Open Connection
The basic function to open a socket connection is fsockopen(). You can establish a connection in just one line of PHP code, pretty simple uh?

//this method will open a connection and store a file handler to $fp variable,
//you can use fgets/fputs on it then later,
//if something goes wrong, you can check $errno and $errdesc variable
$fp=fsockopen("www.host.com",80,$errno,$errdesc);

After we established a connection, let’s close it by using fclose() method.

$fp=fsockopen("www.host.com",80,$errno,$errdesc);
fclose($fp);

Sending a Request
Now I will show you how to send a data (request) to a server and then check the response returned by the server. Once we open a socket, you can send any data to it, and wait for the response.

$fp=fsockopen("www.host.com",80,$errno,$errdesc) or
die("Connection to www.host.com failed");

$request="GET / HTTP/1.1\r\n";
$request.="Host: www.host.com\r\n";
$request.="Referer: www.host.com\r\n";
$request.="Connection: close\r\n";
$request.="\r\n";

fputs($fp,$request); //send the request

while(!feof($fp)){
	$lines[] = fgets($fp, 1024);
}
foreach($lines as $line){ //display each lines
	$line=htmlentities($line);
	echo "LINE:".$line."";
}

fclose($socket); //don't forget to close connection

Using Socket in PHP – POP3 Email Example
Here is an example of socket connection to check POP3 email.

function sendcommand($fp,$command){
	$response="";
	fputs($fp, $command);
	$response=fgets($fp,1024);
	return $response;
}

function checkmail(){
	$host="pop.host.com"; //PHP also support secure connection
			      //you can add "tls://" or "ssl://"
			      //to create secure connection
	$port=110;
	$username="username";
	$password="password";

	$fp=fsockopen($host,$port,$errno,$errstr,10);

	$command="USER ".$username."\r\n"; //send username
	$response=sendcommand($fp,$command);
	echo "LINE:".$response."";
	$command="PASS ".$password."\r\n"; //send password
	$response=sendcommand($fp,$command);
	echo "LINE:".$response."";
	if(strstr($response,"+OK")!=""){ //accepted
		$command="LIST"."\r\n";
		$response=sendcommand($fp,$command);
		echo "LINE:".$response."";
	}
	$command="QUIT"."\r\n";
	$response=sendcommand($fp,$command);
	echo "LINE:".$response."";

	fclose($fp);
}

checkmail();

Now you have learned how to use socket in PHP, you can extend the usage for many purpose, like getting information from another web, query to whois server, check pop3/imap mail, instant messaging, online ftp client, and many more. And the most important thing, it is easy to implement.

Good luck on experimenting!

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