Allowed Relayer

In this segment, we'll delve into the mechanisms of restricting relayers for transmitting messages across Avalanche L1s. While the security in AWM and Interchain Messaging doesn't rely at all on the Relayer, there might be some reasons why you would want to restrict the delivery of the message to certain Relayers.

The more obvious one is when you run your own Relayer, and don't want to incentivize any other to ensure your message gets to the destination. On following sections you will learn how to run your own Relayer so you can restrict the messages to your own.

Let's look at the TeleporterMessageInput structure included when we call the sendCrossChainMessage one more time.

struct TeleporterMessageInput {
    bytes32 destinationBlockchainID;
    address destinationAddress;
    TeleporterFeeInfo feeInfo;
    uint256 requiredGasLimit;
    address[] allowedRelayerAddresses;
    bytes message;
}
 
interface ITeleporterMessenger {
    function sendCrossChainMessage(TeleporterMessageInput calldata messageInput)
        external
        returns (bytes32);
}

As you can see the TeleporterMessageInput allows you to specify an array of addresses for the allowed relayers. Previously we have set that to an empty array, which means that any relayer can pick up the message.

messenger.sendCrossChainMessage( 
    TeleporterMessageInput({
        // Replace with blockchainID of your Subnet (see instructions in Readme)
        destinationBlockchainID: 0x3861e061737eaeb8d00f0514d210ad1062bfacdb4bd22d1d1f5ef876ae3a8921,
        destinationAddress: destinationAddress, 
        feeInfo: TeleporterFeeInfo({feeTokenAddress: address(0), amount: 0}),
        requiredGasLimit: 100000,
        allowedRelayerAddresses: new address[](0), 
        message: abi.encode(message)
    })
);

If you want to restrict the message to a certain relayer, you can simply add the address of the relayer to the array. A Relayer will be identified by the reward address it is associating each time it delivers a message.

messenger.sendCrossChainMessage( 
    TeleporterMessageInput({
        // Replace with blockchainID of your Subnet (see instructions in Readme)
        destinationBlockchainID: 0x3861e061737eaeb8d00f0514d210ad1062bfacdb4bd22d1d1f5ef876ae3a8921,
        destinationAddress: destinationAddress, 
        feeInfo: TeleporterFeeInfo({feeTokenAddress: address(0), amount: 0}),
        requiredGasLimit: 100000,
        allowedRelayerAddresses: [0x321f6B73b6dFdE5C73731C39Fd9C89c7788D5EBc], 
        message: abi.encode(message)
    })
);

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