Objective

Explicitly support choosing how much of the replay buffer should be emitted when subscribing to the replay observable.

Origin Document

While working on #517:

See: https://github.com/pokt-network/poktroll/pull/546#discussion_r1612053839.

    // SubscribeFromBufferEndOffset returns an observer which is initially notified of
    // values in the replay buffer, starting from the replay buffer index which is
    // equal to replayBufferSize - offset. After this range of the replay buffer is
    // notified, the observer continues to be notified, in real-time, when the publishCh
    // channel receives a value. It also returns the current replayBufferSize.
    // If offset is greater than replayBufferSize or the number of elements it
    // currently contains, the observer is notified of all elements in the replayBuffer,
    // starting from the beginning. Passing 0 for offset is equivalent to calling
    // Subscribe() on a non-replay observable.
    SubscribeFromBufferEndOffset(ctx context.Context, offset int) (_ Observer[V], replayBufferSize int)

Goals

Support more explicit behavior when consuming replay observables.

Deliverables

[x] A PR which implements ReplayObservable#SubscribeFromBufferEndOffset()
- 647

[x] A PR which refactors RelayerSessionsManager#waitForBlock() to use it and ensure that the returned replayBufferSize is sufficient to include the pathBlock, erroring otherwise, e.g.:

648

blocksSinceClaimWindowStart := currentHeight - claimWindowStartHeight
observer, bufferLen := #SubscribeFromBufferEndOffset(ctx, blocksSinceClaimWindowStart)
if bufferlen < blocksSinceClaimWindowStart {
// query for blocks between `blocksSinceClaimWindowStart` & `replayBuffer[0]`...
}

Non-goals / Non-deliverables

General deliverables

[ ] Comments: Add/update TODOs and comments alongside the source code so it is easier to follow.
[ ] Testing: Add new tests (unit and/or E2E) to the test suite.
[ ] Makefile: Add new targets to the Makefile to make the new functionality easier to use.
[ ] Documentation: Update architectural or development READMEs; use mermaid diagrams where appropriate.

Creator: @bryanchriswhite Co-Owners: @red-0ne

pokt-network / poktroll

[Relayminer] Add `ReplayObservable#SubscribeFromBufferEndOffset()` method #553