How Can Go Handle Partial JSON Decoding and Updates Efficiently?

Handling Partial JSON Decoding and Updates in Go

In cases where the structure of a JSON object is dynamic, traditional JSON unmarshalling can lead to data loss due to field truncation. To address this, consider a solution combining a regular struct with json.RawMessage, which allows for selective updates while preserving unknown information.

The Color struct illustrates this approach:

type Color struct {
    Space string
    raw   map[string]json.RawMessage
}

During JSON unmarshalling, the UnmarshalJSON method reads the entire data into raw, and retrieves the desired field (e.g., Space) from raw if it exists:

func (c *Color) UnmarshalJSON(bytes []byte) error {
    if err := json.Unmarshal(bytes, &c.raw); err != nil {
        return err
    }
    // ...
    return nil
}

For JSON marshalling, the MarshalJSON method puts the desired field back into raw, ensuring that the updated field is included in the output:

func (c *Color) MarshalJSON() ([]byte, error) {
    // ...
    return json.Marshal(c.raw)
}

This approach allows for selective field updates while preserving the rest of the JSON data, including unknown or dynamic structures.

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