fix: typings of fastify.cache.get (#133)

* fix: typings of fastify.cache.get

* fix

* fix

* fix

* Update index.test-d.ts

Author: Uzlopak

types/index.d.ts

@@ -35,15 +35,28 @@ type FastifyCaching = FastifyPluginCallback<fastifyCaching.FastifyCachingPluginO
   privacy: fastifyCaching.Privacy;
 };
 
+type CacheResult<T> = {
+  item: T,
+  stored: number,
+  ttl: number,
+} | null;
+
 declare namespace fastifyCaching {
   /**
    * @link [`abstract-cache` protocol documentation](https://github.com/jsumners/abstract-cache#protocol)
    */
   export interface AbstractCacheCompliantObject {
-    get(
+    get<T = unknown>(
       key: string | { id: string; segment: string },
-      callback?: (error: unknown, result: unknown) => void
+      callback: (error: unknown, result: CacheResult<T>) => void
     ): void;
+    /**
+     * If AbstractCache is using useAwait = true, then this method-header must be used.
+     * @param key 
+     */
+    get<T = unknown>(
+      key: string | { id: string; segment: string },
+    ): Promise<CacheResult<T>>;
     set(
       key: string | { id: string; segment: string },
       value: unknown,

types/index.test-d.ts

@@ -50,3 +50,20 @@ const badCachingOptions = {
 };
 
 expectError(shouldErrorApp.register(fastifyCaching, badCachingOptions));
+
+fastify.get('/three', async (request, reply) => {
+  expectAssignable<Promise<unknown>>(
+    fastify.cache.get('well-known')
+  );
+  expectAssignable<Promise<{ item: string; stored: number; ttl: number; } | null>>(
+    fastify.cache.get<string>('well-known')
+  );
+  expectType<void>(
+    fastify.cache.get<string>('well-known', (err, value) => {
+      expectType<unknown>(err);
+      expectAssignable<{ item: string; stored: number; ttl: number; } | null>(value);
+    })
+  );
+
+  return { message: 'two' };
+});