feat(api): serve well-known discovery with etag and 304 (#2349)

fluxer_api/src/api/utils/EntityTag.ts

@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+function stripWeakness(entityTag: string): string {
+	return entityTag.startsWith('W/') ? entityTag.slice(2) : entityTag;
+}
+
+export function entityTagMatches(ifNoneMatch: string, etag: string): boolean {
+	const target = stripWeakness(etag.trim());
+	return ifNoneMatch
+		.split(',')
+		.map((candidate) => candidate.trim())
+		.some((candidate) => candidate === '*' || stripWeakness(candidate) === target);
+}