//# Minecraft RMI (Remote method invocation)

Allow multiple addons to communicate by exposing an API

Protocol

The protocol is built on top of an ACK'ed communication that specifies how to send commands and arguments across the addon boundaries.

Raw communication

Note that when sending scriptevents, to prevent Minecraft from trying to convert it to json, we append a "-" at the start of the message.

1. The receiver needs to be ready to accept incoming data by listening to an agreed scriptevent.
2. The sender generates a unique identifier id used across all the message.
3. If the sender has any object to transfer (such as arguments or data), it must be converted to a JSON string (via JSON.stringify) and split into chunks of 2048 (the current limit for message).
4. The sender starts listening on the scriptevent minescripters_rmi:${id}.sender for incoming transactions
5. The sender starts by sending a message header as a JSON string.

interface MessageHeader {
  // Message identifier generated by the sender that identifies this whole message
  id: string;
  // Number of chunks to be sent - if any.
  chunkCount?: number;

  // Additional data - Must be kept at minimum as this whole header cannot excede the limit of 2048 characters when JSONfied
  // https://learn.microsoft.com/en-us/minecraft/creator/commands/commands/scriptevent?view=minecraft-bedrock-stable
  header: unknown;
}

6. The receiver receives the header, grabs the id.

7. If there is any chunk to be received, the receiver starts listening on minescripters_rmi:${id}.receiver

8. The receiver Sends and ack message by sending a scriptevent to ${id}.sender

9. The sender receives the ack message and closes connection to minescripters_rmi:${id}.sender if there are no chunks to be sent.

10. If there is any chunk to be sent, the sender sends them on minescripters_rmi:${id}.receiver Note: Care must be taken into account to not execute more commands than possible. There is still no way to know if we are reaching the limit, so throttling them if required.

11. The receiver receives the chunks, concatenates and parses the result, closes ${id}.receiver.

12. The receiver sends a final ack by sending a scriptevent to ${id}.sender

13. The sender sees the ack and closes ${id}.sender

This allows us to send a message across addons, with json data.