fix(headerinterpreter): use custom interpreter

src/services/api/AxiosInstance.ts

@@ -8,6 +8,8 @@ import logger from "@logger/logger"
 import { getAccessToken } from "@utils/token-retrieval-utils"
 import tracer from "@utils/tracer"
 
+import { headerInterpreter } from "@root/utils/headerInterpreter"
+
 // Env vars
 const GITHUB_ORG_NAME = config.get("github.orgName")
 
@@ -79,6 +81,7 @@ const isomerRepoAxiosInstance = setupCache(
   {
     interpretHeader: true,
     etag: true,
+    headerInterpreter,
   }
 )
 isomerRepoAxiosInstance.interceptors.request.use(requestFormatter)

src/utils/headerInterpreter.ts

@@ -0,0 +1,47 @@
+import { Header, HeadersInterpreter } from "axios-cache-interceptor"
+import { parse } from "cache-parser"
+
+// NOTE: Taken with reference to https://github.com/arthurfiorette/axios-cache-interceptor/blob/v0.9.2/src/header/interpreter.ts
+// The change made is to remove the `maxAge` condition, which is not suitable because
+// we want to revalidate on update.
+// An alternative is to invalidate the cache on `update` but
+// this requires an exhaustive search through our codebase.
+// This incurs an extra network call on every update, which is not ideal but in 304
+// this is an empty request.
+// eslint-disable-next-line import/prefer-default-export
+export const headerInterpreter: HeadersInterpreter = (headers) => {
+  if (!headers) return "not enough headers"
+
+  const cacheControl = headers[Header.CacheControl]
+
+  if (cacheControl) {
+    const { noCache, noStore, mustRevalidate, maxAge, immutable } = parse(
+      String(cacheControl)
+    )
+
+    // Header told that this response should not be cached.
+    if (noCache || noStore) {
+      return "dont cache"
+    }
+
+    if (immutable) {
+      // 1 year is sufficient, as Infinity may cause more problems.
+      // It might not be the best way, but a year is better than none.
+      return 1000 * 60 * 60 * 24 * 365
+    }
+
+    // Already out of date, for cache can be saved, but must be requested again
+    if (mustRevalidate || maxAge) {
+      return 0
+    }
+  }
+
+  const expires = headers[Header.Expires]
+
+  if (expires) {
+    const milliseconds = Date.parse(String(expires)) - Date.now()
+    return milliseconds >= 0 ? milliseconds : "dont cache"
+  }
+
+  return "not enough headers"
+}