PHP uses Socket and EPOLL to send and receive messages in online instant messaging systems

With the continuous development of the Internet, instant messaging (IM) systems have become an indispensable tool in people's lives and work. Among them, how to ensure the rapid transmission and real-time performance of messages has become a crucial part of the system design. This article will introduce how to use PHP's Socket and EPOLL to send and receive messages in an online instant messaging system.

1. Overview of Socket
Socket, or socket, is a way of communicating between computers. It was originally developed by BSD (Berkeley Software Distribution), a startup company of AT&T Bell Labs. It has become one of the technologies that must be mastered in network programming. Through Socket technology, applications can use TCP/IP protocol for network communication to realize data transmission and reception.

2. Overview of EPOLL
EPOLL is an efficient I/O multiplexing mechanism provided by the Linux kernel. In the traditional select and poll mechanism, the entire file descriptor table needs to be traversed for each read and write operation, which is inefficient. EPOLL adopts the method of registering callback functions, which only operates when the data is ready. In comparison, it can improve the concurrency and performance of the system.

3. Use Socket and EPOLL to implement IM system in PHP
1. Server program
In the server program, you can use the socket_create() function to create a new socket resource. The socket_bind() function binds the host name or IP address and port number to associate the socket with the local address. Next, call the socket_listen() function to wait for the client to connect. When there is a connection request, the socket_accept() function is called to receive the connection. At this point, the new connection should be added to the task list.

$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
socket_bind($socket,"0.0.0.0", 8888);
socket_listen($socket);

while(true){

$epoll_events = epoll_wait($epoll, $events, $timeout);
foreach($events as $event){
    if($event['resource'] == $socket){
        $client = socket_accept($socket);
        $client_id = uniqid();
        $client_list[$client_id] = array(
            'socket' => $client,
            'buffer' => '',
        );
        $fd = socket_import_stream($client);
        stream_set_blocking($client, false);
        $event = stream_socket_create($fd, -1);
        stream_set_blocking($event, 0);
        epoll_ctl($epoll, EPOLL_CTL_ADD, $fd, EPOLLIN);
    }

2. Receive messages
Create the epoll object when the program starts, and then add the server socket to its event list. After a new connection is accepted, it can be converted to a file descriptor using stream_socket_create() and then added to the epoll object's event list. And in each event listening loop, use the socket_recv() function to receive messages and store them in the task list.

if($event['events'] & EPOLLIN){

if($event['resource'] == $socket){
    $client = socket_accept($socket);
    $client_id = uniqid();
    $client_list[$client_id] = array(
        'socket' => $client,
        'buffer' => '',
    );
    $fd = socket_import_stream($client);
    stream_set_blocking($client, false);
    $event = stream_socket_create($fd, -1);
    stream_set_blocking($event, 0);
    epoll_ctl($epoll, EPOLL_CTL_ADD, $fd, EPOLLIN);
} else {
    $fd = intval($event['fd']);
    $client_id = array_search($fd, array_column($client_list, 'socket'));
    $buffer = '';
    while(socket_recv($event['resource'], $recv, 1024, MSG_DONTWAIT)){
        $buffer .= $recv;
    }
    $client_list[$client_id]['buffer'] .= $buffer;
}

}

3. Send message
After receiving the message, you can use socket_write() Send the response data to the client.

function send_message($client_id, $message){

global $client_list;
if(isset($client_list[$client_id])){
    $message .= "

";

    socket_write($client_list[$client_id]['socket'], $message, strlen($message));
}

}

4. Summary
By using PHP Socket and With EPOLL technology, we can simply send and receive messages in the IM system, greatly improving the concurrency and performance of the system. At the same time, when designing the IM system, we also need to consider security, data transmission reliability and other aspects. . Therefore, in practical applications, it needs to be adjusted and optimized according to specific needs.

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