Socket Basics

PHP uses the Berkley sockets library to make its connections. You can think of a socket as nothing more than a data structure. You use this socket data structure to start a conversation between a client and a server. The server is always listening to open a new conversation. When a client wants to talk to the server, it opens a conversation through a specific port on which the server is listening. When the server receives the client’s request it completes the connection, thus completing the cycle. Now the client can send information to the server and the server can send information to the client.

To create a socket you will need three variables: a protocol, a socket type, and a common protocol type. There are three protocols that you can choose from when creating a socket. Take a look at Table 10.1 for the names of the protocols and a description of what each protocol does.

When you create your own server you will use the AF_INET protocol. There are five socket types to choose from in the Berkley socket library. Please refer to Table 10.2 for the constant and a description of the socket type.

The final element to creating a socket is to define the type of common protocol that the connection should use. Table 10.3 lists the name and the description of the three common protocol types.

Now that you know the three elements for creating a socket, take a look at the socket_create() function that PHP uses to create a socket. The socket_create() function takes three parameters: a protocol, a socket type, and a common protocol. The socket_create() function returns a resource to the socket if it was created successfully, or it returns false if the socket was not created successfully.

resource socket_create(int protocol, int socketType, int commonProtocol);

Now that you can create a socket, how can you use it? PHP provides several functions to handle sockets. You can bind sockets to an IP, listen for communication on a socket, accept a socket; the list just goes on and on. Start by taking a look at an example to see what functions you will need to create, accept, and listen to a socket.

<?php
$commonProtocol = getprotobyname(“tcp”);

$socket = socket_create(AF_INET, SOCK_STREAM, $commonProtocol);

socket_bind($socket, ‘localhost’, 1337);

socket_listen($socket);

// More socket functionality to come
?>

The example above is a start to creating your own server. The first line of the example,

$commonProtocol = getprotobyname(“tcp”);

gets the protocol type that you are going to use by name. In this case you want to use the TCP common protocol. If you wanted to use UDP or ICMP you would pass “udp” or “icmp” as the parameter to the getprotobyname() function. An alternative to using the getprotobyname() function is specifying either SOL_TCP or SOL_UDP as the final argument to the socket_create() function.

$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);

The second line of the example creates the socket and returns the instance of the socket resource. After you have the instance of the socket resource, you need to bind the socket to a certain port and IP address.

socket_bind($socket, ‘localhost’, 1337);

In this case you are binding the socket to your local computer (127.0.0.1) and you are binding the socket to port 1337. After everything is created and bound you must listen for a connection to come in to the socket.

socket_listen($socket);

These are just four of the functions used in the wonderful world of sockets. Take a look at Table 10.4 to see all the functions that sockets use.

Those are all the functions that PHP offers for use with sockets. You should already have sockets enabled, but if you don’t, then edit the php.ini file and uncomment the line that says:

extension=php_sockets.dll

If you don’t uncomment this line you could load the extension dynamically using the fol-lowing code:

<?php
if(!extension_loaded(‘sockets’))
{
    if(strtoupper(substr(PHP_OS, 3)) == “WIN”)
    {
        dl(‘php_sockets.dll’);
    }
    else
    {
        dl(‘sockets.so’);
    }
}
?>

If you don’t know whether sockets are enabled you can always use the phpinfo() function to determine if sockets are enabled. There should be a section that looks like Figure 10.1.