MarshalJSON bug?

[John DeNero]

Should the following MarshalJSON example work? If so, I'll file a bug.
If not, what am I doing wrong in implementing a custom marshal
function that writes only a single field of a struct? I get:

panic: json: error calling MarshalJSON for type main.S: invalid
character 'N' looking for beginning of value

package main

import (
"encoding/json"
"math"
)

type S struct {
fs []float64
}

func (s S) MarshalJSON() ([]byte, error) {
return json.Marshal(s.fs)
}

func main() {
s := S{[]float64{math.NaN()}}
b, err := json.Marshal(s)
if err != nil {
panic(err)
}
println(string(b))
}

Thanks,
John

[Evan Shaw]

I don't think you're doing anything wrong implementing json.Marshaler.

I suspect the problem is that the JSON spec doesn't define an NaN
value (or infinity), but the Go package is using strconv internally,
which handles NaN. Trying to marshal any value containing NaN,
infinity, or -infinity should probably return an error.

- Evan

[John DeNero]

I see. It seems that some other JSON encoders offer a flag to allow
non-strict JSON that includes NaN & Inf. E.g., http://pypi.python.org/pypi/simplejson/

In any case, I agree that Marshal should error on non-finite floats.
The following round trip doesn't work, which perhaps happened
implicitly somewhere in my previous example.

func main() {
f1 := math.NaN()
b, err := json.Marshal(f1)

if err != nil {
panic(err)
}

var f2 float64
err = json.Unmarshal(b, &f2)

if err != nil {
panic(err)
}

println(f1, f2)