[GitHub] [james-project] remk commented on a change in pull request #287: [ADR] JMAP PUSH over WebSockets

[GitBox <gi...@apache.org>]

remk commented on a change in pull request #287:
URL: https://github.com/apache/james-project/pull/287#discussion_r565377616



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File path: src/adr/0047-jmap-push-over-websockets.md
##########
@@ -0,0 +1,70 @@
+# 47. JMAP PUSH over WebSockets
+
+Date: 2021-01-26
+
+## Status
+
+Accepted (lazy consensus).
+
+Relates to [45. Support JMAP Push with Mailbox/changes implementation](0045-support-jmap-push-with-mailbox-changes-implementation.md)
+
+Requires [46. Generalize EventBus](0046-generalize-event-bus.md)
+
+## Context
+
+JMAP Push notifications allow clients to efficiently update (almost) instantly to stay in sync with data changes on the server. 
+
+In order to support this, we need to have the server emit newest state changes to the client over a PUSH channel.
+
+## Decision
+
+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 does 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.
+
+## Consequences
+
+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.
+
+## Sequence
+
+ 1. Bob authenticates against the `ws://` endpoints. Upgrade to websockets is granted.
+ 2. Bob registers Email and Mailbox updates. A listener listens for state changes related to Bob account.
+ 3. Bob receives a mail. The MailboxManager adds it to Bob's mailbox. An `Added` event is fired on the mailbox event bus.
+ 4. The `MailboxChangeListener` processes the Added event, handles delegation, records 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.

Review comment:
       
   In a setup with multiple james, how do we make sure the listener is running on the node where the ws connection is open ? 
   Should their be one listener per open connection ? 

##########
File path: src/adr/0047-jmap-push-over-websockets.md
##########
@@ -0,0 +1,70 @@
+# 47. JMAP PUSH over WebSockets
+
+Date: 2021-01-26
+
+## Status
+
+Accepted (lazy consensus).
+
+Relates to [45. Support JMAP Push with Mailbox/changes implementation](0045-support-jmap-push-with-mailbox-changes-implementation.md)
+
+Requires [46. Generalize EventBus](0046-generalize-event-bus.md)
+
+## Context
+
+JMAP Push notifications allow clients to efficiently update (almost) instantly to stay in sync with data changes on the server. 
+
+In order to support this, we need to have the server emit newest state changes to the client over a PUSH channel.
+
+## Decision
+
+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 does 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.
+
+## Consequences
+
+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.
+
+## Sequence
+
+ 1. Bob authenticates against the `ws://` endpoints. Upgrade to websockets is granted.
+ 2. Bob registers Email and Mailbox updates. A listener listens for state changes related to Bob account.

Review comment:
       It is maybe not related to this particular ADR but i would like some explanation on the lifecycle of those listeners. When are they created/destroyed ?




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