NAME
    Net::Daemon - Perl extension for portable daemons

SYNOPSIS
      # Create a subclass of Net::Daemon
      require Net::Daemon;
      package MyDaemon;
      @MyDaemon::ISA = qw(Net::Daemon);

      sub Run ($) {
        # This function does the real work; it is invoked whenever a
        # new connection is made.
      }

WARNING
    THIS IS ALPHA SOFTWARE. It is *only* 'Alpha' because the
    interface (API) is not finalised. The Alpha status does not
    reflect code quality or stability.

DESCRIPTION
    Net::Daemon is an abstract base class for implementing portable
    server applications in a very simple way. The module is designed
    for Perl 5.005 and threads, but can work with fork() and Perl
    5.004.

    The Net::Daemon class offers methods for the most common tasks a
    daemon needs: Starting up, logging, accepting clients,
    authorization, restricting its own environment for security and
    doing the true work. You only have to override those methods
    that aren't appropriate for you, but typically inheriting will
    safe you a lot of work anyways.

  Constructors

      $server = Net::Daemon->new($attr, $options);

      $connection = $server->Clone($socket);

    Two constructors are available: The new method is called upon
    startup and creates an object that will basically act as an
    anchor over the complete program. It supports command line
    parsing via the section on "Getopt::Long (3)".

    Arguments of new are *$attr*, an hash ref of attributes (see
    below) and *$options* an array ref of options, typically command
    line arguments (for example \@ARGV) that will be passed to
    Getopt::Long::GetOptions.

    The second constructor is Clone: It is called whenever a client
    connects. It receives the main server object as input and
    returns a new object. This new object will be passed to the
    methods that finally do the true work of communicating with the
    client. Communication occurs over the socket $socket, Clone's
    argument.

    Possible object attributes and the corresponding command line
    arguments are:

    *catchint* (--nocatchint)
        On some systems, in particular Solaris, the functions
        accept(), read() and so on are not safe against interrupts
        by signals. For example, if the user raises a USR1 signal
        (as typically used to reread config files), then the
        function returns an error EINTR. If the *catchint* option is
        on (by default it is, use --nocatchint to turn this off),
        then the package will ignore EINTR errors whereever
        possible.

    *chroot* (--chroot=dir)
        (UNIX only) After doing a bind(), change root directory to
        the given directory by doing a chroot(). This is usefull for
        security operations, but it restricts programming a lot. For
        example, you typically have to load external Perl extensions
        before doing a chroot(), or you need to create hard links to
        Unix sockets. This is typically done in the config file, see
        the --configfile option. See also the --group and --user
        options.

        If you don't know chroot(), think of an FTP server where you
        can see a certain directory tree only after logging in.

    *clients*
        An array ref with a list of clients. Clients are hash refs,
        the attributes *accept* (0 for denying access and 1 for
        permitting) and *mask*, a Perl regular expression for the
        clients IP number or its host name. See the section on
        "Access control" below.

    *configfile* (--configfile=file)
        Net::Daemon supports the use of config files. These files
        are assumed to contain a single hash ref that overrides the
        arguments of the new method. However, command line arguments
        in turn take precedence over the config file. See the the
        section on "Config File" section below for details on the
        config file.

    *debug* (--debug)
        Turn debugging mode on. Mainly this asserts that logging
        messages of level "debug" are created.

    *facility* (--facility=mode)
        (UNIX only) Facility to use for the section on "Sys::Syslog
        (3)". The default is daemon.

    *group* (--group=gid)
        After doing a bind(), change the real and effective GID to
        the given. This is usefull, if you want your server to bind
        to a privileged port (<1024), but don't want the server to
        execute as root. See also the --user option.

        GID's can be passed as group names or numeric values.

    *localaddr* (--localaddr=ip)
        By default a daemon is listening to any IP number that a
        machine has. This attribute allows to restrict the server to
        the given IP number.

    *localpath* (--localpath=path)
        If you want to restrict your server to local services only,
        you'll prefer using Unix sockets, if available. In that case
        you can use this option for setting the path of the Unix
        socket being created. This option implies --proto=unix.

    *localport* (--localport=port)
        This attribute sets the port on which the daemon is
        listening. It must be given somehow, as there's no default.

    *logfile* (--logfile=file)
        By default logging messages will be written to the syslog
        (Unix) or to the event log (Windows NT). On other operating
        systems you need to specify a log file. The special value
        "STDERR" forces logging to stderr.

    *loop-child* (--loop-child)
        This option forces creation of a new child for loops. (See
        the *loop-timeout* option.) By default the loops are
        serialized.

    *loop-timeout* (--loop-timeout=secs)
        Some servers need to take an action from time to time. For
        example the Net::Daemon::Spooler attempts to empty its
        spooling queue every 5 minutes. If this option is set to a
        positive value (zero being the default), then the server
        will call its Loop method every "loop-timeout" seconds.

        Don't trust too much on the precision of the interval: It
        depends on a number of factors, in particular the execution
        time of the Loop() method. The loop is implemented by using
        the *select* function. If you need an exact interval, you
        should better try to use the alarm() function and a signal
        handler. (And don't forget to look at the *catchint*
        option!)

        It is recommended to use the *loop-child* option in
        conjunction with *loop-timeout*.

    *mode* (--mode=modename)
        The Net::Daemon server can run in three different modes,
        depending on the environment.

        If you are running Perl 5.005 and did compile it for
        threads, then the server will create a new thread for each
        connection. The thread will execute the server's Run()
        method and then terminate. This mode is the default, you can
        force it with "--mode=threads".

        If threads are not available, but you have a working fork(),
        then the server will behave similar by creating a new
        process for each connection. This mode will be used
        automatically in the absence of threads or if you use the "-
        -mode=fork" option.

        Finally there's a single-connection mode: If the server has
        accepted a connection, he will enter the Run() method. No
        other connections are accepted until the Run() method
        returns. This operation mode is useful if you have neither
        threads nor fork(), for example on the Macintosh. For
        debugging purposes you can force this mode with "--
        mode=single".

        When running in mode single, you can still handle multiple
        clients at a time by preforking multiple child processes.
        The number of childs is configured with the option "--
        childs".

    *childs*
        Use this parameter to let Net::Daemon run in prefork mode,
        which means it forks the number of childs processes you give
        with this parameter, and all child handle connections
        concurrently. The difference to fork mode is, that the child
        processes continue to run after a connection has terminated
        and are able to accept a new connection. This is useful for
        caching inside the childs process (e.g. DBI::ProxyServer
        connect_cached attribute)

    *options*
        Array ref of Command line options that have been passed to
        the server object via the new method.

    *parent*
        When creating an object with Clone the original object
        becomes the parent of the new object. Objects created with
        new usually don't have a parent, thus this attribute is not
        set.

    *pidfile* (--pidfile=file)
        (UNIX only) If this option is present, a PID file will be
        created at the given location.

    *proto* (--proto=proto)
        The transport layer to use, by default *tcp* or *unix* for a
        Unix socket. It is not yet possible to combine both.

    *socket*
        The socket that is connected to the client; passed as
        $client argument to the Clone method. If the server object
        was created with new, this attribute can be undef, as long
        as the Bind method isn't called. Sockets are assumed to be
        IO::Socket objects.

    *user* (--user=uid)
        After doing a bind(), change the real and effective UID to
        the given. This is usefull, if you want your server to bind
        to a privileged port (<1024), but don't want the server to
        execute as root. See also the --group and the --chroot
        options.

        UID's can be passed as group names or numeric values.

    *version* (--version)
        Supresses startup of the server; instead the version string
        will be printed and the program exits immediately.

    Note that most of these attributes (facility, mode, localaddr,
    localport, pidfile, version) are meaningfull only at startup. If
    you set them later, they will be simply ignored. As almost all
    attributes have appropriate defaults, you will typically use the
    localport attribute only.

  Command Line Parsing

      my $optionsAvailable = Net::Daemon->Options();

      print Net::Daemon->Version(), "\n";

      Net::Daemon->Usage();

    The Options method returns a hash ref of possible command line
    options. The keys are option names, the values are again hash
    refs with the following keys:

    template
        An option template that can be passed to
        Getopt::Long::GetOptions.

    description
        A description of this option, as used in Usage

    The Usage method prints a list of all possible options and
    returns. It uses the Version method for printing program name
    and version.

  Config File

    If the config file option is set in the command line options or
    in the in the "new" args, then the method

      $server->ReadConfigFile($file, $options, $args)

    is invoked. By default the config file is expected to contain
    Perl source that returns a hash ref of options. These options
    override the "new" args and will in turn be overwritten by the
    command line options, as present in the $options hash ref.

    A typical config file might look as follows, we use the
    DBI::ProxyServer as an example:

        # Load external modules; this is not required unless you use
        # the chroot() option.
        #require DBD::mysql;
        #require DBD::CSV;

        {
            # 'chroot' => '/var/dbiproxy',
            'facility' => 'daemon',
            'pidfile' => '/var/dbiproxy/dbiproxy.pid',
            'user' => 'nobody',
            'group' => 'nobody',
            'localport' => '1003',
            'mode' => 'fork'

            # Access control
            'clients' => [
                # Accept the local
                {
                    'mask' => '^192\.168\.1\.\d+$',
                    'accept' => 1
                },
                # Accept myhost.company.com
                {
                    'mask' => '^myhost\.company\.com$',
                    'accept' => 1
                }
                # Deny everything else
                {
                    'mask' => '.*',
                    'accept' => 0
                }
            ]
        }

  Access control

    The Net::Daemon package supports a host based access control
    scheme. By default access is open for anyone. However, if you
    create an attribute $self->{'clients'}, typically in the config
    file, then access control is disabled by default. For any
    connection the client list is processed: The clients attribute
    is an array ref to a list of hash refs. Any of the hash refs may
    contain arbitrary attributes, including the following:

    mask    A Perl regular expression that has to match the clients IP
            number or its host name. The list is processed from the
            left to the right, whenever a 'mask' attribute matches,
            then the related hash ref is choosen as client and
            processing the client list stops.

    accept  This may be set to true or false (default when omitting the
            attribute), the former means accepting the client.

  Event logging

      $server->Log($level, $format, @args);
      $server->Debug($format, @args);
      $server->Error($format, @args);
      $server->Fatal($format, @args);

    The Log method is an interface to the section on "Sys::Syslog
    (3)" or the section on "Win32::EventLog (3)". It's arguments are
    *$level*, a syslog level like debug, notice or err, a format
    string in the style of printf and the format strings arguments.

    The Debug and Error methods are shorthands for calling Log with
    a level of debug and err, respectively. The Fatal method is like
    Error, except it additionally throws the given message as
    exception.

    See the Net::Daemon::Log(3) manpage for details.

  Flow of control

      $server->Bind();
      # The following inside Bind():
      if ($connection->Accept()) {
          $connection->Run();
      } else {
          $connection->Log('err', 'Connection refused');
      }

    The Bind method is called by the application when the server
    should start. Typically this can be done right after creating
    the server object $server. Bind usually never returns, except in
    case of errors.

    When a client connects, the server uses Clone to derive a
    connection object $connection from the server object. A new
    thread or process is created that uses the connection object to
    call your classes Accept method. This method is intended for
    host authorization and should return either FALSE (refuse the
    client) or TRUE (accept the client).

    If the client is accepted, the Run method is called which does
    the true work. The connection is closed when Run returns and the
    corresponding thread or process exits.

  Error Handling

    All methods are supposed to throw Perl exceptions in case of
    errors.

MULTITHREADING CONSIDERATIONS
    All methods are working with lexically scoped data and handle
    data only, the exception being the OpenLog method which is
    invoked before threading starts. Thus you are safe as long as
    you don't share handles between threads. I strongly recommend
    that your application behaves similar.

EXAMPLE
    As an example we'll write a simple calculator server. After
    connecting to this server you may type expressions, one per
    line. The server evaluates the expressions and prints the
    result. (Note this is an example, in real life we'd never
    implement such a security hole. :-)

    For the purpose of example we add a command line option *--base*
    that takes 'hex', 'oct' or 'dec' as values: The servers output
    will use the given base.

      # -*- perl -*-
      #
      # Calculator server
      #
      require 5.004;
      use strict;

      require Net::Daemon;

      package Calculator;

      use vars qw($VERSION @ISA);
      $VERSION = '0.01';
      @ISA = qw(Net::Daemon); # to inherit from Net::Daemon

      sub Version ($) { 'Calculator Example Server, 0.01'; }

      # Add a command line option "--base"
      sub Options ($) {
          my($self) = @_;
          my($options) = $self->SUPER::Options();
          $options->{'base'} = { 'template' => 'base=s',
                                 'description' => '--base                  '
                                        . 'dec (default), hex or oct'
                                  };
          $options;
      }

      # Treat command line option in the constructor
      sub new ($$;$) {
          my($class, $attr, $args) = @_;
          my($self) = $class->SUPER::new($attr, $args);
          if ($self->{'parent'}) {
              # Called via Clone()
              $self->{'base'} = $self->{'parent'}->{'base'};
          } else {
              # Initial call
              if ($self->{'options'}  &&  $self->{'options'}->{'base'}) {
                  $self->{'base'} = $self->{'options'}->{'base'}
              }
          }
          if (!$self->{'base'}) {
              $self->{'base'} = 'dec';
          }
          $self;
      }

      sub Run ($) {
          my($self) = @_;
          my($line, $sock);
          $sock = $self->{'socket'};
          while (1) {
              if (!defined($line = $sock->getline())) {
                  if ($sock->error()) {
                      $self->Error("Client connection error %s",
                                   $sock->error());
                  }
                  $sock->close();
                  return;
              }
              $line =~ s/\s+$//; # Remove CRLF
              my($result) = eval $line;
              my($rc);
              if ($self->{'base'} eq 'hex') {
                  $rc = printf $sock ("%x\n", $result);
              } elsif ($self->{'base'} eq 'oct') {
                  $rc = printf $sock ("%o\n", $result);
              } else {
                  $rc = printf $sock ("%d\n", $result);
              }
              if (!$rc) {
                  $self->Error("Client connection error %s",
                               $sock->error());
                  $sock->close();
                  return;
              }
          }
      }

      package main;

      my $server = Calculator->new({'pidfile' => 'none',
                                    'localport' => 2000}, \@ARGV);
      $server->Bind();

KNOWN PROBLEMS
    Most, or even any, known problems are related to the Sys::Syslog
    module which is by default used for logging events under Unix.
    I'll quote some examples:

    Usage: Sys::Syslog::_PATH_LOG at ...
        This problem is treated in perl bug 20000712.003. A
        workaround is changing line 277 of Syslog.pm to

          my $syslog = &_PATH_LOG() || croak "_PATH_LOG not found in syslog.ph";

AUTHOR AND COPYRIGHT
      Net::Daemon is Copyright (C) 1998, Jochen Wiedmann
                                         Am Eisteich 9
                                         72555 Metzingen
                                         Germany

                                         Phone: +49 7123 14887
                                         Email: joe@ispsoft.de

      All rights reserved.

      You may distribute this package under the terms of either the GNU
      General Public License or the Artistic License, as specified in the
      Perl README file.

SEE ALSO
    the RPC::pServer(3) manpage, the Netserver::Generic(3) manpage,
    the Net::Daemon::Log(3) manpage, the Net::Daemon::Test(3)
    manpage

