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Cadence Ember 0fc8e68f15 support threads
2023-08-19 18:41:57 +12:00

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d2m

Remember that a discord message may be transformed to multiple matrix messages.

A database will be used to store the discord id to matrix event id mapping. Table columns:

  • discord id
  • matrix id
  • the "type" of the matrix id, used to update things properly next time. for example, whether it is the message text or an attachment. alternatively, whether it is a primary or supporting event for the discord message, primary being message content and supporting being embeds or attachments or etc.

There needs to be a way to easily manually trigger something later. For example, it should be easy to manually retry sending a message, or check all members for changes, etc.

Current manual process for setting up a server

  1. Call createSpace.createSpace(discord.guilds.get(GUILD_ID))
  2. Call createRoom.createAllForGuild(GUILD_ID)
  3. Edit source code of event-dispatcher.js isGuildAllowed() and add the guild ID to the list
  4. If developing, make sure SSH port forward is activated, then wait for events to sync over!

Transforming content

  1. Upload attachments to mxc if they are small enough.
  2. Convert discord message text and embeds to matrix event.
    1. Convert discord mentions, names, channel links, message links, and emojis to intermediate formats.
    2. Convert discord text to body.
    3. Convert discord text to formatted_body using custom discord-markdown npm module.
    4. Convert discord embeds to quotes.
  3. Gather relevant reply data.
  4. Send reply+message.
  5. Send attachments.
  6. Store in database.

Discord's permissions in spaces

The space itself

Discord guilds are invite only, so the corresponding space should initially be set to:

  • Find & join access: Invite only
  • Preview space: Yes

Public channels in that server should then use the following settings, so that they can be opened by anyone who was successfully invited to the space:

  • Find & join access: Space members (so users must have been invited to the space already, even if they find out the room ID to join)
  • Who can read history: Anyone (so that people can see messages during the preview before joining)

Step by step process:

  1. Create a space room for the guild. Store the guild-space ID relationship in the database. Configure the space room to act like a space.
    • {"name":"NAME","preset":"private_chat","visibility":"private","power_level_content_override":{"events_default":100,"invite":50},"topic":"TOPIC","creation_content":{"type":"m.space"},"initial_state":[{"type":"m.room.guest_access","state_key":"","content":{"guest_access":"can_join"}},{"type":"m.room.history_visibility","content":{"history_visibility":"invited"}}]}
  2. Create channel rooms for the channels. Store the channel-room ID relationship in the database. (Probably no need to store parent-child relationships in the database?)
  3. Send state events to put the channel rooms in the space.

Private channels

Discord channels that disallow view permission to @everyone should instead have the following room settings in Matrix:

Discord experience: /invite command

The context-sensitive /invite command will invite Matrix users to the corresponding spaces or rooms.

  • In a public channel (i.e. @everyone is allowed access), /invite will invite an MXID to the space, provided the user has Create Invites.
  • In a private channel, /invite will invite a distinct username or MXID to the room, provided the user has Manage Server.
  • In a public or private thread, /invite will invite a distinct username or MXID to the thread room.

d2m events

Login - backfill

Need to backfill any messages that were missed while offline.

After logging in, check last_message_id on each channel and compare against database to see if anything has been missed. However, mustn't interpret old channels from before the bridge was created as being "new". So, something has been missed if:

  • The last_message_id is not in the table of bridged messages
  • The channel is already set up with a bridged room
  • A message has been bridged in that channel before

(If either of the last two conditions is false, that means the channel predates the bridge and we haven't actually missed anything there.)

For channels that have missed messages, use the getChannelMessages function, and bridge each in turn.

Can use custom transaction ID (?) to send the original timestamps to Matrix. See appservice docs for details.

Message sent

  1. Transform content.
  2. Send to matrix.

Webhook message sent

  • Consider using the _ooye_bot account to send all webhook messages to prevent extraneous joins?
    • Downside: the profile information from the most recently sent message would stick around in the member list. This is toleable.
  • Otherwise, could use an account per webhook ID, but if webhook IDs are often deleted and re-created, this could still end up leaving too many accounts in the room.
  • The original bridge uses an account per webhook display name, which does the most sense in terms of canonical accounts, but leaves too many accounts in the room.

Message deleted

  1. Look up equivalents on matrix.
  2. Delete on matrix.

Message edited / embeds added

  1. Look up equivalents on matrix.
  2. Replace content on matrix.

Reaction added

  1. Add reaction on matrix.

Reaction removed

  1. Remove reaction on matrix. Just redact the event.

Member data changed

  1. Compare current member against cached version in database.
  2. Update member on matrix.
  3. Update cached version in database.

Channel created / updated

(but I should be able to manually call this function at any time to run the same code on any given channel)

  1. Compare current channel against cached version in database.
  2. If channel does not yet exist in database:
    1. Create the corresponding room.
    2. Add to database.
  3. Update room details to match.
  4. Make sure the permissions are correct according to the rules above!
  5. Add to space.

Emojis updated

  1. Upload any newly added images to msc.
  2. Create or replace state event for the bridged pack. (Can just use key "ooye" and display name "Discord", or something, for this pack.)
  3. The emojis may now be sent by Matrix users!

TOSPEC: m2d emoji uploads??