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Socket(3pm)                           Perl Programmers Reference Guide                           Socket(3pm)



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.

   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.

   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.

   $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.

   $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>.

   $ipv6_mreq = pack_ipv6_mreq $ip6_address, $ifindex
       Takes an IPv6 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.

   ($ip6_address, $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 humanreadable
       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 humanreadable
       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 humanreadable
       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 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>



perl v5.16.2                                     2012-10-25                                      Socket(3pm)