Verify correct behavior for multiple skipped blocks in sequence

[jsync-swirlds]

Persona

As a Consensus Node

Request

I want to receive skip block and acknowledgements correctly

Goal

So that I can properly process acknowledgements and avoid sending unnecessary blocks

Technical Notes

With multiple publishers sending to a single block node, it is conceivable, though unlikely, that a particular publisher might send a block header that is 2 or more blocks behind the current block "leader".
We wish to ensure that the publisher receives a skip block message for each block header, and also receives an acknowledgement for every block "skipped" in this way.

Note, this is distinct from a Publisher that is "behind" (i.e. sends a header older than the last persisted and verified block known to this block node). The response in that case is a BlockAcknowledgement with the block_already_exists flag and the last known verified block as block_number. The Publisher should resume after the indicated block, in that case.

Example Sequence

The following is a highly unlikely example sequence that reflects correct behaviors in a relatively extreme scenario.

sequenceDiagram
participant BlockLeader
participant Publisher
participant BlockNode

BlockLeader->>BlockNode: Send Header for block 45
Publisher->>BlockNode: Send Header for block 40
Note over BlockNode: There are 5 streams in progress, from 40-45, so 40 is not yet "behind"
BlockNode->>Publisher: SkipBlock[40]
Publisher->>BlockNode: Send Header for block 41
BlockNode->>Publisher: SkipBlock[41]
Publisher->>BlockNode: Send Header for block 42
BlockNode->>Publisher: SkipBlock[42]
Publisher->>BlockNode: Send Header for block 43
Note over BlockNode: Block 40 completes streaming and is verified
BlockNode->>Publisher: Acknowledge block 40
BlockNode->>Publisher: SkipBlock[43]
Publisher->>BlockNode: Send Header for block 44
BlockNode->>Publisher: SkipBlock[44]
Note over BlockNode: Block 41 completes streaming and is verified
BlockNode->>Publisher: Acknowledge block 41
Note over BlockNode: Block 42 completes streaming and is verified
BlockNode->>Publisher: Acknowledge block 42
Note over BlockNode: Block 43 completes streaming and is verified
BlockNode->>Publisher: Acknowledge block 43
Publisher->>BlockNode: Send Header for block 45
BlockNode->>Publisher: SkipBlock[45]
Note over BlockNode: Block 44 completes streaming and is verified
BlockNode->>Publisher: Acknowledge block 44
BlockLeader->>BlockNode: Send Header for block 46
Publisher->>BlockNode: Send Header for block 46
BlockNode->>Publisher: SkipBlock[46]
Note over BlockNode: Block 45 completes streaming and is verified
BlockNode->>Publisher: Acknowledge block 45

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