use IO::Socket;
"IO::Socket" only defines methods for those operations which are common to all types of socket. Operations which are specified to a socket in a particular domain have methods defined in sub classes of "IO::Socket"
"IO::Socket" will export all functions (and constants) defined by Socket.
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As of VERSION 1.18 all IO::Socket objects have autoflush turned on by default. This was not the case with earlier releases.
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socket
socketpair
bind
listen
accept
send
recv
peername (getpeername)
sockname (getsockname)
shutdown
Some methods take slightly different arguments to those defined in perlfunc in attempt to make the interface more flexible. These are
In a scalar context the new socket is returned, or undef upon failure. In a list context a two-element array is returned containing the new socket and the peer address; the list will be empty upon failure.
The timeout in the [PKG] can be specified as zero to effect a ``poll'', but you shouldn't do that because a new IO::Select object will be created behind the scenes just to do the single poll. This is horrendously inefficient. Use rather true select() with a zero timeout on the handle, or non-blocking IO.
Additional methods that are provided are:
use IO::Socket;
my $sock = IO::Socket::INET->new('some_server');
$sock->read($data, 1024) until $sock->atmark;
Note: this is a reasonably new addition to the family of socket functions, so all systems may not support this yet. If it is unsupported by the system, an attempt to use this method will abort the program.
The atmark() functionality is also exportable as sockatmark() function:
use IO::Socket 'sockatmark';
This allows for a more traditional use of sockatmark() as a procedural socket function. If your system does not support sockatmark(), the "use" declaration will fail at compile time.
Note that connected() considers a half-open TCP socket to be ``in a connected state''. Specifically, connected() does not distinguish between the ESTABLISHED and CLOSE-WAIT TCP states; it returns the peer address, rather than undef, in either case. Thus, in general, connected() cannot be used to reliably learn whether the peer has initiated a graceful shutdown because in most cases (see below) the local TCP state machine remains in CLOSE-WAIT until the local application calls shutdown() or close(); only at that point does connected() return undef.
The ``in most cases'' hedge is because local TCP state machine behavior may depend on the peer's socket options. In particular, if the peer socket has SO_LINGER enabled with a zero timeout, then the peer's close() will generate a RST segment, upon receipt of which the local TCP transitions immediately to CLOSED, and in that state, connected() will return undef.
The atmark() implementation: Copyright 2001, Lincoln Stein <lstein@cshl.org>. This module is distributed under the same terms as Perl itself. Feel free to use, modify and redistribute it as long as you retain the correct attribution.