NAME
    IO::Pipely - Portably create pipe() or pipe-like handles, one way or
    another.

VERSION
    version 0.005

SYNOPSIS
    Please read DESCRIPTION for detailed semantics and caveats.

      use IO::Pipely qw(pipely socketpairly);

      # Create a one-directional pipe() or pipe-like thing
      # the best conduit type available.

      my ($read, $write) = pipely();

      # Create a one-directional pipe-like thing using an
      # INET socket specifically.  Other types are available.

      my ($read, $write) = pipely(type => 'inet');

      # Create a bidirectional pipe-like thing using
      # the best conduit type available.

      my (
        $side_a_read,  $side_b_read,
        $side_a_write, $side_b_write,
      ) = socketpairly();

      # Create a bidirectional pipe-like thing using an INET socket
      # specifically.

      my (
        $side_a_read,  $side_b_read,
        $side_a_write, $side_b_write,
      ) = socketpairly(type => 'inet');

DESCRIPTION
    Pipes are troublesome beasts because there are a few different,
    incompatible ways to create them. Not all platforms support all ways,
    and some platforms may have hidden difficulties like incomplete or buggy
    support.

    IO::Pipely provides a couple functions to portably create one- and
    two-way pipes and pipe-like socket pairs. It acknowledges and works
    around known platform issues so you don't have to.

    On the other hand, it doesn't work around unknown issues, so please
    report any problems early and often.

    IO::Pipely currently understands pipe(), UNIX-domain socketpair() and
    regular IPv4 localhost sockets. This covers every platform tested so
    far, but it's hardly complete. Please help support other mechanisms,
    such as INET-domain socketpair() and IPv6 localhost sockets.

    IO::Pipely will use different kinds of pipes or sockets depending on the
    operating system's capabilities and the number of directions requested.
    The autodetection may be overridden by specifying a particular pipe
    type.

  pipely
    pipely() creates a one-directional pipe() or socket. It's modeled after
    Perl's built-in pipe() function, but it creates and returns handles
    rather than opening ones given to it.

    On success, pipely() returns two file handles, the first to read from
    the pipe, and the second writes into the pipe. It returns nothing on
    failure.

      use IO::Pipely qw(pipely);
      my ($a_read, $b_write) = pipely();
      die "pipely() failed: $!" unless $a_read;

    When given a choice, it will prefer to use leaner pipe() calls instead
    of socketpair() and socket().

    pipely()'s choice can be forced using an optional named "type"
    parameter. See "PIPE TYPES" for the types that can be used.

      my ($a_read, $b_write) = pipely(
        type => 'pipe',
      );

    On most systems, pipely() will prefer to open a pipe() first. It will
    fall back to a UNIX socketpair() or two localhost Internet sockets, in
    that order.

    On Windows (ActiveState and Strawberry Perl), pipely() prefers two
    localhost Internet sockets. It will fall back to socketpair() and
    pipe(), both of which will probably fail.

    Cygwin Perl prefers pipe() first, localhost Internet sockets, and then
    socketpair(). socketpair() has been known to have problems on Cygwin.

    MacPerl (MacOS 9 and earlier) has similar capaibilities to Windows.

  socketpairly
    socketpairly() creates a two-directional socket pair. It's modeled after
    Perl's built-in socketpair(), but it creates and returns handles rather
    than opening ones given to it.

    On success, socketpairly() returns four file handles, read and write for
    one end, and read and write for the other. On failure, it returns
    nothing.

      use IO::Pipely qw(socketpairly);
      my ($a_read, $b_read, $a_write, $b_write) = socketpairly();
      die "socketpairly() failed: $!" unless $a_read;

    socketpairly() returns two extra "writer" handles. They exist for the
    fallback case where two pipe() calls are needed instead of one socket
    pair. The extra handles can be ignored whenever pipe() will never be
    used. For example:

      use IO::Pipely qw(socketpairly);
      my ($side_a, $side_b) = socketpairly( type => 'socketpair' );
      die "socketpairly() failed: $!" unless $side_a;

    When given a choice, it will prefer bidirectional sockets instead of
    pipe() calls.

    socketpairly()'s choice can be forced using an optional named "type"
    parameter. See "PIPE TYPES" for the types that can be used. In this
    example, two unidirectional pipes wil be used instead of a more
    efficient pair of sockets:

      my ($a_read, $a_write, $b_read, $b_write) = pipely(
        type => 'pipe',
      );

    On most systems, socketpairly() will try to open a UNIX socketpair()
    first. It will then fall back to a pair of localhost Internet sockets,
    and finally it will try a pair of pipe() calls.

    On Windows (ActiveState and Strawberry Perl), socketpairly() prefers a
    pair of localhost Internet sockets first. It will then fall back to a
    UNIX socketpair(), and finally a couple of pipe() calls. The fallback
    options will probably fail, but the code remains hopeful.

    Cygwin Perl prefers localhost Internet sockets first, followed by a pair
    of pipe() calls, and finally a UNIX socketpair(). Those who know may
    find this counter-intuitive, but it works around known issues in some
    versions of Cygwin socketpair().

    MacPerl (MacOS 9 and earlier) has similar capaibilities to Windows.

  PIPE TYPES
    IO::Pipely currently supports three types of pipe and socket. Other
    types are possible, but these three cover all known uses so far. Please
    ask (or send patches) if additional types are needed.

   pipe
    Attempt to establish a one-way pipe using one pipe() filehandle pair (2
    file descriptors), or a two-way pipe-like connection using two pipe()
    pairs (4 file descriptors).

    IO::Pipely prefers to use pipe() for one-way pipes and some form of
    socket pair for two-way pipelike things.

   socketpair
    Attempt to establish a one- or two-way pipelike connection using a
    single socketpair() call. This uses two file descriptors regardless
    whether the connection is one- or two-way.

    IO::Pipely prefers socketpair() for two-way connections, unless the
    current platform has known issues with the socketpair() call.

    Socket pairs are UNIX domain only for now. INET domain may be added if
    it improves compatibility on some platform, or if someone contributes
    the code.

   inet
    Attempt to establish a one- or two-way pipelike connection using
    localhost socket() calls. This uses two file descriptors regardless
    whether the connection is one- or two-way.

    Localhost INET domain sockets are a last resort for platforms that don't
    support something better. They are the least secure method of
    communication since tools like tcpdump and Wireshark can tap into them.
    On the other hand, this makes them easiest to debug.

KNOWN ISSUES
    These are issues known to the developers at the time of this writing.
    Things change, so check back now and then.

  Cygwin
    CygWin seems to have a problem with socketpair() and exec(). When an
    exec'd process closes, any data on sockets created with socketpair() is
    not flushed. From irc.perl.org channel #poe:

      <dngnand>   Sounds like a lapse in cygwin's exec implementation.
                  It works ok under Unix-ish systems?
      <jdeluise2> yes, it works perfectly
      <jdeluise2> but, if we just use POE::Pipe::TwoWay->new("pipe")
                  it always works fine on cygwin
      <jdeluise2> by the way, it looks like the reason is that
                  POE::Pipe::OneWay works because it tries to make a
                  pipe first instead of a socketpair
      <jdeluise2> this socketpair problem seems like a long-standing
                  one with cygwin, according to searches on google,
                  but never been fixed.

  MacOS 9
    IO::Pipely supports MacOS 9 for historical reasons. It's unclear whether
    anyone still uses MacPerl, but the support is cheap since pipes and
    sockets there have many of the same caveats as they do on Windows.

  Symbol::gensym
    IO::Pipely uses Symbol::gensym() instead of autovivifying file handles.
    The main reasons against gensym() have been stylistic ones so far.
    Meanwhile, gensym() is compatible farther back than handle
    autovivification.

  Windows
    ActiveState and Strawberry Perl don't support pipe() or UNIX
    socketpair(). Localhost Internet sockets are used for everything there,
    including one-way pipes.

    For one-way pipes, the unused socket directions are shut down to avoid
    sending data the wrong way through them. Use socketpairly() instead.

BUGS
    The functions implemented here die outright upon failure, requiring
    eval{} around their calls.

    The following conduit types are currently unsupported because nobody has
    needed them so far. Please submit a request (and/or a patch) if any of
    these is needed:

      UNIX socket()
      INET-domain socketpair()
      IPv4-specific localhost sockets
      IPv6-specific localhost sockets

AUTHOR & COPYRIGHT
    IO::Pipely is copyright 2000-2013 by Rocco Caputo. All rights reserved.
    IO::Pipely is free software; you may redistribute it and/or modify it
    under the same terms as Perl itself.

HISTORY
    IO::Pipely is a spin-off of the POE project's portable pipes. Earlier
    versions of the code have been tested and used in production systems for
    over a decade.

