phpman > man > Socket(3perl)

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.

  IP_PMTUDISC_WANT, IP_PMTUDISC_DONT, ...
    Socket option value constants for "IP_MTU_DISCOVER" socket option.

  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().

    An undefined $port argument is taken as zero; an undefined $ip_address is considered a fatal
    error.

  ($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().

    An undefined $port argument is taken as zero; an undefined $ip6_address is considered a fatal
    error.

  ($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 "EAI_*" 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 "EAI_*" 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 AT leonerd.uk>