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net/http: panic: runtime error: comparing uncomparable type when the underlying type has a map #29768
Description
What version of Go are you using (go version)?
go version go1.10.4 linux/amd64
Does this issue reproduce with the latest release?
Not sure, the error is too rare for me but it seems the reason of the error is easy to discern.
What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/vadmeste/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/vadmeste/work/gospace"
GOPROXY=""
GORACE=""
GOROOT="/home/vadmeste/work/go"
GOTMPDIR=""
GOTOOLDIR="/home/vadmeste/work/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/mnt/p4/vadmeste/tmp/go-build653380043=/tmp/go-build -gno-record-gcc-switches"
What did you do?
Still, the error is so rare to be reproduced but it seems the reason of the error is easy to discern.
What did you expect to see?
No panic
What did you see instead?
panic: runtime error: comparing uncomparable type minio.ErrorResponse
goroutine 352943 [running]:
net/http.(*Request).write(0xc4229baf00, 0xcadce0, 0xc42179c840, 0x0, 0x0, 0x0, 0xcaf100, 0xc4208d4280)
/opt/go/src/net/http/request.go:624 +0x71b
net/http.(*persistConn).writeLoop(0xc421cf3200)
/opt/go/src/net/http/transport.go:1825 +0x1ea
created by net/http.(*Transport).dialConn
/opt/go/src/net/http/transport.go:1238 +0x97f
More information
The following is the definition of minio.ErrorResponse (https://github.com/minio/minio-go/blob/master/api-error-response.go#L38)
// ErrorResponse - Is the typed error returned by all API operations.
type ErrorResponse struct {
XMLName xml.Name `xml:"Error" json:"-"`
Code string
Message string
BucketName string
Key string
RequestID string `xml:"RequestId"`
HostID string `xml:"HostId"`
// Region where the bucket is located. This header is returned
// only in HEAD bucket and ListObjects response.
Region string
// Underlying HTTP status code for the returned error
StatusCode int `xml:"-" json:"-"`
// Headers of the returned S3 XML error
Headers http.Header `xml:"-" json:"-"`
}
Activity
agnivade commentedon Jan 18, 2019
Yes, this is because ErrorResponse has
Headerswhich is actually a map. And maps are not comparable.So, when both
bodyReadErroranderrare internally of typeErrorResponse, the comparison crashes.https://github.com/golang/go/blob/master/src/net/http/request.go#L652
A small reproducer -
@bradfitz - thoughts ? Since we are not in control of the underlying type, things like these can happen.
reflect.DeepEqualdoes bypass the panic, but do we want something like that inside net/http ?[-]Comparing uncomparable type panic inside golang http[/-][+]net/http: panic: runtime error: comparing uncomparable type when the underlying type has a map[/+]bradfitz commentedon Jan 18, 2019
Yeah, sorry, maps aren't comparable. This isn't an HTTP issue, really.
vadmeste commentedon Jan 18, 2019
Someone would easily define an error struct which has a map or a slice inside it to facilitate the construction of the error message.
Since we cannot write a custom comparator in Golang for my custom error struct (ErrorResponse), it doesn't seem there is a way to avoid the panic without restructuring my code.
With this additional context description, @bradfitz do you still feel this is not a http pkg issue ?
bradfitz commentedon Jan 18, 2019
My opinion is unchanged. You'll have to restructure your code so you don't do things not allowed by the language.