Decode unix timestamps into time.Time just like the UnixTime option for Marshal?

[takanuva15]

Hi, this library has a great option UnixTime that "Encode[s] time.Time values as JSON numbers representing Unix timestamps".

In my case, I have to deal with json that sends time values as integer unix timestamps and unmarshal it into structs using time.Time fields. The default encoding/json just throws an error when it sees the unix timestamps, and our team's codebase is too large to replace every time.Time field with a custom type just for the sake of these int timestamps.

I'm aware this library is for marshalling only, but do you know if there's a way we can somehow apply this behavior to work for unmarshalling as well, either through this library or another? (I looked at goccy/go-json but I don't see an option for customizing unmarshal for time.Time)

[wI2L]

@takanuva15
This library does only encoding, and I have no plan to add unmarshaling support.
I'm not aware of any other lib that support time.Time values like this one. The recommended approach would always be to implement a custom type with a specific json.Unmarshaler interface if you use a lib (either official or another one) that implement the same API as encoding/json.

[takanuva15]

Ok after spending hours of looking at Golang code, I finally figured out a way to customize the decoding of epoch milli timestamps into time.Time fields in my own struct without needing to make a dummy wrapper type.

Note: This does require the new experimental json package being developed for Golang, which will eventually be converted to encoding/json/v2 once it gets out of development phase.

go get github.com/go-json-experiment/json

Define your struct like so:

type Author struct {
	CreatedAt             *time.Time            `json:"createdAt,omitempty,omitzero,format:unixmilli"`
}

And then unmarshal json into the Author struct using the above package:

import (
	"fmt"
	"time"

	"github.com/go-json-experiment/json/v1"
)

func main() {
	jsonStr := `{"createdAt":1734558308666}`
	a := Author{}
	_ = json.Unmarshal([]byte(jsonStr), &a)
	res, _ := json.Marshal(a)
	fmt.Println(string(res))
}

Output: {"createdAt":1734558308666}

---

EDIT: As a bonus, I got this to work in gin as well for serializing responses using the new json package. See this comment for details

[wI2L]

@takanuva15 Good find. Didn't notice that feature myself, might have been added after I looked up the v2 experiment, or simply missed it perhaps.