- Introduction
- Smart Contract Design
- User Registration
- Creating Posts
- Interacting with Posts
- Viewing Posts and Comments
- Complete Code
- Setting up Remix for CELO Alfajores
- Basic understanding of Solidity programming language
- Celo testnet faucet faucet
- Access to Remix IDE Remix
In this article, you will learn how to develop a decentralized social media platform. Leveraging the power of the most powerful smart contracts language, Solidity, and the user-friendly Remix IDE, we will explore the process of developing and deploying this blockchain-based social media ecosystem.
Throughout this guide, we will give a deep dive into the fundamental aspects of writing smart contracts. We will handle user registration, post creation, interaction mechanisms such as liking and commenting, and finally, setting up Remix for deployment on the CELO Alfajores network.
contract SocialMedia {
address public owner;
struct User {
string username;
address userAddress;
bool isRegistered;
}
mapping(address => User) public users;
struct Post {
address author;
string content;
uint256 timestamp;
uint256 likes;
uint256 commentsCount;
}
struct Comment {
address commenter;
string content;
uint256 timestamp;
}
mapping(uint256 => mapping(uint256 => Comment)) public postComments;
mapping(uint256 => uint256) public postCommentsCount;
Post[] public posts;
}The SocialMedia contract facilitates interactions on the decentralized social media platform. It stores user information, posts, and comments.
The User struct represents registered users on the platform, containing fields for username, address, and registration status.
The Post struct stores information about each post, including the author's address, content, timestamp, number of likes, and an array of comments.
The Comment struct represents individual comments, containing fields for the commenter's address, content, and timestamp.
The postComments mapping is used to store comments for each post where the first key is the post's index, and the second key is the comment's index.
The postCommentsCount mapping keeps track of the number of comments for each post.
The posts array stores instances of the Post struct, representing individual posts on the decentralized social media platform.
event UserRegistered(address indexed userAddress, string username);This event is emitted when a new user is successfully registered on the platform. It returns the registered user's address (userAddress) and the chosen username (username).
event PostCreated(address indexed author, string content, uint256 timestamp);This event is emitted when a new post is created by a user on the platform. It returns the address of the post's author (author), the content of the post (content), and the timestamp of creation (timestamp).
event PostLiked(address indexed liker, uint256 indexed postId);This event is emitted when a user likes a post on the platform. It provides visibility into user engagement and returns
the address of the user who liked the post (liker) and the index of the liked post (postId).
event CommentAdded(address indexed commenter, uint256 indexed postId, string content, uint256 timestamp);This event is emitted when a user adds a comment to a post on the platform and returns the address of the commenter (commenter), the index of the post being commented on (postId), the content of the comment (content), and the timestamp of comment creation (timestamp).
modifier onlyRegisteredUser() {
require(users[msg.sender].isRegistered, "User is not registered");
_;
}This modifier restricts access to functions to only registered users on the platform and ensures that only users who have completed the registration process can perform certain actions, such as creating posts or adding comments. If an unregistered user attempts to call a function with this modifier, the transaction will be reverted with an error message indicating that the user is not registered.
modifier onlyOwner() {
require(msg.sender == owner, "Only owner can call this function");
_;
}This modifier restricts access to functions to the contract owner. It grants special privileges to the contract owner, such as administrative functions or contract upgrades. If a caller who is not the contract owner attempts to call a function with this modifier, the transaction will be reverted with an error message indicating that only the owner can call the function.
constructor() {
owner = msg.sender;
}Constructor is a special function that is executed only once during contract deployment. In this contract, the constructor initializes the contract owner to the address of the deployer (msg.sender).
function registerUser(string memory _username) external {
require(!users[msg.sender].isRegistered, "User is already registered");
require(bytes(_username).length > 0, "Username should not be empty");
users[msg.sender] = User({
username: _username,
userAddress: msg.sender,
isRegistered: true
});
emit UserRegistered(msg.sender, _username);
}This function ensures that users can register on the platform with a unique username and provides transparency by emitting an event upon successful registration. Additionally, it enforces security by verifying that the user is not already registered and that the provided username is not empty.
function createPost(string memory _content) external onlyRegisteredUser {
require(bytes(_content).length > 0, "Content should not be empty");
posts.push(Post({
author: msg.sender,
content: _content,
timestamp: block.timestamp,
likes: 0,
commentsCount: 0
}));
emit PostCreated(msg.sender, _content, block.timestamp);
}This function ensures that registered users can create posts with non-empty content and provides transparency by emitting an event upon successful post creation. Additionally, it enforces security by restricting access to registered users only.
function likePost(uint256 _postId) external onlyRegisteredUser {
require(_postId < posts.length, "Post does not exist");
Post storage post = posts[_postId];
post.likes++;
emit PostLiked(msg.sender, _postId);
}This function ensures that registered users can like posts and emit an event upon successful post like. Also, it enforces security by restricting access to registered users only and ensuring that the specified post exists before allowing a like action.
function addComment(uint256 _postId, string memory _content) external onlyRegisteredUser {
require(_postId < posts.length, "Post does not exist");
require(bytes(_content).length > 0, "Comment should not be empty");
uint256 commentId = postCommentsCount[_postId];
postComments[_postId][commentId] = Comment({
commenter: msg.sender,
content: _content,
timestamp: block.timestamp
});
postCommentsCount[_postId]++;
posts[_postId].commentsCount++;
emit CommentAdded(msg.sender, _postId, _content, block.timestamp);
}This function ensures that registered users can add comments to posts and emit an event upon successful comment addition. Also, it enforces security by restricting access to registered users only and ensuring that the specified post exists before allowing a comment action.
function getPost(uint256 _postId) external view returns (
address author,
string memory content,
uint256 timestamp,
uint256 likes,
uint256 commentsCount
) {
require(_postId < posts.length, "Post does not exist");
Post memory post = posts[_postId];
return (post.author, post.content, post.timestamp, post.likes, post.commentsCount);
}This function provides a convenient way for users to retrieve essential information about posts on the platform. It verifies that the specified post exists before returning its information.
function getComment(uint256 _postId, uint256 _commentId) external view returns (
address commenter,
string memory content,
uint256 timestamp
) {
require(_postId < posts.length, "Post does not exist");
require(_commentId < postCommentsCount[_postId], "Comment does not exist");
Comment memory comment = postComments[_postId][_commentId];
return (comment.commenter, comment.content, comment.timestamp);
}This function provides an easy way for users to retrieve essential information about comments on posts. It enforces security by verifying that both the specified post and comment exist before returning the comment's information.
function getPostsCount() external view returns (uint256) {
return posts.length;
}This function provides a simple and efficient way for users to query the total number of posts on the platform. It is useful for displaying statistics about the platform's activity and engagement.
This is the complete code for this decentralized social contract.
// SPDX-License-Identifier: MIT
pragma solidity 0.8.0;
contract SocialMedia {
address public owner;
struct User {
string username;
address userAddress;
bool isRegistered;
}
mapping(address => User) public users;
struct Post {
address author;
string content;
uint256 timestamp;
uint256 likes;
uint256 commentsCount;
}
struct Comment {
address commenter;
string content;
uint256 timestamp;
}
mapping(uint256 => mapping(uint256 => Comment)) public postComments;
mapping(uint256 => uint256) public postCommentsCount;
Post[] public posts;
event UserRegistered(address indexed userAddress, string username);
event PostCreated(address indexed author, string content, uint256 timestamp);
event PostLiked(address indexed liker, uint256 indexed postId);
event CommentAdded(address indexed commenter, uint256 indexed postId, string content, uint256 timestamp);
modifier onlyRegisteredUser() {
require(users[msg.sender].isRegistered, "User is not registered");
_;
}
modifier onlyOwner() {
require(msg.sender == owner, "Only owner can call this function");
_;
}
constructor() {
owner = msg.sender;
}
function registerUser(string memory _username) external {
require(!users[msg.sender].isRegistered, "User is already registered");
require(bytes(_username).length > 0, "Username should not be empty");
users[msg.sender] = User({
username: _username,
userAddress: msg.sender,
isRegistered: true
});
emit UserRegistered(msg.sender, _username);
}
function createPost(string memory _content) external onlyRegisteredUser {
require(bytes(_content).length > 0, "Content should not be empty");
posts.push(Post({
author: msg.sender,
content: _content,
timestamp: block.timestamp,
likes: 0,
commentsCount: 0
}));
emit PostCreated(msg.sender, _content, block.timestamp);
}
function likePost(uint256 _postId) external onlyRegisteredUser {
require(_postId < posts.length, "Post does not exist");
Post storage post = posts[_postId];
post.likes++;
emit PostLiked(msg.sender, _postId);
}
function addComment(uint256 _postId, string memory _content) external onlyRegisteredUser {
require(_postId < posts.length, "Post does not exist");
require(bytes(_content).length > 0, "Comment should not be empty");
uint256 commentId = postCommentsCount[_postId];
postComments[_postId][commentId] = Comment({
commenter: msg.sender,
content: _content,
timestamp: block.timestamp
});
postCommentsCount[_postId]++;
posts[_postId].commentsCount++;
emit CommentAdded(msg.sender, _postId, _content, block.timestamp);
}
function getPostsCount() external view returns (uint256) {
return posts.length;
}
function getPost(uint256 _postId) external view returns (
address author,
string memory content,
uint256 timestamp,
uint256 likes,
uint256 commentsCount
) {
require(_postId < posts.length, "Post does not exist");
Post memory post = posts[_postId];
return (post.author, post.content, post.timestamp, post.likes, post.commentsCount);
}
function getComment(uint256 _postId, uint256 _commentId) external view returns (
address commenter,
string memory content,
uint256 timestamp
) {
require(_postId < posts.length, "Post does not exist");
require(_commentId < postCommentsCount[_postId], "Comment does not exist");
Comment memory comment = postComments[_postId][_commentId];
return (comment.commenter, comment.content, comment.timestamp);
}
}
Go to your web browser and open remix IDE. You should see a similar interface like below :
Click on contracts folder and create a new file named Social.sol then paste the full code in the file.
On the left tab, click on compile icon.
Next, click on compile Social.sol to compile your contract.
Upon successful compilation of your contracts, you should see a green checkmark like below :
Now, proceed to deploy your contract by clicking on deploy and run transactions icon on the left side bar.
Before you proceed, ensure you have connected Metamask or the provider you are using to CELO alfajores. You can follow this guide to connect CELO to Metamask.
Next, select injected provider under your environments to connect to Metamask and click on deploy button.
Upon successful deployment of your contract, your interface should look like below :
Congratulations! You have successfully written a decentralized social media platform smart contract and deployed it to CELO on Remix