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SvenGasterstaedt opened this issue Apr 10, 2024 · 4 comments
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encoding/json: unmarshaling into a struct from json fails with "reflect: Field index out of range" #66762

SvenGasterstaedt opened this issue Apr 10, 2024 · 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. WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.

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@SvenGasterstaedt
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SvenGasterstaedt commented Apr 10, 2024 •
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Go version

go version go1.22.2 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/root/.cache/go-build'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.2'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1557993680=/tmp/go-build -gno-record-gcc-switches'

What did you do?

using datadog(https://github.com/DataDog/dd-trace-go) tries to marshal/unmarshal serveral structs as json. Sporadically the marshal/unmarshal of traces and logs fails (even tho the source data look fine).

For example (input data - input data was verified via debugging when the panic occured)

{
    "rate_by_service": {
        "service:,env:": 0.5576923076923077,
        "service:test,env:development": 1,
        "service:test123,env:": 0.5576923076923077,
        "service:test234,env:dev": 0.5576923076923077,
        "service:test456,env:dev": 0.8055555555555556,
        "service:test567,env:dev:": 1
    }
}

which is unmarshalled here:
tracer/sampler.go

	var payload struct {
		Rates map[string]float64 `json:"rate_by_service"`
	}
	if err := json.NewDecoder(rc).Decode(&payload); err != nil {
		return err
	}

What did you see happen?

a panic occured:

panic: reflect: Field index out of range
goroutine 1223 [running]:
reflect.Value.Field({0x1613180, 0xc000400080, 0x199}, 0x3ff2d679f1f26f)
	/usr/local/go/src/reflect/value.go:1288 +0x37c
encoding/json.(*decodeState).object(0xc000286028, {0x1613180, 0xc000400080, 0x199})
	/usr/local/go/src/encoding/json/decode.go:720 +0x3789
encoding/json.(*decodeState).value(0xc000286028, {0x15a5300, 0xc000400080, 0x16})
	/usr/local/go/src/encoding/json/decode.go:374 +0x349
encoding/json.(*decodeState).unmarshal(0xc000286028, {0x15a5300, 0xc000400080})
	/usr/local/go/src/encoding/json/decode.go:181 +0x293
encoding/json.(*Decoder).Decode(0xc000286000, {0x15a5300, 0xc000400080})
	/usr/local/go/src/encoding/json/stream.go:73 +0x42b
gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer.(*prioritySampler).readRatesJSON(0xc00020a8a0, {0x18b6608, 0xc000c32160})
	/app/vendor/gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer/sampler.go:113 +0x16a
gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer.(*agentTraceWriter).flush.func1(0xc000c36c60)
	/app/vendor/gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer/writer.go:115 +0xc76
created by gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer.(*agentTraceWriter).flush in goroutine 12
	/app/vendor/gopkg.in/DataDog/dd-trace-go.v1/ddtrace/tracer/writer.go:91 +0x32d

the weird thing here is that the index of the field (whiuch is trying to be accessed) is very very high 0x3ff2d679f1f26f = 17999926515593839 and looks more like a pointer/address to me.

reflect/value.go
Pasted image 20240410134340 1

What did you expect to see?

the marshal should work find (as the json and the struct look fine to me).
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Apr 10, 2024
@SvenGasterstaedt SvenGasterstaedt mentioned this issue Apr 10, 2024
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@seankhliao seankhliao changed the title reflect: marshalling struct from json fails with "reflect: Field index out of range" encoding/json: unmarshaling into a struct from json fails with "reflect: Field index out of range" Apr 10, 2024
@seankhliao seankhliao added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. and removed compiler/runtime Issues related to the Go compiler and/or runtime. labels Apr 10, 2024
@ianlancetaylor
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Have you tried running your program under the race detector? See https://go.dev/blog/race-detector.

@SvenGasterstaedt
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yes, it revealed one race condition tracked with DataDog/dd-trace-go#2648, but otherwise the code was fine. (i temporary fixed it myself within the vendor code but the panics keep occuring)

@ianlancetaylor
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This looks like a data corruption problem, which could be caused by a race condition. That is the first place to look. If you are convinced that this is a problem in the Go standard library, we will need some way to reproduce the problem ourselves. Is that possible? Thanks.

@seankhliao seankhliao added WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. and removed WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. labels Apr 11, 2024
@SvenGasterstaedt
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SvenGasterstaedt commented Apr 12, 2024 •
edited
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thanks for pointing me in the right direction - some long term race detection has revealed some "questionable" unsafe.Pointer-usage in a vendor library.

see
SolaceProducts/pubsubplus-go-client#16

@benluddy benluddy mentioned this issue Apr 25, 2024
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@gabyhelp gabyhelp mentioned this issue Oct 20, 2024
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