Merge pull request #2231 from balena-os/mdns-improvements

Try MDNS lookup only if regular DNS lookup fails

src/app.ts

@@ -26,6 +26,80 @@ interface DnsLookupOpts {
 	family: number;
 }
 
+/*
+ * =====================================================
+ * NOTE: This is required since Alpine/musl-based images
+ * do not support mDNS name resolution in the musl libs.
+ *
+ * In order to support .local mDNS names in development
+ * and on openBalena setups, this extra code will perform
+ * the lookup instead of passing it to the built-in
+ * function.
+ * ==================================================
+ */
+async function mdnsLookup(
+	name: string,
+	opts: Partial<DnsLookupOpts> | number | null | undefined,
+	cb: DnsLookupCallback,
+) {
+	// determine which resolvers to use...
+	const getResolvers = () => {
+		// logic to determine the families based on Node docs.
+		// See: https://nodejs.org/api/dns.html#dns_dns_lookup_hostname_options_callback
+		const families = (() => {
+			// strictly defined...
+			if (opts === 4 || opts === 6) {
+				return [opts as number];
+			}
+
+			// opts is passed, not a number and the `family` parameter is passed...
+			if (opts && typeof opts !== 'number' && opts.family) {
+				return [opts.family];
+			}
+
+			// default to resolve both v4 and v6...
+			return [4, 6];
+		})();
+
+		// map them and return...
+		return families.map(async (family) => {
+			let address = '';
+			try {
+				address = await mdnsResolver.resolve(name, family === 6 ? 'AAAA' : 'A');
+			} catch {
+				/* noop */
+			}
+
+			return { address, family };
+		});
+	};
+
+	// resolve the addresses...
+	const results = await Promise.all(getResolvers());
+	// remove any that didn't resolve...
+	let allAddresses = results.filter((result) => result.address !== '');
+
+	// unless the results should be returned verbatim, sort them so v4 comes first...
+	if (opts && typeof opts !== 'number' && !opts.verbatim) {
+		allAddresses = allAddresses.sort((a, b) => a.family - b.family);
+	}
+
+	// see if we resolved anything...
+	if (allAddresses.length === 0) {
+		// nothing! return a suitable error...
+		return cb(new DnsLookupError());
+	}
+
+	// all the addresses were requested...
+	if (opts && typeof opts !== 'number' && opts.all) {
+		return cb(null, allAddresses);
+	}
+
+	// only a single address was requested...
+	const [{ address: addr, family: fmly }] = allAddresses;
+	return cb(null, addr, fmly);
+}
+
 // This was originally wrapped in a do block in
 // coffeescript, and it's not clear now why that was the
 // case, so I'm going to maintain that behaviour
@@ -45,79 +119,24 @@ interface DnsLookupOpts {
 			return lookup(name, { verbatim: true }, opts);
 		}
 
-		/* =====================================================
-		 * NOTE: This is required since Alpine/musl-based images
-		 * do not support mDNS name resolution in the musl libs.
-		 *
-		 * In order to support .local mDNS names in development
-		 * and on openBalena setups, this extra code will perform
-		 * the lookup instead of passing it to the built-in
-		 * function.
-			 ================================================== */
-		if (name && name.endsWith('.local')) {
-			// determine which resolvers to use...
-			const getResolvers = () => {
-				// logic to determine the families based on Node docs.
-				// See: https://nodejs.org/api/dns.html#dns_dns_lookup_hostname_options_callback
-				const families = (() => {
-					// strictly defined...
-					if (opts === 4 || opts === 6) {
-						return [opts as number];
-					}
-
-					// opts is passed, not a number and the `family` parameter is passed...
-					if (opts && typeof opts !== 'number' && opts.family) {
-						return [opts.family];
-					}
-
-					// default to resolve both v4 and v6...
-					return [4, 6];
-				})();
-
-				// map them and return...
-				return families.map((family) => {
-					return mdnsResolver
-						.resolve(name, family === 6 ? 'AAAA' : 'A')
-						.catch(() => {
-							return '';
-						})
-						.then((address) => {
-							return {
-								address,
-								family,
-							};
-						});
-				});
-			};
-
-			// resolve the addresses...
-			return Promise.all(getResolvers()).then((results) => {
-				// remove any that didn't resolve...
-				let allAddresses = results.filter((result) => result.address !== '');
-
-				// unless the results should be returned verbatim, sort them so v4 comes first...
-				if (opts && typeof opts !== 'number' && !opts.verbatim) {
-					allAddresses = allAddresses.sort((a, b) => a.family - b.family);
+		// Try a regular dns lookup first
+		return lookup(
+			name,
+			Object.assign({ verbatim: true }, opts),
+			(error: any, address: string, family: number) => {
+				if (error == null) {
+					return cb(null, address, family);
 				}
 
-				// see if we resolved anything...
-				if (allAddresses.length === 0) {
-					// nothing! return a suitable error...
-					return cb(new DnsLookupError());
+				// If the regular lookup fails, we perform a mdns lookup if the
+				// name ends with .local
+				if (name && name.endsWith('.local')) {
+					return mdnsLookup(name, opts, cb);
 				}
 
-				// all the addresses were requested...
-				if (opts && typeof opts !== 'number' && opts.all) {
-					return cb(null, allAddresses);
-				}
-
-				// only a single address was requested...
-				const [{ address, family }] = allAddresses;
-				return cb(null, address, family);
-			});
-		}
-
-		return lookup(name, Object.assign({ verbatim: true }, opts), cb);
+				return cb(error);
+			},
+		);
 	};
 })();