Matrix-doc: Expose DAG to clients

[Lapin0t]

It would be really nice for a lot of applications of matrix to expose the underlying DAG of events within a room. Some usecases:

• clients can order the events how they wish (topological sort is not unique) or even display the links in the UI
• applications could begin using matrix as a generic distributed database for partially ordered messages (collaborative document edition, key-value stores, ...)

A proposal to expose the links: add a new field to all events containing a list of event ids. It could be named parents.

[dumblob]

ping

[maxidorius]

The spec already defines a way via sync filters to get the full events, including parents, auth events, etc.

[turt2live]

Now that the sync filter actually works in (develop) synapse, and the thing is possible for clients to use, I think this can be closed.

[ara4n]

i’m not sure the ability to request federation event fields via cs api is entirely deliberate, fwiw. but if it works...