Aboard Read()/Write() by SetDeadline() with past time

[yudai]

Hello, thanks for the handy library.

Problem Observed

When an HTTP server is served on a yamux.Session, Hijack() onhttp.ResponseWriter blocks forever, which means protocols that depend on hijacking (protocol upgrade) such as Websocket does not work with yamux.

Problem Detail

In net/http, Set(Read/Write)Deadline() with net.aLongTimeAgo is used to abort pending Read()/Write() by setting the unix epoch + 1 second. Hijack() uses this method (and I think there are some more cases) to abort Read() as well.

In the document of net.Conn, SetDeadline() is described as below:

// A deadline is an absolute time after which I/O operations
// fail with a timeout (see type Error) instead of
// blocking. The deadline applies to all future and pending
// I/O, not just the immediately following call to Read or
// Write. After a deadline has been exceeded, the connection
// can be refreshed by setting a deadline in the future.

Setting a past time is supposed to cancel any pending Read()/Write() on the connection.

However, the current implementation of yamux.Stream doesn't support this type of cancelation. Libraries expect this behavior therefore can block forever unexpectedly with yamux.

Suggested Resolution

When SetDeadline() is called, retry Read() or Write() by using the notification channels.

I think there would be no side effects caused by this change, since when you would not provide a past time to SetDeadline() when you actually don't expect cancelation by that.

[itimofeev]

Spent several days because of described problem. When do hijack() conn randomly blocked.
Thank you for PR, hope it will be merged soon.

[itimofeev]

Figured out some issue with this PR. We also need to return net.Error implementation of ErrTimeout. Or in some cases httputil.NewSingleHostReverseProxy() will return context closed error. This commit fixes problem.

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[dadgar]

Closed by #82