How to Handle Boolean Unmarshalling from JSON with \'0\' and \'false\' (and \'1\' and \'true\')?

Unmarshalling Boolean Values from JSON with Both 0 and False

Parsing JSON data requires careful consideration of data types to avoid misinterpretation. In cases where a service interchanges boolean values as 0 and false (as well as 1 and true), achieving proper unmarshalling becomes crucial.

The inbuilt encoding/json package provides a method to customize the unmarshalling process using custom types. By defining a custom type, you can implement bespoke unmarshalling logic to handle the desired conversion.

Custom Unmarshalling Type

Create a custom type that implements the json.Unmarshaler interface. This type will be responsible for converting JSON data to the desired boolean format.

type ConvertibleBoolean bool

func (bit *ConvertibleBoolean) UnmarshalJSON(data []byte) error {
    asString := string(data)
    if asString == "1" || asString == "true" {
        *bit = true
    } else if asString == "0" || asString == "false" {
        *bit = false
    } else {
        return errors.New(fmt.Sprintf("Boolean unmarshal error: invalid input %s", asString))
    }
    return nil
}

In this example, ConvertibleBoolean is a custom boolean type that implements the json.Unmarshaler interface. It overrides the default JSON unmarshalling process and checks the incoming data as a string. If it identifies a string representing true or false (or their numerical counterparts 1 and 0), it sets the ConvertibleBoolean value accordingly. Otherwise, an error is returned.

Using the Custom Type

Now that you have a custom unmarshalling type, use it in a struct to define the expected JSON structure.

type MyType struct {
    AsBoolean ConvertibleBoolean `json:"field1"`
    AlsoBoolean ConvertibleBoolean `json:"field2"`
}

Example Unmarshalling

With the custom type in place, you can unmarshal JSON data into a MyType struct, correctly converting both 0 and false (as well as 1 and true) to boolean values.

input_json := `{
    "field1" : true,
    "field2" : 1
}`

obj := MyType{}
json_err := json.Unmarshal([]byte(input_json), &obj)
fmt.Printf("%v\n", obj.AsBoolean) //"true"
fmt.Printf("%v\n", obj.AlsoBoolean) //"true"

This example JSON data contains "true" and "1", which would be treated as different types by the default unmarshaller. However, by using ConvertibleBoolean, both values are correctly unmarshalled as true.

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