Review of Popular Ethereum Smart Contract Libraries
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In our previous article (How to Handle Ethereum Messages with Whisper), we discussed how to process Ethereum messages with Whisper.
In this article, we survey the most popular libraries for Ethereum smart contract development
As we have learned so far, developing a secure, reusable, and efficient smart contract is not an easy task. It takes a lot of effort, experience, and testing. Once a smart contract has been deployed to a blockchain, anyone in the blockchain can access it. So, developing a top, secure, and quality smart contract becomes a crucial task for any smart contract developer. Well-tested, reusable, and secured libraries become very important. There are many popular open source Ethereum libraries available, as follows:
OpenZeppelin is one of the most popular libraries, and we'll discuss it in the next section. It provides many handy tokens and utility libraries.
OpenZeppelin is an open source framework for Solidity smart contracts. It is one of the most widely used Solidity libraries that provide reusable, secure, and modular smart contract code. All of this smart contract code is fully tested to follow the best practice security patterns. The framework is maintained by the Zeppelin company.
OpenZeppelin libraries provide many useful smart contracts, including access, crowdsale, cryptography, introspection, life cycle, math, ownership, payment, token, and utils. The following table shows all of the library project structures:
OpenZeppelin libraries |
Description |
access |
Provides role-based access control. |
crowdsale |
Provides token-based crowdsale contract libraries. |
Cryptography |
Provides different cryptographic primitives libraries. |
Introspection |
Provides a set of local and global interfaces. |
Draft |
The contract is currently in testing status by OpenZeppelin. |
Lifecycle |
Provides life cycle management for the contract, and supports pausing and unpausing smart contracts via the pauserRole user. |
math |
Provides math-related utilities. |
ownership |
Provides simple authorization and access control mechanisms. |
payment |
Provides payment-related utilities. |
token |
Provides the most popular ERC token utilities. |
utils |
Provides miscellaneous smart contract utility functions. |
Let's explore some OpenZeppelin libraries to understand how we can use these utilities.
To understand more about OpenZeppelin, let's set up a Truffle project and run a simple example to get started:
npm install truffle npx truffle init
npm install openzeppelin-solidity
This should install the OpenZeppelin library under the node_modules directory. A Truffle project can read all of these Solidity classes by using an import-related class.
In Solidity smart contracts, role-based access control is used to restrict unauthorized users from accessing certain functions. With defined access control policies, the smart contract can build the security rule around roles and privileges.
To use the OpenZeppelin Roles function, you need to import Roles.sol from the OpenZeppelin access folder. Then, you have to define the roles you want to use. In our example, we define an admin and minter role. Here is an example of how we can create an admin role and a minter role:
pragma solidity >=0.4.22 <0.6.0;
import "openzeppelin-solidity/contracts/access/Roles.sol"; contract AclRole {
using Roles for Roles.Role; Roles.Role private admins; Roles.Role private minters;
function onlyAdminRole() view public {
//only admin can use this function
require(admins.has(msg.sender), "You must be admin");
}
function onlyMintersRole() view public {
//only minters can use this function require(minters.has(msg.sender), "You must be minter");
}
function anyone() public {
//anyone can use this function
}
}
In the preceding example, we created two role functions:
Next, let's take a look at math functions.
OpenZeppelin libraries provide that SafeMath contract, which has the add, sub, mul, div, and mod methods so that developers can perform safe math operations. Here is the list of functions:
The add function is equivalent to Solidity's + operator. For example, we can add certain balance values:
balances[msg.sender] = balances[msg.sender].add(_value);
The sub function is equivalent to Solidity's - operator. For example, we can subtract certain balance values:
balances[msg.sender] = balances[msg.sender].sub(_value);
The mul function is equivalent to Solidity's * operator. For example, we can multiply a balance value by two:
balances[msg.sender] = balances[msg.sender].mul(2);
The div function is equivalent to Solidity's / operator. For example, we can divide a balance value by 10:
balances[msg.sender] = balances[msg.sender].div(10);
The mod function is equivalent to Solidity's % operator. For example, if we only charge a multiple of one ether (such as 1eth, 2eth, and so on), we can use the weiUnit mod. After the mod operation, we can find out how much of the remaining ether needs to be returned to the sender:
uint weiUnit = 1 * 10 ** 16;
uint returnAmt = msg.value.mod(weiUnit); uint payAmount = msg.value.sub(returnAmt);
OpenZeppelin libraries provide a set of comprehensive token implementations for ERC20, ERC721, and ERC777. The following screenshot shows the ERC20 implemented by OpenZeppelin libraries. It makes token development much easier and safer:
Let's review ERC20 token libraries.
An ERC20 token keeps track of user address and balance information. The IERC20 interface defines functions and events that all ERC20 tokens must implement:
Let's utilize OpenZeppelin-developed token smart contract to implement our ERC20 token. We will use ERC20 for basic ERC20 implementation. ERC20Detailed is for token detail information such as symbol, name, and decimal.
Here is our SampleToken implementation. You can see how easy it is when we use the openzeppelin token libraries. Let's take a look at the code implementation here:
import "openzeppelin-solidity/contracts/ownership/Ownable.sol"; import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
import "openzeppelin-solidity/contracts/token/ERC20/ERC20Detailed.sol"; contract SampleToken is ERC20, ERC20Detailed, Ownable {
uint256 public initialSupply = 100000000000;
constructor () public ERC20Detailed("SampleToken", "ST", 18) {
_mint(msg.sender, initialSupply);
}
}
We can see that we just need to extend our smart contract from the openzeppelin ERC20 token implementation; you can immediately create your own token by doing this. It makes writing token smart contracts much more straightforward.
The OpenZeppelin util libraries provide address, arrays, and the ReentrancyGuard utility. Address has a function, isContract(address account), which will return true if the account is the contract. Arrays have a function, findUpperBound(uint256[] array, uint256 element), which is a sorted search array and returns the upperBound element (first index) that returns a value larger or equal to the element value. ReentrancyGuard prevents a reentrance call to a function.
Next Article
Now that we finished our forth article series, we move on to our next article series discussing how to create Ethereum private chains. Specifically, we cover the following 12 articles:
This article is written in collaboration with Brian Wu who is a leading author of “Learn Ethereum: Build your own decentralized applications with Ethereum and smart contracts” book. He has written 7 books on blockchain development.
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