MarshalJSON错误，顶级字符后的无效字符“ g”

Question

I made a custom type for my IDs:

type ID uint

func (id ID) MarshalJSON() ([]byte, error) {
    e, _ := HashIDs.Encode([]int{int(id)})
    fmt.Println(e) /// 34gj
    return []byte(e), nil
}

func (id *ID) Scan(value interface{}) error {
    *id = ID(value.(int64))
    return nil
}

I use the HashIDs package to encode my ids so that user wont be able to read them on client side. But I'm getting this error:

json: error calling MarshalJSON for type types.ID: invalid character 'g' after top-level value

Answer 1

34gj is not a valid JSON and hence not a valid string representation of your ID. You probably want to wrap this with double quotation mark to indicate this is a string, i.e. returning "34gj".

Try:

func (id ID) MarshalJSON() ([]byte, error) {
    e, _ := HashIDs.Encode([]int{int(id)})
    fmt.Println(e) /// 34gj
    return []byte(`"` + e + `"`), nil
}

http://play.golang.org/p/0ESimzPbAx

Instead of doing it by hand you can also call marshaller for the string, by simply replacing your return with return json.Marshal(e).

My guess would be that invalid character 'g' in your error is due to initial part of the value is being treated as a number and then unexpected character occurs.