Major Description
We will implement [RFC-8887 - A JSON Meta Application Protocol (JMAP) Subprotocol for WebSocket](https://tools.ietf.org/html/rfc8887)
as a transport mechanism for PUSH notifications.
We will [generalize EventBus](0046-generalize-event-bus.md) in order to achieve an out-of-the box Publish-Subscribe
system for JMAP related events, that do not fit in the mailbox API.
We will implement listeners registered on the JMAP event bus for WebSocket clients in order to carry over state changes
to the client.
We expect clients using the PUSH to lead to a drastic performance enhancement, as less data needs to be transmitted upon
resynchronisation.
As mentioned in RFC-8887 the usage of webSockets allows other performance optimizations:
- Requests can easily be compressed, which is not doable over HTTP for most available implementation (HTTP request
compression is not ubiquitous). - WebSockets being connected, authentication can be performed once, when establishing the connection. This can allow to
reduce the load, if needed, on authentication systems. It might ease the use for instance of custom OpenId connect
providers.
People deploying JMAP need to be aware that load-balancing webSockets requires session stickiness.
1. Bob authenticates against the `ws://` endpoints. Upgrade to websockets is granted. 2. Bob registers Email and Mailbox updates. A listener listen for state changes related to Bob account. 3. Bob receives a mail. The MailboxManager adds it to bob mailbox. An `Added` event is fired on the mailbox event bus. 4. The `MailboxChangeListener` process the Added event, handles delegation, record the state change, and fires related events for each account on the JMAP event bus, for both `Email` (as there is an addition) and `Mailbox` (as the counts were updated). 5. Bob's webSocket listener receives a message from RabbitMQ and pushes it to bob. 6. Bob's MUA is aware it needs to re-synchronize. It will perform resynch requests combining `Email/changes`, `Email/get`, `Mailbox/changes` and `Mailbox/get`.