NAME¶
"Socket" - networking constants and support functions
SYNOPSIS¶
"Socket" a low-level module used by, among other things, the
IO::Socket family of modules. The following examples demonstrate some
low-level uses but a practical program would likely use the higher-level API
provided by "IO::Socket" or similar instead.
use Socket qw(PF_INET SOCK_STREAM pack_sockaddr_in inet_aton);
socket(my $socket, PF_INET, SOCK_STREAM, 0)
or die "socket: $!";
my $port = getservbyname "echo", "tcp";
connect($socket, pack_sockaddr_in($port, inet_aton("localhost")))
or die "connect: $!";
print $socket "Hello, world!\n";
print <$socket>;
See also the "EXAMPLES" section.
DESCRIPTION¶
This module provides a variety of constants, structure manipulators and other
functions related to socket-based networking. The values and functions
provided are useful when used in conjunction with Perl core functions such as
socket(),
setsockopt() and
bind(). It also provides
several other support functions, mostly for dealing with conversions of
network addresses between human-readable and native binary forms, and for
hostname resolver operations.
Some constants and functions are exported by default by this module; but for
backward-compatibility any recently-added symbols are not exported by default
and must be requested explicitly. When an import list is provided to the
"use Socket" line, the default exports are not automatically
imported. It is therefore best practice to always to explicitly list all the
symbols required.
Also, some common socket "newline" constants are provided: the
constants "CR", "LF", and "CRLF", as well as
$CR, $LF, and $CRLF, which map to "\015", "\012", and
"\015\012". If you do not want to use the literal characters in your
programs, then use the constants provided here. They are not exported by
default, but can be imported individually, and with the ":crlf"
export tag:
use Socket qw(:DEFAULT :crlf);
$sock->print("GET / HTTP/1.0$CRLF");
The entire
getaddrinfo() subsystem can be exported using the tag
":addrinfo"; this exports the
getaddrinfo() and
getnameinfo() functions, and all the "AI_*",
"NI_*", "NIx_*" and "EAI_*" constants.
CONSTANTS¶
In each of the following groups, there may be many more constants provided than
just the ones given as examples in the section heading. If the heading ends
"..." then this means there are likely more; the exact constants
provided will depend on the OS and headers found at compile-time.
PF_INET, PF_INET6, PF_UNIX, ...¶
Protocol family constants to use as the first argument to
socket() or the
value of the "SO_DOMAIN" or "SO_FAMILY" socket option.
AF_INET, AF_INET6, AF_UNIX, ...¶
Address family constants used by the socket address structures, to pass to such
functions as
inet_pton() or
getaddrinfo(), or are returned by
such functions as
sockaddr_family().
SOCK_STREAM, SOCK_DGRAM, SOCK_RAW, ...¶
Socket type constants to use as the second argument to
socket(), or the
value of the "SO_TYPE" socket option.
SOCK_NONBLOCK. SOCK_CLOEXEC¶
Linux-specific shortcuts to specify the "O_NONBLOCK" and
"FD_CLOEXEC" flags during a
socket(2) call.
socket( my $sockh, PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, 0 )
SOL_SOCKET¶
Socket option level constant for
setsockopt() and
getsockopt().
SO_ACCEPTCONN, SO_BROADCAST, SO_ERROR, ...¶
Socket option name constants for
setsockopt() and
getsockopt() at
the "SOL_SOCKET" level.
IP_OPTIONS, IP_TOS, IP_TTL, ...¶
Socket option name constants for IPv4 socket options at the
"IPPROTO_IP" level.
IPTOS_LOWDELAY, IPTOS_THROUGHPUT, IPTOS_RELIABILITY, ...¶
Socket option value constants for "IP_TOS" socket option.
MSG_BCAST, MSG_OOB, MSG_TRUNC, ...¶
Message flag constants for
send() and
recv().
SHUT_RD, SHUT_RDWR, SHUT_WR¶
Direction constants for
shutdown().
INADDR_ANY, INADDR_BROADCAST, INADDR_LOOPBACK, INADDR_NONE¶
Constants giving the special "AF_INET" addresses for wildcard,
broadcast, local loopback, and invalid addresses.
Normally equivalent to inet_aton('0.0.0.0'), inet_aton('255.255.255.255'),
inet_aton('localhost') and inet_aton('255.255.255.255') respectively.
IPPROTO_IP, IPPROTO_IPV6, IPPROTO_TCP, ...¶
IP protocol constants to use as the third argument to
socket(), the level
argument to
getsockopt() or
setsockopt(), or the value of the
"SO_PROTOCOL" socket option.
TCP_CORK, TCP_KEEPALIVE, TCP_NODELAY, ...¶
Socket option name constants for TCP socket options at the
"IPPROTO_TCP" level.
IN6ADDR_ANY, IN6ADDR_LOOPBACK¶
Constants giving the special "AF_INET6" addresses for wildcard and
local loopback.
Normally equivalent to inet_pton(AF_INET6, "::") and
inet_pton(AF_INET6, "::1") respectively.
IPV6_ADD_MEMBERSHIP, IPV6_MTU, IPV6_V6ONLY, ...¶
Socket option name constants for IPv6 socket options at the
"IPPROTO_IPV6" level.
STRUCTURE MANIPULATORS¶
The following functions convert between lists of Perl values and packed binary
strings representing structures.
$family = sockaddr_family $sockaddr¶
Takes a packed socket address (as returned by
pack_sockaddr_in(),
pack_sockaddr_un() or the perl builtin functions
getsockname()
and
getpeername()). Returns the address family tag. This will be one of
the "AF_*" constants, such as "AF_INET" for a
"sockaddr_in" addresses or "AF_UNIX" for a
"sockaddr_un". It can be used to figure out what unpack to use for a
sockaddr of unknown type.
$sockaddr = pack_sockaddr_in $port, $ip_address¶
Takes two arguments, a port number and an opaque string (as returned by
inet_aton(), or a v-string). Returns the "sockaddr_in"
structure with those arguments packed in and "AF_INET" filled in.
For Internet domain sockets, this structure is normally what you need for the
arguments in
bind(),
connect(), and
send().
($port, $ip_address) = unpack_sockaddr_in $sockaddr¶
Takes a "sockaddr_in" structure (as returned by
pack_sockaddr_in(),
getpeername() or
recv()). Returns a
list of two elements: the port and an opaque string representing the IP
address (you can use
inet_ntoa() to convert the address to the
four-dotted numeric format). Will croak if the structure does not represent an
"AF_INET" address.
In scalar context will return just the IP address.
$sockaddr = sockaddr_in $port, $ip_address¶
($port, $ip_address) = sockaddr_in $sockaddr¶
A wrapper of
pack_sockaddr_in() or
unpack_sockaddr_in(). In list
context, unpacks its argument and returns a list consisting of the port and IP
address. In scalar context, packs its port and IP address arguments as a
"sockaddr_in" and returns it.
Provided largely for legacy compatibility; it is better to use
pack_sockaddr_in() or
unpack_sockaddr_in() explicitly.
$sockaddr = pack_sockaddr_in6 $port, $ip6_address, [$scope_id, [$flowinfo]]¶
Takes two to four arguments, a port number, an opaque string (as returned by
inet_pton()), optionally a scope ID number, and optionally a flow label
number. Returns the "sockaddr_in6" structure with those arguments
packed in and "AF_INET6" filled in. IPv6 equivalent of
pack_sockaddr_in().
($port, $ip6_address, $scope_id, $flowinfo) = unpack_sockaddr_in6 $sockaddr¶
Takes a "sockaddr_in6" structure. Returns a list of four elements: the
port number, an opaque string representing the IPv6 address, the scope ID, and
the flow label. (You can use
inet_ntop() to convert the address to the
usual string format). Will croak if the structure does not represent an
"AF_INET6" address.
In scalar context will return just the IP address.
$sockaddr = sockaddr_in6 $port, $ip6_address, [$scope_id, [$flowinfo]]¶
($port, $ip6_address, $scope_id, $flowinfo) = sockaddr_in6 $sockaddr¶
A wrapper of
pack_sockaddr_in6() or
unpack_sockaddr_in6(). In list
context, unpacks its argument according to
unpack_sockaddr_in6(). In
scalar context, packs its arguments according to
pack_sockaddr_in6().
Provided largely for legacy compatibility; it is better to use
pack_sockaddr_in6() or
unpack_sockaddr_in6() explicitly.
$sockaddr = pack_sockaddr_un $path¶
Takes one argument, a pathname. Returns the "sockaddr_un" structure
with that path packed in with "AF_UNIX" filled in. For
"PF_UNIX" sockets, this structure is normally what you need for the
arguments in
bind(),
connect(), and
send().
($path) = unpack_sockaddr_un $sockaddr¶
Takes a "sockaddr_un" structure (as returned by
pack_sockaddr_un(),
getpeername() or
recv()). Returns a
list of one element: the pathname. Will croak if the structure does not
represent an "AF_UNIX" address.
$sockaddr = sockaddr_un $path¶
($path) = sockaddr_un $sockaddr¶
A wrapper of
pack_sockaddr_un() or
unpack_sockaddr_un(). In a list
context, unpacks its argument and returns a list consisting of the pathname.
In a scalar context, packs its pathname as a "sockaddr_un" and
returns it.
Provided largely for legacy compatibility; it is better to use
pack_sockaddr_un() or
unpack_sockaddr_un() explicitly.
These are only supported if your system has <
sys/un.h>.
$ip_mreq = pack_ip_mreq $multiaddr, $interface¶
Takes an IPv4 multicast address and optionally an interface address (or
"INADDR_ANY"). Returns the "ip_mreq" structure with those
arguments packed in. Suitable for use with the "IP_ADD_MEMBERSHIP"
and "IP_DROP_MEMBERSHIP" sockopts.
($multiaddr, $interface) = unpack_ip_mreq $ip_mreq¶
Takes an "ip_mreq" structure. Returns a list of two elements; the IPv4
multicast address and interface address.
$ip_mreq_source = pack_ip_mreq_source $multiaddr, $source, $interface¶
Takes an IPv4 multicast address, source address, and optionally an interface
address (or "INADDR_ANY"). Returns the "ip_mreq_source"
structure with those arguments packed in. Suitable for use with the
"IP_ADD_SOURCE_MEMBERSHIP" and "IP_DROP_SOURCE_MEMBERSHIP"
sockopts.
($multiaddr, $source, $interface) = unpack_ip_mreq_source $ip_mreq¶
Takes an "ip_mreq_source" structure. Returns a list of three elements;
the IPv4 multicast address, source address and interface address.
$ipv6_mreq = pack_ipv6_mreq $multiaddr6, $ifindex¶
Takes an IPv6 multicast address and an interface number. Returns the
"ipv6_mreq" structure with those arguments packed in. Suitable for
use with the "IPV6_ADD_MEMBERSHIP" and
"IPV6_DROP_MEMBERSHIP" sockopts.
($multiaddr6, $ifindex) = unpack_ipv6_mreq $ipv6_mreq¶
Takes an "ipv6_mreq" structure. Returns a list of two elements; the
IPv6 address and an interface number.
FUNCTIONS¶
$ip_address = inet_aton $string¶
Takes a string giving the name of a host, or a textual representation of an IP
address and translates that to an packed binary address structure suitable to
pass to
pack_sockaddr_in(). If passed a hostname that cannot be
resolved, returns "undef". For multi-homed hosts (hosts with more
than one address), the first address found is returned.
For portability do not assume that the result of
inet_aton() is 32 bits
wide, in other words, that it would contain only the IPv4 address in network
order.
This IPv4-only function is provided largely for legacy reasons. Newly-written
code should use
getaddrinfo() or
inet_pton() instead for IPv6
support.
$string = inet_ntoa $ip_address¶
Takes a packed binary address structure such as returned by
unpack_sockaddr_in() (or a v-string representing the four octets of the
IPv4 address in network order) and translates it into a string of the form
"d.d.d.d" where the "d"s are numbers less than 256 (the
normal human-readable four dotted number notation for Internet addresses).
This IPv4-only function is provided largely for legacy reasons. Newly-written
code should use
getnameinfo() or
inet_ntop() instead for IPv6
support.
$address = inet_pton $family, $string¶
Takes an address family (such as "AF_INET" or "AF_INET6")
and a string containing a textual representation of an address in that family
and translates that to an packed binary address structure.
See also
getaddrinfo() for a more powerful and flexible function to look
up socket addresses given hostnames or textual addresses.
$string = inet_ntop $family, $address¶
Takes an address family and a packed binary address structure and translates it
into a human-readable textual representation of the address; typically in
"d.d.d.d" form for "AF_INET" or
"hhhh:hhhh::hhhh" form for "AF_INET6".
See also
getnameinfo() for a more powerful and flexible function to turn
socket addresses into human-readable textual representations.
($err, @result) = getaddrinfo $host, $service, [$hints]¶
Given both a hostname and service name, this function attempts to resolve the
host name into a list of network addresses, and the service name into a
protocol and port number, and then returns a list of address structures
suitable to
connect() to it.
Given just a host name, this function attempts to resolve it to a list of
network addresses, and then returns a list of address structures giving these
addresses.
Given just a service name, this function attempts to resolve it to a protocol
and port number, and then returns a list of address structures that represent
it suitable to
bind() to. This use should be combined with the
"AI_PASSIVE" flag; see below.
Given neither name, it generates an error.
If present, $hints should be a reference to a hash, where the following keys are
recognised:
- flags => INT
- A bitfield containing "AI_*" constants; see below.
- family => INT
- Restrict to only generating addresses in this address family
- socktype => INT
- Restrict to only generating addresses of this socket type
- protocol => INT
- Restrict to only generating addresses for this protocol
The return value will be a list; the first value being an error indication,
followed by a list of address structures (if no error occurred).
The error value will be a dualvar; comparable to the "EI_*" error
constants, or printable as a human-readable error message string. If no error
occurred it will be zero numerically and an empty string.
Each value in the results list will be a hash reference containing the following
fields:
- family => INT
- The address family (e.g. "AF_INET")
- socktype => INT
- The socket type (e.g. "SOCK_STREAM")
- protocol => INT
- The protocol (e.g. "IPPROTO_TCP")
- addr => STRING
- The address in a packed string (such as would be returned by
pack_sockaddr_in())
- canonname => STRING
- The canonical name for the host if the "AI_CANONNAME" flag was
provided, or "undef" otherwise. This field will only be present
on the first returned address.
The following flag constants are recognised in the $hints hash. Other flag
constants may exist as provided by the OS.
- AI_PASSIVE
- Indicates that this resolution is for a local bind() for a passive
(i.e. listening) socket, rather than an active (i.e. connecting)
socket.
- AI_CANONNAME
- Indicates that the caller wishes the canonical hostname
("canonname") field of the result to be filled in.
- AI_NUMERICHOST
- Indicates that the caller will pass a numeric address, rather than a
hostname, and that getaddrinfo() must not perform a resolve
operation on this name. This flag will prevent a possibly-slow network
lookup operation, and instead return an error if a hostname is
passed.
($err, $hostname, $servicename) = getnameinfo $sockaddr, [$flags, [$xflags]]¶
Given a packed socket address (such as from
getsockname(),
getpeername(), or returned by
getaddrinfo() in a
"addr" field), returns the hostname and symbolic service name it
represents. $flags may be a bitmask of "NI_*" constants, or defaults
to 0 if unspecified.
The return value will be a list; the first value being an error condition,
followed by the hostname and service name.
The error value will be a dualvar; comparable to the "EI_*" error
constants, or printable as a human-readable error message string. The host and
service names will be plain strings.
The following flag constants are recognised as $flags. Other flag constants may
exist as provided by the OS.
- NI_NUMERICHOST
- Requests that a human-readable string representation of the numeric
address be returned directly, rather than performing a name resolve
operation that may convert it into a hostname. This will also avoid
potentially-blocking network IO.
- NI_NUMERICSERV
- Requests that the port number be returned directly as a number
representation rather than performing a name resolve operation that may
convert it into a service name.
- NI_NAMEREQD
- If a name resolve operation fails to provide a name, then this flag will
cause getnameinfo() to indicate an error, rather than returning the
numeric representation as a human-readable string.
- NI_DGRAM
- Indicates that the socket address relates to a "SOCK_DGRAM"
socket, for the services whose name differs between TCP and UDP
protocols.
The following constants may be supplied as $xflags.
- NIx_NOHOST
- Indicates that the caller is not interested in the hostname of the result,
so it does not have to be converted. "undef" will be returned as
the hostname.
- NIx_NOSERV
- Indicates that the caller is not interested in the service name of the
result, so it does not have to be converted. "undef" will be
returned as the service name.
getaddrinfo() / getnameinfo() ERROR CONSTANTS¶
The following constants may be returned by
getaddrinfo() or
getnameinfo(). Others may be provided by the OS.
- EAI_AGAIN
- A temporary failure occurred during name resolution. The operation may be
successful if it is retried later.
- EAI_BADFLAGS
- The value of the "flags" hint to getaddrinfo(), or the
$flags parameter to getnameinfo() contains unrecognised flags.
- EAI_FAMILY
- The "family" hint to getaddrinfo(), or the family of the
socket address passed to getnameinfo() is not supported.
- EAI_NODATA
- The host name supplied to getaddrinfo() did not provide any usable
address data.
- EAI_NONAME
- The host name supplied to getaddrinfo() does not exist, or the
address supplied to getnameinfo() is not associated with a host
name and the "NI_NAMEREQD" flag was supplied.
- EAI_SERVICE
- The service name supplied to getaddrinfo() is not available for the
socket type given in the $hints.
EXAMPLES¶
Lookup for connect()¶
The
getaddrinfo() function converts a hostname and a service name into a
list of structures, each containing a potential way to
connect() to the
named service on the named host.
use IO::Socket;
use Socket qw(SOCK_STREAM getaddrinfo);
my %hints = (socktype => SOCK_STREAM);
my ($err, @res) = getaddrinfo("localhost", "echo", \%hints);
die "Cannot getaddrinfo - $err" if $err;
my $sock;
foreach my $ai (@res) {
my $candidate = IO::Socket->new();
$candidate->socket($ai->{family}, $ai->{socktype}, $ai->{protocol})
or next;
$candidate->connect($ai->{addr})
or next;
$sock = $candidate;
last;
}
die "Cannot connect to localhost:echo" unless $sock;
$sock->print("Hello, world!\n");
print <$sock>;
Because a list of potential candidates is returned, the "while" loop
tries each in turn until it finds one that succeeds both the
socket()
and
connect() calls.
This function performs the work of the legacy functions
gethostbyname(),
getservbyname(),
inet_aton() and
pack_sockaddr_in().
In practice this logic is better performed by IO::Socket::IP.
Making a human-readable string out of an address¶
The
getnameinfo() function converts a socket address, such as returned by
getsockname() or
getpeername(), into a pair of human-readable
strings representing the address and service name.
use IO::Socket::IP;
use Socket qw(getnameinfo);
my $server = IO::Socket::IP->new(LocalPort => 12345, Listen => 1) or
die "Cannot listen - $@";
my $socket = $server->accept or die "accept: $!";
my ($err, $hostname, $servicename) = getnameinfo($socket->peername);
die "Cannot getnameinfo - $err" if $err;
print "The peer is connected from $hostname\n";
Since in this example only the hostname was used, the redundant conversion of
the port number into a service name may be omitted by passing the
"NIx_NOSERV" flag.
use Socket qw(getnameinfo NIx_NOSERV);
my ($err, $hostname) = getnameinfo($socket->peername, 0, NIx_NOSERV);
This function performs the work of the legacy functions
unpack_sockaddr_in(),
inet_ntoa(),
gethostbyaddr() and
getservbyport().
In practice this logic is better performed by IO::Socket::IP.
Resolving hostnames into IP addresses¶
To turn a hostname into a human-readable plain IP address use
getaddrinfo() to turn the hostname into a list of socket structures,
then
getnameinfo() on each one to make it a readable IP address again.
use Socket qw(:addrinfo SOCK_RAW);
my ($err, @res) = getaddrinfo($hostname, "", {socktype => SOCK_RAW});
die "Cannot getaddrinfo - $err" if $err;
while( my $ai = shift @res ) {
my ($err, $ipaddr) = getnameinfo($ai->{addr}, NI_NUMERICHOST, NIx_NOSERV);
die "Cannot getnameinfo - $err" if $err;
print "$ipaddr\n";
}
The "socktype" hint to
getaddrinfo() filters the results to
only include one socket type and protocol. Without this most OSes return three
combinations, for "SOCK_STREAM", "SOCK_DGRAM" and
"SOCK_RAW", resulting in triplicate output of addresses. The
"NI_NUMERICHOST" flag to
getnameinfo() causes it to return a
string-formatted plain IP address, rather than reverse resolving it back into
a hostname.
This combination performs the work of the legacy functions
gethostbyname() and
inet_ntoa().
Accessing socket options¶
The many "SO_*" and other constants provide the socket option names
for
getsockopt() and
setsockopt().
use IO::Socket::INET;
use Socket qw(SOL_SOCKET SO_RCVBUF IPPROTO_IP IP_TTL);
my $socket = IO::Socket::INET->new(LocalPort => 0, Proto => 'udp')
or die "Cannot create socket: $@";
$socket->setsockopt(SOL_SOCKET, SO_RCVBUF, 64*1024) or
die "setsockopt: $!";
print "Receive buffer is ", $socket->getsockopt(SOL_SOCKET, SO_RCVBUF),
" bytes\n";
print "IP TTL is ", $socket->getsockopt(IPPROTO_IP, IP_TTL), "\n";
As a convenience, IO::Socket's
setsockopt() method will convert a number
into a packed byte buffer, and
getsockopt() will unpack a byte buffer
of the correct size back into a number.
AUTHOR¶
This module was originally maintained in Perl core by the Perl 5 Porters.
It was extracted to dual-life on CPAN at version 1.95 by Paul Evans
<leonerd@leonerd.org.uk>