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json.Rawmessage decodes null as "null" #40495

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ohait opened this issue Jul 30, 2020 · 5 comments
Closed

json.Rawmessage decodes null as "null" #40495

ohait opened this issue Jul 30, 2020 · 5 comments
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@ohait
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ohait commented Jul 30, 2020 •
edited

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

$ go version
go version go1.13.1 linux/amd64

Does this issue reproduce with the latest release?

i can reproduce on go version go1.14 linux/amd64

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

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/oha/.cache/go-build"
GOENV="/home/oha/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/oha/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/oha/sdk/go1.13.1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/oha/sdk/go1.13.1/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
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=/tmp/go-build838880304=/tmp/go-build -gno-record-gcc-switches"

What did you do?

package main

import (
        "encoding/json"
        "testing"
)

type Frame struct {
        Data json.RawMessage `json:"data"`
}

func TestJson(t *testing.T) {
        f := Frame{Data: nil}
        t.Logf("%#v (%q)", f, f.Data)

        j, _ := json.Marshal(f)
        t.Logf("json: %s", j)

        var f2 Frame
        json.Unmarshal(j, &f2)
        t.Logf("%#v (%q)", f2, f2.Data)
}

What did you expect to see?

f.Data and f2.Data should be the same (nil)

What did you see instead?

=== RUN   TestJson
--- PASS: TestJson (0.00s)
    json_test.go:14: main.Frame{Data:json.RawMessage(nil)} ("")
    json_test.go:17: json: {"data":null}
    json_test.go:21: main.Frame{Data:json.RawMessage{0x6e, 0x75, 0x6c, 0x6c}} ("null")
PASS

json.Unmarshal decode null as "null"
@ohait
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ohait commented Jul 30, 2020

note, if json:"data,omitempty" than everything works as expected

@DisposaBoy
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I think you're just seeing the result of using the %q format which quotes things. Maybe you meant to use %s.

@ohait
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ohait commented Jul 30, 2020

i included also the %#v which shows how json.RawMessage(nil) is turned into json.RawMessage{0x6e, 0x75, 0x6c, 0x6c} which are the ascii of null

@seankhliao
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I believe this is working as intended, json.RawMessage specifically means not to parse the data and store it as is in json

@ohait
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ohait commented Jul 30, 2020

I believe this is working as intended, json.RawMessage specifically means not to parse the data and store it as is in json

oh yes, i see it now. if further Unmarshalled, it returns nil.

@ohait ohait closed this as completed Jul 30, 2020
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@ohait @DisposaBoy @gopherbot @seankhliao