From 8bbd4916d99dcf6114a0a4902f53f506b7afe346 Mon Sep 17 00:00:00 2001
From: theanarkh <theratliter@gmail.com>
Date: Sat, 9 Jul 2022 20:00:18 +0800
Subject: [PATCH] net: add drop event for net server
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PR-URL: https://github.com/nodejs/node/pull/43582
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>
---
 doc/api/net.md                                | 17 ++++++++++++
 lib/net.js                                    | 20 ++++++++++++++
 .../test-net-server-drop-connections.js       | 26 +++++++++++++++++++
 3 files changed, 63 insertions(+)
 create mode 100644 test/parallel/test-net-server-drop-connections.js

diff --git a/doc/api/net.md b/doc/api/net.md
index ca4d189fd7060a..bfc26b59d2ae4f 100644
--- a/doc/api/net.md
+++ b/doc/api/net.md
@@ -257,6 +257,23 @@ added: v0.1.90
 
 Emitted when the server has been bound after calling [`server.listen()`][].
 
+### Event: `'drop'`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+When the number of connections reaches the threshold of `server.maxConnections`,
+the server will drop new connections and emit `'drop'` event instead. If it is a
+TCP server, the argument is as follows, otherwise the argument is `undefined`.
+
+* `data` {Object} The argument passed to event listener.
+  * `localAddress` {string}  Local address.
+  * `localPort` {number} Local port.
+  * `remoteAddress` {string} Remote address.
+  * `remotePort` {number} Remote port.
+  * `remoteFamily` {string} Remote IP family. `'IPv4'` or `'IPv6'`.
+
 ### `server.address()`
 
 <!-- YAML
diff --git a/lib/net.js b/lib/net.js
index e227914c8741dc..9a1d3117d9b2cb 100644
--- a/lib/net.js
+++ b/lib/net.js
@@ -31,6 +31,7 @@ const {
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
   Symbol,
+  ObjectCreate,
 } = primordials;
 
 const EventEmitter = require('events');
@@ -1656,6 +1657,25 @@ function onconnection(err, clientHandle) {
   }
 
   if (self.maxConnections && self._connections >= self.maxConnections) {
+    if (clientHandle.getsockname || clientHandle.getpeername) {
+      const data = ObjectCreate(null);
+      if (clientHandle.getsockname) {
+        const localInfo = ObjectCreate(null);
+        clientHandle.getsockname(localInfo);
+        data.localAddress = localInfo.address;
+        data.localPort = localInfo.port;
+      }
+      if (clientHandle.getpeername) {
+        const remoteInfo = ObjectCreate(null);
+        clientHandle.getpeername(remoteInfo);
+        data.remoteAddress = remoteInfo.address;
+        data.remotePort = remoteInfo.port;
+        data.remoteFamily = remoteInfo.family;
+      }
+      self.emit('drop', data);
+    } else {
+      self.emit('drop');
+    }
     clientHandle.close();
     return;
   }
diff --git a/test/parallel/test-net-server-drop-connections.js b/test/parallel/test-net-server-drop-connections.js
new file mode 100644
index 00000000000000..4c495bdfb9e981
--- /dev/null
+++ b/test/parallel/test-net-server-drop-connections.js
@@ -0,0 +1,26 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+
+let firstSocket;
+const server = net.createServer(common.mustCall((socket) => {
+  firstSocket = socket;
+}));
+
+server.maxConnections = 1;
+
+server.on('drop', common.mustCall((data) => {
+  assert.strictEqual(!!data.localAddress, true);
+  assert.strictEqual(!!data.localPort, true);
+  assert.strictEqual(!!data.remoteAddress, true);
+  assert.strictEqual(!!data.remotePort, true);
+  assert.strictEqual(!!data.remoteFamily, true);
+  firstSocket.destroy();
+  server.close();
+}));
+
+server.listen(0, () => {
+  net.createConnection(server.address().port);
+  net.createConnection(server.address().port);
+});