Serialize deserialize from Go int64/uint64 from/to Javascript string

Question

Is it possible to modify json serialization and deserialization so that a struct like this:

type Foo struct {
   A int64
   B uint64
   // and other stuff with int64 and uint64 and there's a lot of struct that are like this
}

x := Foo{A: 1234567890987654, B: 987654321012345678}
byt, err := json.Marshal(x)
fmt.Println(err)
fmt.Println(string(byt))

//                                 9223372036854775808      9223372036854775808
err = json.Unmarshal([]byte(`{"A":"12345678901234567", "B":"98765432101234567"}`), &x)
// ^ must be quoted since javascript can't represent those values properly (2^53)
// ^ json: cannot unmarshal string into Go struct field Foo.A of type int64
fmt.Println(err)
fmt.Printf("%#v\n", x)
// main.Foo{A:1234567890987654, B:0xdb4da5f44d20b4e}

https://play.golang.org/p/dHN-FcJ7p-N

So that It could receive json string but parsed as int64/uint64, and can deserialize int64/uint64 as json string without have to modify the struct or struct tag at all

"without have to modify the struct or struct tag at all" no. The struct and struct tags are what determine how it is marshaled and unmarshaled. — Adrian
– Adrian, Commented Aug 19, 2021 at 18:15
You could however write a custom unmarshaling method with an anonymous struct and parse the strings to int64/uint64 locally. — m0r0n
– m0r0n, Commented Aug 19, 2021 at 18:31
Javascript often outputs inconsistent data as json. A more catch-all approach would be to unmarshall in interface{} type and then use a type switch... if it is detected as string you cast it to string and then use strings.ParseInt() if it isn't then you can take another route. — Mihai
– Mihai, Commented Aug 20, 2021 at 1:33

blackgreen · Accepted Answer · 2021-08-19 19:23:42Z

6

Use the string option in the JSON struct tag. It's designed exactly for this use case:

The "string" option signals that a field is stored as JSON inside a JSON-encoded string. It applies only to fields of string, floating point, integer, or boolean types. This extra level of encoding is sometimes used when communicating with JavaScript programs

type Foo struct {
    A int64  `json:"A,string"`
    B uint64 `json:"B,string"`
}

func main() {
    x := &Foo{}
    _ = json.Unmarshal([]byte(`{"A":"12345678901234567", "B":"98765432101234567"}`), x)

    fmt.Println(x) // &{12345678901234567 98765432101234567}

    b, _ := json.Marshal(x)

    fmt.Println(string(b)) // {"A":"12345678901234567","B":"98765432101234567"}
}

Playground: https://play.golang.org/p/IfpcYOlcKMo

If you can't modify existing struct tags (but your example has none), then you have to reinvent the implementation of this string tag option in a custom UnmarshalJSON and MarshalJSON methods.

answered Aug 19, 2021 at 19:23

blackgreen♦

46.9k29 gold badges171 silver badges163 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

m0r0n Over a year ago

Thanks for teaching me something new. This answer is simple and effective

Kokizzu Over a year ago

ah too bad with string tag cannot parse plain integer play.golang.org/p/LIyt9ZdHPeg

blackgreen Over a year ago

@Kokizzu I think that is expected. With these standard tags, you either deserialize JSON strings to integers or JSON numbers to integers. If you need a deserializer that does both, you have to implement it yourself

Collectives™ on Stack Overflow

Serialize deserialize from Go int64/uint64 from/to Javascript string

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related