Sender Contract

Lets start by deploying our sender contract on C-Chain. It will be responsible for calling the the TeleporterMessenger contract, encoding our message and sending it to the destination chain.

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:

contracts/interchain-messaging/send-receive/senderOnCChain.sol

// (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({
                // Replace with blockchainID of your Avalanche L1 (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)
            })
        );
    }
}

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. Make sure to replace the destinationChainId with the one of your Blockchain. We will need to provide the address of the receiving contract on the Avalanche 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.

Get destinationBlockchainID

To get the blockchainID on our Avalanche L1 let's use the Avalanche-CLI built in feature with the command:

avalanche blockchain describe myblockchain

In the output you will find the blockchain details:

+---------------------------------------------------------------------------------------------------------------+
|                                                  MYBLOCKCHAIN                                                 |
+---------------+-----------------------------------------------------------------------------------------------+
| Name          | myblockchain                                                                                  |
+---------------+-----------------------------------------------------------------------------------------------+
| VM ID         | qDNV9vtxZYYNqm7TN1mYBuaaknLdefDbFK8bFmMLTJQJKaWjV                                             |
+---------------+-----------------------------------------------------------------------------------------------+
| VM Version    | v0.6.9                                                                                        |
+---------------+--------------------------+--------------------------------------------------------------------+
| Local Network | ChainID                  | 1                                                                  |
|               +--------------------------+--------------------------------------------------------------------+
|               | SubnetID                 | 2AKbBT8jFUfUsUJ2hhRiDUnAAajJdNhTKeNgEe3q77spMj1N8F                 |
|               +--------------------------+--------------------------------------------------------------------+
|               | Owners (Threhold=1)      | P-custom18jma8ppw3nhx5r4ap8clazz0dps7rv5u9xde7p                    |
|               +--------------------------+--------------------------------------------------------------------+
|               | BlockchainID (CB58)      | krN11ZE6BNgenbX71Wu3YWv2SS5C3p9pD3WLkkRLVhuETGNJb                  |
|               +--------------------------+--------------------------------------------------------------------+
|               | BlockchainID (HEX)       | 0x6391b85bafc78f1b10aec35695c2399c2fb7fff9f3b18ea903f77345e9e96e3e |
+---------------+--------------------------+--------------------------------------------------------------------+

Replace `destinationBlockchainID`

Replace the destinationBlockchainID in senderOnCChain.sol with BlockchainID (HEX)

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({
                // Replace with blockchainID of your Subnet (see instructions in Readme)
                destinationBlockchainID: 0x6391b85bafc78f1b10aec35695c2399c2fb7fff9f3b18ea903f77345e9e96e3e, 
                destinationAddress: destinationAddress,
                feeInfo: TeleporterFeeInfo({feeTokenAddress: address(0), amount: 0}),
                requiredGasLimit: 100000,
                allowedRelayerAddresses: new address[](0),
                message: abi.encode(message)
            })
        );
    }
}

Deploy Sender Contract

To deploy a contract using Foundry use the following command:

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

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

Save Sender Address

Then save the sender contract address in an environment variable:

export SENDER_ADDRESS=0x5DB9A7629912EBF95876228C24A848de0bfB43A9

Read the Sender Contract

Get destinationBlockchainID

Replace destinationBlockchainID

Deploy Sender Contract

Save Sender Address

On this page

Replace `destinationBlockchainID`