# phpman > man > POE::Driver

## NAME
    [POE::Driver](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver/markdown) - an abstract interface for buffered, non-blocking I/O

## SYNOPSIS
    This is a contrived example of how [POE::Filter](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter/markdown) and [POE::Driver](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver/markdown) objects may be used in a
    stand-alone application.

      my $driver = [POE::Driver::SysRW](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver%3A%3ASysRW/markdown)->new();
      my $filter = [POE::Filter::Line](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter%3A%3ALine/markdown)->new();

      my $list_of_octet_chunks = $filter->put("A line of text.");

      $driver->put( $list_of_octet_chunks );

      my $octets_remaining_in_buffer = $driver->flush($filehandle);
      die "couldn't flush everything" if $octets_remaining_in_buffer;

      while (1) {
        my $octets_list = $driver->get($filehandle);
        die $! unless defined $octets_list;

        $filter->get_one_start($octets_list);
        while (my $line = $filter->get_one()) {
          print "Input: $line\n";
        }
      }

    Most programs will use [POE::Filter](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter/markdown) and [POE::Driver](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver/markdown) objects as parameters to [POE::Wheel](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AWheel/markdown)
    constructors. See the synopses for particular classes for details.

## DESCRIPTION
    [POE::Driver](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver/markdown) is a common API for I/O drivers that can read from and write to various files,
    sockets, pipes, and other devices.

    POE "drivers" implement the specifics of reading and writing to devices. Drivers plug into
    [POE::Wheel](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AWheel/markdown) objects so that wheels may support a large number of device types without
    implementing a separate subclass for each.

    As mentioned in the SYNOPSIS, [POE::Driver](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver/markdown) objects may be used in stand-alone applications.

### Public Driver Methods
    These methods are the generic Driver interface, and every driver must implement them. Specific
    drivers may have additional methods related to their particular tasks.

   new
### new
    constructor parameters. The default constructor parameters should configure the driver for the
    most common use case.

   get FILEHANDLE
### get
    success---even if nothing was read from the FILEHANDLE. get() returns undef on error, and $!
    will be set to the reason why get() failed.

    The returned arrayref will be empty if nothing was read from the FILEHANDLE.

    In an EOF condition, get() returns undef with the numeric value of $! set to zero.

    The arrayref returned by get() is suitable for passing to any [POE::Filter](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter/markdown)'s get() or
### get_one_start

    put ARRAYREF
        put() accepts an ARRAYREF of raw octet chunks. These octets are added to the driver's
        internal output queue or buffer. put() returns the number of octets pending output after the
        new octets are buffered.

        Some drivers may flush data immediately from their put() methods.

    flush FILEHANDLE
        flush() attempts to write a driver's buffered data to a given FILEHANDLE. The driver should
        flush as much data as possible in a single flush() call.

        flush() returns the number of octets remaining in the driver's output queue or buffer after
        the maximum amount of data has been written.

        flush() denotes success or failure by the value of $! after it returns. $! will always
        numerically equal zero on success. On failure, $! will contain the usual Errno value. In
        either case, flush() will return the number of octets in the driver's output queue.

    get_out_messages_buffered
        get_out_messages_buffered() returns the number of messages enqueued in the driver's output
        queue, rounded up to the nearest whole message. Some applications require the message count
        rather than the octet count.

        Messages are raw octet chunks enqueued by put(). The following put() call enqueues two
        messages for a total of six octets:

          $filter->put( [ "one", "two" ] );

        It is possible for a flush() call to write part of a message. A partial message still counts
        as one message.

## SEE ALSO
    The SEE ALSO section in POE contains a table of contents covering the entire POE distribution.

    [POE::Wheel](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AWheel/markdown) - A base class for [POE::Session](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ASession/markdown) mix-ins.

    [POE::Filter](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3AFilter/markdown) - A base class for data parsers and serializers.

    [POE::Driver::SysRW](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver%3A%3ASysRW/markdown) - A driver that encapsulates sysread() and buffered syswrite().

## BUGS
    There is no [POE::Driver::SendRecv](https://www.chedong.com/phpMan.php/perldoc/POE%3A%3ADriver%3A%3ASendRecv/markdown), but nobody has needed one so far. sysread() and syswrite()
    manage to do almost everything people need.

    In theory, drivers should be pretty much interchangeable. In practice, there seems to be an
    impermeable barrier between the different SOCK_* types.

AUTHORS & COPYRIGHTS
    Please see POE for more information about authors and contributors.