在Go中编码为JSON时如何强制采用十进制格式的float

Question

I have a big.float which I'm encoding into JSON . However the JSON always end up showing the float in scientific notation rater than decimal notation. I can fix this by changing the JSON to be a string rather than a number and using float.Text('f'), however I would really prefer to keep the type as a number.

I was a taking a look at float.Format but I don't believe this is suitable.

A really condensed gist of what I'm doing is below. I do a lot more modification of the value of supply before encoding it to json.

type TokenSupply struct {
   TotalSupply  *big.Float  `json:"totalSupply, omitempty"`
}
supply := Float.NewFloat(1000000)
json.NewEncoder(w).Encode(TokenSupply{supply})

This returns:

{"totalSupply":"1e+06"}

Answer 1

big.Float is marshaled to string when converted to a JSON type

https://golang.org/pkg/encoding/json/#Marshal

Marshal traverses the value v recursively. If an encountered value implements the Marshaler interface and is not a nil pointer, Marshal calls its MarshalJSON method to produce JSON. If no MarshalJSON method is present but the value implements encoding.TextMarshaler instead, Marshal calls its MarshalText method and encodes the result as a JSON string. The nil pointer exception is not strictly necessary but mimics a similar, necessary exception in the behavior of UnmarshalJSON.

https://golang.org/pkg/math/big/#Float.MarshalText

func (x *Float) MarshalText() (text []byte, err error)

What can you do about it?

since your float may be more than 64 bits it won't play well with other languages that have to read the JSON value as a number. I'd suggest you keep the number as a string.