phpMan > man > IO::Pipely

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

VERSION
    version 0.006

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_a_write,
        $side_b_read, $side_b_write,
      ) = socketpairly();

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

      my (
        $side_a_read, $side_a_write,
        $side_b_read, $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, $a_write, $b_read, $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, undef, $side_b, undef) = 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) = socketpairly(
        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 2000-2021 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.