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Bridge Node JSON-RPC Interface

Original Link: https://notes.ethereum.org/@lithp/r1NB6M4Gu

Author: @lithp

Created: 2021-02-24

Description

Bridge nodes push state into the state availability network. They need to be in communication with an eth1 full node, here is a protocol they could use.

Bridge nodes will send two kinds of messages:

  • (ingress) an account/slot has some value
    • This is useful for adding new accounts/slots to the network, updating existing accounts/slots, as well as for re-inserting cold accounts/slots which the network might have forgotten
  • (egress) an account/slot has been removed
    • The state availability network is not an archive node, it only stores the last x⪅1000 state tries. A recent proof of non-inclusion is enough to convince the network to drop data.
    • There is some logic to selectively ignore these messages. If the account is brand new it’s possible to construct a recent non-inclusion proof but that proof is not relevant.

API

To do this they will rely on a few different RPCs:

  • bridge_waitNewCanonicalChain()

    • Blocks the caller until the canonical chain tip changes (indicating there is more work to be done).

  • bridge_getBlockChanges(blockHash) -> List[(acctAddr, [slotAddr, ...])]

    • Returns a list containing every account/slot which was created, updated, or deleted in the given block.
    • Return type mirrors eth1 mainnet access list API
      • Accounts are represented by (acctAddr, [])
      • Storage slots are represented by (acctAddr, [slotAddr, ...])

  • bridge_getItemWitness(blockHash, acctAddr, slotAddr) -> List[Bytes]

    • Returns a list of RLP-encoded nodes starting with the root node and ending with the requested node.
    • If the account was deleted this returns a proof-of-non-inclusion, and the final node will be null.
    • If slotAddr is null this method returns a witness for the requested account.

  • bridge_getNextItem(blockHash, acctAddr, slotAddr) -> [acctAddr, slotAddr]

    • Used for scanning through the state to find cold items which ought to be re-inserted into the network.

  • bridge_getNextItem(blockHash, '0x0', null) will return the the lowest (hashed) address, throwing that address back into bridge_getNextItem will return the next address.

    • Returns null if there is no next address/slot.

Experimental API Currently implemented by the Nethermind Bridge Node plugin

  • This API should be considered experimental and expected to change / become deprecated in favor of the above API.

  • bridge_getBlockWitness(blockNumber) -> List[Bytes]

    • Returns a list of all RLP-encoded merkle trie values (including contract bytecode) accessed during block execution.