x/net/http2/h2c: support closure of all connections and graceful shutdown

[nhooyr]

Very happy to see h2c supported: golang/net@c4299a1

However, there is no way to enable graceful shutdown, or even close all h2c connections. We should support this.

You could use http2.ConfigureServer to configure a http2 server's graceful shutdown to be called when the http server is shutdown but the http server's shutdown method will not wait for the http2 connections to close because they have been hijacked.

I think it'd be simplest if we added a Shutdown and Close method to *http2.Server analogous to *http.Server's methods.

[obeattie]

Is there a workaround possible for this? As far as I can see it's completely impossible to do at present, as the methods that need to be invoked to gracefully shutdown a connection (eg. serverConn.startGracefulShutdown) are unexported. cc. @bradfitz

[obeattie]

After poking a bit more, it looks like I can do something like this, which is a pretty horrid hack but does appear to work:

h2s := &http2.Server{}
h1s := &http.Server{}
http2.ConfigureServer(h1s, h2s)
// Make use of h2s in a h2c handler…
h1s.Shutdown(ctx)

This works because http2.ConfigureServer adds a shutdown hook into the http.Server such that when its Shutdown() method is invoked, the private startGracefulShutdown method is called. Shutdown() calls this method regardless of the fact that h1s was never "used."

[nhooyr]

That does not work as the Shutdown itself doesn't wait for the h2c connections.

See

go/src/net/http/server.go

Line 2631 in 86ce1cb

go f()

It starts the graceful shutdown of h2c connections in a new goroutine but only wait for the unhijacked connections.

[bradfitz]

Sorry, h2c is super low on my priority list. I don't have time to investigate this enough to be helpful here.

[gopherbot]

Change https://golang.org/cl/185059 mentions this issue: http2: add Close and Shutdown functions to the Server.

[akshayjshah]

Would the Go team be open to CLs that address this? (I see that there's a very old CL open, but it doesn't seem to have been reviewed.) h2c is particularly popular in the gRPC ecosystem, and it'd be nice for gRPC implementations built on net/http to support graceful shutdown. We've had a few Connect users complain about this 😢

Is @neild the right person to take a look at x/net/http and net/http issues?

[AlexanderYastrebov]

That does not work as the Shutdown itself doesn't wait for the h2c connections.
It starts the graceful shutdown of h2c connections in a new goroutine but only wait for the unhijacked connections.

I think I've come up with a workaround. The idea is to use custom listener that would wait until connections are closed, see zalando/skipper#2480