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panic on marshaling values obtained from unexported field #463

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nirekin opened this issue May 10, 2019 · 7 comments · May be fixed by #1059
Open

panic on marshaling values obtained from unexported field #463

nirekin opened this issue May 10, 2019 · 7 comments · May be fixed by #1059

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@nirekin
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nirekin commented May 10, 2019

Output

panic: reflect.Value.Interface: cannot return value obtained from unexported field or method [recovered]
	panic: reflect.Value.Interface: cannot return value obtained from unexported field or method

goroutine 1 [running]:
<installer/vendor/gopkg.in/yaml%2ev2.handleErr(0xc4204e2340)
	/go/src/installer/vendor/gopkg.in/yaml.v2/yaml.go:249 +0x99
panic(0x91e080, 0xa68950)
	/usr/local/go/src/runtime/panic.go:502 +0x229
reflect.valueInterface(0x9b4be0, 0xc42000e650, 0x56, 0x91e001, 0x91e001, 0x16)
	/usr/local/go/src/reflect/value.go:959 +0x1c1
reflect.Value.Interface(0x9b4be0, 0xc42000e650, 0x56, 0x91e000, 0xc420394b60)
	/usr/local/go/src/reflect/value.go:948 +0x44
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshal(0xc420461600, 0x0, 0x0, 0x9b4be0, 0xc42000e650, 0x56)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:106 +0x74
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv.func1()
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:229 +0x24b
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).mappingv(0xc420461600, 0x0, 0x0, 0xc4204e1158)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:259 +0x14e
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv(0xc420461600, 0x0, 0x0, 0x9d5940, 0xc42000e650, 0x19)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:216 +0xf7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshal(0xc420461600, 0x0, 0x0, 0x9d5940, 0xc42000e650, 0x19)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:163 +0x6c7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshal(0xc420461600, 0x0, 0x0, 0x9a90c0, 0xc420114120, 0x194)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:150 +0x632
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv.func1()
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:229 +0x24b
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).mappingv(0xc420461600, 0x0, 0x0, 0xc4204e1670)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:259 +0x14e
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv(0xc420461600, 0x0, 0x0, 0x983de0, 0xc420114120, 0x199)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:216 +0xf7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshal(0xc420461600, 0x0, 0x0, 0x983de0, 0xc420114120, 0x199)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:163 +0x6c7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv.func1()
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:229 +0x24b
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).mappingv(0xc420461600, 0x0, 0x0, 0xc4204e1a88)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:259 +0x14e
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv(0xc420461600, 0x0, 0x0, 0x9ab9e0, 0xc420114120, 0x199)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:216 +0xf7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshal(0xc420461600, 0x0, 0x0, 0x9ab9e0, 0xc420114120, 0x199)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:163 +0x6c7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshal(0xc420461600, 0x0, 0x0, 0x970160, 0xc420162580, 0x96)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:157 +0x53b
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv.func1()
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:229 +0x24b
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).mappingv(0xc420461600, 0x0, 0x0, 0xc4204e1fa0)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:259 +0x14e
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).structv(0xc420461600, 0x0, 0x0, 0x9df060, 0xc420162380, 0x99)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:216 +0xf7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshal(0xc420461600, 0x0, 0x0, 0x9df060, 0xc420162380, 0x99)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:163 +0x6c7
installer/vendor/gopkg.in/yaml%2ev2.(*encoder).marshalDoc(0xc420461600, 0x0, 0x0, 0x9df060, 0xc420162380, 0x99)
	/go/src/installer/vendor/gopkg.in/yaml.v2/encode.go:96 +0x238
installer/vendor/gopkg.in/yaml%2ev2.Marshal(0x9df060, 0xc420162380, 0x0, 0x0, 0x0, 0x0, 0x0)
	/go/src/installer/vendor/gopkg.in/yaml.v2/yaml.go:203 +0xe0

Analysis :

yaml/encode.go

Lines 98 to 103 in 7b8349a

func (e *encoder) marshal(tag string, in reflect.Value) {
if !in.IsValid() || in.Kind() == reflect.Ptr && in.IsNil() {
e.nilv()
return
}
iface := in.Interface()

Solution :
in.CanInterface() should be called before Interface() in order to be sure it won't panic

func (e *encoder) marshal(tag string, in reflect.Value) {
	if !in.CanInterface() || !in.IsValid() || in.Kind() == reflect.Ptr && in.IsNil() {
		e.nilv()
		return
	}
	iface := in.Interface()
       ...
}
@nirekin nirekin changed the title panic on marshalling values obtained from unexported field panic on marshaling values obtained from unexported field May 10, 2019
@niemeyer
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Thanks for the report. Do you have some minimal sample code reproducing the bug?

@johnSchnake
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https://play.golang.org/p/WxT-pwqhNx4 will reproduce the bug. Having an embedded type which is unexported.

@johnSchnake johnSchnake mentioned this issue Nov 13, 2019
Closed
@Mic-U Mic-U mentioned this issue Oct 27, 2021
Closed
@denisvmedia
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This problem seems to be still actual. Even in v3. The solution by @nirekin seems to be working. Are there any plans to include it in the upcoming releases? CC @niemeyer

@roffe
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roffe commented Oct 8, 2022 •
edited
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Still getting it on V3 in 2022 when trying to marshal a ECS service response from aws-sdk-go-v2

This is the struct it's panicing on marshalling https://github.com/aws/aws-sdk-go-v2/blob/main/service/ecs/types/types.go#L2826-L3007

Can confirm fix by @nirekin works

panic: reflect.Value.Interface: cannot return value obtained from unexported field or method [recovered]
        panic: reflect.Value.Interface: cannot return value obtained from unexported field or method

goroutine 1 [running]:
gopkg.in/yaml%2ev2.handleErr(0xc000523998)
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/yaml.go:249 +0x6d
panic({0x15fdb20, 0x1aa5d00})
        /usr/local/go/src/runtime/panic.go:884 +0x212
reflect.valueInterface({0x169d0e0?, 0xc000880220?, 0x0?}, 0x20?)
        /usr/local/go/src/reflect/value.go:1489 +0xd8
reflect.Value.Interface(...)
        /usr/local/go/src/reflect/value.go:1478
gopkg.in/yaml%2ev2.(*encoder).marshal(0xc000136888?, {0x0, 0x0}, {0x169d0e0?, 0xc000880220?, 0x4?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:103 +0xb7
gopkg.in/yaml%2ev2.(*encoder).structv.func1()
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:226 +0x4da
gopkg.in/yaml%2ev2.(*encoder).mappingv(0xc0000f6dc0, {0x0?, 0x0}, 0xc000522f10)
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:256 +0x147
gopkg.in/yaml%2ev2.(*encoder).structv(0xc0000f6dc0, {0x0, 0x0}, {0x1740f00?, 0xc000880210?, 0xc0000f6dc0?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:213 +0xef
gopkg.in/yaml%2ev2.(*encoder).marshal(0x15c1400?, {0x0, 0x0}, {0x1740f00?, 0xc000880210?, 0x8?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:160 +0x9f9
gopkg.in/yaml%2ev2.(*encoder).slicev(0xc0000f6dc0, {0x0?, 0x0}, {0x15c1400?, 0xc000602b60?, 0x12?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:272 +0x1df
gopkg.in/yaml%2ev2.(*encoder).marshal(0xc000136738?, {0x0, 0x0}, {0x15c1400?, 0xc000602b60?, 0x20?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:166 +0x907
gopkg.in/yaml%2ev2.(*encoder).structv.func1()
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:226 +0x4da
gopkg.in/yaml%2ev2.(*encoder).mappingv(0xc0000f6dc0, {0x0?, 0x0}, 0xc0005234f8)
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:256 +0x147
gopkg.in/yaml%2ev2.(*encoder).structv(0xc0000f6dc0, {0x0, 0x0}, {0x17fd5e0?, 0xc000602b60?, 0xb?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:213 +0xef
gopkg.in/yaml%2ev2.(*encoder).marshal(0x163d960?, {0x0, 0x0}, {0x17fd5e0?, 0xc000602b60?, 0x0?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:160 +0x9f9
gopkg.in/yaml%2ev2.(*encoder).marshal(0xc0000f6dc0?, {0x0, 0x0}, {0x163d960?, 0xc000602b60?, 0x109?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:154 +0x855
gopkg.in/yaml%2ev2.(*encoder).marshalDoc(0xc0000f6dc0, {0x0, 0x0}, {0x163d960?, 0xc000602b60?, 0x183b0ef?})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/encode.go:93 +0x125
gopkg.in/yaml%2ev2.Marshal({0x163d960?, 0xc000602b60})
        /home/roffe/go/pkg/mod/gopkg.in/[email protected]/yaml.go:203 +0x379
github.com/tjek/tjek-cli/cmd.printService(0xc000602b60?)
        /home/roffe/go/src/github.com/tjek/tjek-cli/cmd/getService.go:95 +0x8c
github.com/tjek/tjek-cli/cmd.glob..func22(0x25a5ea0?, {0xc0002f7ec0, 0x1, 0x3?})
        /home/roffe/go/src/github.com/tjek/tjek-cli/cmd/scaleRoot.go:53 +0x318
github.com/spf13/cobra.(*Command).execute(0x25a5ea0, {0xc0002f7e30, 0x3, 0x3})
        /home/roffe/go/pkg/mod/github.com/spf13/[email protected]/command.go:856 +0x663
github.com/spf13/cobra.(*Command).ExecuteC(0x25a54a0)
        /home/roffe/go/pkg/mod/github.com/spf13/[email protected]/command.go:960 +0x39d
github.com/spf13/cobra.(*Command).Execute(...)
        /home/roffe/go/pkg/mod/github.com/spf13/[email protected]/command.go:897
github.com/tjek/tjek-cli/cmd.Execute()
        /home/roffe/go/src/github.com/tjek/tjek-cli/cmd/root.go:53 +0x25
main.main()
        /home/roffe/go/src/github.com/tjek/tjek-cli/main.go:11 +0x2a
exit status 2

@roffe
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roffe commented Oct 8, 2022 •
edited
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When can we expect a buggfix to be released @niemeyer

@roffe roffe mentioned this issue Oct 8, 2022
Closed
@saddit
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saddit commented Mar 29, 2023

Why not fix it?

@jjrodenburg jjrodenburg linked a pull request Dec 5, 2024 that will close this issue
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@jjrodenburg
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I encountered this error today so raised another PR and added 2 simple unit tests.

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Fix panics for embedded unexported types jjrodenburg/go-yaml
7 participants
@niemeyer @roffe @denisvmedia @nirekin @johnSchnake @jjrodenburg @saddit