How Can I Customize JSON Field Names for Protobuf Extensions?

Customizing JSON Field Names for Protobuf Extensions

Protobuf extensions, when serialized to JSON, default to field names that include square brackets and a prefix indicating the extension's parent message. This can be inconvenient when you prefer a more concise or semantically meaningful JSON field name.

Background

Protobuf's jsonpb package generates JSON from protobuf messages. The JSON field names are primarily derived from the message field names. However, for extensions, a special format is used: "[message.extension_message_name]". This is designed to prevent field name conflicts when multiple extensions are applied to a message.

Solution: Use the json_name Field Option

The Protobuf language guide provides a workaround for customizing JSON field names for extensions: the json_name field option. By annotating the extension field with this option, you can specify the desired JSON field name.

For example:

message TestMessage {
    extensions 1 to 10;
    extend TestMessage {
        optional string my_extension_field = 1 [json_name="my_custom_field_name"];
    }
}

In this example, the extension field my_extension_field will be serialized to JSON as my_custom_field_name.

Benefits of Using json_name

• Control over JSON field names: Avoids the verbose naming convention used for extensions.
• Consistency with other JSON field names: Aligns extension field names with the naming conventions used for regular message fields.
• Improved readability and maintainability: Makes JSON output more human-readable and easier to work with.

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