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ts-filler

Overview

ts-filler is a backend service built with the Bun JavaScript runtime. It is designed to manage backend operations for RIP-7755 cross-chain call requests between any two blockchains that post state roots to L1. This project serves as an example of how an off-chain "Fulfiller" app might function. Anyone can run a fulfiller app and earn money with RIP-7755!

The role of an RIP-7755 Fulfiller is to listen for cross-chain call requests and submit them to the RIP7755Inbox contract on the destination chain on behalf of the user who submitted the request. In return for fulfilling this duty, your fulfiller signer can claim a reward that gets locked in the source chain RIP7755Outbox contract after a defined delay specified in the CrossChainRequest. To claim the reward, the fulfiller must generate and submit a proof that verifies the existence of a record of the call having been made in RIP7755Inbox on the destination chain. The exact proof mechanics depend on the destination chain. Currently, only Arbitrum and OP Stack chains are supported.

Prerequisites

Before you begin, ensure you have met the following requirements:

Installation

To install the necessary dependencies, follow these steps:

  1. Clone the Repository: Clone the repository to your local machine.

    git clone <repository-url>

  2. Navigate to the ts-filler Directory: Change to the ts-filler directory.

    cd services/ts-filler

  3. Install Dependencies: Use Bun to install the dependencies.

    bun install

  4. Configure Environment Variables: Ensure that the .env file in the services/ts-filler directory is properly configured with the required environment variables.

    NODE=<An Ethereum Beacon Node API URL. Can get from a provider like QuickNode>
ARBITRUM_SEPOLIA_RPC=<An RPC URL for Arbitrum Sepolia>
BASE_SEPOLIA_RPC=<An RPC URL for Base Sepolia>
SEPOLIA_RPC=<An RPC URL for Sepolia>
MONGO_URI=<A MongoDB connection string>
ARBISCAN_API_KEY=<An API key for the Arbiscan API see https://docs.arbiscan.io/getting-started/viewing-api-usage-statistics>
ETHERSCAN_API_KEY=<An API key for the Etherscan API>
BASESCAN_API_KEY=<An API key for the BaseScan API>
OPTIMISM_API_KEY=<An API key for the Optimism Etherscan API>
PRIVATE_KEY=<A wallet private key for the signer that will be submitting transactions / claiming rewards>

Running the Service

To run the backend service, use the following command:

bun run index.ts

Docker Support

The ts-filler service can also be run inside a Docker container. The provided docker-compose.yml file sets up the environment and installs the necessary dependencies.

To build and run the Docker container, use the following command:

  1. Build & Run the Docker Container:

    docker-compose up -d

Fulfiller App Requirements

Running a Fulfiller app in the RIP-7755 ecosystem has minimal requirements, but there are essential guidelines to ensure security and proper functionality:

  • Funded Signer: Ensure the signer used to broadcast transactions is funded with the native currency of the blockchains you intend to support.
  • Address Validation: Do not trust addresses in the Request structure from CrossChainCallRequested events without validating them against the configured chain settings.
  • Reward Verification: Verify that the rewardAsset and rewardAmount are appropriate given the requested transaction.
  • Robust Monitoring: Implement robust monitoring to track successfully submitted calls. After a call is successfully submitted, wait for request.finalityDelaySeconds before claiming your reward from the source chain RIP7755Outbox contract. If you do not claim the reward, the user can reclaim it after a 1-day delay.

License

This project is licensed under the MIT License. See the LICENSE file for more details.