Top-Level Batching

[LayneHaber]

Motivation

Allowing batching to happen natively within the Connext opens up more effective gas optimizations (i.e. batching execute calls). Gas costs can be heavily optimized for transactions if routers are able to batch them safely. By using the Multicall by OZ contract, multiple functions may be called simultaneously while preserving any msg.sender properties (as the contract uses delegatecall).

Design Requirements

• Should be easy for the sequencer to use the batching
• Should not be a requirement for functions where it doesn't make sense (i.e. those called by the user or bridge, like xcall and reconcile)
• Should save gas

Proposal

The Connext contract should inherit the Multicall contract so that there is a .multicall(data) function on the contract itself.

import "@openzeppelin/contracts/utils/Multicall.sol";

contract Connext is Multicall { ... }

This will allow the sequencer to easily batch execute calls by combining the individual payloads and calling exec and is simple to implement. However, it may miss out on more savings that could be included in a more function-specific implementation.

Open Questions

• What are the realistic gains from making a function-specific implementation (i.e. executeMany), and can that be combined with Multicall to make an even more efficient and easy to use implementation? The majority of storage reads/writes are done by transferId, except for the router balance, which is done by router. Could also help when sending out relayer fees, by handling them for multiple execute calls.

• When we start batching the nomad messages, there will still be leaf-based functions that will need to be executed (i.e. process for claiming against a leaf if you provided fast liquidity, and execute to provide fast liquidity for a leaf). These functions can be batched, but it is unlikely many of the per-batch transactions (i.e. dispatch to send a root over nomad, reconcile to update a root from nomad)