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=head1 NAME

Net::Server - Extensible, general Perl server engine

=head1 SYNOPSIS

    #!/usr/bin/perl -w -T
    package MyPackage;

    use base qw(Net::Server);

    sub process_request {
        my $self = shift;
        while (<STDIN>) {
            s/\r?\n$//;
            print "You said '$_'\r\n"; # basic echo
            last if /quit/i;
        }
    }

    MyPackage->run(port => 160);

=head1 FEATURES

 * Single Server Mode
 * Inetd Server Mode
 * Preforking Simple Mode (PreForkSimple)
 * Preforking Managed Mode (PreFork)
 * Forking Mode
 * Multiplexing Mode using a single process
 * Multi port accepts on Single, Preforking, and Forking modes
 * Simultaneous accept/recv on tcp, udp, and unix sockets
 * Safe signal handling in Fork/PreFork avoids perl signal trouble
 * User customizable hooks
 * Chroot ability after bind
 * Change of user and group after bind
 * Basic allow/deny access control
 * Customized logging (choose Syslog, log_file, or STDERR)
 * HUP able server (clean restarts via sig HUP)
 * Dequeue ability in all Fork and PreFork modes.
 * Taint clean
 * Written in Perl
 * Protection against buffer overflow
 * Clean process flow
 * Extensibility

=head1 DESCRIPTION

C<Net::Server> is an extensible, generic Perl server engine.
C<Net::Server> combines the good properties from
C<Net::Daemon> (0.34), C<NetServer::Generic> (1.03), and
C<Net::FTPServer> (1.0), and also from various concepts in
the Apache Webserver.

C<Net::Server> attempts to be a generic server as in
C<Net::Daemon> and C<NetServer::Generic>.  It includes with
it the ability to run as an inetd process
(C<Net::Server::INET>), a single connection server
(C<Net::Server> or C<Net::Server::Single>), a forking server
(C<Net::Server::Fork>), a preforking server which maintains
a constant number of preforked children (C<Net::Server::PreForkSimple>),
or as a managed preforking server which maintains the number
of children based on server load (C<Net::Server::PreFork>).
In all but the inetd type, the server provides the ability to
connect to one or to multiple server ports.

C<Net::Server> uses ideologies of C<Net::FTPServer> in order
to provide extensibility.  The additional server types are
made possible via "personalities" or sub classes of the
C<Net::Server>.  By moving the multiple types of servers out of
the main C<Net::Server> class, the C<Net::Server> concept is
easily extended to other types (in the near future, we would
like to add a "Thread" personality).

C<Net::Server> borrows several concepts from the Apache
Webserver.  C<Net::Server> uses "hooks" to allow custom
servers such as SMTP, HTTP, POP3, etc. to be layered over
the base C<Net::Server> class.  In addition the
C<Net::Server::PreFork> class borrows concepts of
min_start_servers, max_servers, and min_waiting servers.
C<Net::Server::PreFork> also uses the concept of an flock
serialized accept when accepting on multiple ports (PreFork
can choose between flock, IPC::Semaphore, and pipe to control
serialization).

=head1 PERSONALITIES

C<Net::Server> is built around a common class (Net::Server)
and is extended using sub classes, or C<personalities>.
Each personality inherits, overrides, or enhances the base
methods of the base class.

Included with the Net::Server package are several basic
personalities, each of which has their own use.

=over 4

=item Fork

Found in the module Net/Server/Fork.pm (see
L<Net::Server::Fork>).  This server binds to one or more
ports and then waits for a connection.  When a client
request is received, the parent forks a child, which then
handles the client and exits.  This is good for moderately
hit services.

=item INET

Found in the module Net/Server/INET.pm (see
L<Net::Server::INET>).  This server is designed to be used
with inetd.  The C<pre_bind>, C<bind>, C<accept>, and
C<post_accept> are all overridden as these services are
taken care of by the INET daemon.

=item MultiType

Found in the module Net/Server/MultiType.pm (see
L<Net::Server::MultiType>).  This server has no server
functionality of its own.  It is designed for servers which
need a simple way to easily switch between different
personalities.  Multiple C<server_type> parameters may be
given and Net::Server::MultiType will cycle through until it
finds a class that it can use.

=item Multiplex

Found in the module Net/Server/Multiplex.pm (see
L<Net::Server::Multiplex>).  This server binds to one or more
ports.  It uses IO::Multiplex to multiplex between waiting
for new connections and waiting for input on currently
established connections.  This personality is designed to
run as one process without forking.  The C<process_request>
method is never used but the C<mux_input> callback is used
instead (see also L<IO::Multiplex>).  See
examples/samplechat.pl for an example using most of the
features of Net::Server::Multiplex.

=item PreForkSimple

Found in the module Net/Server/PreFork.pm (see
L<Net::Server::PreFork>).  This server binds to one or more
ports and then forks C<max_servers> child process.  The
server will make sure that at any given time there are always
C<max_servers> available to receive a client request.  Each
of these children will process up to C<max_requests> client
connections.  This type is good for a heavily hit site that
can dedicate max_server processes no matter what the load.
It should scale well for most applications.  Multi port accept
is accomplished using either flock, IPC::Semaphore, or pipe to serialize the
children.  Serialization may also be switched on for single
port in order to get around an OS that does not allow multiple
children to accept at the same time.  For a further
discussion of serialization see L<Net::Server::PreFork>.

=item PreFork

Found in the module Net/Server/PreFork.pm (see
L<Net::Server::PreFork>).  This server binds to one or more
ports and then forks C<min_servers> child process.  The
server will make sure that at any given time there are
at least C<min_spare_servers> but not more than C<max_spare_servers>
available to receive a client request, up
to C<max_servers>.  Each of these children will process up
to C<max_requests> client connections.  This type is good
for a heavily hit site, and should scale well for most
applications.  Multi port accept is accomplished using
either flock, IPC::Semaphore, or pipe to serialize the
children.  Serialization may also be switched on for single
port in order to get around an OS that does not allow multiple
children to accept at the same time.  For a further
discussion of serialization see L<Net::Server::PreFork>.

=item Single

All methods fall back to Net::Server.  This personality is
provided only as parallelism for Net::Server::MultiType.

=back

C<Net::Server> was partially written to make it easy to add
new personalities.  Using separate modules built upon an
open architecture allows for easy addition of new features,
a separate development process, and reduced code bloat in
the core module.

=head1 SOCKET ACCESS

Once started, the Net::Server will take care of binding to
port and waiting for connections.  Once a connection is
received, the Net::Server will accept on the socket and
will store the result (the client connection) in
$self-E<gt>{server}-E<gt>{client}.  This property is a
Socket blessed into the the IO::Socket classes.  UDP
servers are slightly different in that they will perform
a B<recv> instead of an B<accept>.

To make programming easier, during the post_accept phase,
STDIN and STDOUT are opened to the client connection.  This
allows for programs to be written using E<lt>STDINE<gt> and
print "out\n" to print to the client connection.  UDP will
require using a -E<gt>send call.

=head1 SAMPLE CODE

The following is a very simple server.  The main
functionality occurs in the process_request method call as
shown below.  Notice the use of timeouts to prevent Denial
of Service while reading.  (Other examples of using
C<Net::Server> can, or will, be included with this distribution).

    #!/usr/bin/perl -w -T

    package MyPackage;

    use strict;
    use base qw(Net::Server::PreFork); # any personality will do

    MyPackage->run;

    ### over-ridden subs below

    sub process_request {
        my $self = shift;
        eval {

            local $SIG{'ALRM'} = sub { die "Timed Out!\n" };
            my $timeout = 30; # give the user 30 seconds to type some lines

            my $previous_alarm = alarm($timeout);
            while (<STDIN>) {
                s/\r?\n$//;
                print "You said '$_'\r\n";
                alarm($timeout);
            }
            alarm($previous_alarm);

        };

        if ($@ =~ /timed out/i) {
            print STDOUT "Timed Out.\r\n";
            return;
        }

    }

    1;

Playing this file from the command line will invoke a
Net::Server using the PreFork personality.  When building a
server layer over the Net::Server, it is important to use
features such as timeouts to prevent Denial Of Service
attacks.

=head1 ARGUMENTS

There are five possible ways to pass arguments to
Net::Server.  They are I<passing to the new method>, I<passing on
command line>, I<passing parameters to run>, I<using a conf file>,
I<returning values in the default_values method>, or I<configuring the
values in post_configure_hook>.

The C<options> method is used to determine which arguments the server
will search for and can be used to extend the parsed parameters.  Any
arguments found from the command line, parameters passed to run, and
arguments found in the conf_file will be matched against the keys of
the options template.  Any commandline parameters that do not match
will be left in place and can be further processed by the server in
the various hooks (by looking at @ARGV).  Arguments passed to new will
automatically win over any other options (this can be used if you
would like to disallow a user passing in other arguments).

Arguments consist of key value pairs.  On the commandline
these pairs follow the POSIX fashion of C<--key value> or
C<--key=value>, and also C<key=value>.  In the conf file the
parameter passing can best be shown by the following regular
expression: ($key,$val)=~/^(\w+)\s+(\S+?)\s+$/.  Passing
arguments to the run method is done as follows:
C<Net::Server->run(key1 => 'val1')>.  Passing arguments via
a prebuilt object can best be shown in the following code:

    #!/usr/bin/perl -w -T

    package MyPackage;
    use strict;
    use base qw(Net::Server);

    my $server = MyPackage->new({
        key1 => 'val1',
    });

    $server->run;

All five methods for passing arguments may be used at the
same time.  Once an argument has been set, it is not over
written if another method passes the same argument.  C<Net::Server>
will look for arguments in the following order:

  1) Arguments passed to the C<new> method.
  2) Arguments passed on command line.
  3) Arguments passed to the C<run> method.
  4) Arguments passed via a conf file.
  5) Arguments set in the C<default_values> method.

Additionally the following hooks are available:

  1) Arguments set in the configure_hook (occurs after new
     but before any of the other areas are checked).
  2) Arguments set and validated in the post_configure_hook
     (occurs after all of the other areas are checked).

Each of these levels will override parameters of the same
name specified in subsequent levels.  For example, specifying
--setsid=0 on the command line will override a value of "setsid 1"
in the conf file.

Note that the configure_hook method doesn't return values
to set, but is there to allow for setting up configured values
before the configure method is called.

Key/value pairs used by the server are removed by the
configuration process so that server layers on top of
C<Net::Server> can pass and read their own parameters.

=head1 ADDING CUSTOM ARGUMENTS

It is possible to add in your own custom parameters to those parsed
by Net::Server.  The following code shows how this is done:

    sub options {
        my $self     = shift;
        my $prop     = $self->{'server'};
        my $template = shift;

        ### setup options in the parent classes
        $self->SUPER::options($template);

        ### add a single value option
        $prop->{'my_option'} ||= undef;
        $template->{'my_option'} = \ $prop->{'my_option'};

        ### add a multi value option
        $prop->{'an_arrayref_item'} ||= [];
        $template->{'an_arrayref_item'} = $prop->{'an_arrayref_item'};
    }

Overriding the C<options> method allows for adding your own custom
fields.  A template hashref is passed in, that should then be modified
to contain an of your custom fields.  Fields which are intended to
receive a single scalar value should have a reference to the
destination scalar given.  Fields which are intended to receive
multiple values should reference the corresponding destination
arrayref.

You are responsible for validating your custom options once they have
been parsed.  The post_configure_hook is a good place to do your
validation.

Some emails have asked why we use this "template" method.  The idea is
that you are creating the the data structure to store the values in,
and you are also creating a way to get the values into the data
structure.  The template is the way to get the values to the servers
data structure.  One of the possibilities (that probably isn't used
that much) is that by letting you specify the mapping, you could build
a nested data structure - even though the passed in arguments are
flat.  It also allows you to setup aliases to your names.

For example, a basic structure might look like this:

   $prop = $self->{'server'}

   $prop->{'my_custom_option'} ||= undef;
   $prop->{'my_custom_array'}  ||= [];

   $template = {
      my_custom_option => \ $prop->{'my_custom_option'},
      mco              => \ $prop->{'my_custom_option'}, # alias
      my_custom_array  => $prop->{'my_custom_array'},
      mca              => $prop->{'my_custom_array'}, # an alias
   };

   $template->{'mco2'} = $template->{'mco'}; # another way to alias

But you could also have more complex data:

   $prop = $self->{'server'};

   $prop->{'one_layer'} = {
       two_layer => [
           undef,
           undef,
       ],
   };

   $template = {
        param1 => \ $prop->{'one_layer'}->{'two_layer'}->[0],
        param2 => \ $prop->{'one_layer'}->{'two_layer'}->[1],
   };

This is of course a contrived example - but it does show that you can
get the data from the flat passed in arguments to whatever type of
structure you need - with only a little bit of effort.

=head1 DEFAULT ARGUMENTS FOR Net::Server

The following arguments are available in the default C<Net::Server> or
C<Net::Server::Single> modules.  (Other personalities may use
additional parameters and may optionally not use parameters from the
base class.)

  Key               Value                    Default
  conf_file         "filename"               undef

  log_level         0-4                      2
  log_file          (filename|Sys::Syslog)   undef

  ## syslog parameters
  syslog_logsock    (native|unix|inet|udp
                     |tcp|stream|console)    unix (on Sys::Syslog < 0.15)
  syslog_ident      "identity"               "net_server"
  syslog_logopt     (cons|ndelay|nowait|pid) pid
  syslog_facility   \w+                      daemon

  port              \d+                      20203
  host              "host"                   "*"
  proto             (tcp|udp|unix)           "tcp"
  listen            \d+                      SOMAXCONN

  reverse_lookups   1                        undef
  allow             /regex/                  none
  deny              /regex/                  none
  cidr_allow        CIDR                     none
  cidr_deny         CIDR                     none

  ## daemonization parameters
  pid_file          "filename"               undef
  chroot            "directory"              undef
  user              (uid|username)           "nobody"
  group             (gid|group)              "nobody"
  background        1                        undef
  setsid            1                        undef

  no_close_by_child (1|undef)                undef

  ## See Net::Server::Proto::(TCP|UDP|UNIX|etc)
  ## for more sample parameters.

=over 4

=item conf_file

Filename from which to read additional key value pair arguments
for starting the server.  Default is undef.

There are two ways that you can specify a default location for
a conf_file.  The first is to pass the default value to the run
method as in:

    MyServer->run({
       conf_file => '/etc/my_server.conf',
    });

If the end user passes in --conf_file=/etc/their_server.conf then
the value will be overridden.

The second way to do this was added in the 0.96 version.  It uses
the default_values method as in:

    sub default_values {
        return {
            conf_file => '/etc/my_server.conf',
        }
    }

This method has the advantage of also being able to be overridden
in the run method.

If you do not want the user to be able to specify a conf_file at
all, you can pass conf_file to the new method when creating your
object:

    MyServer->new({
       conf_file => '/etc/my_server.conf',
    })->run;

If passed this way, the value passed to new will "win" over any of
the other passed in values.

=item log_level

Ranges from 0 to 4 in level.  Specifies what level of error
will be logged.  "O" means logging is off.  "4" means very
verbose.  These levels should be able to correlate to syslog
levels.  Default is 2.  These levels correlate to syslog levels
as defined by the following key/value pairs: 0=>'err',
1=>'warning', 2=>'notice', 3=>'info', 4=>'debug'.

=item log_file

Name of log file to be written to.  If no name is given and
hook is not overridden, log goes to STDERR.  Default is undef.
If the magic name "Sys::Syslog" is used, all logging will
take place via the Sys::Syslog module.  If syslog is used
the parameters C<syslog_logsock>, C<syslog_ident>, and
C<syslog_logopt>,and C<syslog_facility> may also be defined.
If a C<log_file> is given or if C<setsid> is set, STDIN and
STDOUT will automatically be opened to /dev/null and STDERR
will be opened to STDOUT.  This will prevent any output
from ending up at the terminal.

=item pid_file

Filename to store pid of parent process.  Generally applies
only to forking servers.  Default is none (undef).

=item syslog_logsock

Only available if C<log_file> is equal to "Sys::Syslog".  May
be either unix, inet, native, console, stream, udp, or tcp, or
an arrayref of the types to try.  Default is "unix" if the version
of Sys::Syslog < 0.15 - otherwise the default is to not call
setlogsock.

See L<Sys::Syslog>.

=item syslog_ident

Only available if C<log_file> is equal to "Sys::Syslog".  Id
to prepend on syslog entries.  Default is "net_server".
See L<Sys::Syslog>.

=item syslog_logopt

Only available if C<log_file> is equal to "Sys::Syslog".  May
be either zero or more of "pid","cons","ndelay","nowait".
Default is "pid".  See L<Sys::Syslog>.

=item syslog_facility

Only available if C<log_file> is equal to "Sys::Syslog".
See L<Sys::Syslog> and L<syslog>.  Default is "daemon".

=item port

See L<Net::Server::Proto>.
Local port/socket on which to bind.  If low port, process must
start as root.  If multiple ports are given, all will be
bound at server startup.  May be of the form
C<host:port/proto>, C<host:port>, C<port/proto>, or C<port>,
where I<host> represents a hostname residing on the local
box, where I<port> represents either the number of the port
(eg. "80") or the service designation (eg.  "http"), and
where I<proto> represents the protocol to be used.  See
L<Net::Server::Proto>.  If you are working with unix sockets,
you may also specify C<socket_file|unix> or
C<socket_file|type|unix> where type is SOCK_DGRAM or
SOCK_STREAM.  If the protocol is not specified, I<proto> will
default to the C<proto> specified in the arguments.  If C<proto> is not
specified there it will default to "tcp".  If I<host> is not
specified, I<host> will default to C<host> specified in the
arguments.  If C<host> is not specified there it will
default to "*".  Default port is 20203.  Configuration passed
to new or run may be either a scalar containing a single port
number or an arrayref of ports.

=item host

Local host or addr upon which to bind port.  If a value of '*' is
given, the server will bind that port on all available addresses
on the box.  See L<Net::Server::Proto>. See L<IO::Socket>.  Configuration
passed to new or run may be either a scalar containing a single
host or an arrayref of hosts - if the hosts array is shorter than
the ports array, the last host entry will be used to augment the
hosts arrary to the size of the ports array.

=item proto

See L<Net::Server::Proto>.
Protocol to use when binding ports.  See L<IO::Socket>.  As
of release 0.70, Net::Server supports tcp, udp, and unix.  Other
types will need to be added later (or custom modules extending the
Net::Server::Proto class may be used).  Configuration
passed to new or run may be either a scalar containing a single
proto or an arrayref of protos - if the protos array is shorter than
the ports array, the last proto entry will be used to augment the
protos arrary to the size of the ports array.

=item listen

  See L<IO::Socket>.  Not used with udp protocol (or UNIX SOCK_DGRAM).

=item reverse_lookups

Specify whether to lookup the hostname of the connected IP.
Information is cached in server object under C<peerhost>
property.  Default is to not use reverse_lookups (undef).

=item allow/deny

May be specified multiple times.  Contains regex to compare
to incoming peeraddr or peerhost (if reverse_lookups has
been enabled).  If allow or deny options are given, the
incoming client must match an allow and not match a deny or
the client connection will be closed.  Defaults to empty
array refs.

=item cidr_allow/cidr_deny

May be specified multiple times.  Contains a CIDR block to compare to
incoming peeraddr.  If cidr_allow or cidr_deny options are given, the
incoming client must match a cidr_allow and not match a cidr_deny or
the client connection will be closed.  Defaults to empty array refs.

=item chroot

Directory to chroot to after bind process has taken place
and the server is still running as root.  Defaults to
undef.

=item user

Userid or username to become after the bind process has
occured.  Defaults to "nobody."  If you would like the
server to run as root, you will have to specify C<user>
equal to "root".

=item group

Groupid or groupname to become after the bind process has
occured.  Defaults to "nobody."  If you would like the
server to run as root, you will have to specify C<group>
equal to "root".

=item background

Specifies whether or not the server should fork after the
bind method to release itself from the command line.
Defaults to undef.  Process will also background if
C<setsid> is set.

=item setsid

Specifies whether or not the server should fork after the
bind method to release itself from the command line and then
run the C<POSIX::setsid()> command to truly daemonize.
Defaults to undef.  If a C<log_file> is given or if
C<setsid> is set, STDIN and STDOUT will automatically be
opened to /dev/null and STDERR will be opened to STDOUT.
This will prevent any output from ending up at the terminal.

=item no_close_by_child

Boolean.  Specifies whether or not a forked child process has
permission or not to shutdown the entire server process.  If set to 1,
the child may NOT signal the parent to shutdown all children.  Default
is undef (not set).

=item no_client_stdout

Boolean.  Default undef (not set).  Specifies that STDIN and STDOUT
should not be opened on the client handle once a connection has been
accepted.  By default the Net::Server will open STDIN and STDOUT on
the client socket making it easier for many types of scripts to read
directly from and write directly to the socket using normal print and
read methods.  Disabling this is useful on clients that may be opening
their own connections to STDIN and STDOUT.

This option has no affect on STDIN and STDOUT which has a magic client
property that is tied to the already open STDIN and STDOUT.

=item leave_children_open_on_hup

Boolean.  Default undef (not set).  If set, the parent will not attempt
to close child processes if the parent receives a SIG HUP.  The parent
will rebind the the open port and begin tracking a fresh set of children.

Children of a Fork server will exit after their current request.  Children
of a Prefork type server will finish the current request and then exit.

Note - the newly restarted parent will start up a fresh set of servers on
fork servers.  The new parent will attempt to keep track of the children from
the former parent but custom communication channels (open pipes from the child
to the old parent) will no longer be available to the old child processes.  New
child processes will still connect properly to the new parent.

=back

=head1 PROPERTIES

All of the C<ARGUMENTS> listed above become properties of
the server object under the same name.  These properties, as
well as other internal properties, are available during
hooks and other method calls.

The structure of a Net::Server object is shown below:

  $self = bless( {
                   'server' => {
                                 'key1' => 'val1',
                                 # more key/vals
                               }
                 }, 'Net::Server' );

This structure was chosen so that all server related
properties are grouped under a single key of the object
hashref.  This is so that other objects could layer on top
of the Net::Server object class and still have a fairly
clean namespace in the hashref.

You may get and set properties in two ways.  The suggested
way is to access properties directly via

  my $val = $self->{server}->{key1};

Accessing the properties directly will speed the server process -
though some would deem this as bad style.  A second way has been
provided for object oriented types who believe in methods.  The second
way consists of the following methods:

  my $val = $self->get_property( 'key1' );
  my $self->set_property( key1 => 'val1' );

Properties are allowed to be changed at any time with
caution (please do not undef the sock property or you will
close the client connection).

=head1 CONFIGURATION FILE

C<Net::Server> allows for the use of a configuration file to
read in server parameters.  The format of this conf file is
simple key value pairs.  Comments and blank lines are
ignored.

  #-------------- file test.conf --------------

  ### user and group to become
  user        somebody
  group       everybody

  ### logging ?
  log_file    /var/log/server.log
  log_level   3
  pid_file    /tmp/server.pid

  ### optional syslog directive
  ### used in place of log_file above
  #log_file       Sys::Syslog
  #syslog_logsock unix
  #syslog_ident   myserver
  #syslog_logopt  pid|cons

  ### access control
  allow       .+\.(net|com)
  allow       domain\.com
  deny        a.+
  cidr_allow  127.0.0.0/8
  cidr_allow  192.0.2.0/24
  cidr_deny   192.0.2.4/30

  ### background the process?
  background  1

  ### ports to bind (this should bind
  ### 127.0.0.1:20205 and localhost:20204)
  ### See Net::Server::Proto
  host        127.0.0.1
  port        localhost:20204
  port        20205

  ### reverse lookups ?
  # reverse_lookups on

  #-------------- file test.conf --------------

=head1 PROCESS FLOW

The process flow is written in an open, easy to
override, easy to hook, fashion.  The basic flow is
shown below.  This is the flow of the C<$self-E<gt>run> method.

  $self->configure_hook;

  $self->configure(@_);

  $self->post_configure;

  $self->post_configure_hook;

  $self->pre_bind;

  $self->bind;

  $self->post_bind_hook;

  $self->post_bind;

  $self->pre_loop_hook;

  $self->loop;

  ### routines inside a standard $self->loop
  # $self->accept;
  # $self->run_client_connection;
  # $self->done;

  $self->pre_server_close_hook;

  $self->server_close;

The server then exits.

During the client processing phase
(C<$self-E<gt>run_client_connection>), the following
represents the program flow:

  $self->post_accept;

  $self->get_client_info;

  $self->post_accept_hook;

  if( $self->allow_deny

      && $self->allow_deny_hook ){

    $self->process_request;

  }else{

    $self->request_denied_hook;

  }

  $self->post_process_request_hook;

  $self->post_process_request;

  $self->post_client_connection_hook;

The process then loops and waits for the next
connection.  For a more in depth discussion, please
read the code.

During the server shutdown phase
(C<$self-E<gt>server_close>), the following
represents the program flow:

  $self->close_children;  # if any

  $self->post_child_cleanup_hook;

  if( Restarting server ){
     $self->restart_close_hook();
     $self->hup_server;
  }

  $self->shutdown_sockets;

  $self->server_exit;

=head1 MAIN SERVER METHODS

=over 4

=item C<$self-E<gt>run>

This method incorporates the main process flow.  This flow
is listed above.

The method run may be called in any of the following ways.

   MyPackage->run(port => 20201);

   MyPackage->new({port => 20201})->run;

   my $obj = bless {server=>{port => 20201}}, 'MyPackage';
   $obj->run;

The ->run method should typically be the last method called
in a server start script (the server will exit at the end
of the ->run method).

=item C<$self-E<gt>configure>

This method attempts to read configurations from the commandline,
from the run method call, or from a specified conf_file (the conf_file
may be specified by passed in parameters, or in the default_values).
All of the configured parameters are then stored in the {"server"}
property of the Server object.

=item C<$self-E<gt>post_configure>

The post_configure hook begins the startup of the server.  During
this method running server instances are checked for, pid_files are created,
log_files are created, Sys::Syslog is initialized (as needed), process
backgrounding occurs and the server closes STDIN and STDOUT (as needed).

=item C<$self-E<gt>pre_bind>

This method is used to initialize all of the socket objects
used by the server.

=item C<$self-E<gt>bind>

This method actually binds to the inialized sockets (or rebinds
if the server has been HUPed).

=item C<$self-E<gt>post_bind>

During this method priveleges are dropped.
The INT, TERM, and QUIT signals are set to run server_close.
Sig PIPE is set to IGNORE.  Sig CHLD is set to sig_chld.  And sig
HUP is set to call sig_hup.

Under the Fork, PreFork, and PreFork simple personalities, these
signals are registered using Net::Server::SIG to allow for
safe signal handling.

=item C<$self-E<gt>loop>

During this phase, the server accepts incoming connections.
The behavior of how the accepting occurs and if a child process
handles the connection is controlled by what type of Net::Server
personality the server is using.

Net::Server and Net::Server single accept only one connection at
a time.

Net::Server::INET runs one connection and then exits (for use by
inetd or xinetd daemons).

Net::Server::MultiPlex allows for one process to simultaneously
handle multiple connections (but requires rewriting the process_request
code to operate in a more "packet-like" manner).

Net::Server::Fork forks off a new child process for each incoming
connection.

Net::Server::PreForkSimple starts up a fixed number of processes
that all accept on incoming connections.

Net::Server::PreFork starts up a base number of child processes
which all accept on incoming connections.  The server throttles
the number of processes running depending upon the number of
requests coming in (similar to concept to how Apache controls
its child processes in a PreFork server).

Read the documentation for each of the types for more information.

=item C<$self-E<gt>server_close>

This method is called once the server has been signaled to end, or
signaled for the server to restart (via HUP),  or the loop
method has been exited.

This method takes care of cleaning up any remaining child processes,
setting appropriate flags on sockets (for HUPing), closing up
logging, and then closing open sockets.

=item C<$self-E<gt>server_exit>

This method is called at the end of server_close.  It calls exit,
but may be overridden to do other items.  At this point all services
should be shut down.

=back

=head1 MAIN CLIENT CONNECTION METHODS

=over 4

=item C<$self-E<gt>run_client_connection>

This method is run after the server has accepted and received
a client connection.  The full process flow is listed
above under PROCESS FLOWS.  This method takes care of
handling each client connection.

=item C<$self-E<gt>post_accept>

This method opens STDIN and STDOUT to the client socket.
This allows any of the methods during the run_client_connection
phase to print directly to and read directly from the
client socket.

=item C<$self-E<gt>get_client_info>

This method looks up information about the client connection
such as ip address, socket type, and hostname (as needed).

=item C<$self-E<gt>allow_deny>

This method uses the rules defined in the allow and deny configuration
parameters to determine if the ip address should be accepted.

=item C<$self-E<gt>process_request>

This method is intended to handle all of the client communication.
At this point STDIN and STDOUT are opened to the client, the ip
address has been verified.  The server can then
interact with the client connection according to whatever API or
protocol the server is implementing.  Note that the stub implementation
uses STDIN and STDOUT and will not work if the no_client_stdout flag
is set.

This is the main method to override.

The default method implements a simple echo server that
will repeat whatever is sent.  It will quit the child if "quit"
is sent, and will exit the server if "exit" is sent.

=item C<$self-E<gt>post_process_request>

This method is used to clean up the client connection and
to handle any parent/child accounting for the forking servers.

=back

=head1 HOOKS

C<Net::Server> provides a number of "hooks" allowing for
servers layered on top of C<Net::Server> to respond at
different levels of execution without having to "SUPER" class
the main built-in methods.  The placement of the hooks
can be seen in the PROCESS FLOW section.

Almost all of the default hook methods do nothing.  To use a hook
you simply need to override the method in your subclass.  For example
to add your own post_configure_hook you could do something like the following:

    package MyServer;

    sub post_configure_hook {
        my $self = shift;
        my $prop = $self->{'server'};

        # do some validation here
    }

The following describes the hooks available in the plain Net::Server class
(other flavors such as Fork or PreFork have additional hooks).

=over 4

=item C<$self-E<gt>configure_hook()>

This hook takes place immediately after the C<-E<gt>run()>
method is called.  This hook allows for setting up the
object before any built in configuration takes place.
This allows for custom configurability.

=item C<$self-E<gt>post_configure_hook()>

This hook occurs just after the reading of configuration
parameters and initiation of logging and pid_file creation.
It also occurs before the C<-E<gt>pre_bind()> and
C<-E<gt>bind()> methods are called.  This hook allows for
verifying configuration parameters.

=item C<$self-E<gt>post_bind_hook()>

This hook occurs just after the bind process and just before
any chrooting, change of user, or change of group occurs.
At this point the process will still be running as the user
who started the server.

=item C<$self-E<gt>pre_loop_hook()>

This hook occurs after chroot, change of user, and change of
group has occured.  It allows for preparation before looping
begins.

=item C<$self-E<gt>can_read_hook()>

This hook occurs after a socket becomes readible on an
accept_multi_port request (accept_multi_port is used if there are
multiple bound ports to accept on, or if the "multi_port"
configuration parameter is set to true).  This hook is intended to
allow for processing of arbitrary handles added to the IO::Select used
for the accept_multi_port.  These handles could be added during the
post_bind_hook.  No internal support is added for processing these
handles or adding them to the IO::Socket.  Care must be used in how
much occurs during the can_read_hook as a long response time will
result in the server being susceptible to DOS attacks.  A return value
of true indicates that the Server should not pass the readible handle
on to the post_accept and process_request phases.

It is generally suggested that other avenues be pursued for sending
messages via sockets not created by the Net::Server.

=item C<$self-E<gt>post_accept_hook()>

This hook occurs after a client has connected to the server.
At this point STDIN and STDOUT are mapped to the client
socket.  This hook occurs before the processing of the
request.

=item C<$self-E<gt>allow_deny_hook()>

This hook allows for the checking of ip and host information
beyond the C<$self-E<gt>allow_deny()> routine.  If this hook
returns 1, the client request will be processed,
otherwise, the request will be denied processing.

=item C<$self-E<gt>request_denied_hook()>

This hook occurs if either the C<$self-E<gt>allow_deny()> or
C<$self-E<gt>allow_deny_hook()> have taken place.

=item C<$self-E<gt>post_process_request_hook()>

This hook occurs after the processing of the request, but
before the client connection has been closed.

=item C<$self-E<gt>post_client_connection_hook>

This is one final hook that occurs at the very end of the
run_client_connection method.  At this point all other methods
and hooks that will run during the run_client_connection
have finished and the client connection has already been closed.

=item C<$self-E<gt>pre_server_close_hook()>

This hook occurs before the server begins shutting down.

=item C<$self-E<gt>write_to_log_hook>

This hook handles writing to log files.  The default hook
is to write to STDERR, or to the filename contained in
the parameter C<log_file>.  The arguments passed are a
log level of 0 to 4 (4 being very verbose), and a log line.
If log_file is equal to "Sys::Syslog", then logging will
go to Sys::Syslog and will bypass the write_to_log_hook.

=item C<$self-E<gt>fatal_hook>

This hook occurs when the server has encountered an
unrecoverable error.  Arguments passed are the error
message, the package, file, and line number.  The hook
may close the server, but it is suggested that it simply
return and use the built in shut down features.

=item C<$self-E<gt>post_child_cleanup_hook>

This hook occurs in the parent server process after all
children have been shut down and just before the server
either restarts or exits.  It is intended for additional
cleanup of information.  At this point pid_files and
lockfiles still exist.

=item C<$self-E<gt>restart_open_hook>

This hook occurs if a server has been HUPed (restarted
via the HUP signal.  It occurs just before reopening to
the filenos of the sockets that were already opened.

=item C<$self-E<gt>restart_close_hook>

This hook occurs if a server has been HUPed (restarted
via the HUP signal.  It occurs just before restarting the
server via exec.

=back

=head1 OTHER METHODS

=over 4

=item C<$self-E<gt>default_values>

Allow for returning configuration values that will be used if no
other value could be found.

Should return a hashref.

    sub default_values {
      return {
        port => 20201,
      };
    }

=item C<$self-E<gt>handle_syslog_error>

Called when log_file is set to 'Sys::Syslog' and an error occurs
while writing to the syslog.  It is passed two arguments, the
value of $@, and an arrayref containing the arguments that
were passed to the log method when the error occured.

=item C<$self-E<gt>log>

Parameters are a log_level and a message.

If log_level is set to 'Sys::Syslog', the parameters may alternately
be a log_level, a format string, and format string parameters.
(The second parameter is assumed to be a format string if additional
arguments are passed along).  Passing arbitrary format strings to
Sys::Syslog will allow the server to be vulnerable to exploit.  The
server maintainer should make sure that any string treated as
a format string is controlled.

    # assuming log_file = 'Sys::Syslog'

    $self->log(1, "My Message with %s in it");
    # sends "%s", "My Message with %s in it" to syslog

    $self->log(1, "My Message with %s in it", "Foo");
    # sends "My Message with %s in it", "Foo" to syslog

If log_file is set to a file (other than Sys::Syslog), the message
will be appended to the log file by calling the write_to_log_hook.

If the log_file is Sys::Syslog and an error occurs during write,
the handle_syslog_error method will be called and passed the
error exception.  The default option of handle_syslog_error is
to die - but could easily be told to do nothing by using the following
code in your subclassed server:

    sub handle_syslog_error {}

It the log had been closed, you could attempt to reopen it in the error
handler with the following code:

    sub handle_syslog_error {
      my $self = shift;
      $self->open_syslog;
    }

=item C<$self-E<gt>new>

As of Net::Server 0.91 there is finally a new method.  This method
takes a class name and an argument hashref as parameters.  The argument
hashref becomes the "server" property of the object.

   package MyPackage;
   use base qw(Net::Server);

   my $obj = MyPackage->new({port => 20201});

   # same as

   my $obj = bless {server => {port => 20201}}, 'MyPackage';

=item C<$self-E<gt>open_syslog>

Called during post_configure when the log_file option is set to 'Sys::Syslog'.
By default it use the parsed configuration options listed in this document.
If more custom behavior is desired, the method could be overridden and
Sys::Syslog::openlog should be called with the custom parameters.

=item C<$self-E<gt>shutdown_sockets>

This method will close any remaining open sockets.  This is called
at the end of the server_close method.

=back

=head1 RESTARTING

Each of the server personalities (except for INET), support
restarting via a HUP signal (see "kill -l").  When a HUP
is received, the server will close children (if any), make
sure that sockets are left open, and re-exec using
the same commandline parameters that initially started the
server.  (Note: for this reason it is important that @ARGV
is not modified until C<-E<gt>run> is called).

The Net::Server will attempt to find out the commandline used for
starting the program.  The attempt is made before any configuration
files or other arguments are processed.  The outcome of this attempt
is stored using the method C<-E<gt>commandline>.  The stored
commandline may also be retrieved using the same method name.  The
stored contents will undoubtedly contain Tainted items that will cause
the server to die during a restart when using the -T flag (Taint
mode).  As it is impossible to arbitrarily decide what is taint safe
and what is not, the individual program must clean up the tainted
items before doing a restart.

  sub configure_hook{
    my $self = shift;

    ### see the contents
    my $ref  = $self->commandline;
    use Data::Dumper;
    print Dumper $ref;

    ### arbitrary untainting - VERY dangerous
    my @untainted = map {/(.+)/;$1} @$ref;

    $self->commandline(\@untainted)
  }

=head1 FILES

The following files are installed as part of this
distribution.

    Net/Server.pm
    Net/Server/Fork.pm
    Net/Server/INET.pm
    Net/Server/MultiType.pm
    Net/Server/PreForkSimple.pm
    Net/Server/PreFork.pm
    Net/Server/Single.pm
    Net/Server/Daemonize.pm
    Net/Server/SIG.pm
    Net/Server/Proto.pm
    Net/Server/Proto/*.pm

=head1 INSTALL

Download and extract tarball before running
these commands in its base directory:

    perl Makefile.PL
    make
    make test
    make install

=head1 AUTHOR

Paul Seamons <paul at seamons.com>

=head1 THANKS

Thanks to Rob Brown (bbb at cpan.org) for help with
miscellaneous concepts such as tracking down the
serialized select via flock ala Apache and the reference
to IO::Select making multiport servers possible.  And for
researching into allowing sockets to remain open upon
exec (making HUP possible).

Thanks to Jonathan J. Miner <miner at doit.wisc.edu> for
patching a blatant problem in the reverse lookups.

Thanks to Bennett Todd <bet at rahul.net> for
pointing out a problem in Solaris 2.5.1 which does not
allow multiple children to accept on the same port at
the same time.  Also for showing some sample code
from Viktor Duchovni which now represents the semaphore
option of the serialize argument in the PreFork server.

Thanks to I<traveler> and I<merlyn> from http://perlmonks.org
for pointing me in the right direction for determining
the protocol used on a socket connection.

Thanks to Jeremy Howard <j+daemonize at howard.fm> for
numerous suggestions and for work on Net::Server::Daemonize.

Thanks to Vadim <vadim at hardison.net> for patches to
implement parent/child communication on PreFork.pm.

Thanks to Carl Lewis for suggesting "-" in user names.

Thanks to Slaven Rezic for suggesing Reuse => 1 in Proto::UDP.

Thanks to Tim Watt for adding udp_broadcast to Proto::UDP.

Thanks to Christopher A Bongaarts for pointing out problems with
the Proto::SSL implementation that currently locks around the socket
accept and the SSL negotiation. See L<Net::Server::Proto::SSL>.

Thanks to Alessandro Zummo for pointing out various bugs including
some in configuration, commandline args, and cidr_allow.

Thanks to various other people for bug fixes over the years.
These and future thank-you's are available in the Changes file
as well as CVS comments.

Thanks to Ben Cohen and tye (on Permonks) for finding and diagnosing
more correct behavior for dealing with re-opening STDIN and STDOUT on
the client handles.

Thanks to Mark Martinec for trouble shooting other problems with STDIN
and STDOUT (he proposed having a flag that is now the no_client_stdout
flag).

Thanks to David (DSCHWEI) on cpan for asking for the nofatal option
with syslog.

Thanks to Andreas Kippnick and Peter Beckman for suggesting leaving
open child connections open during a HUP (this is now available via
the leave_children_open_on_hup flag).

Thanks to LUPE on cpan for helping patch HUP with taint on.

Thanks to Michael Virnstein for fixing a bug in the check_for_dead
section of PreFork server.

Thanks to Rob Mueller for patching PreForkSimple to only open
lock_file once during parent call.  This patch should be portable on
systems supporting flock.  Rob also suggested not closing STDIN/STDOUT
but instead reopening them to /dev/null to prevent spurious warnings.
Also suggested short circuit in post_accept if in UDP.  Also for
cleaning up some of the child managment code of PreFork.

Thanks to Mark Martinec for suggesting additional log messages for
failure during accept.

Thanks to Bill Nesbitt and Carlos Velasco for pointing out double
decrement bug in PreFork.pm (rt #21271)

Thanks to John W. Krahn for pointing out glaring precended with
non-parened open and ||.

Thanks to Ricardo Signes for pointing out setuid bug for perl 5.6.1
(rt #21262).

Thanks to Carlos Velasco for updating the Syslog options (rt #21265).
And for additional fixes later.

Thanks to Steven Lembark for pointing out that no_client_stdout wasn't
working with the Multiplex server.

Thanks to Peter Beckman for suggesting allowing Sys::SysLog keyworks
be passed through the ->log method and for suggesting we allow more
types of characters through in syslog_ident.  Also to Peter Beckman
for pointing out that a poorly setup localhost will cause tests to
hang.

Thanks to Curtis Wilbar for pointing out that the Fork server called
post_accept_hook twice.  Changed to only let the child process call
this, but added the pre_fork_hook method.

And just a general Thanks You to everybody who is using Net::Server or
who has contributed fixes over the years.

Thanks to Paul Miller for some ->autoflush, FileHandle fixes.

Thanks to Patrik Wallstrom for suggesting handling syslog errors better.

Thanks again to Rob Mueller for more logic cleanup for child accounting in PreFork server.

Thanks to David Schweikert for suggesting handling setlogsock a little better on newer
versions of Sys::Syslog (>= 0.15).

Thanks to Mihail Nasedkin for suggesting adding a hook that is now
called post_client_connection_hook.

=head1 SEE ALSO

Please see also
L<Net::Server::Fork>,
L<Net::Server::INET>,
L<Net::Server::PreForkSimple>,
L<Net::Server::PreFork>,
L<Net::Server::MultiType>,
L<Net::Server::Single>

=head1 TODO

  Improve test suite to fully cover code (using Devel::Cover).  Anybody
  that wanted to send me patches to the t/*.t tests that improved coverage
  would earn a big thank you :) (Sorry there isn't a whole lot more than that to give).

=head1 AUTHOR

  Paul Seamons <paul at seamons.com>
  http://seamons.com/

  Rob Brown <bbb at cpan.org>

=head1 LICENSE

This package may be distributed under the terms of either the

  GNU General Public License
    or the
  Perl Artistic License

All rights reserved.

=cut