File:  [LON-CAPA] / loncom / loncnew
Revision 1.4: download - view: text, annotated - select for diffs
Thu Apr 24 10:56:55 2003 UTC (20 years, 11 months ago) by foxr
Branches: MAIN
CVS tags: HEAD
Added code to roll back connection counts.  Also added code to show
status of daemon on ps -axuww: show who 'I'm connected to and current connection
count

#!/usr/bin/perl
# The LearningOnline Network with CAPA
# lonc maintains the connections to remote computers
#
# $Id: loncnew,v 1.4 2003/04/24 10:56:55 foxr Exp $
#
# Copyright Michigan State University Board of Trustees
#
# This file is part of the LearningOnline Network with CAPA (LON-CAPA).
#
# LON-CAPA is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# LON-CAPA is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with LON-CAPA; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
# /home/httpd/html/adm/gpl.txt
#
# http://www.lon-capa.org/
#
#
# new lonc handles n requestors spread out bver m connections to londs.
# This module is based on the Event class.
#   Development iterations:
#    - Setup basic event loop.   (done)
#    - Add timer dispatch.       (done)
#    - Add ability to accept lonc UNIX domain sockets.  (done)
#    - Add ability to create/negotiate lond connections (done).
#    - Add general logic for dispatching requests and timeouts.
#    - Add support for the lonc/lond requests.
#    - Add logging/status monitoring.
#    - Add Signal handling - HUP restarts. USR1 status report.
#    - Add Configuration file I/O
#    - Add Pending request processing on startup.
#    - Add management/status request interface.

use lib "/home/httpd/lib/perl/";
use lib "/home/foxr/newloncapa/types";
use Event qw(:DEFAULT );
use POSIX qw(:signal_h);
use IO::Socket;
use IO::Socket::INET;
use IO::Socket::UNIX;
use Socket;
use Crypt::IDEA;
use LONCAPA::Queue;
use LONCAPA::Stack;
use LONCAPA::LondConnection;
use LONCAPA::Configuration;
use LONCAPA::HashIterator;

print "Loncnew starting\n";

#
#   Disable all signals we might receive from outside for now.
#
$SIG{QUIT}  = IGNORE;
$SIG{HUP}   = IGNORE;
$SIG{USR1}  = IGNORE;
$SIG{INT}   = IGNORE;
$SIG{CHLD}  = IGNORE;
$SIG{__DIE__}  = IGNORE;


# Read the httpd configuration file to get perl variables
# normally set in apache modules:

my $perlvarref = LONCAPA::Configuration::read_conf('loncapa.conf');
my %perlvar    = %{$perlvarref};

#
#  parent and shared variables.

my %ChildHash;			# by pid -> host.


my $MaxConnectionCount = 5;	# Will get from config later.
my $ClientConnection = 0;	# Uniquifier for client events.

my $DebugLevel = 5;
my $IdleTimeout= 3600;		# Wait an hour before pruning connections.

#
#  The variables below are only used by the child processes.
#
my $RemoteHost;			# Name of host child is talking to.
my $UnixSocketDir= "/home/httpd/sockets"; 
my $IdleConnections = Stack->new(); # Set of idle connections
my %ActiveConnections;		# Connections to the remote lond.
my %ActiveTransactions;		# Transactions in flight.
my %ActiveClients;		# Serial numbers of active clients by socket.
my $WorkQueue       = Queue->new(); # Queue of pending transactions.
my $ClientQueue     = Queue->new(); # Queue of clients causing xactinos.
my $ConnectionCount = 0;
my $IdleSeconds     = 0;	# Number of seconds idle.

#

=pod

=head2 GetPeerName

Returns the name of the host that a socket object is connected to.

=cut

sub GetPeername {
    my $connection = shift;
    my $AdrFamily  = shift;
    my $peer       = $connection->peername();
    my $peerport;
    my $peerip;
    if($AdrFamily == AF_INET) {
	($peerport, $peerip) = sockaddr_in($peer);
	my $peername    = gethostbyaddr($iaddr, $AdrFamily);
	return $peername;
    } elsif ($AdrFamily == AF_UNIX) {
	my $peerfile;
	($peerfile) = sockaddr_un($peer);
	return $peerfile;
    }
}
#----------------------------- Timer management ------------------------
=pod

=head2 Debug

Invoked to issue a debug message.

=cut

sub Debug {
    my $level   = shift;
    my $message = shift;
    if ($level <= $DebugLevel) {
	print $message." host = ".$RemoteHost."\n";
    }
}

sub SocketDump {
    my $level = shift;
    my $socket= shift;
    if($level <= $DebugLevel) {
	$socket->Dump();
    }
}

=pod

=head2 Tick

Invoked  each timer tick.

=cut

sub Tick {
    my $client;
    $0 = 'lonc: '.GetServerHost()." Connection count: ".$ConnectionCount;
    Debug(6, "Tick");
    Debug(6, "    Current connection count: ".$ConnectionCount);
    foreach $client (keys %ActiveClients) {
	Debug(7, "    Have client:  with id: ".$ActiveClients{$client});
    }
    # Is it time to prune connection count:


    if($IdleConnections->Count()  && 
       ($WorkQueue->Count() == 0)) { # Idle connections and nothing to do?
	$IdleSeconds++;
	if($IdleSeconds > $IdleTimeout) { # Prune a connection...
	    $Socket = $IdleConnections->pop();
	    KillSocket($Socket, 0);
	}
    } else {
	$IdleSeconds = 0;	# Reset idle count if not idle.
    }
}

=pod

=head2 SetupTimer

Sets up a 1 per sec recurring timer event.  The event handler is used to:

=item

Trigger timeouts on communications along active sockets.

=item

Trigger disconnections of idle sockets.

=cut

sub SetupTimer {
    Debug(6, "SetupTimer");
    Event->timer(interval => 1, debug => 1, cb => \&Tick );
}

=pod

=head2 ServerToIdle

This function is called when a connection to the server is
ready for more work.

If there is work in the Work queue the top element is dequeued
and the connection will start to work on it.  If the work queue is
empty, the connection is pushed on the idle connection stack where
it will either get another work unit, or alternatively, if it sits there
long enough, it will be shut down and released.

=cut

sub ServerToIdle {
    my $Socket   = shift;	# Get the socket.

    &Debug(6, "Server to idle");

    #  If there's work to do, start the transaction:

    $reqdata = $WorkQueue->dequeue();
    Debug(9, "Queue gave request data: ".$reqdata);
    unless($reqdata eq undef)  {
	my $unixSocket = $ClientQueue->dequeue();
	&Debug(6, "Starting new work request");
	&Debug(7, "Request: ".$reqdata);
	
	&StartRequest($Socket, $unixSocket, $reqdata);
    } else {
	
    #  There's no work waiting, so push the server to idle list.
	&Debug(8, "No new work requests, server connection going idle");
	delete($ActiveTransactions{$Socket});
	$IdleConnections->push($Socket);
    }
}

=pod

=head2 ClientWritable

Event callback for when a client socket is writable.

This callback is established when a transaction reponse is
avaiable from lond.  The response is forwarded to the unix socket
as it becomes writable in this sub.

Parameters:

=item Event

The event that has been triggered. Event->w->data is
the data and Event->w->fd is the socket to write.

=cut

sub ClientWritable {
    my $Event    = shift;
    my $Watcher  = $Event->w;
    my $Data     = $Watcher->data;
    my $Socket   = $Watcher->fd;

    # Try to send the data:

    &Debug(6, "ClientWritable writing".$Data);
    &Debug(9, "Socket is: ".$Socket);

    my $result = $Socket->send($Data, 0);

    # $result undefined: the write failed.
    # otherwise $result is the number of bytes written.
    # Remove that preceding string from the data.
    # If the resulting data is empty, destroy the watcher
    # and set up a read event handler to accept the next
    # request.

    &Debug(9,"Send result is ".$result." Defined: ".defined($result));
    if(defined($result)) {
	&Debug(9, "send result was defined");
	if($result == length($Data)) { # Entire string sent.
	    &Debug(9, "ClientWritable data all written");
	    $Watcher->cancel();
	    #
	    #  Set up to read next request from socket:
	    
	    my $descr     = sprintf("Connection to lonc client %d",
				    $ActiveClients{$Socket});
	    Event->io(cb    => \&ClientRequest,
		      poll  => 'r',
		      desc  => $descr,
		      data  => "",
		      fd    => $Socket);

	} else {		# Partial string sent.
	    $Watcher->data(substr($Data, $result));
	}
	
    } else {			# Error of some sort...

	# Some errnos are possible:
	my $errno = $!;
	if($errno == POSIX::EWOULDBLOCK   ||
	   $errno == POSIX::EAGAIN        ||
	   $errno == POSIX::EINTR) {
	    # No action taken?
	} else {		# Unanticipated errno.
	    &Debug(5,"ClientWritable error or peer shutdown".$RemoteHost);
	    $Watcher->cancel;	# Stop the watcher.
	    $Socket->shutdown(2); # Kill connection
	    $Socket->close();	# Close the socket.
	}
	
    }
}

=pod

=head2 CompleteTransaction

Called when the reply data has been received for a lond 
transaction.   The reply data must now be sent to the
ultimate client on the other end of the Unix socket.  This is
done by setting up a writable event for the socket with the
data the reply data.

Parameters:

=item Socket

Socket on which the lond transaction occured.  This is a
LondConnection. The data received is in the TransactionReply member.

=item Client

Unix domain socket open on the ultimate client.

=cut

sub CompleteTransaction {
    &Debug(6,"Complete transaction");
    my $Socket = shift;
    my $Client = shift;

    my $data   = $Socket->GetReply(); # Data to send.

    &Debug(8," Reply was: ".$data);
    my $Serial         = $ActiveClients{$Client};
    my $desc           = sprintf("Connection to lonc client %d",
				 $Serial);
    Event->io(fd       => $Client,
	      poll     => "w",
	      desc     => $desc,
	      cb       => \&ClientWritable,
	      data     => $data);
}
=pod
=head2 FailTransaction

  Finishes a transaction with failure because the associated lond socket
  disconnected.  It is up to our client to retry if desired.  

Parameters:

=item client  
 
   The UNIX domain socket open on our client.

=cut

sub FailTransaction {
    my $client = shift;

    &Debug(8, "Failing transaction due to disconnect");
    my $Serial = $ActiveClients{$client};
    my $desc   = sprintf("Connection to lonc client %d", $Serial);
    my $data   = "error: Connection to lond lost\n";

    Event->io(fd     => $client,
	      poll   => "w",
	      desc   => $desc,
	      cb     => \&ClientWritable,
	      data   => $data);

}

=pod

=head2 KillSocket
 
Destroys a socket.  This function can be called either when a socket
has died of 'natural' causes or because a socket needs to be pruned due to
idleness.  If the socket has died naturally, if there are no longer any 
live connections a new connection is created (in case there are transactions
in the queue).  If the socket has been pruned, it is never re-created.

Parameters:

=item Socket
 
  The socket to kill off.

=item Restart

nonzero if we are allowed to create a new connection.


=cut
sub KillSocket {
    my $Socket = shift;
    my $Restart= shift;

    #  If the socket came from the active connection set, delete it.
    # otherwise it came from the idle set and has already been destroyed:
    
    if(exists($ActiveTransactions{$Socket})) {
	delete ($ActiveTransactions{$Socket});
    }
    if(exists($ActiveConnections{$Socket})) {
	delete($ActiveConnections{$Socket});
    }
    $ConnectionCount--;
    if( ($ConnectionCount = 0) && ($Restart)) {
	MakeLondConnection();
    }

}

=pod

=head2 LondReadable

This function is called whenever a lond connection
is readable.  The action is state dependent:

=head3 State=Initialized

We''re waiting for the challenge, this is a no-op until the
state changes.

=head3 State=Challenged 

The challenge has arrived we need to transition to Writable.
The connection must echo the challenge back.

=head3 State=ChallengeReplied

The challenge has been replied to.  The we are receiveing the 
'ok' from the partner.

=head3 State=RequestingKey

The ok has been received and we need to send the request for
an encryption key.  Transition to writable for that.

=head3 State=ReceivingKey

The the key has been requested, now we are reading the new key.

=head3 State=Idle 

The encryption key has been negotiated or we have finished 
reading data from the a transaction.   If the callback data has
a client as well as the socket iformation, then we are 
doing a transaction and the data received is relayed to the client
before the socket is put on the idle list.

=head3 State=SendingRequest

I do not think this state can be received here, but if it is,
the appropriate thing to do is to transition to writable, and send
the request.

=head3 State=ReceivingReply

We finished sending the request to the server and now transition
to readable to receive the reply. 

The parameter to this function are:

The event. Implicit in this is the watcher and its data.  The data 
contains at least the lond connection object and, if a 
transaction is in progress, the socket attached to the local client.

=cut

sub LondReadable {
    my $Event      = shift;
    my $Watcher    = $Event->w;
    my $Socket     = $Watcher->data;
    my $client     = undef;


    my $State = $Socket->GetState(); # All action depends on the state.

    &Debug(6,"LondReadable called state = ".$State);
    SocketDump(6, $Socket);

    if($Socket->Readable() != 0) {
	 # bad return from socket read. Currently this means that
	# The socket has become disconnected. We fail the transaction.

	if(exists($ActiveTransactions{$Socket})) {
	    Debug(3,"Lond connection lost failing transaction");
	    FailTransaction($ActiveTransactions{$Socket});
	}
	$Watcher->cancel();
	KillSocket($Socket, 1);
	return;
    }
    SocketDump(6,$Socket);

    $State = $Socket->GetState(); # Update in case of transition.
    &Debug(6, "After read, state is ".$State);

   if($State eq "Initialized") {


    } elsif ($State eq "ChallengeReceived") {
	#  The challenge must be echoed back;  The state machine
	# in the connection takes care of setting that up.  Just
	# need to transition to writable:

	$Watcher->poll("w");
	$Watcher->cb(\&LondWritable);

    } elsif ($State eq "ChallengeReplied") {


    } elsif ($State eq "RequestingKey") {
	#  The ok was received.  Now we need to request the key
	#  That requires us to be writable:

	$Watcher->poll("w");
	$Watcher->cb(\&LondWritable);

    } elsif ($State eq "ReceivingKey") {

    } elsif ($State eq "Idle") {
	# If necessary, complete a transaction and then go into the
	# idle queue.
	if(exists($ActiveTransactions{$Socket})) {
	    Debug(8,"Completing transaction!!");
	    CompleteTransaction($Socket, 
				$ActiveTransactions{$Socket});
	}
	$Watcher->cancel();
	ServerToIdle($Socket);	# Next work unit or idle.

    } elsif ($State eq "SendingRequest") {
	#  We need to be writable for this and probably don't belong
	#  here inthe first place.

	Deubg(6, "SendingRequest state encountered in readable");
	$Watcher->poll("w");
	$Watcher->cb(\&LondWritable);

    } elsif ($State eq "ReceivingReply") {


    } else {
	 # Invalid state.
	Debug(4, "Invalid state in LondReadable");
    }
}

=pod

=head2 LondWritable

This function is called whenever a lond connection
becomes writable while there is a writeable monitoring
event.  The action taken is very state dependent:

=head3 State = Connected 

The connection is in the process of sending the 'init' hailing to the
lond on the remote end.  The connection object''s Writable member is
called.  On error, ConnectionError is called to destroy the connection
and remove it from the ActiveConnections hash

=head3 Initialized

'init' has been sent, writability monitoring is removed and
readability monitoring is started with LondReadable as the callback.

=head3 ChallengeReceived

The connection has received the who are you challenge from the remote
system, and is in the process of sending the challenge
response. Writable is called.

=head3 ChallengeReplied

The connection has replied to the initial challenge The we switch to
monitoring readability looking for the server to reply with 'ok'.

=head3 RequestingKey

The connection is in the process of requesting its encryption key.
Writable is called.

=head3 ReceivingKey

The connection has sent the request for a key.  Switch to readability
monitoring to accept the key

=head3 SendingRequest

The connection is in the process of sending a request to the server.
This request is part of a client transaction.  All the states until
now represent the client setup protocol. Writable is called.

=head3 ReceivingReply

The connection has sent a request.  Now it must receive a reply.
Readability monitoring is requested.

This function is an event handler and therefore receives as
a parameter the event that has fired.  The data for the watcher
of this event is a reference to a list of one or two elements,
depending on state. The first (and possibly only) element is the
socket.  The second (present only if a request is in progress)
is the socket on which to return a reply to the caller.

=cut

sub LondWritable {
    my $Event   = shift;
    my $Watcher = $Event->w;
    my @data    = $Watcher->data;
    Debug(6,"LondWritable State = ".$State." data has ".@data." elts.\n");

    my $Socket  = $data[0];	# I know there's at least a socket.

    #  Figure out what to do depending on the state of the socket:
    

    my $State   = $Socket->GetState();


    SocketDump(6,$Socket);

    if      ($State eq "Connected")         {

	if ($Socket->Writable() != 0) {
	    #  The write resulted in an error.
	    # We'll treat this as if the socket got disconnected:
	    if(exists($ActiveTransactions{$Socket})) {
		Debug(3, "Lond connection lost, failing transactions");
		FailTransaction($ActiveTransactions{$Socket});
	    }
	    $Watcher->cancel();
	    KillSocket($Socket, 1);
	    return;
	}
	#  "init" is being sent...

	
    } elsif ($State eq "Initialized")       {

	# Now that init was sent, we switch 
	# to watching for readability:

	$Watcher->poll("r");
	$Watcher->cb(\&LondReadable);

    } elsif ($State eq "ChallengeReceived") {
	# We received the challenge, now we 
	# are echoing it back. This is a no-op,
	# we're waiting for the state to change
	
	if($Socket->Writable() != 0) {
	    # Write of the next chunk resulted in an error.
	}
	
    } elsif ($State eq "ChallengeReplied")  {
	# The echo was sent back, so we switch
	# to watching readability.

	$Watcher->poll("r");
	$Watcher->cb(\&LondReadable);

    } elsif ($State eq "RequestingKey")     {
	# At this time we're requesting the key.
	# again, this is essentially a no-op.
	# we'll write the next chunk until the
	# state changes.

	if($Socket->Writable() != 0) {
	    # Write resulted in an error.
	}

    } elsif ($State eq "ReceivingKey")      {
	# Now we need to wait for the key
	# to come back from the peer:

	$Watcher->poll("r");
	$Watcher->cb(\&LondReadable);

    } elsif ($State eq "SendingRequest")    {
	# At this time we are sending a request to the
	# peer... write the next chunk:

	if($Socket->Writable() != 0) {
	    # Write resulted in an error.

	}

    } elsif ($State eq "ReceivingReply")    {
	# The send has completed.  Wait for the
	# data to come in for a reply.
	Debug(8,"Writable sent request/receiving reply");
	$Watcher->poll("r");
	$Watcher->cb(\&LondReadable);

    } else {
	#  Control only passes here on an error: 
	#  the socket state does not match any
	#  of the known states... so an error
	#  must be logged.

	&Debug(4, "Invalid socket state ".$State."\n");
    }
    
}

=pod

=head2 MakeLondConnection

Create a new lond connection object, and start it towards its initial
idleness.  Once idle, it becomes elligible to receive transactions
from the work queue.  If the work queue is not empty when the
connection is completed and becomes idle, it will dequeue an entry and
start off on it.

=cut

sub MakeLondConnection {     
    Debug(4,"MakeLondConnection to ".GetServerHost()." on port "
	  .GetServerPort());

    my $Connection = LondConnection->new(&GetServerHost(),
					 &GetServerPort());

    if($Connection == undef) {	# Needs to be more robust later.
	die "Failed to make a connection!!".$!."\n";
	
    } 
    # The connection needs to have writability 
    # monitored in order to send the init sequence
    # that starts the whole authentication/key
    # exchange underway.
    #
    my $Socket = $Connection->GetSocket();
    if($Socket == undef) {
	die "did not get a socket from the connection";
    } else {
	&Debug(9,"MakeLondConnection got socket: ".$Socket);
    }

    
    $event = Event->io(fd       => $Socket,
		       poll     => 'w',
		       cb       => \&LondWritable,
		       data     => ($Connection, undef),
		       desc => 'Connection to lond server');
    $ActiveConnections{$Connection} = $event;

    $ConnectionCount++;
   
    
}

=pod

=head2 StartRequest

Starts a lond request going on a specified lond connection.
parameters are:

=item $Lond

Connection to the lond that will send the transaction and receive the
reply.

=item $Client

Connection to the client that is making this request We got the
request from this socket, and when the request has been relayed to
lond and we get a reply back from lond it will get sent to this
socket.

=item $Request

The text of the request to send.

=cut

sub StartRequest {
    my $Lond     = shift;
    my $Client   = shift;
    my $Request  = shift;
    
    Debug(6, "StartRequest: ".$Request);

    my $Socket = $Lond->GetSocket();
    
    $ActiveTransactions{$Lond} = $Client; # Socket to relay to client.

    $Lond->InitiateTransaction($Request);
    $event = Event->io(fd      => $Lond->GetSocket(),
		       poll    => "w",
		       cb      => \&LondWritable,
		       data    => $Lond,
		       desc    => "lond transaction connection");
    $ActiveConnections{$Lond} = $event;
    Debug(8," Start Request made watcher data with ".$event->data."\n");
}

=pod

=head2 QueueTransaction

If there is an idle lond connection, it is put to work doing this
transaction.  Otherwise, the transaction is placed in the work queue.
If placed in the work queue and the maximum number of connections has
not yet been created, a new connection will be started.  Our goal is
to eventually have a sufficient number of connections that the work
queue will typically be empty.  parameters are:

=item Socket

open on the lonc client.

=item Request

data to send to the lond.

=cut

sub QueueTransaction {
    my $requestSocket = shift;
    my $requestData   = shift;

    Debug(6,"QueueTransaction: ".$requestData);

    my $LondSocket    = $IdleConnections->pop();
    if(!defined $LondSocket) {	# Need to queue request.
	Debug(8,"Must queue...");
	$ClientQueue->enqueue($requestSocket);
	$WorkQueue->enqueue($requestData);
	if($ConnectionCount < $MaxConnectionCount) {
	    Debug(4,"Starting additional lond connection");
	    MakeLondConnection();
	}
    } else {			# Can start the request:
	Debug(8,"Can start...");
	StartRequest($LondSocket, $requestSocket, $requestData);
    }
}

#-------------------------- Lonc UNIX socket handling ---------------------

=pod

=head2 ClientRequest

Callback that is called when data can be read from the UNIX domain
socket connecting us with an apache server process.

=cut

sub ClientRequest {
    Debug(6, "ClientRequest");
    my $event   = shift;
    my $watcher = $event->w;
    my $socket  = $watcher->fd;
    my $data    = $watcher->data;
    my $thisread;

    Debug(9, "  Watcher named: ".$watcher->desc);

    my $rv = $socket->recv($thisread, POSIX::BUFSIZ, 0);
    Debug(8, "rcv:  data length = ".length($thisread)
	  ." read =".$thisread);
    unless (defined $rv && length($thisread)) {
	 # Likely eof on socket.
	Debug(5,"Client Socket closed on lonc for ".$RemoteHost);
	close($socket);
	$watcher->cancel();
	delete($ActiveClients{$socket});
    }
    Debug(8,"Data: ".$data." this read: ".$thisread);
    $data = $data.$thisread;	# Append new data.
    $watcher->data($data);
    if($data =~ /(.*\n)/) {	# Request entirely read.
	Debug(8, "Complete transaction received: ".$data);
	QueueTransaction($socket, $data);
	$watcher->cancel();	# Done looking for input data.
    }

}


=pod

=head2  NewClient

Callback that is called when a connection is received on the unix
socket for a new client of lonc.  The callback is parameterized by the
event.. which is a-priori assumed to be an io event, and therefore has
an fd member that is the Listener socket.  We Accept the connection
and register a new event on the readability of that socket:

=cut

sub NewClient {
    Debug(6, "NewClient");
    my $event      = shift;		# Get the event parameters.
    my $watcher    = $event->w; 
    my $socket     = $watcher->fd;	# Get the event' socket.
    my $connection = $socket->accept();	# Accept the client connection.
    Debug(8,"Connection request accepted from "
	  .GetPeername($connection, AF_UNIX));


    my $description = sprintf("Connection to lonc client %d",
			      $ClientConnection);
    Debug(9, "Creating event named: ".$description);
    Event->io(cb      => \&ClientRequest,
	      poll    => 'r',
	      desc    => $description,
	      data    => "",
	      fd      => $connection);
    $ActiveClients{$connection} = $ClientConnection;
    $ClientConnection++;
}

=pod

=head2 GetLoncSocketPath

Returns the name of the UNIX socket on which to listen for client
connections.

=cut

sub GetLoncSocketPath {
    return $UnixSocketDir."/".GetServerHost();
}

=pod

=head2 GetServerHost

Returns the host whose lond we talk with.

=cut

sub GetServerHost {		# Stub - get this from config.
    return $RemoteHost;		# Setup by the fork.
}

=pod

=head2 GetServerPort

Returns the lond port number.

=cut

sub GetServerPort {		# Stub - get this from config.
    return $perlvar{londPort};
}

=pod

=head2 SetupLoncListener

Setup a lonc listener event.  The event is called when the socket
becomes readable.. that corresponds to the receipt of a new
connection.  The event handler established will accept the connection
(creating a communcations channel), that int turn will establish
another event handler to subess requests.

=cut

sub SetupLoncListener {

    my $socket;
    my $SocketName = GetLoncSocketPath();
    unlink($SocketName);
    unless ($socket = IO::Socket::UNIX->new(Local  => $SocketName,
					    Listen => 10, 
					    Type   => SOCK_STREAM)) {
	die "Failed to create a lonc listner socket";
    }
    Event->io(cb     => \&NewClient,
	      poll   => 'r',
	      desc   => 'Lonc listener Unix Socket',
	      fd     => $socket);
}

=pod

=head2 ChildProcess

This sub implements a child process for a single lonc daemon.

=cut

sub ChildProcess {

    print "Loncnew\n";

    # For now turn off signals.
    
    $SIG{QUIT}  = IGNORE;
    $SIG{HUP}   = IGNORE;
    $SIG{USR1}  = IGNORE;
    $SIG{INT}   = IGNORE;
    $SIG{CHLD}  = IGNORE;
    $SIG{__DIE__}  = IGNORE;

    SetupTimer();
    
    SetupLoncListener();
    
    $Event::Debuglevel = $DebugLevel;
    
    Debug(9, "Making initial lond connection for ".$RemoteHost);

# Setup the initial server connection:
    
    &MakeLondConnection();
    
    Debug(9,"Entering event loop");
    my $ret = Event::loop();		#  Start the main event loop.
    
    
    die "Main event loop exited!!!";
}

#  Create a new child for host passed in:

sub CreateChild {
    my $host = shift;
    $RemoteHost = $host;
    Debug(3, "Forking off child for ".$RemoteHost);
    sleep(5);
    $pid          = fork;
    if($pid) {			# Parent
	$ChildHash{$pid} = $RemoteHost;
    } else {			# child.
	ChildProcess;
    }

}
#
#  Parent process logic pass 1:
#   For each entry in the hosts table, we will
#  fork off an instance of ChildProcess to service the transactions
#  to that host.  Each pid will be entered in a global hash
#  with the value of the key, the host.
#  The parent will then enter a loop to wait for process exits.
#  Each exit gets logged and the child gets restarted.
#

my $HostIterator = LondConnection::GetHostIterator;
while (! $HostIterator->end()) {

    $hostentryref = $HostIterator->get();
    CreateChild($hostentryref->[0]);
    $HostIterator->next();
}

# Maintain the population:

while(1) {
    $deadchild = wait();
    if(exists $ChildHash{$deadchild}) {	# need to restart.
	$deadhost = $ChildHash{$deadchild};
	delete($ChildHash{$deadchild});
	Debug(4,"Lost child pid= ".$deadchild.
	      "Connected to host ".$deadhost);
	CreateChild($deadhost);
    }
}

=head1 Theory

The event class is used to build this as a single process with an
event driven model.  The following events are handled:

=item UNIX Socket connection Received

=item Request data arrives on UNIX data transfer socket.

=item lond connection becomes writable.

=item timer fires at 1 second intervals.

All sockets are run in non-blocking mode.  Timeouts managed by the timer
handler prevents hung connections.

Key data structures:

=item RequestQueue

A queue of requests received from UNIX sockets that are
waiting for a chance to be forwarded on a lond connection socket.

=item ActiveConnections

A hash of lond connections that have transactions in process that are
available to be timed out.

=item ActiveTransactions

A hash indexed by lond connections that contain the client reply
socket for each connection that has an active transaction on it.

=item IdleConnections

A hash of lond connections that have no work to do.  These connections
can be closed if they are idle for a long enough time.

=cut

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