[GitHub] [james-project] rouazana commented on a change in pull request #276: JAMES-XXXX ADR for Mailbox/changes

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

rouazana commented on a change in pull request #276:
URL: https://github.com/apache/james-project/pull/276#discussion_r538176412



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File path: src/adr/0045-support-jmap-push-with-mailbox-changes-implementation.md
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+# 45. Support JMAP Push with Mailbox/changes implementation
+
+Date: 2020-12-08
+
+## Status
+
+Accepted (lazy consensus).
+
+## 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 support the **state** property that comes with JMAP get/set request. This means that James needs to be able 
+to record a new state for objects whenever a change happens as well as return the most recent state to the client when fetching objects. 
+
+First step is to implement Mailbox/changes. 
+
+## Decision
+
+We will implement a mechanism to record all the changes happen to Mailbox objects in the form of a list of **mailboxId**. When an event such as  
+created/updated/destroyed occur, or when message is appended to a mailbox we will store their **mailboxIds** along with a **state** object
+in a Cassandra table.  
+
+Each state will have a list of changes, and all the **mailboxId** will be stored as separated lists corresponding to the change which they represent: **created**, **updated**, **destroyed**.
+For the case when message are appended to a mailbox, it will be counted as an updated event and that mailboxId should be store in **updated** list. 
+
+Leveraging the **MailboxChanges** table, We can now fetch all the changes that have occured since a particular **state**.
+
+States are stored in Cassandra as time based UUID (**TimeUUID**). This ensures that no conflicting changes will happen in the case when two or more events occur at the same point in time.
+**TimeUUID** also allows **state** to be sorted in chronological order.
+
+Components that need to be implemented:
+
+- MailboxChangesRepository: Allow storing and fetching the **state** along with the lists of **mailboxId** in **MailboxChanges** table.
+- MailboxChangeListener: Listen to changes and trigger the record creation in **MailboxChanges** table.
+- MailboxChangeMethod: Handle the **state** property, allowing client to fetch the changes since a particular state. 
+- MailboxSetMethod/MailboxGetMethod needs to query the MailboxChangesRepository for their states properties.
+ 
+## Example of a Mailbox/changes request/response
+
+**Request**
+
+```
+[["Mailbox/changes", {
+  "accountId": "29883977c13473ae7cb7678ef767cbfbaffc8a44a6e463d971d23a65c1dc4af6",
+  "sinceState": "000001"

Review comment:
       if state is a timeuuid maybe you can change the examples? I assume it will be in an other format




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