net: support blocklist for net.Server

doc/api/net.md

@@ -1713,6 +1713,11 @@ changes:
     **Default:** `false`.
   * `pauseOnConnect` {boolean} Indicates whether the socket should be
     paused on incoming connections. **Default:** `false`.
+  * `blocklist` {net.BlockList} `blocklist` can be used for disabling inbound
+    access to specific IP addresses, IP ranges, or IP subnets. This does not
+    work if the server is behind a reverse proxy, NAT, etc. because the address
+    checked against the blocklist is the address of the proxy, or the one
+    specified by the NAT.
 
 * `connectionListener` {Function} Automatically set as a listener for the
   [`'connection'`][] event.

lib/net.js

@@ -1791,6 +1791,13 @@ function Server(options, connectionListener) {
   this.keepAlive = Boolean(options.keepAlive);
   this.keepAliveInitialDelay = ~~(options.keepAliveInitialDelay / 1000);
   this.highWaterMark = options.highWaterMark ?? getDefaultHighWaterMark();
+  if (options.blocklist) {
+    // TODO: use BlockList.isBlockList (https://github.com/nodejs/node/pull/56078)
+    if (!(options.blocklist instanceof module.exports.BlockList)) {
+      throw new ERR_INVALID_ARG_TYPE('options.blocklist', 'net.BlockList', options.blocklist);
+    }
+    this.blocklist = options.blocklist;
+  }
 }
 ObjectSetPrototypeOf(Server.prototype, EventEmitter.prototype);
 ObjectSetPrototypeOf(Server, EventEmitter);
@@ -2239,7 +2246,15 @@ function onconnection(err, clientHandle) {
     clientHandle.close();
     return;
   }
-
+  if (self.blocklist && typeof clientHandle.getpeername === 'function') {
+    const remoteInfo = { __proto__: null };
+    clientHandle.getpeername(remoteInfo);
+    const addressType = isIP(remoteInfo.address);
+    if (addressType && self.blocklist.check(remoteInfo.address, `ipv${addressType}`)) {
+      clientHandle.close();
+      return;
+    }
+  }
   const socket = new Socket({
     handle: clientHandle,
     allowHalfOpen: self.allowHalfOpen,

test/parallel/test-net-server-blocklist.js

@@ -0,0 +1,19 @@
+'use strict';
+const common = require('../common');
+const net = require('net');
+
+const blocklist = new net.BlockList();
+blocklist.addAddress(common.localhostIPv4);
+
+const server = net.createServer({ blocklist }, common.mustNotCall());
+server.listen(0, common.localhostIPv4, common.mustCall(() => {
+  const adddress = server.address();
+  const socket = net.connect({
+    localAddress: common.localhostIPv4,
+    host: adddress.address,
+    port: adddress.port
+  });
+  socket.on('close', common.mustCall(() => {
+    server.close();
+  }));
+}));