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Creating and Publishing a Solidity Contract from Scratch

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For the last year I’ve been really interested in Blockchain technologies and specially the creation of Solidity Contracts. Unfortunately most of the tutorials that you find on the Internet assume that you don’t want publish contract on a blockchain, that you don’t want to use a local blockchain or that you have a dev environment already in place.

So in this article I’m going to create a very simple contract assuming only that I have installed node and Visual Studio Code. No extensions and no global npm packages are needed to follow along.

In this article, I will not be explaining what Solidity and blockchain are, or what smart contracts is. Those subjects for another article… Maybe 🤷.

Setup your editor

Before we begin, lets start by getting our editor ready for Solidity development. For Visual Studio Code I recommend 2 extensions:

The Solidity Visual Studio Code extension by Juan Blanco is a must since it offers:

The DeFi extension by Eric Lau is a nice addition if you are thinking or creating real life contracts that are actually going to be on a real blockchain. Some of the reasons are:

To install this extension directly from the terminal you just have to issue:

code --install-extension JuanBlanco.solidity
code --install-extension ericglau.defi-ls

If you are using Vim or NeoVim then I recommend you install the Vim Polyglot plugin so you get syntax highlight.

Truffle Intro

You can think of Smart Contracts as back end applications that need to be deployed in an Application Container or Virtual Machine. There are multiple virtual machines, but by far the Ethereum Virtual Machine the most used one. It’s so popular that is used in different networks like the Binance Chain or the Polygon chain.

Additionally the Ethereum Virtual Machine “compatible” contracts can be written in multiple programming languages, being Solidity and Vyper the most used ones. Solidity resembles C++ while Vyper resembles Python.

But before deploying a Smart Contract to a blockchain, you need to test it, migrate it and compile it. That’s where a Smart Contract Framework comes into play. They include all the tools to develop, compile, test, migrate and deploy Smart Contracts on a blockchain.

In the case of Ethereum Virtual Machine contracts, there are 3 very famous frameworks:

Of the 3, Truffle is the most popular framework for writing smart contracts in Solidity and Vyper, even though Hardhat is rising in popularity.

Some of the properties of Truffle are:

Even tough Truffle is an npm pacakge you still write your contracts in Solidity or Vyper but the testing, configuration and deployment are done using JavaScript.

Setup a truffle project

Most of the Truffle tutorials you can find on the net, ask you to install truffle globally with npm -g truffle, but I really don’t like that option since difference in versions can come into play, which is not good if you are working on a team and not by yourself. So that’s why I use npx and install it locally:

mkdir truffle-test-project
cd $_
npm init -y
npm install --save-dev truffle
npm audit fix

The npm audit fix is to remove some of the warnings but not all of them.

You can verify that all went well by executing npx truffle version:

$ npx truffle version

Truffle v5.4.26 (core: 5.4.26)
Solidity - 0.8.10 (solc-js)
Node v16.13.1
Web3.js v1.5.3

Up to this point you have a Node Project in place. To actually create a smart contract project you have to issue npx truffle init:

npx truffle init

This will create the project structure and some initial files you’ll need for the development of your smart contract.

The tree command should return something like this:

$ tree -I node_modules # To get a list of files
.
├── contracts
│   └── Migrations.sol
├── migrations
│   └── 1_initial_migration.js
├── package-lock.json
├── package.json
├── test
└── truffle-config.js

3 directories, 5 files

We’re done as far a setup goes. Now we have to create a test contract.

Creating the first contract

One of the things the define Truffle is that the project structure is always the same. This means that our contracts will be stored in the contracts/ directory and the should have the .sol extension.

If you go into that folder, you’ll find a Migrations.sol contract, which helps with the migrations and is used internally by Truffle. Don’t delete it, but also don’t mind it either.

For our contract, we’ll be creating the contracts/SimpleStorage.sol file with the following contents:

// contracts/SimpleStorage.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.4.22 <0.9.0;

contract SimpleStorage {

  uint data;

  function updateData(uint _data) external {
    data = _data;
  }

  function readData() external view returns(uint) {
    return data;
  }
}

This contract is very simple, it has 2 functions:

Now that we have our contract created, lets compile it.

Compiling with truffle

Actually, compiling Solidity contracts is very easy, just issue npx truffle compile, but there is a caveat. By default Truffle will compile your contracts with version of your compiler 0.5.0. So if you want to use newer features of solidity, you can change this version by editing the truffle-config.js file, and on the section compilers uncomment and change the version to something more current like 0.8.10

modules.exports = {
  // ...

  // Configure your compilers
  compilers: {
    solc: {
      version: "0.8.10", // Fetch exact version from solc-bin (default: truffle's version)
      // docker: true,        // Use "0.5.1" you've installed locally with docker (default: false)
      // settings: {          // See the solidity docs for advice about optimization and evmVersion
      //  optimizer: {
      //    enabled: false,
      //    runs: 200
      //  },
      //  evmVersion: "byzantium"
      // }
    },
  },
  // ...
};

Now we can do the compiling with:

npx truffle compile

And it will return something like:

Compiling your contracts...
___________________________
> Compiling ./contracts/Migrations.sol
> Compiling ./contracts/SimpleStorage.sol
> Artifacts written to /Users/mario/Projects/truffle-test-project/build/contracts
> Compiled successfully using:
   - solc: 0.8.10+commit.fc410830.Emscripten.clang

As you can see, Truffle stores the compile contracts in the build/contracts/ folder as .jsonc files. And if you open them you can find the encoded bytecode that will get deployed in the blockchain.

NOTE

  1. Jsonc files support comments
  2. If you have incompatibility of Solidity versions between contracts the compiler will fail

Testing your contract

This part is not absolutely required, but will help us understand how to interact with the contract when is already deployed.

Some things to consider about testing Solidity Smart Contracts in Truffle:

The test we’re going to create for our contract is very simple. We’re going to store a number in the contract, and then we’re going to retrieve it:

// test/SimpleStorage.js

const SimpleStorage = artifacts.require("SimpleStorage.sol");

contract("SimpleStorage", function () {
  it("should return the stored data", async function () {
    const expected = 10;
    const storage = await SimpleStorage.new();
    await storage.updateData(expected);
    const actual = await storage.readData();
    assert(actual.toString() === expected.toString());
  });
});

NOTE

  1. Numbers on JavaScript are floats, and they are much smaller than regular numbers on Smart Contracts. That’s why on your tests the results of contracts are returned as BigNum or bn.js objects. So, on your tests, you have to use the .toString() function, and make comparisons against strings for your asserts to work.

  2. Mocha recommends you use function() {} instead of ()=> {} in the tests since in some asserts use the this object, and assume it to point to the current function.

To run the test you need to execute npx truffle test.

And you get something like:

$ npx truffle test
Using network 'test'.


Compiling your contracts...
___________________________
> Everything is up to date, there is nothing to compile.

  Contract: SimpleStorage
    ‚úì should return the stored data (109ms)

  1 passing (125ms)

Now that we have our test, we can deploy our contract to a block chain. But in order to do that, we need to start up our own blockchain with Ganache. A

Creating contract migrations

So you can think on the blockchain as a database (this is not 100% accurate, but it helps on the learning process) where you have to migrate your contracts much like you migrate tables when you are developing in a Web framework like Laravel or Django. This means that you have to create scripts that instruct the blockchain how to deploy your newly created contracts.

With Truffle, you create your migrations the migrations/ folder and you create them as JavaScript scripts with the convention of create them as numbered files so you migrate them in the right order.

By default Truffle gives you the 1_initial_migration.js file, which you shouldn’t delete, as a managing script for future migrations. To create the migration of our contract we would need to create the migrations/2_simple_storage_migration.js file and place the following code:

// migrations/2_simple_storage.js

const SimpleStorage = artifacts.require("SimpleStorage.sol");

module.exports = (deployer) => {
  deployer.deploy(SimpleStorage);
};

As a side note, if the SimpleStorage object required arguments on the constructor, you could have added it in the deployer line like:

deployer.deploy(SimpleStorage, "fist arg", "second arg");

By default, migration scripts are pretty simple. That’s because we’re creating just one contract that does not depend on other contracts or libraries. If where where to create complex constructors for our contracts we would need to use promises and async/await to execute them.

Now lets get deploy that contract on a local blockchain, but for that lest first creates a local blockchain.

Creating a local development blockchain with Ganache

When you install Truffle you get a built in version of Ganache, which is a local blockchain, that is managed by Truffle. This means that in order to start it up you actually use the truffle command.

Note 5: You can install Ganache by itself in case you want to use the same blockchain for multiple projects

npx truffle develop

This will output something like (notice the change of prompt change at the end):

Truffle Develop started at http://127.0.0.1:9545/

Accounts:
(0) 0x882cfda71609db31b3a017de9d45998f4a6c0eb1
(1) 0x27e61daa454e619330bca0b3644baaba0341746d
(2) 0x4e9867504cc391dbd8f8f65b09feddbe7badb665
(3) 0x0f0599efbdc19aa04c4cfd072e9faef4d3946ed7
(4) 0x67eae8abd1eb0a16f0c2f04f404db7704985b61d
(5) 0xa79d3ec588959781fa272cfdbbf3093371b00ce6
(6) 0x0719f251960775fcd01232426d37a203a6c10af1
(7) 0x65f1f031a79ac6620e1f638d7a89328ae164d5ee
(8) 0x98bdc323eeb8ad9d3619fe1ad69fb3fb1f07b9d2
(9) 0x6205dff8519baabcef1b7dda09d9548db0813586

Private Keys:
(0) 85a29a3cd8e26d66fb71f42255f00d30c099945eeb9f25aa34fb231d91dda358
(1) 5b180395d6cbb8cd798873efc5e10f8b1d94d8ff4e574cad4b9a45b3a4956508
(2) 3328fcf001472901ed7c7cd466774bd865635a64f6465fa9b2799864817cc849
(3) 1e8a0b686291503c90587bef9115866ec362b18b1ff27ea3b3c562fdf102e7bf
(4) 3275940f19298b9cf0181b8eb4cd78ba416ad3108b56e270076ec8e0368c9d5c
(5) 1697c05e7e17d994cceb51409d8263a96aec5679c818ff36418222a68ddd9e28
(6) cfc0fac718890928c1a5275d42072411ffde26427ca33ffc3cb0e8a3652900f6
(7) 7ad066a4c570e10625d5055dfac22c0a83d607d7f2b1e0c750b5f9ac14573e84
(8) 07f112a10055f7cad8a687c0f6ff918de2034a58461d3eb9a44b2059ae323e53
(9) ad5711bd1903266865ba4e743390465a083d53b1f5a8bb9f4ed356987bcc819d

Mnemonic: check guess glad cruise project oven digital couple truck frost estate chuckle

⚠️  Important ⚠️ : This mnemonic was created for you by Truffle. It is not secure.
Ensure you do not use it on production blockchains, or else you risk losing funds.

truffle(develop)>

This means that you just started the blockchain and that is waiting for you to type blockchain specific commands.

There are a few things to notice when you start a Ganache blockchain:

Deploy the contract in the development blockchain

While still in ganache execute the migrate command:

You can use migrate --reset to remove any migration you already have an start from scatch

truffle(develop)> migrate

And this will return the information of the deployment of both the Migration.sol contract as the SimpleStorage.sol contract.

1_initial_migration.js

...

2_simple_storage_migration.js

---

Deploying 'SimpleStorage'

---

> transaction hash: 0xf21ffbca00dafaa46a3e2b39f7aa4e6e533676e2a38c8cc2f180216c5ec24fa4
> Blocks: 0 Seconds: 0
> contract address: 0x9f41eb766f8cDFB7c93107f0061565e838621F11
> block number: 3
> block timestamp: 1641440134
> account: 0x882cfDa71609db31B3A017DE9D45998F4A6c0eb1
> balance: 99.99916596
> gas used: 125653 (0x1ead5)
> gas price: 2 gwei
> value sent: 0 ETH
> total cost: 0.000251306 ETH

> Saving migration to chain.
> Saving artifacts

---

> Total cost: 0.000251306 ETH

Things to notice:

Interacting with the contract

Unfortunately, interacting with the contract like Remix allows you to is not possible. You have to use commands while still in the Ganashe console.

The cool thing is that you can use JavaScript to do it. So creating variables with let or const is possible.

truffle(develop)> let myContract;
undefined
truffle(develop)> myContract = await SimpleStorage.deployed();
undefined
truffle(develop)> myContract.updateData(123);
{
  tx: '0xa63e9cbf3e8a23daf43043c7e3ff609a3f0210be67d387150edf9e77b3ea473c',
  receipt: {
    transactionHash: '0xa63e9cbf3e8a23daf43043c7e3ff609a3f0210be67d387150edf9e77b3ea473c',
    transactionIndex: 0,
    blockHash: '0x24468cf6edebf238c25a3c1f3d44bc41a80f914be02e96e1f298a35ffc92a10f',
    blockNumber: 5,
    from: '0x882cfda71609db31b3a017de9d45998f4a6c0eb1',
    to: '0x9f41eb766f8cdfb7c93107f0061565e838621f11',
    gasUsed: 41602,
    cumulativeGasUsed: 41602,
    contractAddress: null,
    logs: [],
    status: true,
    logsBloom: '0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000',
    rawLogs: []
  },
  logs: []
}
truffle(develop)>

And to read the newly assigned value:

truffle(develop)> myContract.readData();
BN {
  negative: 0,
  words: [ 123, <1 empty item> ],
  length: 1,
  red: null
}

truffle(develop)> const contractValue = await myContract.readData();
undefined
truffle(develop)> contractValue.toString();
'123'
truffle(develop)>

Remember, you are doing this in a local blockchain and not on an real one. That’s why the commands take so little to execute and it’s so “cheap” to make a transaction.

Doing this on a real blockchain can cost you a lot of money.

Extras

There a couple of YouTube videos that show you this process: