SimpleX-Chat/docs/rfcs/2022-03-02-number-chat-items.md

Message replies and chat item sequential numbers

Problem

Many chat features require referring to the previous chat items in the same conversation:

• item editing
• item deletion
• item reply (with quoting)
• delivery/read receipts
• any interactive features mutating chat item state
• group message integrity via DAG

The most in-demand feature is replies.

Proposed solution

As group message integrity is needed not for chat items, but for messages, the updated proposal is to introduce a random, non-sequential message id, unique per conversation and per sender.

All above features would rely on this ID, e.g. reply would use the ID of the message that created the item.

We will add an optional property msgId into all chat messages (not only visible to the users) and msgRef into messages that need to reference other messages.

msgId property is a base64 encoded 12 byte binary

JTD for quoting messages:

definitions:
  msgRef:
    discriminator: type
    mapping:
      direct:
        properties:
          msgId: type: string
          sentAt: type: datetime
          sent: type: boolean # true if it is in reference to the item that the sender of the message originally sent, false for references to received items
      group:
        properties:
          msgId: type: string
          sentAt: type: datetime
          memberId: type: string # base64 member ID of the sender known to all group members for group chats
  content:
    properties:
      type: type: string
      text:  type: string
properties:
  msgId: string
  event: enum: ["x.msg.new"]
  params:
    properties:
      content: ref: content
      quote:
        properties:
          content: ref: content
          msgRef: ref: msgRef

This format ensures that replies with quoting show as normal messages on the clients that do not support showing quotes (quote property will be ignored).

The only feature that would not work in case chatItem/chatItemRef is missing is navigating to the message to which the message is in reply to.