Provided by: libsocket-perl_2.013-1_amd64 bug

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>