|
Chapter 13 Sockets |
|
The IO::Socket module included in the core Perl distribution provides an object-oriented approach to socket programming. This module provides a convenient way to handle the large number of options you have to deal with, and it handles the laborious task of forming addresses. IO::Socket is built upon the Socket module provided in the standard library. It inherits from IO::Handle, which supports a class of filehandle objects for much of the IO library. The following IO::Socket functions are simply frontends for the corresponding built-in functions and use the same syntax:
Thesocket socketpair bind listen send recv peername (same as getpeername) sockname (same as getsockname)
accept
function in IO::Socket is slightly different from the equivalent function, however, and is described later in the chapter.
IO:Socket contains two subclasses: INET and UNIX. The INET subclass is used to create and manipulate Internet-domain sockets, such as the ones used in the examples. The UNIX subclass creates Unix domain sockets.
IO::Socket greatly simplifies the implementation of a socket for client communications. The following example creates an Internet-domain socket (using the INET subclass) and attempts to connect to the specified server:
use IO::Socket; $sock = new IO::Socket::INET (PeerAddr => 'www.ora.com', PeerPort => 80, Proto => 'tcp'); die "$!" unless $sock;
IO::Socket::INET::new
creates an object containing a socket filehandle and connects it to the host and port specified in
PeerAddr
and
PeerPort
. The object
$sock
can then be written to and read from like other socket filehandles.
On the server side, IO::Socket provides a nice wrapper for creating server sockets. The wrapper encompasses the
socket
,
bind
, and
listen
procedures, while creating a new IO::Socket object. For example, we can create an Internet-domain socket with
IO::Socket::INET
:
The parameters for the new socket object determine whether it is a server or a client socket. Because we're creating a server socket,use IO::Socket; $sock = new IO::Socket::INET (LocalAddr => 'maude.ora.com', LocalPort => 8888, Proto => 'tcp', Listen => 5); die "$!" unless $sock;
LocalAddr
and
LocalPort
provide the address and port to bind to the socket. The
Listen
parameter gives the queue size for the number of client requests that can wait for an
accept
at any one time.
When the server receives a client request, it calls the
accept
method on the socket object. This creates a new socket object on which the rest of the communication can take place:
When communication is finished on both client and server sockets, they should be destroyed with$new_sock = $sock->accept();
close
. If a socket is not properly closed, the next time you attempt to use a socket with the same name, the system will complain that the socket is already in use.
The following methods are defined in IO::Socket and can be used on socket objects of either the INET or UNIX class:
An Internet-domain socket is created with the
new
method from the IO::Socket::INET subclass. The constructor can take the following options:
PeerAddr =>
hostname
[:
port
]
Specifies the remote host and optional port number for a client connection.
hostname
can be either a name, like
www.oreilly.com
, or an IP number of the form 207.44.21.2.
PeerPort =>
port
Specifies the port number on the remote host for a client connection. The name of the service (such as
http
or
nntp
) may be used for the argument if the port number is not known.
LocalAddr =>
hostname
[:
port
]
Specifies the local address (and optional port number) to bind to a server-side socket.
LocalPort =>
port
Specifies the local port number (or service name) to bind to a server-side socket.
Proto =>
name
Specifies the protocol to be run on the socket, i.e.,
tcp
or
udp
.
Type => SOCK_STREAM | SOCK_DGRAM
Specifies the type of socket.
SOCK_STREAM
indicates a stream-based socket connection, and
SOCK_DGRAM
indicates a message-based (datagram) connection.
Listen =>
n
Reuse => 1
Given a non-zero number, this option allows the local bind address to be reused should the socket need to be reopened after an error.
Timeout =>
n
Whether a server (receiving) or client (requesting) socket is created depends on the parameters provided to the constructor. If
Listen
is defined, a server socket is automatically created. If no protocol is specified, it is derived from the service on the given port number. If no port number is given,
tcp
is used by default.
The IO::Socket::UNIX subclass creates a Unix-domain socket. Unix-domain sockets are local to the current host and are used internally to implement pipes, thus providing communication between unrelated processes. Using sockets provides finer control than using named pipes, also called FIFO (first-in, first-out) buffers. This is because receiving sockets can distinguish between different client connections, which can then be assigned to different sessions with the
accept
call.
The IO::Socket::UNIX constructor (
new()
) creates the socket and returns an object containing a filehandle. The constructor can take the following options:
Type => SOCK_STREAM | SOCK_DGRAM
Indicates the type of socket:
SOCK_STREAM
for streaming,
SOCK_DGRAM
for packets or datagrams.
Local =>
pathname
Provides the pathname of the FIFO buffer to bind to the socket.
Peer =>
pathname
Listen =>
n
The following methods can be used on an object created with IO::Socket::UNIX.
|
|
|
|
| 13.1 Built-in Socket Functions |
|
14. Email Connectivity |