fix: add sequence number of subscriptions revision #187
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Context
Fixes #185
Problem
There is a race condition if multiple subscription updates happen at the same time that a client will receive them out-of-order and display an outdated version.
Solution
Notify Server will now store a version for the subscriptions list. I.e. everytime a subscription is updated (in a way that would trigger subscriptions changed e.g. a subscribe, update, or delete), then this sequence number will also be incremented.
The sequence number is sent to the account alongside the list of subscriptions which clients will then store with their local list of subscriptions. Whenever the client processes an incoming
sbs
value it must first check the sequence number, and if it is smaller than the current number then it must disregard the update.