Derive Macro Command 

#[derive(Command)]
{
    // Attributes available to this derive:
    #[subject]
    #[command]
}

Re-exported so services only need to depend on arminius-lib-nats.

The message-bus Subscriber trait is intentionally not re-exported here to avoid clashing with the async_nats::Subscriber re-export above; reach it via arminius_lib_message_bus::Subscriber. Derive macro that implements arminius_lib_message_bus::Command for a struct.

Attributes

• #[subject(...)] — the NATS subject the command is sent on. Accepts a bare literal (#[subject("rooms.create")]) or the name = "...", version = ... form (which appends .v{version}).
• #[command(reply = Type)] — the reply type returned by the handler.

Subject rules (differ from Event)

• No struct-name fallback. A command must name an explicit subject, so it has a namespace segment for its stream filter; a namespace-less subject would collapse to the catch-all > filter.
• No compatible list.

Payload and dynamic subjects

The whole struct is serialized as the request payload, so the command must also derive serde::Serialize and serde::Deserialize. Any number of fields is allowed.

Fields named in {…} placeholders become wildcard segments in the subject: the derive interpolates them from the struct’s own fields, so the subject and the payload copies cannot drift.

Example

#[derive(Serialize, Deserialize, Command)]
#[subject("rooms.{room_id}.create")]
#[command(reply = Result<OwnedRoomId, CreateRoomError>)]
pub struct CreateRoomCommand {
    pub room_id: OwnedRoomId,
    pub name: String,
    pub preset: RoomPreset,
}

#[command(...)] also takes delivery = at_least_once | at_most_once. For a detailed explanation look at arminius_lib_message_bus::command::Delivery.