http: set socket timeout when socket connects

`request.setTimeout()` calls `socket.setTimeout()` as soon as a socket
is assigned to the request. This makes the `timeout` event to be
emitted on the request even if the underlying socket never connects.

This commit makes `socket.setTimeout()` to be called only when the
underlying socket is connected.

PR-URL: nodejs/node#8895
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

lib/_http_client.js

@@ -739,7 +739,9 @@ ClientRequest.prototype.setTimeout = function setTimeout(msecs, callback) {
   }
 
   this.once('socket', function(sock) {
-    sock.setTimeout(msecs, emitTimeout);
+    sock.once('connect', function() {
+      sock.setTimeout(msecs, emitTimeout);
+    });
   });
 
   return this;

test/parallel/test-http-client-timeout-on-connect.js

@@ -0,0 +1,26 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+
+const server = http.createServer((req, res) => {
+  // This space is intentionally left blank.
+});
+
+server.listen(0, common.localhostIPv4, common.mustCall(() => {
+  const port = server.address().port;
+  const req = http.get(`http://${common.localhostIPv4}:${port}`);
+
+  req.setTimeout(1);
+  req.on('socket', common.mustCall((socket) => {
+    assert.strictEqual(socket._idleTimeout, undefined);
+    socket.on('connect', common.mustCall(() => {
+      assert.strictEqual(socket._idleTimeout, 1);
+    }));
+  }));
+  req.on('timeout', common.mustCall(() => req.abort()));
+  req.on('error', common.mustCall((err) => {
+    assert.strictEqual('socket hang up', err.message);
+    server.close();
+  }));
+}));