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

Try MDNS lookup only if regular DNS lookup fails

src/app.ts

@@ -26,26 +26,8 @@ interface DnsLookupOpts {
 	family: number;
 }
 
-// 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
-(() => {
-	// Make NodeJS RFC 3484 compliant for properly handling IPv6
-	// See: https://github.com/nodejs/node/pull/14731
-	//      https://github.com/nodejs/node/pull/17793
-	const dns = require('dns');
-	const { lookup } = dns;
-
-	dns.lookup = (
-		name: string,
-		opts: Partial<DnsLookupOpts> | number | null | undefined,
-		cb: DnsLookupCallback,
-	) => {
-		if (typeof cb !== 'function') {
-			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.
  *
@@ -53,8 +35,13 @@ interface DnsLookupOpts {
  * 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')) {
+ */
+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.
@@ -75,23 +62,20 @@ interface DnsLookupOpts {
 		})();
 
 		// map them and return...
-				return families.map((family) => {
+		return families.map(async (family) => {
-					return mdnsResolver
+			let address = '';
-						.resolve(name, family === 6 ? 'AAAA' : 'A')
+			try {
-						.catch(() => {
+				address = await mdnsResolver.resolve(name, family === 6 ? 'AAAA' : 'A');
-							return '';
+			} catch {
-						})
+				/* noop */
-						.then((address) => {
+			}
-							return {
+
-								address,
+			return { address, family };
-								family,
-							};
-						});
 		});
 	};
 
 	// resolve the addresses...
-			return Promise.all(getResolvers()).then((results) => {
+	const results = await Promise.all(getResolvers());
 	// remove any that didn't resolve...
 	let allAddresses = results.filter((result) => result.address !== '');
 
@@ -112,12 +96,47 @@ interface DnsLookupOpts {
 	}
 
 	// only a single address was requested...
-				const [{ address, family }] = allAddresses;
+	const [{ address: addr, family: fmly }] = allAddresses;
-				return cb(null, address, family);
+	return cb(null, addr, fmly);
-			});
 }
 
-		return lookup(name, Object.assign({ verbatim: true }, opts), cb);
+// 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
+(() => {
+	// Make NodeJS RFC 3484 compliant for properly handling IPv6
+	// See: https://github.com/nodejs/node/pull/14731
+	//      https://github.com/nodejs/node/pull/17793
+	const dns = require('dns');
+	const { lookup } = dns;
+
+	dns.lookup = (
+		name: string,
+		opts: Partial<DnsLookupOpts> | number | null | undefined,
+		cb: DnsLookupCallback,
+	) => {
+		if (typeof cb !== 'function') {
+			return lookup(name, { verbatim: true }, opts);
+		}
+
+		// 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);
+				}
+
+				// 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);
+				}
+
+				return cb(error);
+			},
+		);
 	};
 })();