net/http: make Client use Request.Cancel for timeouts instead of CancelRequest
In the beginning, there was no way to cancel an HTTP request. We later added Transport.CancelRequest to cancel an in-flight HTTP request by breaking its underlying TCP connection, but it was hard to use correctly and didn't work in all cases. And its error messages were terrible. Some of those issues were fixed over time, but the most unfixable problem was that it didn't compose well. All RoundTripper implementations had to choose to whether to implement CancelRequest and both decisions had negative consequences. In Go 1.5 we added Request.Cancel, which composed well, worked in all phases, had nice error messages, etc. But we forgot to use it in the implementation of Client.Timeout (a timeout which spans multiple requests and reading request bodies). In Go 1.6 (upcoming), we added HTTP/2 support, but now Client.Timeout didn't work because the http2.Transport didn't have a CancelRequest method. Rather than add a CancelRequest method to http2, officially deprecate it and update the only caller (Client, for Client.Cancel) to use Request.Cancel instead. The http2 Client timeout tests are enabled now. For compatibility, we still use CancelRequest in Client if we don't recognize the RoundTripper type. But documentation has been updated to tell people that CancelRequest is deprecated. Fixes #13540 Change-Id: I15546b90825bb8b54905e17563eca55ea2642075 Reviewed-on: https://go-review.googlesource.com/18260Reviewed-by:Andrew Gerrand <adg@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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