=head1 NAME

Arc::Connection::Server - Class to handle one connection on the server side 

=head1 DESCRIPTION

ARC allows non-privileged users to run privileged commands on the server.
The server decides if the user is allowed to run this command through ACL.

This file is a part of the Perl ARCv2 module suite. ARCv2 is a 
rewrite of ARC by R.Toebbicke, CERN, Switzerland in Perl. 

=head1 ABSTRACT

From ARC by R. Toebbicke, modified by me:
User requests are shipped from a client machine to a server using a
SASL-authenticated socket connection. The purpose is to convey
requests such as privileged commands (e.g. AFS, Crontab) to be executed on the
server under appropriate privileges. Given that all privileges are
confined to the server and the server can be programmed as to filter and
check the command to be executed, the client machine can be less trusted
than the server.

Because ARC-v1-Commands are written in perl anyway, implementing the client/server
in perl makes sense. Platform-independence and "easy-to-read" source code are welcome
too. This package provides two perl command line scripts (arcx, arcxd). They can
be used for working with the ARC server from the command line, resp. to start the
server.

=head1 SYNOPSIS

Arc::Connection::Server - Server handle for ARCv2.
This class is called by Arc::Server for each incoming connection.


=head1 Class VARIABLES

=head3 PUBLIC MEMBERS

=over 2

=item commands 

B<Description>: hash of assignment between B<Command Name> and B<Command Class>. See L<Arc::Command>

B<Default value>: undef

=item logfileprefix I<reimplemented from Arc>

B<Default value>: "server"

=item sasl_cb_checkpass 

B<Description>: Callback for SASL (if PLAIN (or equal) mechanisms are used). See Authen::SASL(::Cyrus).

=item sasl_cb_getsecret 

B<Description>: Callback for SASL (if PLAIN (or equal) mechanisms are used). See Authen::SASL(::Cyrus).

B<Default value>: ""

=item sasl_mechanisms 

B<Description>: array of allowed SASL mechanisms

B<Default value>: undef

=back 

=over 2

=item protocol I<inherited from Arc::Connection>

B<Description>: Which protocol is used (0 = ARC/2.0, 1 = ARC/2.1)

B<Default value>: undef

=item service I<inherited from Arc::Connection>

B<Description>: name of the server (for SASL)

B<Default value>: undef

=item timeout I<inherited from Arc::Connection>

B<Description>: timeout for all connections (ARCv2 and command) in seconds

B<Default value>: undef

=back 

=over 2

=item logdestination I<inherited from Arc>

B<Description>: Where should all the log output go to ('stderr','syslog')

B<Default value>: 'syslog'

=item loglevel I<inherited from Arc>

B<Description>: loglevel is combination of bits (1=AUTH,2=USER,4=ERR,8=CMDDEBUG,16=VERBSIDE,32=DEBUG) see _Log method

B<Default value>: 7

=back 

=over 2

=back 

=head3 PROTECTED MEMBERS

=over 2

=item _realm 

B<Description>: Name of the SASL realm, if the user is from the default realm, this is empty

B<Default value>: ""

=back 

=over 2

=item _authenticated I<inherited from Arc::Connection>

B<Description>: Are we authenticated

=item _cmdclientsock I<inherited from Arc::Connection>

B<Description>: IO::Socket for the command connection (encrypted)

B<Default value>: undef

=item _cmdparameter I<inherited from Arc::Connection>

B<Description>: parameter after the command

B<Default value>: undef

=item _connected I<inherited from Arc::Connection>

B<Description>: are we connected

=item _connection I<inherited from Arc::Connection>

B<Description>: IO::Socket for the ARCv2 Connection

B<Default value>: undef

=item _expectedcmds I<inherited from Arc::Connection>

B<Description>: array, which ARCv2 protocol commands are allowed to come next

B<Default value>: undef

=item _select I<inherited from Arc::Connection>

B<Description>: IO::Select for the ARCv2 Connection

B<Default value>: undef

=item _username I<inherited from Arc::Connection>

B<Description>: username extracted from SASL

B<Default value>: "anonymous"

=back 

=over 2

=item _error I<inherited from Arc>

B<Description>: contains the error message

B<Default value>: undef

=item _syslog I<inherited from Arc>

B<Description>: log to syslog or to STDERR

B<Default value>: 1

=back 

=over 2

=back 

=head3 PRIVATE MEMBERS

=head1 Class METHODS

=head3 PUBLIC METHODS

=over 2

=item HandleClient ( $clientsock (IO::Socket) ) 

B<Description>: Public function, gets the clientsocket (from Arc::Server) and handles it.
Handles a connection (main loop).


B<Returns:> true on success, otherwise false


B<Example:>

$arc->HandleClient(sock);


=item Quit (  ) 

B<Description>: Ends the connection.
Do some cleanup.


B<Returns:> always true


B<Example:>

$arc->Quit();


=item tonne (  ) 

B<Description>: See source code for this method. /dev/null for unwanted output.


=back 

=over 2

=item clean (  ) I<inherited from Arc::Connection>

=item IsConnected (  ) I<inherited from Arc::Connection>

B<Description>: are we connected?


B<Returns:> true, if the ARCv2 control connection is connected, otherwise false


B<Example:>

last unless $arc->IsConnected;


=back 

=over 2

=item DESTROY (  ) I<inherited from Arc>

B<Description>: Destructor


=item IsError (  ) I<inherited from Arc>

B<Description>: User function to get the error msg.


B<Returns:> the error message if any otherwise undef


B<Example:>

unless (my $err = $arc->IsError()) { .. } else { print STDERR $err; }


=item Log ( $facility, ... (message) ) I<inherited from Arc>

B<Description>: Log function.
Logs messages to 'logdestination' if 'loglevel' is is set appropriatly.
loglevel behaviour has changed in the 1.0 release of ARCv2, the "Arc"-class can export
LOG_AUTH (authentication information), LOG_USER (connection information), LOG_ERR (errors), 
LOG_CMD (ARCv2 addition internal command information), LOG_SIDE (verbose client/server-specific
information), LOG_DEBUG (verbose debug information). It possible to combine the 
levels with or (resp. +) to allow a message to appear when not all loglevels are 
requested by the user.
Commonly used for logging errors from application level.


B<Returns:> always false


B<Example:>

return $arc->Log(LOG_ERR,"Message");


=item new ( %hash, key => val, ... ) I<inherited from Arc>

B<Description>: Constructor. 
Initializes the object and returns it blessed.
For all sub classes, please override C<_Init> to check the 
parameter which are passed to the C<new> function. This
is necessary because you are not able to call the the new method of a
parent class, when having a class name (new $class::SUPER::new, does not work.).


B<Returns:> blessed object of the class


B<Example:>

my $this = new Arc::Class ( key => value, key2 => value2 );


=back 

=over 2

=back 

=head3 PROTECTED METHODS

=over 2

=item _Auth (  ) 

B<Description>: send the available SASL mechanisms.
Protocol command: AUTH <comma-seperated list of SASL mechansims>\r\n


B<Returns:> true when succesful, otherwise false


B<Example:>

$this->_Auth();


=item _Authtype (  ) 

B<Description>: tell the client, which SASL mechanism is used.
Protocol command: AUTHTYPE <SASL mechansism>\r\n


B<Returns:> true when succesful, otherwise false


B<Example:>

$this->_Authtype();


=item _CBCanonUser (  ) 

B<Description>: Callback function to canonicalize the username (SASL)
see Authen::SASL(::Cyrus) for parameter list and how to use.


=item _CheckCmd (  ) 

=item _CmdError (  ) 

B<Description>: send a command error msg to client.
Protocol command: CMDERR <msg>\r\n


B<Returns:> true when succesful, otherwise false


B<Example:>

$this->_CmdError("failure.");


=item _Done (  ) 

B<Description>: command is ready.
When the ARCv2 command is ready with its work, the server
sends the DONE command on the control connection.
Protocol command: DONE\r\n


B<Returns:> true when succesful, otherwise false


B<Example:>

$this->_Done();


=item _Error (  ) 

B<Description>: send an error msg to client (Server error).
Protocol command: ERR <msg>\r\n


B<Returns:> true when succesful, otherwise false


B<Example:>

$this->_Error("failure.");


=item _Init (  ) I<reimplemented from Arc::Connection>

=item _RAUTHENTICATE (  ) 

B<Description>: parses the AUTHENTICATE[ <SASL mech>]\r\n, sent by the client.
Checks if the demanded SASL mechanism is allowed and returns the
selected mechanism.


=item _RCMD (  ) 

B<Description>: parses the CMD <cmd>\r\n, sent by the client.
check if the command exists, prepares the command connection, executes the command and
does cleanups after execution.


=item _RQUIT (  ) 

B<Description>: does nothing, placeholder for QUIT\r\n command, sent by the client.


=item _RSASL (  ) 

B<Description>: parses the SASL <base64 encoded SASL string>\r\n, sent by the client.
Sasl challenge/response from the client


=item _RunCmd (  ) 

=item _SplitCmdArgs (  ) 

=item _StartAuthentication (  ) 

B<Description>: Creates the sasl object (server_new)
and sends the first sasl challenge/response.
Protocol command: SASL <base64 encoded SASL output>\r\n


B<Returns:> true when succesful, otherwise false


B<Example:>

$this->_StartAuthentication();


=item _StepAuthentication ( bool $first_step ) 

B<Description>: Another SASL step
Response of a SASL command from the client
Protocol command: SASL <base64 encoded SASL outout>\r\n


B<Returns:> true when succesful, otherwise false


B<Example:>

$this->_StepAuthentication(1);


=back 

=over 2

=item _CommandConnection (  ) I<inherited from Arc::Connection>

B<Description>: initializes command connection. (protocol)
Starts listen on the Command socket and sends the B<CMDPASV> command.


B<Returns:> true if everything went like expected, otherwise false.


B<Example:>

$this->_CommandConnection();


=item _PrepareAuthentication (  ) I<inherited from Arc::Connection>

B<Description>: initialize sasl.
This function initializes the C<__sasl> member with an object
of C<Authen::SASL>.


B<Returns:> true if successful, otherwise false


B<Example:>

$this->_PrepareAuthentication() || return;


=item _ProcessLine ( $cmd ) I<inherited from Arc::Connection>

B<Description>: process an ARCv2 command. (protocol)
Process a command by evaling $this->_R$cmd. Also checks if 
this command was expected now (looks into the $this->{_expectedcmds} array). 
Used by client and server.


B<Returns:> true, if ARCv2 command has been in place, otherwise false


B<Example:>

while (my $cmd = $this->_RecvCommand() && $this->_ProcessLine($cmd)) {}


=item _ReadWriteBinary ( *locfdin, *locfdout ) I<inherited from Arc::Connection>

B<Description>: function for reading and writing on the command connection.
This function is always used by the C<Arc::Connection::Server> to handle 
command data. When calling the C<ProcessCommand> from C<Arc::Connection::Client> 
this function is also used.
Data is read from the local socket resp. pipe and is written encrypted 
to the network socket. The other side reads the data from network socket, 
decrypts it and writes it to its local socket. This function behaves differently on 
client and server sides, when the local or network socket is closed.


B<Returns:> always true


B<Example:>

$this->ReadWriteBinary(*STDIN,*STDOUT);


=item _RecvCommand (  ) I<inherited from Arc::Connection>

B<Description>: receives an ARCv2 Command. (protocol)
This function gets a line from C<_RecvLine> and extracts the ARCv2 command and
the optional command parameter C<_cmdparameter>.


B<Returns:> ARCv2 command and true if everything works fine, otherwise false


B<Example:>

while (my $cmd = $this->_RecvCommand()) { ... }


=item _RecvLine (  ) I<inherited from Arc::Connection>

B<Description>: receive a line (command). (protocol)
This function receives data from the ARCv2 connection and
fills the internal C<__linequeue> and C<__partial>. It returns 
a line from the internal buffer if there is any. It also handles
timeouts and "connection closed by foreign host"'s.


B<Returns:> true (and the line) if everything worked fine, otherwise false (undef)


B<Example:>

if (my $line = $this->_RecvLine()) { ... }


=item _Sasl ( $saslstr ) I<inherited from Arc::Connection>

B<Description>: send the ARCv2 SASL command. (protocol)
This function encodes the output from sasl_*_start and sasl_*_step with Base-64 and sends
it to the other side


B<Returns:> true if successful, otherwise false


B<Example:>

$this->_Sasl($sasl->client_start());


=item _SendCommand ( $cmd, $parameter ) I<inherited from Arc::Connection>

B<Description>: send a command. (protocol)  
Send a command to the ARCv2 socket.


B<Returns:> true if successful, otherwise false


B<Example:>

$this->_SendCommand("CMDPASV",$consock->sockhost.':'.$consock->sockport);


=item _SendLine ( ... (line) ) I<inherited from Arc::Connection>

B<Description>: send a line. (protocol)
This function sends a command line to the ARCv2 socket.


B<Returns:> true if writing has succeeded, otherwise false.


B<Example:>

$this->_SendLine($cmd,"test"); 


=back 

=over 2

=item _Debug ( ... (message) ) I<inherited from Arc>

B<Description>: Debug function.
Logs messages with "DEBUG" 


B<Returns:> always false


B<Example:>

$this->_Debug("hello","world"); # message will be "hello world"


=item _SetError ( ... (message)  ) I<inherited from Arc>

B<Description>: SetError function.
This function prepends the error message (@_) to an existing error message (if any) and
logs the message with LOG_ERR facility.
Use this function for setting an error from class level. Users should use IsError 
to get the message if a function failed.


B<Returns:> always false


B<Example:>

return $this->_SetError("User is not allowed to do this."); # breaks when an error occured


=back 

=over 2

=back 

=head3 PRIVATE METHODS

=head1 SEE ALSO

L<Arc>, L<Arc::Command>, L<Arc::Connection>, 
L<Arc::Connection::Server>, L<Arc::Connection::Client>,
L<arcx>, L<arcxd>, L<Authen::SASL>, L<Authen::SASL::Cyrus>
L<Net::Server::PreFork>

=head1 AUTHOR

 Patrick Boettcher <patrick.boettcher@desy.de>

=head1 COPYRIGHT AND LICENSE

Copyright (c) 2003-5 Patrick Boettcher <patrick.boettcher@desy.de> and others.
All rights reserved.
Zeuthen, Germany, (old) Europe

 This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

 Special thanks go to:
DESY Zeuthen, in particular:

- Wolfgang Friebel for bleeding edge testing and heavy bug reporting (and the idea of reimplementing ARC).

- Waltraut Niepraschk and Andreas Haupt for their help and support during the development. 

=cut