lib: return this from net.Socket.end()

PR-URL: https://github.com/nodejs/node/pull/13481
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

doc/api/net.md

@@ -648,6 +648,8 @@ server will still send some data.
 If `data` is specified, it is equivalent to calling
 `socket.write(data, encoding)` followed by [`socket.end()`][].
 
+Returns `socket`.
+
 ### socket.localAddress
 <!-- YAML
 added: v0.9.6

lib/net.js

@@ -497,6 +497,8 @@ Socket.prototype.end = function(data, encoding) {
     this.read(0);
   else
     maybeDestroy(this);
+
+  return this;
 };
 
 

test/parallel/test-socket-write-after-fin.js

@@ -2,7 +2,7 @@
 const common = require('../common');
 const assert = require('assert');
 const net = require('net');
-const expected = 'hello1hello2hello3\nTHUNDERMUSCLE!';
+const expected = 'hello1hello2hello3\nbye';
 
 const server = net.createServer({
   allowHalfOpen: true
@@ -35,5 +35,6 @@ server.listen(0, common.mustCall(function() {
   sock.write('hello1');
   sock.write('hello2');
   sock.write('hello3\n');
-  sock.end('THUNDERMUSCLE!');
+  assert.strictEqual(sock.end('bye'), sock);
+
 }));