How to Prevent Stack Overflow Errors When Using json.Unmarshal within UnmarshalJSON?

Avoiding Stack Overflow when Calling json.Unmarshal in UnmarshalJSON

Calling json.Unmarshal(b, type) within your custom UnmarshalJSON implementation can lead to a stack overflow error. This occurs because the JSON decoder repeatedly attempts to find a custom UnmarshalJSON implementation for the type, resulting in an infinite loop.

Solution: Create a New Type

To avoid this issue, create a new type using the type keyword. This new type will not inherit the methods of the original type, including UnmarshalJSON.

type person2 Person

Usage:

Convert the original type's value to the new type using a type conversion:

if err := json.Unmarshal(data, (*person2)(p)); err != nil {
    return err
}

Example:

type Person struct {
    Name string `json:"name"`
    Age  int    `json:"age"`
}

func (p *Person) UnmarshalJSON(data []byte) error {
    type person2 Person
    if err := json.Unmarshal(data, (*person2)(p)); err != nil {
        return err
    }
    // Custom processing
    if p.Age < 0 {
        p.Age = 0
    }
    return nil
}

Benefits:

• Prevents stack overflows
• Incurs no runtime overhead since the underlying representation remains unchanged

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