IO::Socket::IP(3perl) Perl Programmers Reference Guide IO::Socket::IP(3perl)
NAME
"IO::Socket::IP" - Family-neutral IP socket supporting both IPv4 and
IPv6
SYNOPSIS
use IO::Socket::IP;
my $sock = IO::Socket::IP->new(
PeerHost => "www.google.com",
PeerPort => "http",
Type => SOCK_STREAM,
) or die "Cannot construct socket - $IO::Socket::errstr";
my $familyname = ( $sock->sockdomain == PF_INET6 ) ? "IPv6" :
( $sock->sockdomain == PF_INET ) ? "IPv4" :
"unknown";
printf "Connected to google via %s\n", $familyname;
DESCRIPTION
This module provides a protocol-independent way to use IPv4 and IPv6
sockets, intended as a replacement for IO::Socket::INET. Most
constructor arguments and methods are provided in a backward-compatible
way. For a list of known differences, see the "IO::Socket::INET"
INCOMPATIBILITES section below.
It uses the getaddrinfo(3) function to convert hostnames and service
names or port numbers into sets of possible addresses to connect to or
listen on. This allows it to work for IPv6 where the system supports
it, while still falling back to IPv4-only on systems which don't.
REPLACING "IO::Socket" DEFAULT BEHAVIOUR
By placing "-register" in the import list to "IO::Socket::IP", it will
register itself with IO::Socket as the class that handles "PF_INET". It
will also ask to handle "PF_INET6" as well, provided that constant is
available.
Changing "IO::Socket"'s default behaviour means that calling the
"IO::Socket" constructor with either "PF_INET" or "PF_INET6" as the
"Domain" parameter will yield an "IO::Socket::IP" object.
use IO::Socket::IP -register;
my $sock = IO::Socket->new(
Domain => PF_INET6,
LocalHost => "::1",
Listen => 1,
) or die "Cannot create socket - $IO::Socket::errstr\n";
print "Created a socket of type " . ref($sock) . "\n";
Note that "-register" is a global setting that applies to the entire
program; it cannot be applied only for certain callers, removed, or
limited by lexical scope.
CONSTRUCTORS
new
$sock = IO::Socket::IP->new( %args )
Creates a new "IO::Socket::IP" object, containing a newly created socket
handle according to the named arguments passed. The recognised arguments
are:
PeerHost => STRING
PeerService => STRING
Hostname and service name for the peer to connect() to. The
service name may be given as a port number, as a decimal string.
PeerAddr => STRING
PeerPort => STRING
For symmetry with the accessor methods and compatibility with
"IO::Socket::INET", these are accepted as synonyms for
"PeerHost" and "PeerService" respectively.
PeerAddrInfo => ARRAY
Alternate form of specifying the peer to connect() to. This
should be an array of the form returned by
"Socket::getaddrinfo".
This parameter takes precedence over the "Peer*", "Family",
"Type" and "Proto" arguments.
LocalHost => STRING
LocalService => STRING
Hostname and service name for the local address to bind() to.
LocalAddr => STRING
LocalPort => STRING
For symmetry with the accessor methods and compatibility with
"IO::Socket::INET", these are accepted as synonyms for
"LocalHost" and "LocalService" respectively.
LocalAddrInfo => ARRAY
Alternate form of specifying the local address to bind() to.
This should be an array of the form returned by
"Socket::getaddrinfo".
This parameter takes precedence over the "Local*", "Family",
"Type" and "Proto" arguments.
Family => INT
The address family to pass to "getaddrinfo" (e.g. "AF_INET",
"AF_INET6"). Normally this will be left undefined, and
"getaddrinfo" will search using any address family supported by
the system.
Type => INT
The socket type to pass to "getaddrinfo" (e.g. "SOCK_STREAM",
"SOCK_DGRAM"). Normally defined by the caller; if left undefined
"getaddrinfo" may attempt to infer the type from the service
name.
Proto => STRING or INT
The IP protocol to use for the socket (e.g. 'tcp',
"IPPROTO_TCP", 'udp',"IPPROTO_UDP"). Normally this will be left
undefined, and either "getaddrinfo" or the kernel will choose an
appropriate value. May be given either in string name or numeric
form.
GetAddrInfoFlags => INT
More flags to pass to the getaddrinfo() function. If not
supplied, a default of "AI_ADDRCONFIG" will be used.
These flags will be combined with "AI_PASSIVE" if the "Listen"
argument is given. For more information see the documentation
about getaddrinfo() in the Socket module.
Listen => INT
If defined, puts the socket into listening mode where new
connections can be accepted using the "accept" method. The value
given is used as the listen(2) queue size.
ReuseAddr => BOOL
If true, set the "SO_REUSEADDR" sockopt
ReusePort => BOOL
If true, set the "SO_REUSEPORT" sockopt (not all OSes implement
this sockopt)
Broadcast => BOOL
If true, set the "SO_BROADCAST" sockopt
Sockopts => ARRAY
An optional array of other socket options to apply after the
three listed above. The value is an ARRAY containing 2- or
3-element ARRAYrefs. Each inner array relates to a single
option, giving the level and option name, and an optional value.
If the value element is missing, it will be given the value of a
platform-sized integer 1 constant (i.e. suitable to enable most
of the common boolean options).
For example, both options given below are equivalent to setting
"ReuseAddr".
Sockopts => [
[ SOL_SOCKET, SO_REUSEADDR ],
[ SOL_SOCKET, SO_REUSEADDR, pack( "i", 1 ) ],
]
V6Only => BOOL
If defined, set the "IPV6_V6ONLY" sockopt when creating
"PF_INET6" sockets to the given value. If true, a listening-mode
socket will only listen on the "AF_INET6" addresses; if false it
will also accept connections from "AF_INET" addresses.
If not defined, the socket option will not be changed, and
default value set by the operating system will apply. For
repeatable behaviour across platforms it is recommended this
value always be defined for listening-mode sockets.
Note that not all platforms support disabling this option. Some,
at least OpenBSD and MirBSD, will fail with "EINVAL" if you
attempt to disable it. To determine whether it is possible to
disable, you may use the class method
if( IO::Socket::IP->CAN_DISABLE_V6ONLY ) {
...
}
else {
...
}
If your platform does not support disabling this option but you
still want to listen for both "AF_INET" and "AF_INET6"
connections you will have to create two listening sockets, one
bound to each protocol.
MultiHomed
This "IO::Socket::INET"-style argument is ignored, except if it
is defined but false. See the "IO::Socket::INET"
INCOMPATIBILITES section below.
However, the behaviour it enables is always performed by
"IO::Socket::IP".
Blocking => BOOL
If defined but false, the socket will be set to non-blocking
mode. Otherwise it will default to blocking mode. See the NON-
BLOCKING section below for more detail.
Timeout => NUM
If defined, gives a maximum time in seconds to block per
connect() call when in blocking mode. If missing, no timeout is
applied other than that provided by the underlying operating
system. When in non-blocking mode this parameter is ignored.
Note that if the hostname resolves to multiple address
candidates, the same timeout will apply to each connection
attempt individually, rather than to the operation as a whole.
Further note that the timeout does not apply to the initial
hostname resolve operation, if connecting by hostname.
This behaviour is copied inspired by "IO::Socket::INET"; for
more fine grained control over connection timeouts, consider
performing a nonblocking connect directly.
If neither "Type" nor "Proto" hints are provided, a default of
"SOCK_STREAM" and "IPPROTO_TCP" respectively will be set, to maintain
compatibility with "IO::Socket::INET". Other named arguments that are
not recognised are ignored.
If neither "Family" nor any hosts or addresses are passed, nor any
*AddrInfo, then the constructor has no information on which to decide a
socket family to create. In this case, it performs a "getaddinfo" call
with the "AI_ADDRCONFIG" flag, no host name, and a service name of "0",
and uses the family of the first returned result.
If the constructor fails, it will set $IO::Socket::errstr and $@ to an
appropriate error message; this may be from $! or it may be some other
string; not every failure necessarily has an associated "errno" value.
new (one arg)
$sock = IO::Socket::IP->new( $peeraddr )
As a special case, if the constructor is passed a single argument (as
opposed to an even-sized list of key/value pairs), it is taken to be the
value of the "PeerAddr" parameter. This is parsed in the same way,
according to the behaviour given in the "PeerHost" AND "LocalHost"
PARSING section below.
METHODS
As well as the following methods, this class inherits all the methods in
IO::Socket and IO::Handle.
sockhost_service
( $host, $service ) = $sock->sockhost_service( $numeric )
Returns the hostname and service name of the local address (that is, the
socket address given by the "sockname" method).
If $numeric is true, these will be given in numeric form rather than
being resolved into names.
The following four convenience wrappers may be used to obtain one of the
two values returned here. If both host and service names are required,
this method is preferable to the following wrappers, because it will
call getnameinfo(3) only once.
sockhost
$addr = $sock->sockhost
Return the numeric form of the local address as a textual representation
sockport
$port = $sock->sockport
Return the numeric form of the local port number
sockhostname
$host = $sock->sockhostname
Return the resolved name of the local address
sockservice
$service = $sock->sockservice
Return the resolved name of the local port number
sockaddr
$addr = $sock->sockaddr
Return the local address as a binary octet string
peerhost_service
( $host, $service ) = $sock->peerhost_service( $numeric )
Returns the hostname and service name of the peer address (that is, the
socket address given by the "peername" method), similar to the
"sockhost_service" method.
The following four convenience wrappers may be used to obtain one of the
two values returned here. If both host and service names are required,
this method is preferable to the following wrappers, because it will
call getnameinfo(3) only once.
peerhost
$addr = $sock->peerhost
Return the numeric form of the peer address as a textual representation
peerport
$port = $sock->peerport
Return the numeric form of the peer port number
peerhostname
$host = $sock->peerhostname
Return the resolved name of the peer address
peerservice
$service = $sock->peerservice
Return the resolved name of the peer port number
peeraddr
$addr = $peer->peeraddr
Return the peer address as a binary octet string
as_inet
$inet = $sock->as_inet
Returns a new IO::Socket::INET instance wrapping the same filehandle.
This may be useful in cases where it is required, for backward-
compatibility, to have a real object of "IO::Socket::INET" type instead
of "IO::Socket::IP". The new object will wrap the same underlying
socket filehandle as the original, so care should be taken not to
continue to use both objects concurrently. Ideally the original $sock
should be discarded after this method is called.
This method checks that the socket domain is "PF_INET" and will throw an
exception if it isn't.
NON-BLOCKING
If the constructor is passed a defined but false value for the
"Blocking" argument then the socket is put into non-blocking mode. When
in non-blocking mode, the socket will not be set up by the time the
constructor returns, because the underlying connect(2) syscall would
otherwise have to block.
The non-blocking behaviour is an extension of the "IO::Socket::INET"
API, unique to "IO::Socket::IP", because the former does not support
multi-homed non-blocking connect.
When using non-blocking mode, the caller must repeatedly check for
writeability on the filehandle (for instance using "select" or
"IO::Poll"). Each time the filehandle is ready to write, the "connect"
method must be called, with no arguments. Note that some operating
systems, most notably "MSWin32" do not report a connect() failure using
write-ready; so you must also select() for exceptional status.
While "connect" returns false, the value of $! indicates whether it
should be tried again (by being set to the value "EINPROGRESS", or
"EWOULDBLOCK" on MSWin32), or whether a permanent error has occurred
(e.g. "ECONNREFUSED").
Once the socket has been connected to the peer, "connect" will return
true and the socket will now be ready to use.
Note that calls to the platform's underlying getaddrinfo(3) function may
block. If "IO::Socket::IP" has to perform this lookup, the constructor
will block even when in non-blocking mode.
To avoid this blocking behaviour, the caller should pass in the result
of such a lookup using the "PeerAddrInfo" or "LocalAddrInfo" arguments.
This can be achieved by using Net::LibAsyncNS, or the getaddrinfo(3)
function can be called in a child process.
use IO::Socket::IP;
use Errno qw( EINPROGRESS EWOULDBLOCK );
my @peeraddrinfo = ... # Caller must obtain the getaddinfo result here
my $socket = IO::Socket::IP->new(
PeerAddrInfo => \@peeraddrinfo,
Blocking => 0,
) or die "Cannot construct socket - $@";
while( !$socket->connect and ( $! == EINPROGRESS || $! == EWOULDBLOCK ) ) {
my $wvec = '';
vec( $wvec, fileno $socket, 1 ) = 1;
my $evec = '';
vec( $evec, fileno $socket, 1 ) = 1;
select( undef, $wvec, $evec, undef ) or die "Cannot select - $!";
}
die "Cannot connect - $!" if $!;
...
The example above uses select(), but any similar mechanism should work
analogously. "IO::Socket::IP" takes care when creating new socket
filehandles to preserve the actual file descriptor number, so such
techniques as "poll" or "epoll" should be transparent to its
reallocation of a different socket underneath, perhaps in order to
switch protocol family between "PF_INET" and "PF_INET6".
For another example using "IO::Poll" and "Net::LibAsyncNS", see the
examples/nonblocking_libasyncns.pl file in the module distribution.
PeerHost" AND "LocalHost" PARSING
To support the "IO::Socket::INET" API, the host and port information may
be passed in a single string rather than as two separate arguments.
If either "LocalHost" or "PeerHost" (or their "...Addr" synonyms) have
any of the following special forms then special parsing is applied.
The value of the "...Host" argument will be split to give both the
hostname and port (or service name):
hostname.example.org:http # Host name
192.0.2.1:80 # IPv4 address
[2001:db8::1]:80 # IPv6 address
In each case, the port or service name (e.g. 80) is passed as the
"LocalService" or "PeerService" argument.
Either of "LocalService" or "PeerService" (or their "...Port" synonyms)
can be either a service name, a decimal number, or a string containing
both a service name and number, in a form such as
http(80)
In this case, the name ("http") will be tried first, but if the resolver
does not understand it then the port number (80) will be used instead.
If the "...Host" argument is in this special form and the corresponding
"...Service" or "...Port" argument is also defined, the one parsed from
the "...Host" argument will take precedence and the other will be
ignored.
split_addr
( $host, $port ) = IO::Socket::IP->split_addr( $addr )
Utility method that provides the parsing functionality described above.
Returns a 2-element list, containing either the split hostname and port
description if it could be parsed, or the given address and "undef" if
it was not recognised.
IO::Socket::IP->split_addr( "hostname:http" )
# ( "hostname", "http" )
IO::Socket::IP->split_addr( "192.0.2.1:80" )
# ( "192.0.2.1", "80" )
IO::Socket::IP->split_addr( "[2001:db8::1]:80" )
# ( "2001:db8::1", "80" )
IO::Socket::IP->split_addr( "something.else" )
# ( "something.else", undef )
join_addr
$addr = IO::Socket::IP->join_addr( $host, $port )
Utility method that performs the reverse of "split_addr", returning a
string formed by joining the specified host address and port number. The
host address will be wrapped in "[]" brackets if required (because it is
a raw IPv6 numeric address).
This can be especially useful when combined with the "sockhost_service"
or "peerhost_service" methods.
say "Connected to ", IO::Socket::IP->join_addr( $sock->peerhost_service );
IO::Socket::INET" INCOMPATIBILITES
• The behaviour enabled by "MultiHomed" is in fact implemented by
"IO::Socket::IP" as it is required to correctly support searching
for a useable address from the results of the getaddrinfo(3) call.
The constructor will ignore the value of this argument, except if it
is defined but false. An exception is thrown in this case, because
that would request it disable the getaddrinfo(3) search behaviour in
the first place.
• "IO::Socket::IP" implements both the "Blocking" and "Timeout"
parameters, but it implements the interaction of both in a different
way.
In "::INET", supplying a timeout overrides the non-blocking
behaviour, meaning that the connect() operation will still block
despite that the caller asked for a non-blocking socket. This is not
explicitly specified in its documentation, nor does this author
believe that is a useful behaviour - it appears to come from a quirk
of implementation.
In "::IP" therefore, the "Blocking" parameter takes precedence - if
a non-blocking socket is requested, no operation will block. The
"Timeout" parameter here simply defines the maximum time that a
blocking connect() call will wait, if it blocks at all.
In order to specifically obtain the "blocking connect then non-
blocking send and receive" behaviour of specifying this combination
of options to "::INET" when using "::IP", perform first a blocking
connect, then afterwards turn the socket into nonblocking mode.
my $sock = IO::Socket::IP->new(
PeerHost => $peer,
Timeout => 20,
) or die "Cannot connect - $@";
$sock->blocking( 0 );
This code will behave identically under both "IO::Socket::INET" and
"IO::Socket::IP".
TODO
• Investigate whether "POSIX::dup2" upsets BSD's "kqueue" watchers,
and if so, consider what possible workarounds might be applied.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
perl v5.40.1 2026-08-30 IO::Socket::IP(3perl)
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