CCTP EVM Contracts and Interfaces

• TokenMessengerV2: Entrypoint for cross-chain USDC transfer. Routes messages to burn USDC on a source chain, and mint USDC on a destination chain.

• MessageTransmitterV2: Generic message passing. Sends all messages on the source chain, and receives all messages on the destination chain.

• TokenMinterV2: Responsible for minting and burning USDC. Contains chain-specific settings used by burners and minters.

• MessageV2: Provides helper functions for cross-chain transfers, such as bytes32ToAddress and addressToBytes32, which are commonly used when bridging between EVM and non-EVM chains. These conversions are simple: prepend 12 zero bytes to an EVM address, or strip them to convert back.

  Note: If you're writing your own integration, it's more gas-efficient to include this logic directly in your contract rather than calling an external one.

Full contract source code is available on GitHub.

This section provides the Smart Contract Interface exposed by CCTP V2, outlining the available functions, and their parameters.

The interface below serves as a reference for permissionless messaging functions exposed by the TokenMessengerV2 and MessageTransmitterV2 functions.

• TokenMessengerV2#depositForBurnWithHook (extends depositForBurn by adding hook data)
• TokenMessengerV2#handleReceiveUnfinalizedMessage (replaces handleReceiveMessage)
• TokenMessengerV2#handleReceiveFinalizedMessage (replaces handleReceiveMessage)

• TokenMessengerV2#depositForBurn
• MessageTransmitterV2#sendMessage
• MessageTransmitterV2#receiveMessage

• TokenMessengerV2#handleReceiveMessage
• TokenMessengerV2#replaceDepositForBurn
• TokenMessengerV2#depositForBurnWithCaller
• MessageTransmitterV2#replaceMessage
• MessageTransmitterV2#sendMessageWithCaller

Deposits and burns tokens from sender to be minted on destination domain, and emits a cross-chain message by calling MessageTransmitter's sendMessage function. Minted tokens will be transferred to mintRecipient.

Parameters

Deposits and burns tokens from sender to be minted on destination domain, and emits a cross-chain message with additional hook data appended. In addition to the standard depositForBurn parameters, depositForBurnWithHook accepts a dynamic-length hookData parameter, allowing the caller to include additional metadata to the attested message, which can be used to trigger custom logic on the destination chain.

Parameters

Calculates and returns the minimum fee required for a given amount in a Standard Transfer. If the minFee (per unit of burnToken) is non-zero, the specified maxFee must be at least the returned minimum fee. Otherwise, the burn will revert onchain.

Parameters

Handles incoming message received by the local MessageTransmitter, and takes the appropriate action. For a burn message, mints the associated token to the requested recipient on the local domain. Validates the function sender is the local MessageTransmitter, and the remote sender is a registered remote TokenMessenger for remoteDomain.

Parameters

Handles incoming message received by the local MessageTransmitter, and takes the appropriate action. For a burn message, mints the associated token to the requested recipient on the local domain. Validates the function sender is the local MessageTransmitter, and the remote sender is a registered remote TokenMessenger for remoteDomain.

Similar to handleReceiveFinalizedMessage, but is called for messages which are not finalized (finalityThresholdExecuted < 2000).

Unlike handleReceiveFinalizedMessage, handleReceiveUnfinalizedMessage has the following messageBody parameters:

• expirationBlock. If expirationBlock ≤ blockNumber on the destination domain, the message will revert and must be re-signed without the expiration block.
• feeExecuted. If nonzero, the feeExecuted is minted to the feeRecipient.

Parameters

Receive message on destination chain by passing message and attestation. Emits MessageReceived event. Messages with a given nonce can only be broadcast successfully once for a pair of domains. The message body of a valid message is passed to the specified recipient for further processing.

Parameters

Sends a message to the recipient on the destination domain. Emits a MessageSent event which will be attested by Circle's attestation service.

Parameters

This table highlights the key workflow improvements of CCTP V2 over CCTP V1 in terms of enhanced cross-chain messaging, fewer manual steps, and greater control over message acceptance:

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