Tutorial

What better way to start than to lead by example? And a simple one we’re all familiar with: “Hello World!”

One-time setup

Install nodejs. Run node -v to check your installation.

You should use node version 18. If needed, you can switch your node version via

npm i -g n
sudo n v18

Clone this repo:

git clone https://github.com/ferrumnet/QP-examples.git

Build contracts and tests:

cd QP-examples
npm ci
npm run build

Set up a private key

npm run setup

Deploy and run “Hello World”

In order to run the examples against the local emulator, use a separate terminal window.

npm run start

Leave this terminal open to keep your local server running for all of these examples.

Run the “Call Contract” example. The application sends a message - “Hello World” - from a source to a destination chain using the callContract function.

1. Deploy locally

To deploy the contract, use the following command:

npm run deploy evm/call-contract local

Output:

Deploying ExecutableSample for Moonbeam.
Deploying ExecutableSample for Avalanche.
Deploying ExecutableSample for Fantom.
Deploying ExecutableSample for Ethereum.
Deploying ExecutableSample for Polygon.
Deployed ExecutableSample for Ethereum at 0x775C53cd1F4c36ac74Cb4Aa1a3CA1508e9C4Bd24.
Deployed ExecutableSample for Moonbeam at 0xF8f92930AD2C4d627a96819E67aD3BcD95b5E063.
Deployed ExecutableSample for Polygon at 0x775C53cd1F4c36ac74Cb4Aa1a3CA1508e9C4Bd24.
Deployed ExecutableSample for Avalanche at 0x775C53cd1F4c36ac74Cb4Aa1a3CA1508e9C4Bd24.
Deployed ExecutableSample for Fantom at 0x775C53cd1F4c36ac74Cb4Aa1a3CA1508e9C4Bd24.

2. Run locally

To execute the example, use the following command:

npm run execute evm/call-contract [local|testnet] ${srcChain} ${destChain} ${message}

For example:

npm run execute evm/call-contract local "Moonbeam" "Avalanche" "Hello World"

Output:

--- Initially ---
value at Avalanche is
--- After ---
value at Avalanche is Hello World

3. Run in testnet

When you’re ready, you can take the actual local example above and change the local environment parameters in the deploy/run scripts to testnet. You’ll need testnet tokens for each testnet you want to work with.

That’s it!

Summary

In the above, we sent a message - “Hello World” - from a smart contract on Moonbeam to a smart contract on Avalanche, updating the latter’s “value” property to our “Hello World” message.

The full transaction flow was:

1. Started the local developer environment to run local EVM blockchains.
2. The first node script deployed this smart contract to all the EVM chains in our local developer environment.
3. The second node script ran this test script on local Moonbeam, which:
   • Calculated the estimated gas cost of executing the method on Avalanche.
   • Invoked setRemoteValue on the deployed Moonbeam smart contract. This method first pays the gas receiver on Moonbeam the estimated gas cost, then calls callContractWithToken on the Moonbeam Gateway contract.
4. After some time, the relay services detect the gas paid on Moonbeam and executes the smart contract on Avalanche, invoking the _execute method that updated the value to the message parameter.