On-chain Validator Checkpoint Syncer with Smart Contract Storage

[XxAxe1xX]

Overview

Currently, Hyperlane validators use web2 storage solutions (AWS S3, GCS) for publishing checkpoints. This bounty proposes implementing an on-chain checkpoint syncer, allowing validators to publish checkpoints directly on-chain through a smart contract, making the system more decentralized and web3-native.

Technical Specifications

Smart Contract Implementation

• Create a contract implementing checkpoint storage functionality
• Support URI format: onchain://chainName/contractAddress
• Implement checkpoint publishing for authenticated accounts
• Support all required CheckpointSyncer trait methods:
  • latest_index
  • write_latest_index
  • update_latest_index
  • fetch_checkpoint
  • write_checkpoint
  • write_metadata
  • write_announcement
  • announcement_location

Validator Integration

• Utilize existing chain signer abstraction for checkpoint submission
• Support signature verification (optional, depending on implementation choice)
• Handle gas optimization for frequent checkpoint submissions

Key Considerations

1. Storage optimization for on-chain data
2. Gas cost efficiency for frequent updates
3. Proper handling of Arbitrum's multi-dimensional gas fees
4. Compatibility with upcoming checkpoint store methods (ref feat: checkpoint syncer fraud flag #4587)

Implementation Notes

• The contract should be simple and focused on storage/retrieval
• Consider making write_latest_index a no-op as suggested in discussions
• Implement gas overrides consistently across the system
• Add special handling for Arbitrum Nitro if feasible

Dependencies

• Base implementation from CheckpointSyncer trait in hyperlane-base/src/traits/checkpoint_syncer.rs
• Integration with existing validator infrastructure

Testing Requirements

• Unit tests for contract functionality
• Integration tests with validator implementation
• Gas optimization tests
• Cross-chain compatibility verification