Sender Contract

Read the Sender Contract

The following contract is located inside contracts/interchain-messaging/send-receive directory. Read through the contract below and and understand what is happening:

// (c) 2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
 
// SPDX-License-Identifier: Ecosystem
 
pragma solidity ^0.8.18;
 
import "@teleporter/ITeleporterMessenger.sol";
 
contract SenderOnCChain {
    ITeleporterMessenger public immutable messenger = ITeleporterMessenger(0x253b2784c75e510dD0fF1da844684a1aC0aa5fcf);
 
    /**
     * @dev Sends a message to another chain.
     */
    function sendMessage(address destinationAddress, string calldata message) external {
        messenger.sendCrossChainMessage(
            TeleporterMessageInput({
                // BlockchainID of Dispatch L1
                destinationBlockchainID: 0x9f3be606497285d0ffbb5ac9ba24aa60346a9b1812479ed66cb329f394a4b1c7,
                destinationAddress: destinationAddress, 
                feeInfo: TeleporterFeeInfo({feeTokenAddress: address(0), amount: 0}),
                requiredGasLimit: 100000,
                allowedRelayerAddresses: new address[](0),
                message: abi.encode(message)
            })
        );
    }
}

The key things to understand:

• Importing ITeleporterMessenger (Line 8): We are importing the ITeleporterMessenger Interface we looked at in the previous activity.
• Defining teleporterMessenger contract (Line 12): We are defining a teleporterMessenger contract using the imported interface. It is important to note, that our cross-chain dApp is not implementing the interface itself, but initializes a contract using that interface.
• Sending the message (Line 21): We are sending the message by calling the function of our teleporterMessenger. As an input we are defining a TeleporterMessageInput. The destinationChainId should be set to the Dispatch test L1's blockchain ID. We will need to provide the address of the receiving contract on the Dispatch test L1 as a parameter to the function, since we have not deployed it yet and don't know the address at this time.
• No fees (Line 25): In this exercise we are not providing any fees to the relayer for relaying the message. This is only possible since the relayer we are running here is configured to pick up any message even if it does not provide any rewards.
• Encoding the Message (Line 31): The TeleporterMessageInput defines a message as an array of bytes. For now we will just simply encode the string with abi.encode(). In the future activities, you will see how we can encode multiple values of any type in that message.
• Hardcoded destinationBlockchainId: For this course, we are using Dispatch, but normally you will have to replace the destinationBlockchainID with whatever chain you want to send a message to.

Deploy Sender Contract

To deploy a contract using Foundry use the following command:

forge create --rpc-url fuji-c --private-key $PK contracts/interchain-messaging/send-receive/senderOnCChain.sol:SenderOnCChain --broadcast

[⠊] Compiling...
[⠒] Compiling 2 files with Solc 0.8.18
[⠢] Solc 0.8.18 finished in 81.53ms
Compiler run successful!
Deployer: 0x8db97C7cEcE249c2b98bDC0226Cc4C2A57BF52FC // [$FUNDED_ADDRESS]
Deployed to: 0x5DB9A7629912EBF95876228C24A848de0bfB43A9 // [$SENDER_ADDRESS]
Transaction hash: 0xcde7873e9e3c68fb00a2ad6644dceb64a01a41941da46de5a0f559d6d70a1638

Save Sender Address

Then save the sender contract address in an environment variable:

export SENDER_ADDRESS={your-sender-address}