From 46d4a1535d54719dc0e842185f0eca9b4d3212d5 Mon Sep 17 00:00:00 2001
From: deepshekhardas <deepshekharadas1234@gmail.com>
Date: Wed, 19 Aug 2026 12:12:52 +0530
Subject: [PATCH] fix(node:dns) don't expose ARES errno on query errors
 (#37320)

---
 src/js/node/dns.ts                | 11 +++++++++++
 test/js/node/dns/node-dns.test.js | 25 +++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/src/js/node/dns.ts b/src/js/node/dns.ts
index 8d17bf0e0352..17f479382fd7 100644
--- a/src/js/node/dns.ts
+++ b/src/js/node/dns.ts
@@ -57,6 +57,17 @@ function withTranslatedError(error: any) {
   if (code?.startsWith?.("DNS_")) {
     error.code = code.slice(4);
   }
+  // c-ares errors are surfaced with the raw ARES_* number in `errno`, but
+  // Node's DNSException leaves `errno` unset for c-ares query errors; only
+  // getaddrinfo / getnameinfo (libuv) errors carry a numeric errno.
+  const syscall = error?.syscall;
+  if (
+    syscall !== "getaddrinfo" &&
+    syscall !== "getnameinfo" &&
+    typeof error?.errno === "number"
+  ) {
+    delete error.errno;
+  }
   return error;
 }
 
diff --git a/test/js/node/dns/node-dns.test.js b/test/js/node/dns/node-dns.test.js
index 8bac8693cda6..6be54d7bca2b 100644
--- a/test/js/node/dns/node-dns.test.js
+++ b/test/js/node/dns/node-dns.test.js
@@ -609,6 +609,31 @@ describe("test invalid arguments", () => {
     await promise.catch(() => {}); // result depends on the environment's resolver
   });
 
+  // https://github.com/oven-sh/bun/issues/37320
+  describe("DNS error errno matches Node.js", () => {
+    it("dns.promises.resolve errors have no errno", async () => {
+      const error = await dns_promises.resolveAny("invalid.invalid").catch(e => e);
+      expect(error.code).toBe("ENOTFOUND");
+      expect(error.errno).toBeUndefined();
+    });
+
+    it("dns.resolve callback errors have no errno", async () => {
+      const error = await new Promise(resolve => {
+        dns.resolveAny("invalid.invalid", (err, records) => resolve(err));
+      });
+      expect(error.code).toBe("ENOTFOUND");
+      expect(error.errno).toBeUndefined();
+    });
+
+    it("dns.lookup errors keep a numeric errno", async () => {
+      const error = await new Promise(resolve => {
+        dns.lookup("invalid.invalid", err => resolve(err));
+      });
+      expect(error.code).toBe("ENOTFOUND");
+      expect(typeof error.errno).toBe("number");
+    });
+  });
+
   it("dns.lookupService", async () => {
     expect(() => {
       dns.lookupService("", 443, (err, hostname, service) => {});