From bbe11804fae2f00f2b4387081a8fee42b6b82511 Mon Sep 17 00:00:00 2001
From: theanarkh <theratliter@gmail.com>
Date: Mon, 27 Jun 2022 02:02:41 +0800
Subject: [PATCH] net: add drop event for net server

---
 doc/api/net.md                                | 20 ++++++++++++++
 lib/net.js                                    | 19 ++++++++++++++
 .../test-net-server-drop-connections.js       | 26 +++++++++++++++++++
 3 files changed, 65 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 e0858e314f4ae7..82d164018931be 100644
--- a/doc/api/net.md
+++ b/doc/api/net.md
@@ -281,6 +281,26 @@ 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 arguments is as follow, otherwise return `undefined`.
+
+```json
+{
+  "localAddress": "::ffff:127.0.0.1",
+  "localPort": 61054,
+  "remoteAddress": "::ffff:127.0.0.1",
+  "remotePort": 61060,
+  "remoteFamily": "IPv6"
+}
+```
+
 ### `server.address()`
 
 <!-- YAML
diff --git a/lib/net.js b/lib/net.js
index f72a745bcc7ef3..6b0ec0ee09c461 100644
--- a/lib/net.js
+++ b/lib/net.js
@@ -1647,6 +1647,25 @@ function onconnection(err, clientHandle) {
   }
 
   if (self.maxConnections && self._connections >= self.maxConnections) {
+    if (clientHandle.getsockname || clientHandle.getpeername) {
+      const data = {};
+      if (clientHandle.getsockname) {
+        const localInfo = {};
+        clientHandle.getsockname(localInfo);
+        data.localAddress = localInfo.address;
+        data.localPort = localInfo.port;
+      }
+      if (clientHandle.getpeername) {
+        const remoteInfo = {};
+        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);
+});