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encoding/json: Unmarshalling *websocket.Conn over a websocket with JSON crashes #14665

dolanor opened this issue Mar 6, 2016 · 3 comments


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dolanor commented Mar 6, 2016

  1. What version of Go are you using (go version)?
    go version go1.6 linux/amd64
  2. What operating system and processor architecture are you using (go env)?
    GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
  3. What did you do?
    I sent a *websocket.Conn on a websocket in JSON (by pure laziness, without caring about having it on the other side).
  4. What did you expect to see?
    I expected to get unmarshalling kind of working, even if the *websocket.Conn wouldn't work: I didn't really wanted to get this information on the other side, but it was part of a struct I wanted to send over the wire.

If I put this *websocket.Conn to nil, then I don't get problems on the other side.

  1. What did you see instead?
    panic: reflect: reflect.Value.Set using value obtained using unexported field [recovered]
        panic: interface conversion: string is not error: missing method Error

    goroutine 7 [running]:
    panic(0x752c40, 0xc820010680)
        /usr/local/go/src/runtime/panic.go:464 +0x3e6
        /usr/local/go/src/encoding/json/decode.go:156 +0xba
    panic(0x6c2ba0, 0xc8200e8650)
        /usr/local/go/src/runtime/panic.go:426 +0x4e9
        /usr/local/go/src/reflect/value.go:226 +0x161
    reflect.Value.Set(0x762fa0, 0xc82008c430, 0x1d4, 0x762fa0, 0xc8200e8640, 0x94)
        /usr/local/go/src/reflect/value.go:1328 +0x25
    encoding/json.(*decodeState).literalStore(0xc820106000, 0xc8201040f9, 0x4, 0x507, 0x762fa0, 0xc82008c430, 0x1d4, 0xc8200da700)
        /usr/local/go/src/encoding/json/decode.go:786 +0x3549
    encoding/json.(*decodeState).literal(0xc820106000, 0x762fa0, 0xc82008c430, 0x1d4)
        /usr/local/go/src/encoding/json/decode.go:717 +0xe9
    encoding/json.(*decodeState).value(0xc820106000, 0x762fa0, 0xc82008c430, 0x1d4)
        /usr/local/go/src/encoding/json/decode.go:370 +0x37b
    encoding/json.(*decodeState).object(0xc820106000, 0x7a7320, 0xc82008c3f0, 0x199)
        /usr/local/go/src/encoding/json/decode.go:684 +0x116a
    encoding/json.(*decodeState).value(0xc820106000, 0x7a9260, 0xc820010648, 0x196)
        /usr/local/go/src/encoding/json/decode.go:367 +0x3a1
    encoding/json.(*decodeState).object(0xc820106000, 0x795d40, 0xc820010640, 0x199)
        /usr/local/go/src/encoding/json/decode.go:684 +0x116a
    encoding/json.(*decodeState).value(0xc820106000, 0x7a19e0, 0xc8200c5da0, 0x196)
        /usr/local/go/src/encoding/json/decode.go:367 +0x3a1
    encoding/json.(*decodeState).array(0xc820106000, 0x6c3220, 0xc8200c5d60, 0x197)
        /usr/local/go/src/encoding/json/decode.go:518 +0xa6b
    encoding/json.(*decodeState).value(0xc820106000, 0x6c3220, 0xc8200c5d60, 0x197)
        /usr/local/go/src/encoding/json/decode.go:364 +0x3c1
    encoding/json.(*decodeState).object(0xc820106000, 0x741a80, 0xc8200c5d60, 0x199)
        /usr/local/go/src/encoding/json/decode.go:684 +0x116a
    encoding/json.(*decodeState).value(0xc820106000, 0x6a6400, 0xc820056b78, 0x196)
        /usr/local/go/src/encoding/json/decode.go:367 +0x3a1
    encoding/json.(*decodeState).object(0xc820106000, 0x79e600, 0xc820056b60, 0x199)
        /usr/local/go/src/encoding/json/decode.go:684 +0x116a
    encoding/json.(*decodeState).value(0xc820106000, 0x6a61c0, 0xc820056b60, 0x16)
        /usr/local/go/src/encoding/json/decode.go:367 +0x3a1
    encoding/json.(*decodeState).unmarshal(0xc820106000, 0x6a61c0, 0xc820056b60, 0x0, 0x0)
        /usr/local/go/src/encoding/json/decode.go:168 +0x196
    encoding/json.Unmarshal(0xc820104000, 0x23b, 0x600, 0x6a61c0, 0xc820056b60, 0x0, 0x0)
        /usr/local/go/src/encoding/json/decode.go:96 +0x12b, 0x23b, 0x600, 0x201, 0x6a61c0, 0xc820056b60, 0x0, 0x0)
        /home/dolanor/.local/gopath/src/ +0x57, 0x861568, 0xc82008c240, 0x6a61c0, 0xc820056b60, 0x0, 0x0)
        /home/dolanor/.local/gopath/src/ +0x34d

@mikioh mikioh changed the title Unmarshalling *websocket.Conn over a websocket with JSON crashes encoding/json: Unmarshalling *websocket.Conn over a websocket with JSON crashes Apr 3, 2016
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mikioh commented Apr 3, 2016

I have no strong opinion on how unexposed, non-assignable fields should be treated in encoding/json package.

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OneOfOne commented Apr 3, 2016

the json package maybe should just check if a field is exported or not for the internal type cache?

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I am unable to reproduce this.

Do you have a repro?

I tried:

package main

import (


func main() {
        type T struct {
                Foo  string
                conn *websocket.Conn
        t := &T{"bar", new(websocket.Conn)}
        enc, err := json.Marshal(t)
        if err != nil {
                log.Fatalf("Marshal: %v", err)
        var t2 T
        if err := json.Unmarshal(enc, &t2); err != nil {
                log.Fatalf("Unmarshal: %v", err)
        fmt.Printf("%#v\n", t2)

But it works at tip, Go 1.6, and Go 1.5 just fine with:

main.T{Foo:"bar", conn:(*websocket.Conn)(nil)}

Let me know and I can reopen this.

@golang golang locked and limited conversation to collaborators Apr 10, 2017
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