fix(node:dns): fix three bugs in dns lookup and resolver (#6128)

Author: dknecht

src/node/internal/internal_dns.ts

@@ -154,10 +154,10 @@ export function lookup(
             address: answer.data,
             family: 4,
           })) ?? [];
-        const ipv6Addresses: { address: string; family: 4 }[] =
+        const ipv6Addresses: { address: string; family: 6 }[] =
           ipv6Response.Answer?.map((answer) => ({
             address: answer.data,
-            family: 4,
+            family: 6,
           })) ?? [];
 
         // No addresses found
@@ -178,10 +178,43 @@ export function lookup(
       .catch((error: unknown): void => {
         process.nextTick(callback, error);
       });
+  } else if (family === 0) {
+    // family=0, all=false: query both A and AAAA, return first result based on dnsOrder
+    Promise.all([
+      sendDnsRequest(hostname, 'A').catch(() => ({ Answer: [] })),
+      sendDnsRequest(hostname, 'AAAA').catch(() => ({ Answer: [] })),
+    ])
+      .then(([ipv4Response, ipv6Response]): void => {
+        const ipv4 = ipv4Response.Answer?.at(0)?.data;
+        const ipv6 = ipv6Response.Answer?.at(0)?.data;
+
+        if (ipv4 == null && ipv6 == null) {
+          callback(new DnsError(hostname, errorCodes.NOTFOUND, 'queryA'));
+          return;
+        }
+
+        // Return the preferred address based on dnsOrder
+        if (dnsOrder === 'ipv6first') {
+          if (ipv6 != null) {
+            callback(null, ipv6, 6);
+          } else {
+            callback(null, ipv4 as string, 4);
+          }
+        } else {
+          if (ipv4 != null) {
+            callback(null, ipv4, 4);
+          } else {
+            callback(null, ipv6 as string, 6);
+          }
+        }
+      })
+      .catch((error: unknown): void => {
+        process.nextTick(callback, error);
+      });
   } else {
     const requestType = family === 4 ? 'A' : 'AAAA';
 
-    // Single request for all other cases (including when all=true but family is specified)
+    // Single request when family is specified (with or without all=true)
     sendDnsRequest(hostname, requestType)
       .then((json): void => {
         validateAnswer(json.Answer, hostname, `query${requestType}`);

src/node/internal/internal_dns_promises.ts

@@ -126,7 +126,7 @@ export class Resolver implements dns.Resolver {
     return resolveNs(name);
   }
 
-  esolvePtr(name: string): Promise<string[]> {
+  resolvePtr(name: string): Promise<string[]> {
     return resolvePtr(name);
   }
 

src/workerd/api/node/tests/dns-nodejs-test.js

@@ -371,6 +371,96 @@ export const getServers = {
   },
 };
 
+// Regression: dns.lookup() with all:true and family:0 must return family:6 for
+// IPv6 addresses (was returning family:4 due to copy-paste bug).
+export const lookupAllFamilyZeroIPv6Family = {
+  async test() {
+    const results = await dnsPromises.lookup(addresses.INET_HOST, {
+      all: true,
+      family: 0,
+    });
+    ok(Array.isArray(results), 'expected array of addresses');
+    ok(results.length > 0, 'expected at least one address');
+
+    for (const entry of results) {
+      strictEqual(typeof entry.address, 'string');
+      ok(
+        entry.family === 4 || entry.family === 6,
+        `family must be 4 or 6, got ${entry.family}`
+      );
+    }
+
+    // If any IPv6 addresses are returned, they must have family:6
+    const ipv6Entries = results.filter((e) => e.address.includes(':'));
+    for (const entry of ipv6Entries) {
+      strictEqual(
+        entry.family,
+        6,
+        `IPv6 address ${entry.address} should have family:6 but got family:${entry.family}`
+      );
+    }
+
+    // If any IPv4 addresses are returned, they must have family:4
+    const ipv4Entries = results.filter((e) => !e.address.includes(':'));
+    for (const entry of ipv4Entries) {
+      strictEqual(
+        entry.family,
+        4,
+        `IPv4 address ${entry.address} should have family:4 but got family:${entry.family}`
+      );
+    }
+  },
+};
+
+// Regression: dns.lookup() with default family (0) and all:false must resolve
+// hosts that only have A records (was only querying AAAA, failing for IPv4-only).
+export const lookupDefaultFamilyResolvesIPv4 = {
+  async test() {
+    // Default options (family:0, all:false) — should return an address
+    const result = await dnsPromises.lookup(addresses.INET4_HOST);
+    ok(result != null, 'expected a result');
+    strictEqual(typeof result.address, 'string');
+    ok(result.address.length > 0, 'expected non-empty address');
+    ok(
+      result.family === 4 || result.family === 6,
+      `family must be 4 or 6, got ${result.family}`
+    );
+
+    // Also verify via callback API
+    const { promise, resolve, reject } = Promise.withResolvers();
+    dns.lookup(addresses.INET4_HOST, (error, address, family) => {
+      if (error) {
+        reject(error);
+        return;
+      }
+      strictEqual(typeof address, 'string');
+      ok(address.length > 0, 'expected non-empty address from callback');
+      ok(family === 4 || family === 6, `family must be 4 or 6, got ${family}`);
+      resolve();
+    });
+    await promise;
+  },
+};
+
+// Regression: Resolver.resolvePtr must exist (was misspelled as 'esolvePtr').
+export const resolverResolvePtrExists = {
+  async test() {
+    const resolver = new dnsPromises.Resolver();
+    strictEqual(
+      typeof resolver.resolvePtr,
+      'function',
+      'Resolver.resolvePtr should be a function'
+    );
+    // Actually call it to verify it works end-to-end
+    const result = await resolver.resolvePtr(addresses.PTR_HOST);
+    ok(Array.isArray(result), 'expected array result');
+    ok(result.length > 0, 'expected at least one PTR record');
+    for (const item of result) {
+      strictEqual(typeof item, 'string');
+    }
+  },
+};
+
 // Tests are taken from
 // https://github.com/nodejs/node/blob/3153c8333e3a8f2015b795642def4d81ec7cd7b3/test/parallel/test-dns-lookup.js
 export const testDnsLookup = {