How to Handle Non-RFC 3339 Time Formats in Go's JSON Unmarshaling?

JSON Unmarshaling of Non-RFC 3339 Time Formats in Go

The default behavior of the encoding/json package in Go is to marshal and unmarshal time values in RFC 3339 format. However, what if you encounter JSON data with time values in a different format?

Solution with Manual Transformation

One approach is to deserialize the time value into a string, manually transform it into RFC 3339 format, and then apply json.Unmarshal again. While this method works, it introduces additional processing overhead and clutters code.

Custom Time Type

A more elegant solution is to implement the json.Marshaler and json.Unmarshaler interfaces on a custom time type. This allows for custom handling of time value serialization and deserialization.

Example Implementation

Here's an example of a custom time type named CustomTime:

type CustomTime struct {
    time.Time
}

const ctLayout = "2006/01/02|15:04:05"

func (ct *CustomTime) UnmarshalJSON(b []byte) (err error) {
    s := strings.Trim(string(b), "\"")
    if s == "null" {
       ct.Time = time.Time{}
       return
    }
    ct.Time, err = time.Parse(ctLayout, s)
    return
}

func (ct *CustomTime) MarshalJSON() ([]byte, error) {
  if ct.Time.IsZero() {
    return []byte("null"), nil
  }
  return []byte(fmt.Sprintf("\"%s\"", ct.Time.Format(ctLayout))), nil
}

var nilTime = (time.Time{}).UnixNano()
func (ct *CustomTime) IsSet() bool {
    return !ct.IsZero()
}

In this custom time type:

• UnmarshalJSON handles deserialization of non-RFC 3339 time formats into the CustomTime type.
• MarshalJSON handles serialization of CustomTime values into a custom format.
• IsSet provides a way to check if the CustomTime has been actually set.

Usage

Now, you can use the CustomTime type in your JSON deserialization code:

type Args struct {
    Time CustomTime
}

var data = `
    {
        "Time": "2014/08/01|11:27:18"
    }
`

func main() {
    a := Args{}
    fmt.Println(json.Unmarshal([]byte(data), &a))
    fmt.Println(a.Time.String())
}

This approach allows you to handle non-RFC 3339 time formats in JSON data elegantly and efficiently without compromising flexibility. It also showcases the power of implementing custom json.Marshaler and json.Unmarshaler interfaces for handling data type serialization and deserialization.

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