dendrite/docs/peeking.md
Matthew Hodgson 39507bacc3
Peeking via MSC2753 (#1370)
Initial implementation of MSC2753, as tested by https://github.com/matrix-org/sytest/pull/944.
Doesn't yet handle unpeeks, peeked EDUs, or history viz changing during a peek - these will follow.
https://github.com/matrix-org/dendrite/pull/1370 has full details.
2020-09-10 14:39:18 +01:00

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## Peeking
Peeking is implemented as per [MSC2753](https://github.com/matrix-org/matrix-doc/pull/2753).
Implementationwise, this means:
* Users call `/peek` and `/unpeek` on the clientapi from a given device.
* The clientapi delegates these via HTTP to the roomserver, which coordinates peeking in general for a given room
* The roomserver writes an NewPeek event into the kafka log headed to the syncserver
* The syncserver tracks the existence of the local peek in its DB, and then starts waking up the peeking devices for the room in question, putting it in the `peek` section of the /sync response.
Questions (given this is [my](https://github.com/ara4n) first time hacking on Dendrite):
* The whole clientapi -> roomserver -> syncapi flow to initiate a peek seems very indirect. Is there a reason not to just let syncapi itself host the implementation of `/peek`?
In future, peeking over federation will be added as per [MSC2444](https://github.com/matrix-org/matrix-doc/pull/2444).
* The `roomserver` will kick the `federationsender` much as it does for a federated `/join` in order to trigger a federated `/peek`
* The `federationsender` tracks the existence of the remote peek in question
* The `federationsender` regularly renews the remote peek as long as there are still peeking devices syncing for it.
* TBD: how do we tell if there are no devices currently syncing for a given peeked room? The syncserver needs to tell the roomserver
somehow who then needs to warn the federationsender.