Etan Kissling 613f4a9a50
accelerate EL sync with LC with --sync-light-client (#4041)
When the BN-embedded LC makes sync progress, pass the corresponding
execution block hash to the EL via `engine_forkchoiceUpdatedV1`.
This allows the EL to sync to wall slot while the chain DAG is behind.
Renamed `--light-client` to `--sync-light-client` for clarity, and
`--light-client-trusted-block-root` to `--trusted-block-root` for
consistency with `nimbus_light_client`.

Note that this does not work well in practice at this time:
- Geth sticks to the optimistic sync:
  "Ignoring payload while snap syncing" (when passing the LC head)
  "Forkchoice requested unknown head" (when updating to LC head)
- Nethermind syncs to LC head but does not report ancestors as VALID,
  so the main forward sync is still stuck in optimistic mode:
  "Pre-pivot block, ignored and returned Syncing"

To aid EL client teams in fixing those issues, having this available
as a hidden option is still useful.
2022-08-29 12:16:35 +00:00
..
2022-08-17 11:33:19 +00:00

Gossip Processing

This folder holds a collection of modules to:

  • validate raw gossip data before
    • rebroadcasting it (potentially aggregated)
    • sending it to one of the consensus object pools

Validation

Gossip validation is different from consensus verification in particular for blocks.

There are multiple consumers of validated consensus objects:

  • a ValidationResult.Accept output triggers rebroadcasting in libp2p
    • We jump into method validate(PubSub, Message) in libp2p/protocols/pubsub/pubsub.nim
    • which was called by rpcHandler(GossipSub, PubSubPeer, RPCMsg)
  • a blockValidator message enqueues the validated object to the processing queue in block_processor
    • blockQueue: AsyncQueue[BlockEntry] (shared with request_manager and sync_manager)
    • This queue is then regularly processed to be made available to the consensus object pools.
  • a xyzValidator message adds the validated object to a pool in eth2_processor
    • Attestations (unaggregated and aggregated) get collected into batches.
    • Once a threshold is exceeded or after a timeout, they get validated together using BatchCrypto.

Security concerns

As the first line of defense in Nimbus, modules must be able to handle bursts of data that may come:

  • from malicious nodes trying to DOS us
  • from long periods of non-finality, creating lots of forks, attestations