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BEP-89: Visual Fork of Binance Smart Chain

1. Summary

This BEP describes a proposal to enable the chain to display the whole view of validators that on different upcoming forks.

2. Abstract

The four bytes of Header.Extra[28:32] will be fulfilled with NEXT_FORK_HASH. The NEXT_FORK_HASH indicates which fork the signer of this block is going to stay on. By analysing N (N is the amount of validators) continuous block headers, we are able to know which fork is supported by the majority of validators and exact which validator has not upgraded yet.

3. Status

This BEP is already implemented

4. Motivation

Binance Smart Chain will have some hard forks inevitably in the long run. Binance Smart Chain takes a risk of halt during hard fork once the validators can not reach a consensus. A validator could be slashed if it is not on the canonical fork which could be avoidable if the maintainer received alerts in time. A new protocol should be introduced to enable the chain to display the whole view of validators that on different upcoming forks. Any nodes/validators can decide to upgrade/fork or not accordingly.

5. Specification

5.1 Fork Hash

Fork Hash is introduced in EIP-2124. It is a mechanism that can let ethereum nodes precisely identify whether another node will be useful.

  • FORK_HASH. IEEE CRC32 checksum ([4]byte) of the genesis hash and fork blocks numbers that already passed. E.g. Fork Hash for mainnet would be: forkhash₂ = 0x91d1f948 (DAO fork) = CRC32(<genesis-hash> || uint64(1150000) || uint64(1920000)).
  • FORK_NEXT. Block number (uint64) of the next upcoming fork, or 0 if no next fork is known.
  • NEXT_FORK_HASH, whose algorithm is same with FORK_HASH, but FORK_NEXT will be included as well if it is not 0.

5.2 Vanity

Format of Header.Extra:

|   32 bytes       |       20 * N bytes      |   65 bytes     |
|   extraVanity    |   validatorSetBytes     |   extraSeal    |

extraVanity field is customized now, validator can use it to record NEXT_FORK_HASH of itself. The NEXT_FORK_HASH will only use the last 4 bytes of extraVanity.

5.3 Clients

  • For validator. It will fill in Header.Extra with NEXT_FORK_HASH during preparing block header.
  • For witness. It will log a warning message if the majority NEXT_FORK_HASH is different from local.
  • For light client. No impact.

5.4 Backwards Compatibility

  • This BEP itself is not a hardfork one, it breaks nothing of consensus.
  • Downstream service is completely compatible with this BEP.

6. License

The content is licensed under CC0.