Socket Programming in PHP

Introduction

Sockets are used for interprocess communication. Interprocess communication is generally based on client-server model. In this case, client-server are the applications that interact with each other. Interaction between client and server requires a connection. Socket programming is responsible for establishing that connection between applications to interact.

By the end of this tip, we will learn how to create a simple client-server in PHP. We will also learn how client application sends message to server and receives it from the same.

Using the Code

Aim: Develop a client to send a string message to server and server to return reverse of the same message to client.

PHP SERVER

Step 1: Set variables such as "host" and "port"

$host = "127.0.0.1";
$port = 5353;
// No Timeout 
set_time_limit(0);

Port number can be any positive integer between 1024 -65535.

Step 2: Create Socket

$socket = socket_create(AF_INET, SOCK_STREAM, 0) or die("Could not create socket\n");

Step 3: Bind the socket to port and host

Here the created socket resource is bound to IP address and port number.

$result = socket_bind($socket, $host, $port) or die("Could not bind to socket\n");

Step 4: Start listening to the socket

After getting bound with IP and port server waits for the client to connect. Till then it keeps on waiting.

$result = socket_listen($socket, 3) or die("Could not set up socket listener\n");

Step 5: Accept incoming connection

This function accepts incoming connection request on the created socket. After accepting the connection from client socket, this function returns another socket resource that is actually responsible for communication with the corresponding client socket. Here “$spawn” is that socket resource which is responsible for communication with client socket.

$spawn = socket_accept($socket) or die("Could not accept incoming connection\n");

So far, we have prepared our server socket but the script doesn't actually do anything. Keeping to our aforesaid aim, we will read message from client socket and then send back reverse of the received message to the client socket again.

Step 6: Read the message from the Client socket

$input = socket_read($spawn, 1024) or die("Could not read input\n");

Step 7: Reverse the message

$output = strrev($input) . "\n";

Step 8: Send message to the client socket

socket_write($spawn, $output, strlen ($output)) or die("Could not write output\n"); 

Close the socket

socket_close($spawn);
socket_close($socket);

This completes with the server. Now we will learn to create PHP client.

PHP CLIENT

The first two steps are the same as in the server.

Step 1: Set variables such as "host" and "port"

$host = "127.0.0.1";
$port = 5353;
// No Timeout 
set_time_limit(0);

Note: Here the port and host should be same as defined in server.

Step 2: Create Socket

$socket = socket_create(AF_INET, SOCK_STREAM, 0) or die("Could not create socket\n");

Step 3: Connect to the server

$result = socket_connect($socket, $host, $port) or die("Could not connect toserver\n");

Here unlike server, client socket is not bound with port and host. Instead it connects to server socket, waiting to accept the connection from client socket. Connection of client socket to server socket is established in this step.

Step 4: Write to server socket

socket_write($socket, $message, strlen($message)) or die("Could not send data to server\n");

In this step, client socket data is sent to the server socket.

Step 5: Read the response from the server

$result = socket_read ($socket, 1024) or die("Could not read server response\n");
echo "Reply From Server  :".$result;

Step 6: Close the socket

socket_close($socket);

Complete Code

SERVER (server.php)

// set some variables
$host = "127.0.0.1";
$port = 25003;
// don't timeout!
set_time_limit(0);
// create socket
$socket = socket_create(AF_INET, SOCK_STREAM, 0) or die("Could not create socket\n");
// bind socket to port
$result = socket_bind($socket, $host, $port) or die("Could not bind to socket\n");
// start listening for connections
$result = socket_listen($socket, 3) or die("Could not set up socket listener\n");

// accept incoming connections
// spawn another socket to handle communication
$spawn = socket_accept($socket) or die("Could not accept incoming connection\n");
// read client input
$input = socket_read($spawn, 1024) or die("Could not read input\n");
// clean up input string
$input = trim($input);
echo "Client Message : ".$input;
// reverse client input and send back
$output = strrev($input) . "\n";
socket_write($spawn, $output, strlen ($output)) or die("Could not write output\n");
// close sockets
socket_close($spawn);
socket_close($socket);

CLIENT (client.php)

$host    = "127.0.0.1";
$port    = 25003;
$message = "Hello Server";
echo "Message To server :".$message;
// create socket
$socket = socket_create(AF_INET, SOCK_STREAM, 0) or die("Could not create socket\n");
// connect to server
$result = socket_connect($socket, $host, $port) or die("Could not connect to server\n");  
// send string to server
socket_write($socket, $message, strlen($message)) or die("Could not send data to server\n");
// get server response
$result = socket_read ($socket, 1024) or die("Could not read server response\n");
echo "Reply From Server  :".$result;
// close socket
socket_close($socket);

After creating the above files (server.php and client.php), do as follows:

1. Copy these files in www directory (in case of WAMP), located at C:\wamp.
2. Open your web browser and type localhost in the address bar.
3. Browse server.php first followed by client.php.