net: add local family

PR-URL: #43975
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/net.md

@@ -270,6 +270,7 @@ 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.
+  * `localFamily` {string} Local family.
   * `remoteAddress` {string} Remote address.
   * `remotePort` {number} Remote port.
   * `remoteFamily` {string} Remote IP family. `'IPv4'` or `'IPv6'`.
@@ -1007,6 +1008,16 @@ added: v0.9.6
 
 The numeric representation of the local port. For example, `80` or `21`.
 
+### `socket.localFamily`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* {string}
+
+The string representation of the local IP family. `'IPv4'` or `'IPv6'`.
+
 ### `socket.pause()`
 
 * Returns: {net.Socket} The socket itself.

lib/net.js

@@ -849,6 +849,9 @@ protoGetter('localPort', function localPort() {
   return this._getsockname().port;
 });
 
+protoGetter('localFamily', function localFamily() {
+  return this._getsockname().family;
+});
 
 Socket.prototype[kAfterAsyncWrite] = function() {
   this[kLastWriteQueueSize] = 0;
@@ -1683,6 +1686,7 @@ function onconnection(err, clientHandle) {
         clientHandle.getsockname(localInfo);
         data.localAddress = localInfo.address;
         data.localPort = localInfo.port;
+        data.localFamily = localInfo.family;
       }
       if (clientHandle.getpeername) {
         const remoteInfo = ObjectCreate(null);

test/parallel/test-net-local-address-port.js

@@ -27,6 +27,7 @@ const net = require('net');
 const server = net.createServer(common.mustCall(function(socket) {
   assert.strictEqual(socket.localAddress, common.localhostIPv4);
   assert.strictEqual(socket.localPort, this.address().port);
+  assert.strictEqual(socket.localFamily, this.address().family);
   socket.on('end', function() {
     server.close();
   });