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NAME
    `IO::Socket::IP' - A drop-in replacement for `IO::Socket::INET'
    supporting both IPv4 and IPv6

SYNOPSIS
     use IO::Socket::IP;

     my $sock = IO::Socket::IP->new(
        PeerHost => "www.google.com",
        PeerPort => "http",
        Type     => SOCK_STREAM,
     ) or die "Cannot construct socket - $@";

     my $familyname = ( $sock->sockdomain == PF_INET6 ) ? "IPv6" :
                      ( $sock->sockdomain == PF_INET  ) ? "IPv4" :
                                                          "unknown";

     printf "Connected to google via %s\n", $familyname;

DESCRIPTION
    This module provides a protocol-independent way to use IPv4 and IPv6
    sockets, as a drop-in replacement for IO::Socket::INET. Most constructor
    arguments and methods are provided in a backward-compatible way. For a
    list of known differences, see the `IO::Socket::INET' INCOMPATIBILITES
    section below.

    It uses the `getaddrinfo(3)' function to convert hostnames and service
    names or port numbers into sets of possible addresses to connect to or
    listen on. This allows it to work for IPv6 where the system supports it,
    while still falling back to IPv4-only on systems which don't.

REPLACING `IO::Socket' DEFAULT BEHAVIOUR
    By placing `-register' in the import list, `IO::Socket' uses
    `IO::Socket::IP' rather than `IO::Socket::INET' as the class that
    handles `PF_INET'. `IO::Socket' will also use `IO::Socket::IP' rather
    than `IO::Socket::INET6' to handle `PF_INET6', provided that the
    `AF_INET6' constant is available.

    Changing `IO::Socket''s default behaviour means that calling the
    `IO::Socket' constructor with either `PF_INET' or `PF_INET6' as the
    `Domain' parameter will yield an `IO::Socket::IP' object.

     use IO::Socket::IP -register;

     my $sock = IO::Socket->new(
        Domain    => PF_INET6,
        LocalHost => "::1",
        Listen    => 1,
     ) or die "Cannot create socket - $@\n";

     print "Created a socket of type " . ref($sock) . "\n";

    Note that `-register' is a global setting that applies to the entire
    program; it cannot be applied only for certain callers, removed, or
    limited by lexical scope.

CONSTRUCTORS
  $sock = IO::Socket::IP->new( %args )
    Creates a new `IO::Socket::IP' object, containing a newly created socket
    handle according to the named arguments passed. The recognised arguments
    are:

    PeerHost => STRING
    PeerService => STRING
            Hostname and service name for the peer to `connect()' to. The
            service name may be given as a port number, as a decimal string.

    PeerAddr => STRING
    PeerPort => STRING
            For symmetry with the accessor methods and compatibility with
            `IO::Socket::INET', these are accepted as synonyms for
            `PeerHost' and `PeerService' respectively.

    PeerAddrInfo => ARRAY
            Alternate form of specifying the peer to `connect()' to. This
            should be an array of the form returned by
            `Socket::getaddrinfo'.

            This parameter takes precedence over the `Peer*', `Family',
            `Type' and `Proto' arguments.

    LocalHost => STRING
    LocalService => STRING
            Hostname and service name for the local address to `bind()' to.

    LocalAddr => STRING
    LocalPort => STRING
            For symmetry with the accessor methods and compatibility with
            `IO::Socket::INET', these are accepted as synonyms for
            `LocalHost' and `LocalService' respectively.

    LocalAddrInfo => ARRAY
            Alternate form of specifying the local address to `bind()' to.
            This should be an array of the form returned by
            `Socket::getaddrinfo'.

            This parameter takes precedence over the `Local*', `Family',
            `Type' and `Proto' arguments.

    Family => INT
            The address family to pass to `getaddrinfo' (e.g. `AF_INET',
            `AF_INET6'). Normally this will be left undefined, and
            `getaddrinfo' will search using any address family supported by
            the system.

    Type => INT
            The socket type to pass to `getaddrinfo' (e.g. `SOCK_STREAM',
            `SOCK_DGRAM'). Normally defined by the caller; if left undefined
            `getaddrinfo' may attempt to infer the type from the service
            name.

    Proto => STRING or INT
            The IP protocol to use for the socket (e.g. `'tcp'',
            `IPPROTO_TCP', `'udp'',`IPPROTO_UDP'). Normally this will be
            left undefined, and either `getaddrinfo' or the kernel will
            choose an appropriate value. May be given either in string name
            or numeric form.

    GetAddrInfoFlags => INT
            More flags to pass to the `getaddrinfo()' function. If not
            supplied, a default of `AI_ADDRCONFIG' will be used.

            These flags will be combined with `AI_PASSIVE' if the `Listen'
            argument is given. For more information see the documentation
            about `getaddrinfo()' in the Socket module.

    Listen => INT
            If defined, puts the socket into listening mode where new
            connections can be accepted using the `accept' method. The value
            given is used as the `listen(2)' queue size.

    ReuseAddr => BOOL
            If true, set the `SO_REUSEADDR' sockopt

    ReusePort => BOOL
            If true, set the `SO_REUSEPORT' sockopt (not all OSes implement
            this sockopt)

    Broadcast => BOOL
            If true, set the `SO_BROADCAST' sockopt

    V6Only => BOOL
            If defined, set the `IPV6_V6ONLY' sockopt when creating
            `PF_INET6' sockets to the given value. If true, a listening-mode
            socket will only listen on the `AF_INET6' addresses; if false it
            will also accept connections from `AF_INET' addresses.

            If not defined, the socket option will not be changed, and
            default value set by the operating system will apply. For
            repeatable behaviour across platforms it is recommended this
            value always be defined for listening-mode sockets.

            Note that not all platforms support disabling this option. Some,
            at least OpenBSD and MirBSD, will fail with `EINVAL' if you
            attempt to disable it. To determine whether it is possible to
            disable, you may use the class method

             if( IO::Socket::IP->CAN_DISABLE_V6ONLY ) {
                ...
             }
             else {
                ...
             }

            If your platform does not support disabling this option but you
            still want to listen for both `AF_INET' and `AF_INET6'
            connections you will have to create two listening sockets, one
            bound to each protocol.

    Timeout This `IO::Socket::INET'-style argument is not currently
            supported. See the `IO::Socket::INET' INCOMPATIBILITES section
            below.

    MultiHomed
            This `IO::Socket::INET'-style argument is ignored, except if it
            is defined but false. See the `IO::Socket::INET'
            INCOMPATIBILITES section below.

            However, the behaviour it enables is always performed by
            `IO::Socket::IP'.

    Blocking => BOOL
            If defined but false, the socket will be set to non-blocking
            mode. Otherwise it will default to blocking mode. See the
            NON-BLOCKING section below for more detail.

    If neither `Type' nor `Proto' hints are provided, a default of
    `SOCK_STREAM' and `IPPROTO_TCP' respectively will be set, to maintain
    compatibility with `IO::Socket::INET'. Other named arguments that are
    not recognised are ignored.

    If neither `Family' nor any hosts or addresses are passed, nor any
    `*AddrInfo', then the constructor has no information on which to decide
    a socket family to create. In this case, it performs a `getaddinfo' call
    with the `AI_ADDRCONFIG' flag, no host name, and a service name of
    `"0"', and uses the family of the first returned result.

    If the constructor fails, it will set `$@' to an appropriate error
    message; this may be from `$!' or it may be some other string; not every
    failure necessarily has an associated `errno' value.

  $sock = IO::Socket::IP->new( $peeraddr )
    As a special case, if the constructor is passed a single argument (as
    opposed to an even-sized list of key/value pairs), it is taken to be the
    value of the `PeerAddr' parameter. This is parsed in the same way,
    according to the behaviour given in the `PeerHost' AND `LocalHost'
    PARSING section below.

METHODS
    As well as the following methods, this class inherits all the methods in
    IO::Socket and IO::Handle.

  ( $host, $service ) = $sock->sockhost_service( $numeric )
    Returns the hostname and service name of the local address (that is, the
    socket address given by the `sockname' method).

    If `$numeric' is true, these will be given in numeric form rather than
    being resolved into names.

    The following four convenience wrappers may be used to obtain one of the
    two values returned here. If both host and service names are required,
    this method is preferable to the following wrappers, because it will
    call `getnameinfo(3)' only once.

  $addr = $sock->sockhost
    Return the numeric form of the local address as a textual representation

  $port = $sock->sockport
    Return the numeric form of the local port number

  $host = $sock->sockhostname
    Return the resolved name of the local address

  $service = $sock->sockservice
    Return the resolved name of the local port number

  $addr = $sock->sockaddr
    Return the local address as a binary octet string

  ( $host, $service ) = $sock->peerhost_service( $numeric )
    Returns the hostname and service name of the peer address (that is, the
    socket address given by the `peername' method), similar to the
    `sockhost_service' method.

    The following four convenience wrappers may be used to obtain one of the
    two values returned here. If both host and service names are required,
    this method is preferable to the following wrappers, because it will
    call `getnameinfo(3)' only once.

  $addr = $sock->peerhost
    Return the numeric form of the peer address as a textual representation

  $port = $sock->peerport
    Return the numeric form of the peer port number

  $host = $sock->peerhostname
    Return the resolved name of the peer address

  $service = $sock->peerservice
    Return the resolved name of the peer port number

  $addr = $peer->peeraddr
    Return the peer address as a binary octet string

  $inet = $sock->as_inet
    Returns a new IO::Socket::INET instance wrapping the same filehandle.
    This may be useful in cases where it is required, for
    backward-compatibility, to have a real object of `IO::Socket::INET' type
    instead of `IO::Socket::IP'. The new object will wrap the same
    underlying socket filehandle as the original, so care should be taken
    not to continue to use both objects concurrently. Ideally the original
    `$sock' should be discarded after this method is called.

    This method checks that the socket domain is `PF_INET' and will throw an
    exception if it isn't.

NON-BLOCKING
    If the constructor is passed a defined but false value for the
    `Blocking' argument then the socket is put into non-blocking mode. When
    in non-blocking mode, the socket will not be set up by the time the
    constructor returns, because the underlying `connect(2)' syscall would
    otherwise have to block.

    The non-blocking behaviour is an extension of the `IO::Socket::INET'
    API, unique to `IO::Socket::IP', because the former does not support
    multi-homed non-blocking connect.

    When using non-blocking mode, the caller must repeatedly check for
    writeability on the filehandle (for instance using `select' or
    `IO::Poll'). Each time the filehandle is ready to write, the `connect'
    method must be called, with no arguments. Note that some operating
    systems, most notably `MSWin32' do not report a `connect()' failure
    using write-ready; so you must also `select()' for exceptional status.

    While `connect' returns false, the value of `$!' indicates whether it
    should be tried again (by being set to the value `EINPROGRESS', or
    `EWOULDBLOCK' on MSWin32), or whether a permanent error has occurred
    (e.g. `ECONNREFUSED').

    Once the socket has been connected to the peer, `connect' will return
    true and the socket will now be ready to use.

    Note that calls to the platform's underlying `getaddrinfo(3)' function
    may block. If `IO::Socket::IP' has to perform this lookup, the
    constructor will block even when in non-blocking mode.

    To avoid this blocking behaviour, the caller should pass in the result
    of such a lookup using the `PeerAddrInfo' or `LocalAddrInfo' arguments.
    This can be achieved by using Net::LibAsyncNS, or the `getaddrinfo(3)'
    function can be called in a child process.

     use IO::Socket::IP;
     use Errno qw( EINPROGRESS EWOULDBLOCK );

     my @peeraddrinfo = ... # Caller must obtain the getaddinfo result here

     my $socket = IO::Socket::IP->new(
        PeerAddrInfo => \@peeraddrinfo,
        Blocking     => 0,
     ) or die "Cannot construct socket - $@";

     while( !$socket->connect and ( $! == EINPROGRESS || $! == EWOULDBLOCK ) ) {
        my $wvec = '';
        vec( $wvec, fileno $socket, 1 ) = 1;
        my $evec = '';
        vec( $evec, fileno $socket, 1 ) = 1;

        select( undef, $wvec, $evec, undef ) or die "Cannot select - $!";
     }

     die "Cannot connect - $!" if $!;

     ...

    The example above uses `select()', but any similar mechanism should work
    analogously. `IO::Socket::IP' takes care when creating new socket
    filehandles to preserve the actual file descriptor number, so such
    techniques as `poll' or `epoll' should be transparent to its
    reallocation of a different socket underneath, perhaps in order to
    switch protocol family between `PF_INET' and `PF_INET6'.

    For another example using `IO::Poll' and `Net::LibAsyncNS', see the
    examples/nonblocking_libasyncns.pl file in the module distribution.

`PeerHost' AND `LocalHost' PARSING
    To support the `IO::Socket::INET' API, the host and port information may
    be passed in a single string rather than as two separate arguments.

    If either `LocalHost' or `PeerHost' (or their `...Addr' synonyms) have
    any of the following special forms, and `LocalService' or `PeerService'
    (or their `...Port' synonyms) are absent, special parsing is applied.

    The value of the `...Host' argument will be split to give both the
    hostname and port (or service name):

     hostname.example.org:http    # Host name
     192.0.2.1:80                 # IPv4 address
     [2001:db8::1]:80             # IPv6 address

    In each case, the port or service name (e.g. `80') is passed as the
    `LocalService' or `PeerService' argument.

    Either of `LocalService' or `PeerService' (or their `...Port' synonyms)
    can be either a service name, a decimal number, or a string containing
    both a service name and number, in a form such as

     http(80)

    In this case, the name (`http') will be tried first, but if the resolver
    does not understand it then the port number (`80') will be used instead.

  ( $host, $port ) = IO::Socket::IP->split_addr( $addr )
    Utility method that provides the parsing functionality described above.
    Returns a 2-element list, containing either the split hostname and port
    description if it could be parsed, or the given address and `undef' if
    it was not recognised.

     IO::Socket::IP->split_addr( "hostname:http" )
                                  # ( "hostname",  "http" )

     IO::Socket::IP->split_addr( "192.0.2.1:80" )
                                  # ( "192.0.2.1", "80"   )

     IO::Socket::IP->split_addr( "[2001:db8::1]:80" )
                                  # ( "2001:db8::1", "80" )

     IO::Socket::IP->split_addr( "something.else" )
                                  # ( "something.else", undef )

  $addr = IO::Socket::IP->join_addr( $host, $port )
    Utility method that performs the reverse of `split_addr', returning a
    string formed by joining the specified host address and port number. The
    host address will be wrapped in `[]' brackets if required (because it is
    a raw IPv6 numeric address).

    This can be especially useful when combined with the `sockhost_service'
    or `peerhost_service' methods.

     say "Connected to ", IO::Socket::IP->join_addr( $sock->peerhost_service );

`IO::Socket::INET' INCOMPATIBILITES
    *   The `Timeout' constructor argument is currently not recognised.

        The behaviour enabled by `MultiHomed' is in fact implemented by
        `IO::Socket::IP' as it is required to correctly support searching
        for a useable address from the results of the `getaddrinfo(3)' call.
        The constructor will ignore the value of this argument, except if it
        is defined but false. An exception is thrown in this case, because
        that would request it disable the `getaddrinfo(3)' search behaviour
        in the first place.

TODO
    *   Investigate whether `POSIX::dup2' upsets BSD's `kqueue' watchers,
        and if so, consider what possible workarounds might be applied.

AUTHOR
    Paul Evans <leonerd@leonerd.org.uk>