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x/net/context/ctxhttp: implementation for <1.7 may not be correct #16668

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lujiajing1126 opened this issue Aug 11, 2016 · 4 comments
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x/net/context/ctxhttp: implementation for <1.7 may not be correct #16668

lujiajing1126 opened this issue Aug 11, 2016 · 4 comments
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FrozenDueToAge WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.

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@lujiajing1126
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lujiajing1126 commented Aug 11, 2016 •
edited 

go version go1.6.3 darwin/amd64

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/megrez/Code/project/wosai/push/worker"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.6.3/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.6.3/libexec/pkg/tool/darwin_amd64"
GO15VENDOREXPERIMENT="1"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fno-common"
CXX="clang++"
CGO_ENABLED="1"

I dont think the ctx implementation in go 1.6 is semantically correct https://github.com/golang/net/blob/master/context/ctxhttp/ctxhttp_pre17.go

It simply start a goroutine to do the request and discard response

It will send request first and the peer will receive the request and make response, which will make some mistake in some specific situations

Like a MQ server will consider A client has been received message so that the message cannot be consumed by B client who should have received this message.

consider following flow:

  1. cancel A client, but the request R is under flying, for R is a blocking request
  2. start client B and send a message M
  3. A client may have chance to receive the message M for we cannot determine who will receive the message, so i have to wait all A's requests fail then start B which may a waste of time
@bradfitz
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I'm not sure I understand your scenario. The ctxhttp has a bunch of tests, though. Perhaps you can write a test which demonstrates how it's wrong? Or explain it in pseudo-code?

/cc @broady @okdave

@bradfitz bradfitz added the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Aug 11, 2016
@bradfitz bradfitz changed the title ctx for <1.7 implementation may not correct x/net/context/ctxhttp: implementation for <1.7 may not be correct Aug 11, 2016
@lujiajing1126
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https://gist.github.com/lujiajing1126/d46af42294015274e926d52c850212d4

I wrote a server and client to reproduce the issue

It may express my idea more clearly

I mean calling cancel not really close the socket but just waits for the request done and discard the response

@lujiajing1126
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Sorry I may confused about that. I used tcpdump and lsof to diagnose the network problem and I found that there may be some error at server-end. It's nothing about the ctxhttp lib.

The CLOSE_WAIT and the tcpdump logs show that the server did not response correctly

And I change my gist

@broady
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broady commented Aug 12, 2016

Great, thanks for the follow up, @lujiajing1126.

@golang golang locked and limited conversation to collaborators Aug 12, 2017
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@bradfitz @broady @lujiajing1126 @gopherbot