Token Bridge＃
Introduction＃
Wormhole's Token Bridge enables seamless cross-chain token transfers using a lock-and-mint mechanism. The bridge locks tokens on the source chain and mints them as wrapped assets on the destination chain. Additionally, the Token Bridge supports contract controlled transfers (transfers with messages), where arbitrary byte payloads can be attached to the token transfer, enabling more complex chain interactions.
This page outlines the core contract methods needed to integrate Token Bridge functionality into your smart contracts. To understand the theoretical workings of the Token Bridge, refer to the Token Bridge page in the Learn section.
Prerequisites＃
To interact with the Wormhole Token Bridge, you'll need the following:
- The address of the Token Bridge contract on the chains you're working with
- The Wormhole chain ID of the chains you're targeting for token transfers
How to Interact with Token Bridge Contracts＃
The primary functions of the Token Bridge contracts revolve around:
- Attesting a token - registering a new token for cross-chain transfers
- Transferring tokens - locking and minting tokens across chains
- Transferring tokens with a payload - including additional data for contract-controlled transfers
Attest a token＃
Suppose a token has never been transferred to the target chain before transferring it cross-chain. In that case, its metadata must be registered so the Token Bridge can recognize it and create a wrapped version if necessary.
The attestation process doesn't require you to manually input token details like name, symbol, or decimals. Instead, the Token Bridge contract retrieves these values from the token contract itself when you call the attestToken() method.
function attestToken(
address tokenAddress,
uint32 nonce
) external payable returns (uint64 sequence);
Parameters
tokenAddress address
The contract address of the token to be attested.
nonce uint32
An arbitrary value provided by the caller to ensure uniqueness.
Returns
sequence uint64
A unique identifier for the attestation transaction.
When attestToken() is called, the contract emits a Verifiable Action Approval (VAA) containing the token's metadata, which the Guardians sign and publish.
You must ensure the token is ERC-20 compliant. The attestation may fail or produce incomplete metadata if it does not implement the standard functions.
Transfer Tokens＃
Once a token is attested, a cross-chain token transfer can be initiated following the lock-and-mint mechanism. On the source chain, tokens are locked (or burned if they're already a wrapped asset), and a VAA is emitted. On the destination chain, that VAA is used to mint or release the corresponding amount of wrapped tokens.
Call transferTokens() to lock/burn tokens and produce a VAA with transfer details.
function transferTokens(
address token,
uint256 amount,
uint16 recipientChain,
bytes32 recipient,
uint256 arbiterFee,
uint32 nonce
) external payable returns (uint64 sequence);
Parameters
token address
The address of the token being transferred.
amount uint256
The amount of tokens to be transferred.
recipientChain uint16
The Wormhole chain ID of the destination chain.
recipient bytes32
The recipient's address on the destination chain.
arbiterFee uint256
Optional fee to be paid to an arbiter for relaying the transfer.
nonce uint32
A unique identifier for the transaction.
Returns
sequence uint64
A unique identifier for the transfer transaction.
Once a transfer VAA is obtained from the Wormhole Guardian network, the final step is to redeem the tokens on the destination chain. Redemption verifies the VAA's authenticity and releases (or mints) tokens to the specified recipient. To redeem the tokens, call completeTransfer().
Parameters
encodedVm bytes memory
The signed VAA containing the transfer details.
Note
- The Token Bridge normalizes token amounts to 8 decimals when passing them between chains. Make sure your application accounts for potential decimal truncation
- The VAA ensures the integrity of the message. Only after the Guardians sign the VAA can it be redeemed on the destination chain
Transfer tokens with payload＃
While a standard token transfer moves tokens between chains, a transfer with a payload allows you to embed arbitrary data in the VAA. This data can be used on the destination chain to execute additional logic—such as automatically depositing tokens into a DeFi protocol, initiating a swap on a DEX, or interacting with a custom smart contract.
Call transferTokensWithPayload() instead of transferTokens() to include a custom payload (arbitrary bytes) with the token transfer.
function transferTokensWithPayload(
address token,
uint256 amount,
uint16 recipientChain,
bytes32 recipient,
uint32 nonce,
bytes memory payload
) external payable returns (uint64 sequence);
Parameters
token address
The address of the token being transferred.
amount uint256
The amount of tokens to be transferred.
recipientChain uint16
The Wormhole chain ID of the destination chain.
recipient bytes32
The recipient's address on the destination chain.
nonce uint32
A unique identifier for the transaction.
payload bytes memory
Arbitrary data payload attached to the transaction.
Returns
sequence uint64
A unique identifier for the transfer transaction.
After initiating a transfer on the source chain, the Wormhole Guardian network observes and signs the resulting message, creating a Verifiable Action Approval (VAA). You'll need to fetch this VAA and then call completeTransferWithPayload().
Only the designated recipient contract can redeem tokens. This ensures that the intended contract securely handles the attached payload. On successful redemption, the tokens are minted (if foreign) or released (if native) to the recipient address on the destination chain. For payload transfers, the designated contract can execute the payload's logic at this time.
Parameters
encodedVm bytes memory
The signed VAA containing the transfer details.
Returns
bytes memory
The extracted payload data.
Source Code References＃
For a deeper understanding of the Token Bridge implementation and to review the actual source code, please refer to the following links:
Portal Bridge＃
A practical implementation of the Wormhole Token Bridge can be seen in Portal Bridge, which provides an easy-to-use interface for transferring tokens across multiple blockchain networks. It leverages the Wormhole infrastructure to handle cross-chain asset transfers seamlessly, offering users a convenient way to bridge their assets while ensuring security and maintaining token integrity.