Channel attach with resume from serial

[mattheworiordan]

In future, when we have global time serials, customers may want to easily resume a channel from a time serial, that could for example be two days old.

In order to achieve this we'll need to consider:

• An API to expose last time serial on a channel
• An channel option to resume from a serial number, along with other options such as { limit: 5 } to indicate the channel should not recover a limitless number of messages. It would be useful to also have an option such as { last: 2 } to request on attach that the last two publishes messages are sent
• An ACK mechanism from the server to the client to ensure the client is keeping up with the potentially huge stream of messages it's about to receive

┆Issue is synchronized with this Jira Task by Unito

[mattheworiordan]

Note this is somewhat done now with Channel Rewind, although without a global time serial yet in place, and no way to inspect a serial and resume from a serial, this feature is still outstanding.

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-2810