• Version: v11.6.0
• Platform: all
• Subsystem: http, net

This was originally discovered by @szmarczak and reported as sindresorhus/got#690.

Unless we're mistaken, setTimeout(0) on an HTTP request (and then socket) can lead to a timeout listener not being removed. This is problematic because combined with a keepalive agent, it can lead to a memory leak.

This Gist by Szymon illustrates the issue. For convenience, I'm also quoting his inline explanation here:

1. request.setTimeout calls listenSocketTimeout:
   https://github.com/nodejs/node/blob/v11.6.0/lib/_http_client.js#L736
2. listenSocketTimeout creates a proxy (timeout event) Socket -> ClientRequest: https://github.com/nodejs/node/blob/v11.6.0/lib/_http_client.js#L673
3. The proxy event is released on the response end event:
   https://github.com/nodejs/node/blob/v11.6.0/lib/_http_client.js#L682

In this case this never happens, because we set the timeout on that particular event. The correct behaviour would be to prevent calling listenSocketTimeout if msecs is 0.