net: defer synchronous destroy calls in internalConnect

Defer socket.destroy() calls in internalConnect and
internalConnectMultiple to the next tick. This ensures that error
handlers have a chance to be set up before errors are emitted,
particularly important when using http.request with a custom
lookup function that returns synchronously.

Previously, if a synchronous lookup function returned an IP that
triggered an immediate error (e.g., via blockList), the error would
be emitted before the HTTP client had set up its error handler
(which happens via process.nextTick in onSocket). This caused
unhandled 'error' events.

Fixes: #48771

Author: RajeshKumar11

lib/net.js

@@ -1125,7 +1125,7 @@ function internalConnect(
     err = checkBindError(err, localPort, self._handle);
     if (err) {
       const ex = new ExceptionWithHostPort(err, 'bind', localAddress, localPort);
-      self.destroy(ex);
+      process.nextTick(emitErrorAndDestroy, self, ex);
       return;
     }
   }
@@ -1135,7 +1135,7 @@ function internalConnect(
 
   if (addressType === 6 || addressType === 4) {
     if (self.blockList?.check(address, `ipv${addressType}`)) {
-      self.destroy(new ERR_IP_BLOCKED(address));
+      process.nextTick(emitErrorAndDestroy, self, new ERR_IP_BLOCKED(address));
       return;
     }
     const req = new TCPConnectWrap();
@@ -1167,12 +1167,20 @@ function internalConnect(
     }
 
     const ex = new ExceptionWithHostPort(err, 'connect', address, port, details);
-    self.destroy(ex);
+    process.nextTick(emitErrorAndDestroy, self, ex);
   } else if ((addressType === 6 || addressType === 4) && hasObserver('net')) {
     startPerf(self, kPerfHooksNetConnectContext, { type: 'net', name: 'connect', detail: { host: address, port } });
   }
 }
 
+// Helper function to defer socket destruction to the next tick.
+// This ensures that error handlers have a chance to be set up
+// before the error is emitted, particularly important when using
+// http.request with a custom lookup function.
+function emitErrorAndDestroy(self, err) {
+  self.destroy(err);
+}
+
 
 function internalConnectMultiple(context, canceled) {
   clearTimeout(context[kTimeout]);
@@ -1186,11 +1194,11 @@ function internalConnectMultiple(context, canceled) {
   // All connections have been tried without success, destroy with error
   if (canceled || context.current === context.addresses.length) {
     if (context.errors.length === 0) {
-      self.destroy(new ERR_SOCKET_CONNECTION_TIMEOUT());
+      process.nextTick(emitErrorAndDestroy, self, new ERR_SOCKET_CONNECTION_TIMEOUT());
       return;
     }
 
-    self.destroy(new NodeAggregateError(context.errors));
+    process.nextTick(emitErrorAndDestroy, self, new NodeAggregateError(context.errors));
     return;
   }
 

test/parallel/test-http-request-lookup-error-catchable.js

@@ -0,0 +1,47 @@
+'use strict';
+const common = require('../common');
+const http = require('http');
+const net = require('net');
+
+// This test verifies that errors occurring synchronously during connection
+// when using http.request with a custom lookup function and blockList
+// can be caught by the error handler.
+// Regression test for https://github.com/nodejs/node/issues/48771
+
+// The issue occurs when:
+// 1. http.request() is called with a custom synchronous lookup function
+// 2. The lookup returns an IP that triggers a synchronous error (e.g., blockList)
+// 3. The error is emitted before http's error handler is set up (via nextTick)
+//
+// The fix defers socket.destroy() calls in internalConnect to the next tick,
+// giving http.request() time to set up its error handlers.
+
+const blockList = new net.BlockList();
+blockList.addAddress(common.localhostIPv4);
+
+// Synchronous lookup that returns the blocked IP
+const lookup = (_hostname, _options, callback) => {
+  callback(null, common.localhostIPv4, 4);
+};
+
+const req = http.request({
+  host: 'example.com',
+  port: 80,
+  lookup,
+  family: 4, // Force IPv4 to use simple lookup path
+  createConnection: (opts) => {
+    // Pass blockList to trigger synchronous ERR_IP_BLOCKED error
+    return net.createConnection({ ...opts, blockList });
+  },
+}, common.mustNotCall());
+
+// This error handler must be called.
+// Without the fix, the error would be emitted before http.request()
+// returns, causing an unhandled 'error' event.
+req.on('error', common.mustCall((err) => {
+  if (err.code !== 'ERR_IP_BLOCKED') {
+    throw new Error(`Expected ERR_IP_BLOCKED but got ${err.code}`);
+  }
+}));
+
+req.end();