Writing Smart Contracts on Avalanche

Introduction

Avalanche is an open-source platform for launching decentralized applications and enterprise blockchain deployments in one interoperable, highly scalable ecosystem. Avalanche gives you complete control on both the network and application layers—helping you build anything you can imagine.

Avalanche can do anything a typical Ethereum client can by using the Ethereum-standard RPC calls. The immediate benefits of using Avalanche rather than Ethereum are speed, scale and throughput. Avalanche offers thousands of transactions per second with sub-second finality at inexpensive fees. These properties will considerably improve the performance of DApps and the user experience of smart-contracts.

The goal of this guide is to lay out a best-practices regarding writing, testing and deploying smart-contracts to Avalanche. We'll be building smart contracts with Hardhat which is an Avalanche development environment for professionals.

Prerequisites

NodeJS and Yarn

First install the LTS of nodejs which is 14.15.4 at the time of writing. NodeJS bundles npm.

Next install yarn:

npm install -g yarn

AvalancheGo and Avash

AvalancheGo is our full node written in Golang. Avash is our local test network. Together, you can deploy private local networks and run tests on them.

Solidity and Avalanche

It is also helpful to have a basic understanding of Solidity and Avalanche.

Dependencies

First clone this repo and download the necessary packages.

git clone https://github.com/ava-labs/avalanche-smart-contract-quickstart.git
cd avalanche-smart-contract-quickstart
yarn

Write Contracts

Edit the Coin.sol contract in contracts/. Coin.sol is an Open Zeppelin ERC20 contract. ERC20 is a popular smart contract interface for interoperability. You can also add your own contracts.

Building

In package.json there's a compile script.

"compile": "npx hardhat compile",

Run yarn compile to make sure your project compiles.

Prepare to Deploy

Edit the deployment script in scripts/deploy.js

Deploy

Hardhat enables deploying to multiple environments. In package.json there is a script for deploying.

"deploy": "npx hardhat run scripts/deploy.js",

You can chose which environment that you want to deploy to by passing in the --network flag with avash, fuji, or mainnet for each respective environment. If you don't pass in --network then it will default to the hardhat network. For example, if you want to deploy to mainnet

yarn deploy --network mainnet

When you deploy to avash, fuji or mainnet you can add your private key(s) as an array to the respective environment's accounts field in hardhat.config.js.

Hardhat Tasks

You can define custom hardhat tasks in hardhat.config.js. There are two tasks included as examples—accounts and balances both of which have scripts in package.json.

"accounts": "npx hardhat accounts",
"balances": "npx hardhat balances"

yarn accounts will print the list of accounts. yarn balances prints the list of AVAX account balances. As with other yarn scripts you can pass in a --network flag to hardhat tasks.

Accounts

Print a list of accounts on the avash network.

yarn accounts --network avash
yarn run v1.22.4
$ npx hardhat accounts --network avash
0x8db97C7cEcE249c2b98bDC0226Cc4C2A57BF52FC
0x9632a79656af553F58738B0FB750320158495942
0x55ee05dF718f1a5C1441e76190EB1a19eE2C9430
0x4Cf2eD3665F6bFA95cE6A11CFDb7A2EF5FC1C7E4
0x0B891dB1901D4875056896f28B6665083935C7A8
0x01F253bE2EBF0bd64649FA468bF7b95ca933BDe2
0x78A23300E04FB5d5D2820E23cc679738982e1fd5
0x3C7daE394BBf8e9EE1359ad14C1C47003bD06293
0x61e0B3CD93F36847Abbd5d40d6F00a8eC6f3cfFB
0x0Fa8EA536Be85F32724D57A37758761B86416123

Balances

Print a list of accounts and their corresponding AVAX balances on the avash network.

yarn balances --network avash
yarn run v1.22.4
$ npx hardhat balances --network avash
0x8db97C7cEcE249c2b98bDC0226Cc4C2A57BF52FC has balance 0
0x9632a79656af553F58738B0FB750320158495942 has balance 0
0x55ee05dF718f1a5C1441e76190EB1a19eE2C9430 has balance 0
0x4Cf2eD3665F6bFA95cE6A11CFDb7A2EF5FC1C7E4 has balance 0
0x0B891dB1901D4875056896f28B6665083935C7A8 has balance 0
0x01F253bE2EBF0bd64649FA468bF7b95ca933BDe2 has balance 0
0x78A23300E04FB5d5D2820E23cc679738982e1fd5 has balance 0
0x3C7daE394BBf8e9EE1359ad14C1C47003bD06293 has balance 0
0x61e0B3CD93F36847Abbd5d40d6F00a8eC6f3cfFB has balance 0
0x0Fa8EA536Be85F32724D57A37758761B86416123 has balance 0

Sending AVAX

package.json has a send-avax script which is found in scripts/sendAvax.js.

"send-avax": "npx hardhat run scripts/sendAvax.js",

Run it with yarn send-avax.

Funding Accounts

package.json has a fund-cchain-addresses script. fund-cchain-addresses will fund each of the C-Chain accounts on the avash network with 1000 AVAX.

"scripts": {
  ...
  "fund-cchain-addresses": "npx hardhat run scripts/fund-cchain-addresses.js"
}

This is a utility script which handles funding accounts on the C-Chain since it's a prerequisite for running smart contracts. It's currently hardcoded to use the 12345 or avash network.

yarn fund-cchain-addresses
yarn run v1.22.4
$ npx hardhat run scripts/fund-cchain-addresses.js
Exporting 1000 AVAX to each address on the C-Chain...
2b75ae74ScLkWe5GVFTYJoP2EniMywkcZySQUoFGN2EJLiPDgp
Importing AVAX to the C-Chain...
2dyXcQGiCk1ckCX4Fs8nLgL8GJgsM72f9Ga13rX5v9TAguVJYM
✨  Done in 4.07s.

You can confirm that it worked by running yarn balance --network avash.

yarn balances --network avash
yarn run v1.22.4
$ npx hardhat balances --network avash
0x8db97C7cEcE249c2b98bDC0226Cc4C2A57BF52FC has balance 1000000000000000000000
0x9632a79656af553F58738B0FB750320158495942 has balance 1000000000000000000000
0x55ee05dF718f1a5C1441e76190EB1a19eE2C9430 has balance 1000000000000000000000
0x4Cf2eD3665F6bFA95cE6A11CFDb7A2EF5FC1C7E4 has balance 1000000000000000000000
0x0B891dB1901D4875056896f28B6665083935C7A8 has balance 1000000000000000000000
0x01F253bE2EBF0bd64649FA468bF7b95ca933BDe2 has balance 1000000000000000000000
0x78A23300E04FB5d5D2820E23cc679738982e1fd5 has balance 1000000000000000000000
0x3C7daE394BBf8e9EE1359ad14C1C47003bD06293 has balance 1000000000000000000000
0x61e0B3CD93F36847Abbd5d40d6F00a8eC6f3cfFB has balance 1000000000000000000000
0x0Fa8EA536Be85F32724D57A37758761B86416123 has balance 1000000000000000000000
✨  Done in 0.62s.

Hardhat Help

You can run yarn hardhat to list hardhat version, usage instructions, global options and available tasks.

Typical avash workflow

First confirm you have the latest and greatest AvalancheGo built.

cd /path/to/avalanchego
git fetch -p
git checkout master
./scripts/build.sh

Next fire up avash and run a script to configure your network.

cd /path/to/avash
git fetch -p
git checkout master
go build
 ./avash
Config file set: /Users/username/.avash.yaml
Avash successfully configured.
avash> runscript scripts/five_node_staking.lua
RunScript: Running scripts/five_node_staking.lua
RunScript: Successfully ran scripts/five_node_staking.lua

Now you have a local avalanche network with 5 staking nodes. Next transfer 1000 AVAX from the X-Chain to each of the 10 avash accounts in hardhat.config.js.

cd /path/to/avalanche-smart-contract-quickstart
yarn fund-cchain-addresses
yarn run v1.22.4
$ npx hardhat run scripts/fund-cchain-addresses.js --network avash
Exporting 1000 AVAX to each address on the C-Chain...
2b75ae74ScLkWe5GVFTYJoP2EniMywkcZySQUoFGN2EJLiPDgp
Importing AVAX to the C-Chain...
2dyXcQGiCk1ckCX4Fs8nLgL8GJgsM72f9Ga13rX5v9TAguVJYM
✨  Done in 5.03s.

Confirm each of the accounts are funded with 1000 AVAX.

yarn balances --network avash
yarn run v1.22.4
$ npx hardhat balances --network avash
0x8db97C7cEcE249c2b98bDC0226Cc4C2A57BF52FC has balance 1000000000000000000000
0x9632a79656af553F58738B0FB750320158495942 has balance 1000000000000000000000
0x55ee05dF718f1a5C1441e76190EB1a19eE2C9430 has balance 1000000000000000000000
0x4Cf2eD3665F6bFA95cE6A11CFDb7A2EF5FC1C7E4 has balance 1000000000000000000000
0x0B891dB1901D4875056896f28B6665083935C7A8 has balance 1000000000000000000000
0x01F253bE2EBF0bd64649FA468bF7b95ca933BDe2 has balance 1000000000000000000000
0x78A23300E04FB5d5D2820E23cc679738982e1fd5 has balance 1000000000000000000000
0x3C7daE394BBf8e9EE1359ad14C1C47003bD06293 has balance 1000000000000000000000
0x61e0B3CD93F36847Abbd5d40d6F00a8eC6f3cfFB has balance 1000000000000000000000
0x0Fa8EA536Be85F32724D57A37758761B86416123 has balance 1000000000000000000000
✨  Done in 0.72s.

Send each of the accounts some AVAX from the first account.

yarn send-avax --network avash
yarn run v1.22.4
$ npx hardhat run scripts/sendAvax.js --network avash
Seeding addresses with AVAX
✨  Done in 1.33s.

Confirm that the balances are updated

yarn balances --network avash
yarn run v1.22.4
$ npx hardhat balances --network avash
0x8db97C7cEcE249c2b98bDC0226Cc4C2A57BF52FC has balance 999821170000000000000
0x9632a79656af553F58738B0FB750320158495942 has balance 1000010000000000000000
0x55ee05dF718f1a5C1441e76190EB1a19eE2C9430 has balance 1000010000000000000000
0x4Cf2eD3665F6bFA95cE6A11CFDb7A2EF5FC1C7E4 has balance 1000010000000000000000
0x0B891dB1901D4875056896f28B6665083935C7A8 has balance 1000010000000000000000
0x01F253bE2EBF0bd64649FA468bF7b95ca933BDe2 has balance 1000010000000000000000
0x78A23300E04FB5d5D2820E23cc679738982e1fd5 has balance 1000010000000000000000
0x3C7daE394BBf8e9EE1359ad14C1C47003bD06293 has balance 1000010000000000000000
0x61e0B3CD93F36847Abbd5d40d6F00a8eC6f3cfFB has balance 1000010000000000000000
0x0Fa8EA536Be85F32724D57A37758761B86416123 has balance 1000010000000000000000

Compile the smart contract.

yarn compile
yarn run v1.22.4
$ rimraf ./build/
$ npx hardhat compile
Compiling 1 file with 0.6.4
Compilation finished successfully
✨  Done in 2.13s.

Deploy the contract to the avash local network

yarn deploy --network avash
yarn run v1.22.4
$ npx hardhat run scripts/deploy.js --network avash
Coin deployed to: 0x789a5FDac2b37FCD290fb2924382297A6AE65860
✨  Done in 1.28s.

We now have a token deployed at 0x789a5FDac2b37FCD290fb2924382297A6AE65860. The constructor function of this token mints the TOTAL_BALANCE to the account which called the contract which is the first address in the avash accounts array in hardhat.config.js.

  "0x56289e99c94b6912bfc12adc093c9b51124f0dc54ac7a766b2bc5ccf558d8027", 
  "0x7b4198529994b0dc604278c99d153cfd069d594753d471171a1d102a10438e07",

Import them both into MetaMask.

Now we add the SYM token to each account in MetaMask. Add Token -> Custom Token and paste in the Token Contract Address. The Token Symbol and Decimals of Precision should populate.

NOTE the 2nd account doesn't have any SYM because it was all minted to the 1st account in the Coin's constructor function.

You can now send SYM from the 1st account to the 2nd account. Go to the 1st account in MetaMask and click Send SYM, Transfer between my accounts, next select the 2nd account.

Next you'll land on the Send Tokens screen. Here you can set the amount to 507 and the Gas Price to 470. This gas price is very important. If you set the value below 470 then the transaction won't go through so make sure and double confirm this is correct.

After clicking Next you'll land on the final confirmation screen. Make sure that everything looks good and click Confirm.

Lastly note that the 2nd account has 507 SYM.