SimpleLRU: fix repeated calls fetching

src/utils/SimpleLRU.test.ts

@@ -0,0 +1,21 @@
+import { SimpleLRU } from '@/utils/SimpleLRU.ts';
+import { assertEquals, assertRejects } from '@std/assert';
+
+Deno.test("SimpleLRU doesn't repeat failed calls", async () => {
+  let calls = 0;
+
+  const cache = new SimpleLRU(
+    // deno-lint-ignore require-await
+    async () => {
+      calls++;
+      throw new Error('gg');
+    },
+    { max: 100 },
+  );
+
+  await assertRejects(() => cache.fetch('foo'));
+  assertEquals(calls, 1);
+
+  await assertRejects(() => cache.fetch('foo'));
+  assertEquals(calls, 1);
+});

src/utils/SimpleLRU.ts

@@ -22,7 +22,13 @@ export class SimpleLRU<
 
   constructor(fetchFn: FetchFn<K, V, { signal: AbortSignal }>, private opts: SimpleLRUOpts<K, V>) {
     this.cache = new LRUCache({
-      fetchMethod: (key, _staleValue, { signal }) => fetchFn(key, { signal: signal as unknown as AbortSignal }),
+      async fetchMethod(key, _staleValue, { signal }) {
+        try {
+          return await fetchFn(key, { signal: signal as unknown as AbortSignal });
+        } catch {
+          return null as unknown as V;
+        }
+      },
       ...opts,
     });
   }
@@ -32,7 +38,7 @@ export class SimpleLRU<
 
     this.opts.gauge?.set(this.cache.size);
 
-    if (result === undefined) {
+    if (result === undefined || result === null) {
       throw new Error('SimpleLRU: fetch failed');
     }