Socket
- networking constants and support functions
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.
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.
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.
Protocol family constants to use as the first argument to socket() or the
value of the SO_DOMAIN
or SO_FAMILY
socket option.
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().
Socket type constants to use as the second argument to socket(), or the value
of the SO_TYPE
socket option.
Linux-specific shortcuts to specify the O_NONBLOCK
and FD_CLOEXEC
flags
during a socket(2) call.
Socket option level constant for setsockopt() and getsockopt().
Socket option name constants for setsockopt() and getsockopt() at the
SOL_SOCKET
level.
Socket option name constants for IPv4 socket options at the IPPROTO_IP
level.
Socket option value constants for IP_TOS
socket option.
Message flag constants for send() and recv().
Direction constants for shutdown().
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.
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.
Socket option name constants for TCP socket options at the IPPROTO_TCP
level.
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.
Socket option name constants for IPv6 socket options at the IPPROTO_IPV6
level.
The following functions convert between lists of Perl values and packed binary strings representing structures.
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.
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().
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.
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.
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().
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.
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.
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().
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.
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>.
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.
Takes an ip_mreq
structure. Returns a list of two elements; the IPv4
multicast address and interface address.
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.
Takes an ip_mreq_source
structure. Returns a list of three elements; the
IPv4 multicast address, source address and interface address.
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.
Takes an ipv6_mreq
structure. Returns a list of two elements; the IPv6
address and an interface number.
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.
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.
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.
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.
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:
A bitfield containing AI_*
constants; see below.
Restrict to only generating addresses in this address family
Restrict to only generating addresses of this socket type
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:
The address family (e.g. AF_INET
)
The socket type (e.g. SOCK_STREAM
)
The protocol (e.g. IPPROTO_TCP
)
The address in a packed string (such as would be returned by pack_sockaddr_in())
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.
Indicates that this resolution is for a local bind() for a passive (i.e. listening) socket, rather than an active (i.e. connecting) socket.
Indicates that the caller wishes the canonical hostname (canonname
) field
of the result to be filled in.
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.
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.
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.
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.
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.
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.
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.
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.
The following constants may be returned by getaddrinfo() or getnameinfo(). Others may be provided by the OS.
A temporary failure occurred during name resolution. The operation may be successful if it is retried later.
The value of the flags
hint to getaddrinfo(), or the $flags parameter to
getnameinfo() contains unrecognised flags.
The family
hint to getaddrinfo(), or the family of the socket address
passed to getnameinfo() is not supported.
The host name supplied to getaddrinfo() did not provide any usable address data.
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.
The service name supplied to getaddrinfo() is not available for the socket type given in the $hints.
The getaddrinfo() function converts a hostname and a service name into a list of structures, each containing a potential way to connect() to the named service on the named host.
- use IO::Socket;
- use Socket qw(SOCK_STREAM getaddrinfo);
- my %hints = (socktype => SOCK_STREAM);
- my ($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.
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 $hostname\n";
Since in this example only the hostname was used, the redundant conversion of
the port number into a service name may be omitted by passing the
NIx_NOSERV
flag.
This function performs the work of the legacy functions unpack_sockaddr_in(), inet_ntoa(), gethostbyaddr() and getservbyport().
In practice this logic is better performed by IO::Socket::IP.
To turn a hostname into a human-readable plain IP address use getaddrinfo() to turn the hostname into a list of socket structures, then getnameinfo() on each one to make it a readable IP address again.
- use Socket qw(:addrinfo SOCK_RAW);
- my ($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().
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.
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>