MSC4144: Per-message profiles

[tulir]

Rendered

Implementations:

• Clients rendering profiles:
  • gomuks web: Render MSC4144 Per-Message Profiles gomuks/gomuks#566
  • Cinny: nexy7574/cinny@38454be
• Bots sending profiles:
  • Linear maubot: beeper/linear-maubot@88dfdd4
  • GitHub maubot: maubot/github@c6d768b
  • mautrix-discord: https://github.com/mautrix/discord/blob/v0.7.3/portal_convert.go#L360-L373
  • mautrix-slack: https://github.com/mautrix/slack/blame/v0.2.1/pkg/msgconv/from-slack.go#L92-L100

Signed-off-by: Tulir Asokan tulir@beeper.com

[sumnerevans]

Reminds me of MSC3464. This is more general than that MSC, though.

[Half-Shot]

I wonder if with extensible messages, it would make sense to support the (horrible) format of {name}: {body}. E.g.

{
  "msgtype": "m.text",
  "body": "Hello, World!",
  "m.text": [
      { "body": "<strong>cat</strong>: Hello, world", "mimetype": "text/html" },
      { "body": "cat: Hello, world" }
  ],
  "m.per_message_profile": {
    "id": "meow",
    "displayname": "cat",
    "avatar_url": "mxc://maunium.net/hgXsKqlmRfpKvCZdUoWDkFQo"
  }
}

as currently the fallback for unsupported clients isn't great.

[tulir]

That might cause ptsd from reply fallbacks 😹 Maybe it is the best option though. Needs very strict rules to ensure the fallback can always be safely stripped out. An indicator for whether the fallback is present at all is probably also a good idea.

I don't think extensible events would help at all unless you duplicated the entire message (one copy with a fallback and another without), but duplication is also bad

Perhaps something along the lines of

{
  "msgtype": "m.text",
  "body": "cat: Hello, World!",
  "format": "org.matrix.custom.html",
  "formatted_body": "<strong data-mx-profile-fallback>cat: </strong>Hello, World!",
  "m.per_message_profile": {
    "id": "meow",
    "displayname": "cat",
    "avatar_url": "mxc://maunium.net/hgXsKqlmRfpKvCZdUoWDkFQo",
    "has_fallback": true
  }
}

where if has_fallback is true, body MUST be prefixed with the exact value of displayname, followed by a colon and a space, and formatted_body (if present) MUST have the same prefix inside a strong tag with the data-mx-profile-fallback attribute

[tulir]

Having the has_fallback flag would make the change fully compatible with all existing per-message profile messages and it would allow removing it in the future like reply fallbacks

The HTML version might have to allow not being the prefix, because otherwise it wouldn't really work with paragraph tags (you'd get a forced linebreak if you did something like <strong data-mx-profile-fallback>cat: </strong><p>message text</p>). A HTML parser should still be able to just drop anything with the data-mx-profile-fallback attribute and it might be reasonably safe to regex too because there won't be any html inside like there were in reply fallbacks

[tulir]

I have added fallbacks as per my example above to the MSC