How to Unmarshal Incorrectly Formatted Datetime in Go?

Unmarshalling Incorrectly Formatted Datetime

When encountering JSON with incorrectly formatted datetime fields, it becomes essential to devise a robust strategy to parse and unmarshal them into Go structs. The incorrect format typically involves an absence of the colon character ":" in the timezone offset, leading to unmarshalling errors.

Solution: Custom Type and UnmarshalJSON Method

To resolve this issue, a custom type can be defined to support both the correct and incorrect formats:

<code class="go">type MyTime struct {
    time.Time
}

func (self *MyTime) UnmarshalJSON(b []byte) (err error) {
    s := string(b)
    s = s[1:len(s)-1]

    t, err := time.Parse(time.RFC3339Nano, s)
    if err != nil {
        t, err = time.Parse("2006-01-02T15:04:05.999999999Z0700", s)
    }
    self.Time = t
    return
}</code>

When unmarshalling, this type's UnmarshalJSON method is invoked. It first removes the surrounding quotes from the JSON string. It then attempts to parse the datetime using the standard time.RFC3339Nano format. If that fails, it proceeds to try parsing using the incorrect format without the colon character ("2006-01-02T15:04:05.999999999Z0700").

Struct Definition

To use this custom type within a Go struct:

<code class="go">type Test struct {
    Time MyTime `json:"time"`
}</code>

This ensures that JSON with both correct and incorrect datetime formats can be unmarshalled into the same Go struct.

Conclusion

By defining a custom time field type with a suitable UnmarshalJSON method, it is possible to parse and unmarshal incorrectly formatted datetime fields seamlessly in Go programs. This allows for greater flexibility in handling input data and ensures that the Go struct representation accurately reflects the data, regardless of its format.

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