fix: don't cache rejected promises

packages/forestadmin-client/src/utils/ttl-cache.ts

@@ -5,11 +5,11 @@
 export default class TTLCache<V> {
   private readonly stateMap = new Map<
     string,
-    { promise: Promise<V | undefined> | V | undefined; expirationTimestamp: number }
+    { promise: Promise<V | undefined>; expirationTimestamp: number }
   >();
 
   constructor(
-    private readonly fetchMethod: (key: string) => Promise<V | undefined> | V | undefined,
+    private readonly fetchMethod: (key: string) => Promise<V | undefined>,
     private readonly ttl = 1000,
   ) {}
 
@@ -24,6 +24,11 @@ export default class TTLCache<V> {
     const fetch = this.fetchMethod(key);
     this.stateMap.set(key, { promise: fetch, expirationTimestamp: now + this.ttl });
 
+    fetch.catch(() => {
+      // Don't cache rejected promises
+      this.stateMap.delete(key);
+    });
+
     return fetch;
   }
 

packages/forestadmin-client/test/utils/ttl-cache.test.ts

@@ -60,6 +60,22 @@ describe('TTL Cache', () => {
 
       expect(fetchMethod).toHaveBeenCalledTimes(2);
     });
+
+    it('should not cache a rejected promise', async () => {
+      const fetchMethod = jest
+        .fn()
+        .mockRejectedValueOnce(new Error('first'))
+        .mockResolvedValueOnce('second');
+
+      const cache = new TTLCache<string>(fetchMethod);
+
+      await expect(() => cache.fetch('key')).rejects.toThrow('first');
+
+      const fetch2 = await cache.fetch('key');
+      expect(fetch2).toEqual('second');
+
+      expect(fetchMethod).toHaveBeenCalledTimes(2);
+    });
   });
 
   describe('clear', () => {