net/http: Server closeIdleConns does not close StateNew connections

[kcburge]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.9.2

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

any (linux x86_64)

What did you do?

Long Story: my web app was not closing when calling Shutdown on my http server. Google Chrome for some reason was creating a couple new connections to my server, but not making any requests on them. I'm guessing this is for performance, but I couldn't find any explanation. These extra connections stay in "StateNew" state, so, Shutdown does not close them when closing idle connections.

Short Story: Tried to "Shutdown" http server with StateNew connections.

https://play.golang.org/p/dP4vQZkKdx

What did you expect to see?

Since StateNew is an idle state, I'd expect it to be closed during Shutdown.

What did you see instead?

Shutdown must be cancelled to clear StateNew connections.

[gbbr]

The returned error is correct, it is of type contextDeadlineExceededError and is thrown because the context timed out. See here: https://play.golang.org/p/JmX0nEqeqa

[gbbr]

From net/http/#Server.Shutdown:

Shutdown works by first closing all open listeners, then closing all idle connections, and then waiting indefinitely for connections to return to idle and then shut down. If the provided context expires before the shutdown is complete, Shutdown returns the context's error, otherwise it returns any error returned from closing the Server's underlying Listener(s).

[gbbr]

As a potential solution to your problem, you might have more luck experimenting with the IdleConnTimeout setting from http.Transport. I and others would be more than happy to help if you post this as a question on the go-nuts mailling list.

Closing, since there is no bug.

[kcburge]

Thanks for the quick response. I apologize if the problem description and example did not make the issue clear. The problem is that a new, unused connection is NOT considered "idle" by closeIdleConns and is therefore NOT closed during Shutdown. The only reason I added a context with a timer to my example was to clearly show that the idle connection was not being closed, instead, the context is timing out. The only difference between StateNew and StateIdle is that a StateNew connection has never made a request, correct? So, as you quoted "Shutdown works by ... closing all idle connections..." A StateNew is an idle connection, is it not?

[bradfitz]

Since StateNew is an idle state

Go has StateNew different from StateIdle intentionally. New isn't idle. A new connection is expected to have a request sent on it soon, and browsers have certain expectations of the server not hanging up on them for new connections. But keep-alive (idle) connections are much more likely to be closed at random times, and clients expect this more.

It's intentional that Shutdown doesn't close StateNew connections.

But if Chrome is keep some warmed up TCP connections in StateNew, maybe we need to do something. Maybe close StateNew after some duration (~2-5 seconds?).

/cc @tombergan

[kcburge]

This is somewhat duplicated by #21204

[tombergan]

There are cases where clients will leave a connection open and not use it. For example: an HTTP/1 client might start a new connection but switch to an existing connection if one becomes idle before the dial completes. If that happens, and there are no more requests to send, the new connection will sit around unused. Clients might also "preconnect" to origins that the client predicts it will visit shortly.

@kcburge, have you tried using ReadHeaderTimeout? I think that will solve your problem. If you set ReadHeaderTimeout to 10s, then Shutdown should return within 10s after all outstanding requests complete.