Appendix D: CommandMessage Helper Methods

When writing external modules (see Writing External Modules), these helper methods on CommandMessage from the mechutil crate are available:

Constructors:

Method	Description
`CommandMessage::new()`	Empty message with defaults
`CommandMessage::request(topic, data)`	Generic Request (message_type = 10)
`CommandMessage::read(topic)`	Read request (message_type = 2)
`CommandMessage::write(topic, data)`	Write request (message_type = 3)
`CommandMessage::subscribe(topic)`	Subscribe request (message_type = 4)
`CommandMessage::broadcast(topic, data)`	Broadcast message (message_type = 6)
`CommandMessage::response(tid, data)`	Success response
`CommandMessage::error_response(tid, err)`	Error response
`CommandMessage::control(type, data)`	Control message (message_type = 8)

Mutation methods (used inside handle_message):

Method	Description
`msg.set_success(data)`	Mark as successful, set response data
`msg.set_error("reason")`	Mark as failed, set error message
`msg.into_response(data)`	Consume and return a success response
`msg.into_error_response("reason")`	Consume and return an error response

Query methods:

Method	Description
`msg.domain()`	First segment of `topic` (e.g., `"gm"` from `"gm.motor_speed"`)
`msg.subtopic()`	Everything after the first dot (e.g., `"motor_speed"` from `"gm.motor_speed"`)
`msg.is_response()`	`true` if `message_type == Response`
`msg.is_request()`	`true` if Read, Write, Subscribe, Unsubscribe, or Request
`msg.is_broadcast()`	`true` if `message_type == Broadcast`