Coinbase Commerce Onchain Payment Protocol

The protocol relies on two main abstractions: Operators and Transfer Intents.

1. Operators: Before use, an operator must register with the contract and specify a fee destination. Operators are responsible for setting up merchants and providing the UI for interaction. Registration is permissionless. Coinbase Commerce uses a specific address maintained by Coinbase as its operator.

2. Transfer Intents: These are the primitives used to facilitate individual payments. A TransferIntent is a Solidity struct that must be signed by an operator. This signature ensures the intent cannot be forged or modified and allows operators to enforce policies (legal, internal, etc.) before a payment is allowed.

TransferIntent Fields:

• merchant: The merchant's address.
• currency: The currency the merchant wishes to receive.
• amount: The amount of that currency requested.
• deadline: The expiration time for the payment.
• payer: The payer's address.
• chain: The chain the payer will pay on.
• refundAddress: Where any refunds should be directed.
• operator: The operator facilitating the payment.
• fee: The fee the operator should receive.
• id: A unique identifier for the payment.
• signature: The operator's signature (and optional prefix).

A frontend must select a payment method based on the settlement token, the input token, and how the payer allows token movement.

Note: For EVM networks where ETH is not the native gas currency (e.g., Polygon), substitute ETH with the native currency (e.g., MATIC).

- `transferNative`: The merchant wants ETH and the payer wants to pay ETH
- `transferToken`: The merchant wants a token and the payer wants to pay with that token. Uses Permit2 for token movement.
- `transferTokenPreApproved`: Same as `transferToken`, except the Transfers contract is directly approved by the payer for the payment token
- `wrapAndTransfer`: The merchant wants WETH and the payer wants to pay ETH
- `unwrapAndTransfer`: The merchant wants ETH and the payer wants to pay WETH
- `unwrapAndTransferPreApproved`: Same as `unwrapAndTransfer`, except the Transfers contract is directly approved by the payer for WETH
- `swapAndTransferUniswapV3Native`: The merchant wants a token and the payer wants to pay ETH. The token must have sufficient liquidity with ETH on Uniswap V3.
- `swapAndTransferUniswapV3Token`: The merchant wants either ETH or a token and the payer wants to pay with a different token. The payment token must have sufficient liquidity with the settlement token on Uniswap V3.
- `swapAndTransferUniswapV3TokenPreApproved`: Same as `swapAndTransferUniswapV3Token`, except the Transfers contract is directly approved by the payer for the payment token