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Brad Fitzpatrick authored
The Transport had a delicate protocol between its readLoop goroutine and the goroutine calling RoundTrip. The basic concern is that the caller's RoundTrip goroutine wants to wait for either a connection-level error (the conn dying) or the response. But sometimes both happen: there's a valid response (without a body), but the conn is also going away. Both goroutines' logic dealing with this had grown large and complicated with hard-to-follow comments over the years. Simplify and document. Pull some bits into functions and do all bodyless stuff in one place (it's special enough), rather than having a bunch of conditionals scattered everywhere. One test is no longer even applicable since the race it tested is no longer possible (the code doesn't exist). The bug that this fixes is that when the Transport reads a bodyless response from a server, it was returning that response before returning the persistent connection to the idle pool. As a result, ~1/1000 of serial requests would end up creating a new connection rather than re-using the just-used connection due to goroutine scheduling chance. Instead, this now adds bodyless responses' connections back to the idle pool first, then sends the response to the RoundTrip goroutine, but making sure that the RoundTrip goroutine is outside of its select on the connection dying. There's a new buffered channel involved now, which is a minor complication, but it's much more self-contained and well-documented than the previous complexity. (The alternative of making the responseAndError channel itself unbuffered is too invasive and risky at this point; it would require a number of changes to avoid deadlocked goroutines in error cases) In any case, flakes look to be gone now. We'll see if trybots agree. Fixes #13633 Change-Id: I95a22942b2aa334ae7c87331fddd751d4cdfdffc Reviewed-on: https://go-review.googlesource.com/17890Reviewed-by:
Russ Cox <rsc@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
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