Net::Server(3)

NAME
Net::Server - Extensible, general Perl server engine

SYNOPSIS
  #!/usr/bin/perl -w -T
  package MyPackage;
  use Net::Server;
  @ISA = qw(Net::Server);
  sub process_request {
     #...code...
  }
  MyPackage->run(port => 160);
  exit;

OBTAINING
Visit http://seamons.com/ for the latest version.

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

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

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

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

`Net::Server' borrows several concepts from the Apache Webserver. `Net::Server' uses "hooks" to allow custom servers such as SMTP, HTTP, POP3, etc. to be layered over the base `Net::Server' class. In addition the `Net::Server::PreFork' class borrows concepts of min_start_servers, max_servers, and min_waiting servers. `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).

PERSONALITIES
`Net::Server' is built around a common class (Net::Server) and is extended using sub classes, or `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. Found in the module Net/Server/Fork.pm (see the Net::Server::Fork manpage). 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. Found in the module Net/Server/INET.pm (see the Net::Server::INET manpage). This server is designed to be used with inetd. The `pre_bind', `bind', `accept', and `post_accept' are all overridden as these services are taken care of by the INET daemon. Found in the module Net/Server/MultiType.pm (see the Net::Server::MultiType manpage). 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 `server_type' parameters may be given and Net::Server::MultiType will cycle through until it finds a class that it can use. Found in the module Net/Server/Multiplex.pm (see the Net::Server::Multiplex manpage). 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 `process_request' method is never used but the `mux_input' callback is used instead (see also the IO::Multiplex manpage). See examples/samplechat.pl for an example using most of the features of Net::Server::Multiplex. Found in the module Net/Server/PreFork.pm (see the Net::Server::PreFork manpage). This server binds to one or more ports and then forks `max_servers' child process. The server will make sure that at any given time there are always `max_servers' available to receive a client request. Each of these children will process up to `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 the Net::Server::PreFork manpage. Found in the module Net/Server/PreFork.pm (see the Net::Server::PreFork manpage). This server binds to one or more ports and then forks `min_servers' child process. The server will make sure that at any given time there are at least `min_spare_servers' but not more than `max_spare_servers' available to receive a client request, up to `max_servers'. Each of these children will process up to `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 the Net::Server::PreFork manpage. All methods fall back to Net::Server. This personality is provided only as parallelism for Net::Server::MultiType.

`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.

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->{server}->{client}. This property is a Socket blessed into the the IO::Socket classes. UDP servers are slightly different in that they will perform a recv instead of an 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 <STDIN> and print "out\n" to print to the client connection. UDP will require using a ->send call.

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 `Net::Server' can, or will, be included with this distribution).

  #!/usr/bin/perl -w -T
  #--------------- file test.pl ---------------
  package MyPackage;
  use strict;
  use vars qw(@ISA);
  use Net::Server::PreFork; # any personality will do
  @ISA = qw(Net::Server::PreFork);
  MyPackage->run();
  exit;
  ### 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 a line
      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;
  #--------------- file test.pl ---------------
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.

ARGUMENTS
There are four possible ways to pass arguments to Net::Server. They are passing on command line, using a conf file, passing parameters to run, or using a pre-built object to call the run method.

Arguments consist of key value pairs. On the commandline these pairs follow the POSIX fashion of `--key value' or `--key=value', and also `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: `Net::Server-'run(key1 => 'val1')>. Passing arguments via a prebuilt object can best be shown in the following code:

  #!/usr/bin/perl -w -T
  #--------------- file test2.pl ---------------
  package MyPackage;
  use strict;
  use vars (@ISA);
  use Net::Server;
  @ISA = qw(Net::Server);
  my $server = bless {
    key1 => 'val1',
    }, 'MyPackage';
  $server->run();
  #--------------- file test.pl ---------------
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. `Net::Server' will look for arguments in the following order:

  1) Arguments contained in the prebuilt object.
  2) Arguments passed on command line.
  3) Arguments passed to the run method.
  4) Arguments passed via a conf file.
  5) Arguments set in the configure_hook.
Key/value pairs used by the server are removed by the configuration process so that server layers on top of `Net::Server' can pass and read their own parameters. Currently, Getopt::Long is not used. The following arguments are available in the default `Net::Server' or `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    (unix|inet)              unix
  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
  ## 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.
Filename from which to read additional key value pair arguments for starting the server. Default is undef. 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'. 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 `syslog_logsock', `syslog_ident', and `syslog_logopt',and `syslog_facility' may also be defined. If a `log_file' is given or if `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. Filename to store pid of parent process. Generally applies only to forking servers. Default is none (undef). Only available if `log_file' is equal to "Sys::Syslog". May be either "unix" of "inet". Default is "unix". See the Sys::Syslog manpage. Only available if `log_file' is equal to "Sys::Syslog". Id to prepend on syslog entries. Default is "net_server". See the Sys::Syslog manpage. Only available if `log_file' is equal to "Sys::Syslog". May be either zero or more of "pid","cons","ndelay","nowait". Default is "pid". See the Sys::Syslog manpage. Only available if `log_file' is equal to "Sys::Syslog". See the Sys::Syslog manpage and the syslog manpage. Default is "daemon". See the Net::Server::Proto manpage. 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 `host:port/proto', `host:port', `port/proto', or `port', where host represents a hostname residing on the local box, where port represents either the number of the port (eg. "80") or the service designation (eg. "http"), and where proto represents the protocol to be used. See the Net::Server::Proto manpage. If you are working with unix sockets, you may also specify `socket_file|unix' or `socket_file|type|unix' where type is SOCK_DGRAM or SOCK_STREAM. If the protocol is not specified, proto will default to the `proto' specified in the arguments. If `proto' is not specified there it will default to "tcp". If host is not specified, host will default to `host' specified in the arguments. If `host' is not specified there it will default to "*". Default port is 20203. 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 the Net::Server::Proto manpage. See the IO::Socket manpage. See the Net::Server::Proto manpage. Protocol to use when binding ports. See the IO::Socket manpage. 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).
  See L<IO::Socket>.  Not used with udp protocol (or UNIX SOCK_DGRAM).
Specify whether to lookup the hostname of the connected IP. Information is cached in server object under `peerhost' property. Default is to not use reverse_lookups (undef). 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. Directory to chroot to after bind process has taken place and the server is still running as root. Defaults to undef. 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 `user' equal to "root". 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 `group' equal to "root". 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 `setsid' is set. Specifies whether or not the server should fork after the bind method to release itself from the command line and then run the `POSIX::setsid()' command to truly daemonize. Defaults to undef. If a `log_file' is given or if `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. 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).

PROPERTIES
All of the `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. 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).

CONFIGURATION FILE
`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 white space 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.+
  ### 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 --------------

PROCESS FLOW
The process flow is written in an open, easy to override, easy to hook, fashion. The basic flow is shown below.

  $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 (`$self->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;
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 (`$self->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;
  }
  exit;

HOOKS
`Net::Server' provides a number of "hooks" allowing for servers layered on top of `Net::Server' to respond at different levels of execution. This hook takes place immediately after the `->run()' method is called. This hook allows for setting up the object before any built in configuration takes place. This allows for custom configurability. This hook occurs just after the reading of configuration parameters and initiation of logging and pid_file creation. It also occurs before the `->pre_bind()' and `->bind()' methods are called. This hook allows for verifying configuration parameters. 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. This hook occurs after chroot, change of user, and change of group has occured. It allows for preparation before looping begins. 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. This hook allows for the checking of ip and host information beyond the `$self->allow_deny()' routine. If this hook returns 1, the client request will be processed, otherwise, the request will be denied processing. This hook occurs if either the `$self->allow_deny()' or `$self->allow_deny_hook()' have taken place. This hook occurs after the processing of the request, but before the client connection has been closed. This hook occurs before the server begins shutting down. This hook handles writing to log files. The default hook is to write to STDERR, or to the filename contained in the parameter `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. 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. 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. 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. This hook occurs if a server has been HUPed (restarted via the HUP signal. It occurs just before restarting the server via exec.

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 `->run' is called.

TO DO
There are several tasks to perform before the alpha label can be removed from this software: The best way to further the status of this project is to use it. There are immediate plans to use this as a base class in implementing some mail servers and banner servers on a high hit site. Explore any other personalities Create various types of servers. Possibly, port exising servers to user Net::Server as a base layer.

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

AUTHOR
Paul T. Seamons <paul at seamons.com>

THANKS
Thanks to Rob Brown <rbrown at about-inc.com> 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@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 traveler and 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.

SEE ALSO
Please see also the Net::Server::Fork manpage, the Net::Server::INET manpage, the Net::Server::PreForkSimple manpage, the Net::Server::PreFork manpage, the Net::Server::MultiType manpage, the Net::Server::Single manpage

COPYRIGHT
  Copyright (C) 2001, Paul T Seamons
                      paul at seamons.com
                      http://seamons.com/
  This package may be distributed under the terms of either the
  GNU General Public License
    or the
  Perl Artistic License
  All rights reserved.