Parsing Non-Standard Time Format from JSON

When decoding JSON data into a custom structure, inconsistencies in date formats can arise. To address this, Golang provides the option of implementing custom marshal and unmarshal functions.

Custom Marshaler and Unmarshaler Functions

To specify a custom parsing format, a type alias is created for the time field, and the Marshaler and Unmarshaler interfaces are implemented as follows:

type JsonBirthDate time.Time

// UnmarshalJSON translates a JSON string to a time value.
func (j *JsonBirthDate) UnmarshalJSON(b []byte) error {
    s := strings.Trim(string(b), `"`)
    t, err := time.Parse("2006-01-02", s)
    if err != nil {
        return err
    }
    *j = JsonBirthDate(t)
    return nil
}

// MarshalJSON converts a time value to a JSON string.
func (j JsonBirthDate) MarshalJSON() ([]byte, error) {
    return json.Marshal(time.Time(j))
}

This custom logic checks if the JSON value is in the desired format and parses it accordingly.

Updated Structure and Parsing

The struct is updated to use the custom type, and decoding can proceed as usual:

type Person struct {
    Name string `json:"name"`
    BirthDate JsonBirthDate `json:"birth_date"`
}

decoder := json.NewDecoder(req.Body)
if err := decoder.Decode(&person); err != nil {
    log.Println(err)
}

Additional Features

For convenience, a Format method can be added to provide a formatted representation of the date:

// Format prints the date using the specified format string.
func (j JsonBirthDate) Format(s string) string {
    t := time.Time(j)
    return t.Format(s)
}

This custom marshaling and unmarshaling approach allows for flexible parsing of time values from JSON even when they deviate from standard formats.