nodejs · wehamed · Aug 12, 2026
diff --git a/lib/net.js b/lib/net.js
@@ -376,6 +376,13 @@ function closeSocketHandle(self, isException, isCleanupPending = false) {
 const kBytesRead = Symbol('kBytesRead');
 const kBytesWritten = Symbol('kBytesWritten');
 const kSetTOS = Symbol('kSetTOS');
+// Generation token for a Socket's connection lifecycle. Async work started by
+// a connect() attempt (e.g. a DNS lookup) captures the current generation; the
+// generation is advanced once per lifecycle, in _destroy, so stale async work
+// from a destroyed lifecycle cannot drive a newer lifecycle established by a
+// later connect() (e.g. reconnect after 'close'). Multiple connect() calls
+// within one undestroyed lifecycle share a generation.
+const kConnectGeneration = Symbol('kConnectGeneration');
 // Marks a Socket whose handle is an adopted, already-bound BoundSocket.
 const kBoundSource = Symbol('kBoundSource');
 
@@ -1100,6 +1107,9 @@ Socket.prototype._destroy = function(exception, cb) {
   debug('destroy');
 
   this.connecting = false;
+  // The connection lifecycle ends here; invalidate async work (e.g. a DNS
+  // lookup) still in flight so it cannot drive a newer lifecycle.
+  this[kConnectGeneration] = (this[kConnectGeneration] || 0) + 1;
 
   for (let s = this; s !== null; s = s._parent) {
     clearTimeout(s[kTimeout]);
@@ -1415,6 +1425,13 @@ function internalConnectMultiple(context, canceled) {
   clearTimeout(context[kTimeout]);
   const self = context.socket;
 
+  // The connection lifecycle that created this context may have been destroyed
+  // and a newer connect() established; a stale context must not drive the new
+  // lifecycle's handle.
+  if (self[kConnectGeneration] !== context.connectGeneration) {
+    return;
+  }
+
   // We were requested to abort. Stop all operations
   if (self._aborted) {
     return;
@@ -1778,14 +1795,18 @@ function lookupAndConnect(self, options) {
     return;
   }
 
+  const connectGeneration = self[kConnectGeneration];
+
   defaultTriggerAsyncIdScope(self[async_id_symbol], function() {
     lookup(host, dnsopts, function emitLookup(err, ip, addressType) {
       self.emit('lookup', err, ip, addressType, host);
 
       // It's possible we were destroyed while looking this up.
       // XXX it would be great if we could cancel the promise returned by
       // the look up.
-      if (!self.connecting) return;
+      // A stale callback may also arrive after the attempt was destroyed and a
+      // newer connect() attempt was started; it must not drive the new attempt.
+      if (!self.connecting || self[kConnectGeneration] !== connectGeneration) return;
 
       if (err) {
         // net.createConnection() creates a net.Socket object and immediately
@@ -1815,12 +1836,16 @@ function lookupAndConnect(self, options) {
 function lookupAndConnectMultiple(
   self, async_id_symbol, lookup, host, options, dnsopts, port, localAddress, localPort, timeout,
 ) {
+  const connectGeneration = self[kConnectGeneration];
+
   defaultTriggerAsyncIdScope(self[async_id_symbol], function emitLookup() {
     lookup(host, dnsopts, function emitLookup(err, addresses) {
       // It's possible we were destroyed while looking this up.
       // XXX it would be great if we could cancel the promise returned by
       // the look up.
-      if (!self.connecting) {
+      // A stale callback may also arrive after the attempt was destroyed and a
+      // newer connect() attempt was started; it must not drive the new attempt.
+      if (!self.connecting || self[kConnectGeneration] !== connectGeneration) {
         return;
       } else if (err) {
         self.emit('lookup', err, undefined, undefined, host);
@@ -1843,7 +1868,7 @@ function lookupAndConnectMultiple(
         const { address: ip, family: addressType } = address;
         self.emit('lookup', err, ip, addressType, host);
         // It's possible we were destroyed while looking this up.
-        if (!self.connecting) {
+        if (!self.connecting || self[kConnectGeneration] !== connectGeneration) {
           return;
         }
         if (isIP(ip) && (addressType === 4 || addressType === 6)) {
@@ -1914,6 +1939,7 @@ function lookupAndConnectMultiple(
         socket: self,
         addresses: toAttempt,
         current: 0,
+        connectGeneration,
         port,
         localPort,
         timeout,
@@ -2087,6 +2113,14 @@ function afterConnectMultiple(context, current, status, handle, req, readable, w
 
   const self = context.socket;
 
+  // The connection lifecycle that created this context may have been destroyed
+  // and a newer connect() established; drop the stale completion, closing the
+  // completed handle so it cannot leak.
+  if (self[kConnectGeneration] !== context.connectGeneration) {
+    handle.close();
+    return;
+  }
+
   // Some error occurred, add to the list of exceptions
   if (status !== 0) {
     const ex = createConnectionError(req, status);
@@ -2115,6 +2149,14 @@ function afterConnectMultiple(context, current, status, handle, req, readable, w
 
 function internalConnectMultipleTimeout(context, req, handle) {
   debug('connect/multiple: connection to %s:%s timed out', req.address, req.port);
+
+  // The connection lifecycle that created this context may have been destroyed
+  // and a newer connect() established; drop the stale timeout so it cannot
+  // emit a spurious connectionAttemptTimeout or drive further attempts.
+  if (context.socket[kConnectGeneration] !== context.connectGeneration) {
+    return;
+  }
+
   context.socket.emit('connectionAttemptTimeout', req.address, req.port, req.addressType);
 
   req.oncomplete = undefined;

diff --git a/test/parallel/test-net-connect-immediate-destroy-reconnect.js b/test/parallel/test-net-connect-immediate-destroy-reconnect.js
@@ -0,0 +1,114 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+
+// Regression test for https://github.com/nodejs/node/issues/55519.
+//
+// Destroying a socket while its DNS lookup is still in flight and then
+// reconnecting on 'close' must not let the stale lookup callback from the
+// destroyed attempt drive internalConnect on the new attempt's handle. Doing
+// so would issue a second connect on the same handle and fail the connection
+// with EALREADY (EINVAL on Windows).
+//
+// The flow is driven deterministically: the custom lookup captures the
+// callbacks of both attempts and the stale (attempt 1) callback is invoked
+// before the callback of the current (attempt 2) attempt.
+
+const cases = [
+  { autoSelectFamily: false },
+  { autoSelectFamily: true },
+];
+
+function runCase(options, done) {
+  let connected = false;
+  let accepted = false;
+
+  const watchdog = setTimeout(() => {
+    console.error(`test-case timed out: ${JSON.stringify(options)}`);
+    process.exit(1);
+  }, 10_000);
+
+  const socket = new net.Socket();
+
+  const finish = common.mustCall(() => {
+    clearTimeout(watchdog);
+    socket.destroy();
+    server.close();
+    done();
+  });
+
+  // Teardown only after both the client has connected and the server has
+  // accepted the connection, so the accept callback is never dropped by an
+  // early server.close().
+  const server = net.createServer(common.mustCall(() => {
+    accepted = true;
+    if (connected) {
+      finish();
+    }
+  }));
+
+  server.listen(0, common.localhostIPv4, common.mustCall(() => {
+    const port = server.address().port;
+    const lookupCalls = [];
+    let reconnected = false;
+    let connectionAttempts = 0;
+
+    function lookup(host, dnsopts, cb) {
+      lookupCalls.push({ dnsopts, cb });
+    }
+
+    socket.on('connectionAttempt', () => {
+      connectionAttempts++;
+    });
+
+    socket.on('connect', common.mustCall(() => {
+      // Only the current (second) attempt may have connected: the stale
+      // callback must not have started a connect on the new attempt's handle.
+      assert.strictEqual(connectionAttempts, 1);
+      connected = true;
+      if (accepted) {
+        finish();
+      }
+    }));
+
+    socket.on('error', common.mustNotCall());
+
+    socket.on('close', common.mustCallAtLeast(() => {
+      if (reconnected) {
+        return;
+      }
+      reconnected = true;
+      // Start a new connection attempt; the lookup callback of the first
+      // attempt is still pending.
+      socket.connect({ host: 'host.example', port, lookup, ...options });
+      assert.strictEqual(lookupCalls.length, 2);
+
+      const fire = (call) => {
+        if (call.dnsopts.all === true) {
+          call.cb(null, [{ address: common.localhostIPv4, family: 4 }]);
+        } else {
+          call.cb(null, common.localhostIPv4, 4);
+        }
+      };
+      // Invoke the stale callback first, then the current attempt's callback.
+      // The stale callback must be ignored.
+      fire(lookupCalls[0]);
+      fire(lookupCalls[1]);
+    }));
+
+    socket.connect({ host: 'host.example', port, lookup, ...options });
+    socket.destroy();
+  }));
+}
+
+let index = 0;
+function next() {
+  if (index >= cases.length) {
+    return;
+  }
+  runCase(cases[index++], next);
+}
+
+next();