PHP implements instant messaging chat message sending function

With the continuous development of the Internet, instant messaging has become the main form of daily communication in modern society. Therefore, the function of sending instant messages and chat messages has become an essential feature of various websites and applications. This article will introduce the steps and precautions for implementing the instant messaging chat message sending function in PHP.

1. Database creation

First, we need to create a database to store real-time data of chat messages. In this article, we take MySQL as an example to create a database named "chat". Then, we create a data table named "messages", which will contain the following fields:

• id: an auto-incrementing integer that serves as the unique identifier of the message
• sender_id: The ID of the sender, used to distinguish different users
• receiver_id: The ID of the receiver, also used to distinguish different users
• content: the content of the message
• created_at: Message creation time, used for subsequent queries

2. User authentication

Before implementing the instant messaging function, we need to ensure that the user has logged in and the session has been successfully authenticated. You can use PHP's Session mechanism to implement user authentication.

3. Chat page

First, we need to create a chat page and add HTML and CSS code. You can use front-end frameworks such as Bootstrap to simplify page design.

Next, we need to call the PHP code in order to render the chat message for the user. We can use the following code to query the chat messages in the database:

SELECT * FROM messages 
WHERE (sender_id = $user_id AND receiver_id = $friend_id)
OR (sender_id = $friend_id AND receiver_id = $user_id)
ORDER BY created_at ASC

where $user_id and $friend_id are the IDs of the user and friend.

4. Message sending function

In order to implement the instant messaging function, we need to write an Ajax script to send data to the server and parse the response without refreshing the entire page.

The core logic of instant messaging chat is the WebSockets protocol, but in this article, we will use Ajax polling to simulate real-time communication.

In the front-end page, we need to use JavaScript code to implement the Ajax request:

$('#send').click(function() {
    var message = $('#message').val();
    $.ajax({
        type: 'POST',
        url: 'send_message.php',
        data: {
            receiver_id: receiver_id,
            content: message,
            csrf_token: csrf_token
        },
        success: function(data) {
            // code for successful execution
        }
    });
});

After sending the message successfully, we need to insert the message into the database:

INSERT INTO messages 
(sender_id, receiver_id, content, created_at) 
VALUES 
($user_id, $friend_id, '$content', NOW())

In subsequent rounds In the query request, we need to query the latest message from the database and then send it back to the front-end page. This can be achieved using the following code:

SELECT * FROM messages 
WHERE (sender_id = $friend_id AND receiver_id = $user_id AND created_at > '$last_update')
ORDER BY created_at ASC

In the above code, $last_update is the timestamp of the last poll.

5. Security

Like many web applications, the chat sending function may also face a series of security issues. For example:

• SQL injection: An attacker may insert executable SQL code in the message, thereby compromising the security of the database. To prevent this type of attack, you can use PHP's prepared statements.
• Cross-site scripting attack (XSS): An attacker may insert executable JavaScript code into a message to steal users' sensitive information. To prevent this type of attack, you should use JavaScript's built-in entity encoding replacement function in your front-end pages.
• Cross-site request forgery (CSRF) attack: An attacker may forge a user's identity and send illegal requests to the server. To prevent this type of attack, you can use tokens and session cookies in your front-end pages.

6. Summary

In this article, we introduced how to use PHP to implement the instant messaging chat message sending function. First, we created a database and rendered the chat page after user authentication. Then, we used Ajax polling and SQL queries to implement instant messaging. Finally, we discuss security issues and provide solutions.

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