Build
Run a relayer
The relayer completes deposits. It watches deposit addresses on Arc, mints incoming CCTP transfers, sweeps the hub, waits for Circle's attestation, and executes the adapter on the destination chain. Every step checks the chain before acting, so the process can restart at any point.
Everything it does is permissionless
sweep and refund on the hub, receiveMessage on Circle's MessageTransmitter on Arc, receiveAndExecute and claim on the receiver. A relayer makes deposits fast. It cannot redirect one, and it is not needed to finish one. A protocol can run its own relayer, or point the widget at the hosted one at https://inlet-relayer.wonderfulforest-6c3e22a4.westeurope.azurecontainerapps.io.
Run it
cd services/relayer
cp .env.example .env
pnpm dev| Variable | Meaning |
|---|---|
RELAYER_PRIVATE_KEY | Pays gas on Arc, in USDC, and on the destination chains |
DB_PATH | The SQLite file that holds intent state |
ARC_RPC, BASE_SEPOLIA_RPC, ARBITRUM_SEPOLIA_RPC, UNICHAIN_SEPOLIA_RPC, ETHEREUM_SEPOLIA_RPC, MONAD_TESTNET_RPC | RPC endpoints, with public defaults |
CORS_ORIGIN | Comma separated origins allowed to call the API, or * |
UNISWAP_API_KEY | Turns on the Uniswap Trading API quotes behind /quotes/uniswap |
Destination chains and receivers come from config/deployments.testnet.json. The relayer serves every chain that has a receiver there: Arbitrum Sepolia, Base Sepolia, Unichain Sepolia, Ethereum Sepolia and Monad Testnet today. It manages its nonces locally and retries nonce errors after five seconds, which matters on public RPCs that lag.
Pipeline
| From | To | What happens |
|---|---|---|
| created | funded | A CCTP mint or a Gateway mint landed at the deposit address on Arc |
| funded | swept | The relayer called sweep on the hub |
| swept | attested | Circle's Iris API returned the attestation for the hub's burn |
| attested | executed | The relayer called receiveAndExecute on the receiver |
| attested | claimable | The adapter reverted inside receiveAndExecute and the receiver kept the USDC for the beneficiary |
| funded or created | refunding, refunded, expired | The deadline passed; refund burned the balance back, or nothing was there |
End to end scripts
pnpm e2e burns one USDC on the source chain, routes it through Arc and deposits it into the chosen destination, printing every transaction hash. pnpm gateway:deposit funds a Gateway balance once, and pnpm e2e:gateway runs the same deposit from that balance without the source chain wait. Both read DESTINATION, SOURCE, E2E_AMOUNT, USER_PRIVATE_KEY and RELAYER_URL. pnpm e2e:solana does the same from Solana Devnet with a keypair file in SOLANA_KEYPAIR or the wallet's exported secret in SOLANA_PRIVATE_KEY, and with SIMULATE=1 it only simulates the burn for any funded OWNER.
Hosting
The hosted relayer runs as an Azure Container App from the infra folder in the repository, provisioned with the Azure Developer CLI. Any container host with a persistent volume for the SQLite file works.