName);
+		cached = await cache.match(event.request);
+	}
 
 	const { requestId, promise } = resourceRequestStore.create();