MSC4185: Event Visibility API #4185
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Looks very sensible to me and fixes a long standing issue we've had with visibility overall. I'd be curious to hear from the homeserver developer community if there are pitfalls with requesting this information frequently.
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| While the homeserver is likely to have event visibility information cached for its local users, | ||
| the operation could be end up costly when performed for remote users. | ||
| Still, even for that case, the homeserver is probably in the best position to calculate this. |
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I wonder if caching is a thing we should mention, or whether that's an implementation detail?
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tulir
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| GET /_matrix/client/v1/can_user_see_event/<room_id>/<user_id>/<event_id> | ||
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| That responds with a boolean, revealing if `<user_id>` has access to `<event_id>` in `<room_id>`. |
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What determines if a user has access to an event?
I assume this has to do with room membership and history visibility but I feel we should probably explain this explicitly.
And for example, room encryption has nothing to do with this since that happens out of band on the client. (or redactions, etc)
| the operation could be end up costly when performed for remote users. | ||
| Still, even for that case, the homeserver is probably in the best position to calculate this. | ||
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| ## Alternatives |
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One alternative would be to just try fetching the event GET /_matrix/client/v3/rooms/{roomId}/event/{eventId}.
Responses
Status Description 200The full event. 404The event was not found or you do not have permission to read this event.
Application services can already request on the behalf of another user using the ?user_id=@example:example.org query parameter.
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I think that would indeed solve the problem for ASes. As the MSC notes, however, it excludes potential integrations that are not ASes (bots, for instance). Perhaps that's a YAGNI though, and this is worth setting aside until such need arises, if at all.
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Plugging this for the record: https://spec.matrix.org/v1.11/application-service-api/#identity-assertion
I don't think it will work for us in the general case. This can only apply to users in Appservice's control, which won't work for remote users even with very generous configuration.
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Fixes matrix-org/matrix-spec#1747
Synapse implementation: element-hq/synapse#17973
IRC bridge implementation: matrix-org/matrix-appservice-irc#1833