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internal/poll: Changed error string breaks user application #19252

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typeless opened this issue Feb 23, 2017 · 4 comments
Closed

internal/poll: Changed error string breaks user application #19252

typeless opened this issue Feb 23, 2017 · 4 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
Milestone
Go1.9

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@typeless
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typeless commented Feb 23, 2017 •
edited

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version devel +3792db5 Mon Feb 13 18:36:28 2017 +0000 linux/amd64
It works on Go 1.8

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/mura/devel/go"
GORACE=""
GOROOT="/home/mura/tools/go"
GOTOOLDIR="/home/mura/tools/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build174238897=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

make integration-test for the code I am working on.
go-gitea/gitea#741 (comment)
But I think that doesn't matter after all.

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.

What did you expect to see?

All tests passed.

What did you see instead?

All tests failed.

It turned out that one of the dependent libraries ( (See https://github.com/facebookgo/httpdown/blob/master/httpdown.go#L338) uses the exact error string to make its decision and the string in question was changed at some point of time (3792db5#diff-18782360650b1a2ccfee593591ff45bbR17). This may not be the fault of the error string changing but I'd like to know what the recommended solution (an idimatic way for differentiating errors) is for the case. And maybe the possible impact can be prepared before the next production release.
@mvdan
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mvdan commented Feb 23, 2017

As far as I know, error strings are not under the Go1 compatibility contract. If your program depends on them, it might break in the future or not be portable at all (e.g. some os errors change between operating systems, I believe).

The way to do this in a portable and backwards/forwards compatible way is to check for error types, not error messages. Although that won't be possible if the package just uses errors.New().

@ianlancetaylor
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This is related to #4373.

@bradfitz bradfitz added this to the Go1.9 milestone Mar 21, 2017
@bradfitz
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Marking for Go 1.9.

This may not be the fault of the error string changing but I'd like to know what the recommended solution (an idimatic way for differentiating errors) is for the case

Indeed.

@bradfitz bradfitz added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Mar 21, 2017
@gopherbot
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CL https://golang.org/cl/39997 mentions this issue.

@golang golang locked and limited conversation to collaborators Apr 26, 2018
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@bradfitz @typeless @ianlancetaylor @mvdan @gopherbot