Interchain gas payments
Pay for message delivery on the origin chain
Successful interchain messages require two transactions; one on the origin chain to send the message, and one on the destination chain to deliver the message.
For convenience, Hyperlane provides an on-chain API on the origin chain that allows message senders to pay one or more Relayers to deliver a message on the destination chain. This payment is called an interchain gas payment.
Interchain gas payments are facilitated by
InterchainGasPaymaster(IGP) smart contract contracts.
These contracts expose the Interchain gas paymaster API, which allows users to pay Relayers with native tokens on the origin chain to cover the costs of delivering a message on the destination chain.
InterchainGasPaymastercontract corresponds to exactly one relayer.
In order to support the Interchain gas paymaster API, IGP contracts may be configured with gas oracles, which are responsible for tracking remote token gas prices and exchange rates.
This allows the
quoteGasPaymentfunction to provide an accurate quote for the price of gas on a remote chain, denominated in the local chain's native token.
Eventually, relayers will be able to automatically update their gas oracles in order to ensure that their IGP always quotes a fair price for remote gas.
Interchain gas payments are based on a social contract between the message sender and relayer.
In other words, a relayer may receive interchain gas payments without delivering the corresponding messages.
Therefore, when making interchain gas payments, it is recommended to use an IGP contract that is associated with a known and reputable relayer.
An honest relayer implementation will honor any successful gas payments made to its IGP, no matter how many tokens were actually paid. By keeping Gas oracles up to date, the relayer can ensure that gas payments succeed if and only if a "fair" price was paid.
There are no trust assumptions with respect to relayers in the Hyperlane protocol, and under no circumstances will a malicious relayer be able to censor or falsify messages. The worst thing that a relayer can do is accept payments without delivering a message.