Leaf, ATProto and ActivityPub
As a part of our work on Weird we're developing the Leaf Protocol, an experimental peer-to-peer federation protocol built on top of Willow.
During development we've kept our eye on how ActivityPub and ATProto do things; now seems like a good time to talk about how Leaf compares to prior art.
In ATProto users store all their data in their own Personal Data Store ( PDS ). This is cool because you can host a PDS on your own server and have complete control over your data if you want to.
To create the global feeds and notify people when you post something, your PDS will send all of its posts to the big, central Relay.
The relay takes all the messages that it receives from all of the PDSes and it combines them all into what is called the Firehose: basically a stream of every post from everybody.
Because it's really hard to make a nice-to-use app if all you have is a mega stream of messages from the firehose, we need an AppView that listens to the kinds of messages it's interested in, then saves data about those messages in its own database. The AppView presents a nice app API that can be accessed by the Client.
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