UDP Socket Programming in Php – How to Code Client and Server

UDP Sockets in Php

In a previous article we learnt about writing simple server and clients using TCP sockets in php.

In this article we are going to use udp sockets for the same.

UDP sockets are much simpler to work with since they are connection-less.

A udp server just has an socket that waits to receive some data and a socket client can send data on a socket without connection.

UDP Server

So lets code up the server.

<?php

//Reduce errors
error_reporting(~E_WARNING);

//Create a UDP socket
if(!($sock = socket_create(AF_INET, SOCK_DGRAM, 0)))
{
	$errorcode = socket_last_error();
    $errormsg = socket_strerror($errorcode);
    
    die("Couldn't create socket: [$errorcode] $errormsg \n");
}

echo "Socket created \n";

// Bind the source address
if( !socket_bind($sock, "0.0.0.0" , 9999) )
{
	$errorcode = socket_last_error();
    $errormsg = socket_strerror($errorcode);
    
    die("Could not bind socket : [$errorcode] $errormsg \n");
}

echo "Socket bind OK \n";

//Do some communication, this loop can handle multiple clients
while(1)
{
	echo "Waiting for data ... \n";
	
	//Receive some data
	$r = socket_recvfrom($sock, $buf, 512, 0, $remote_ip, $remote_port);
	echo "$remote_ip : $remote_port -- " . $buf;
	
	//Send back the data to the client
	socket_sendto($sock, "OK " . $buf , 100 , 0 , $remote_ip , $remote_port);
}

socket_close($sock);

The above program opens a udp server on port 9999 of localhost.

Run the above program from the terminal and it should show

$ php server.php 
Socket created 
Socket bind OK 
Waiting for data ...

This udp server can handle multiple clients since it does not use a hardbound connection and simply replies to whoever came in.

UDP Client

Now that our server is running fine, its time to code a client program that would connect to the server and communicate.

<?php

/*
	Simple php udp socket client
*/

//Reduce errors
error_reporting(~E_WARNING);

$server = '127.0.0.1';
$port = 9999;

if(!($sock = socket_create(AF_INET, SOCK_DGRAM, 0)))
{
	$errorcode = socket_last_error();
    $errormsg = socket_strerror($errorcode);
    
    die("Couldn't create socket: [$errorcode] $errormsg \n");
}

echo "Socket created \n";

//Communication loop
while(1)
{
	//Take some input to send
	echo 'Enter a message to send : ';
	$input = fgets(STDIN);
	
	//Send the message to the server
	if( ! socket_sendto($sock, $input , strlen($input) , 0 , $server , $port))
	{
		$errorcode = socket_last_error();
		$errormsg = socket_strerror($errorcode);
		
		die("Could not send data: [$errorcode] $errormsg \n");
	}
		
	//Now receive reply from server and print it
	if(socket_recv ( $sock , $reply , 2045 , MSG_WAITALL ) === FALSE)
	{
		$errorcode = socket_last_error();
		$errormsg = socket_strerror($errorcode);
		
		die("Could not receive data: [$errorcode] $errormsg \n");
	}
	
	echo "Reply : $reply";
}

The above client asks user to input some message which is send to the server. Then whatever reply the server sends back is printed.

The output shall be like this

$ php client.php 
Socket created 
Enter a message to send : Hello
Reply : OK Hello
Enter a message to send : World
Reply : OK World
Enter a message to send :

Conclusion

So in the above demonstration we saw how udp sockets can be used in php. UDP sockets are used in those type of network communication where reliability is not very important due to a number of reasons.

The above shown examples are very basic and would need a lot of modification to make ready for suitable use. So try them out.

To learn about the basics of socket programming Php check out this post:
PHP Socket programming Tutorial - How to code Client and Server