Do not dns.lookup() in background to prevent memory leaks

source/index.js

@@ -329,53 +329,29 @@ class CacheableLookup {
 			return this._dnsLookup(hostname, all);
 		}
 
-		const resolverPromise = this._resolve(hostname);
-		const lookupPromise = this._lookup(hostname);
-
-		let query;
-
 		try {
-			query = await Promise.race([
-				resolverPromise,
-				lookupPromise
-			]);
+			let query = await this._resolve(hostname);
 
 			if (query.entries.length === 0) {
-				if (query.isLookup) {
-					query = await resolverPromise;
-				} else {
-					query = await lookupPromise;
+				query = await this._lookup(hostname);
+
+				if (query.entries.length !== 0) {
+					// Use `dns.lookup(...)` for that particular hostname
+					this._hostnamesToFallback.add(hostname);
 				}
 			}
-		} catch (error) {
-			delete this._pending[hostname];
-
-			throw error;
-		}
 
-		(async () => {
-			if (query.isLookup) {
-				try {
-					const realDnsQuery = await resolverPromise;
-
-					// If no DNS entries found
-					if (realDnsQuery.entries.length === 0) {
-						// Use `dns.lookup(...)` for that particular hostname
-						this._hostnamesToFallback.add(hostname);
-					} else {
-						await this._set(hostname, realDnsQuery.entries, realDnsQuery.cacheTtl);
-					}
-				} catch (_) {}
-			} else {
-				const cacheTtl = query.entries.length === 0 ? this.errorTtl : query.cacheTtl;
+			const cacheTtl = query.entries.length === 0 ? this.errorTtl : query.cacheTtl;
+			await this._set(hostname, query.entries, cacheTtl);
 
-				await this._set(hostname, query.entries, cacheTtl);
-			}
+			delete this._pending[hostname];
 
+			return query.entries;
+		} catch (error) {
 			delete this._pending[hostname];
-		})();
 
-		return query.entries;
+			throw error;
+		}
 	}
 
 	_tick(ms) {

tests/test.js

@@ -792,7 +792,7 @@ test.serial('fallback works', async t => {
 	});
 });
 
-test('fallback works #2', async t => {
+test('real DNS queries first', async t => {
 	const resolver = createResolver({delay: 0});
 	const cacheable = new CacheableLookup({
 		resolver,
@@ -802,8 +802,8 @@ test('fallback works #2', async t => {
 
 	{
 		const entries = await cacheable.lookupAsync('outdated', {all: true});
-		t.deepEqual(entries, [
-			{address: '127.0.0.127', family: 4}
+		verify(t, entries, [
+			{address: '127.0.0.1', family: 4}
 		]);
 	}
 
@@ -875,7 +875,7 @@ test('prevents overloading DNS', async t => {
 	t.deepEqual(resolver.counter, {
 		4: 1,
 		6: 1,
-		lookup: 1
+		lookup: 0
 	});
 });