File:  [LON-CAPA] / nsdl / bin / gatewayc
Revision 1.1: download - view: text, annotated - select for diffs
Tue May 28 05:12:09 2002 UTC (19 years, 6 months ago) by harris41
Branches: MAIN
CVS tags: HEAD
based on LON-CAPA's lonc/lond functionality; these scripts are not yet
customized for gateway service

#!/usr/bin/perl

# gatewayc - LONCAPA-NSDL Gateway TCP-Client Domain-Socket-Server
# provides persistent TCP connections to the LON-CAPA servers in the network
# through multiplexed domain sockets
#
# $Id: gatewayc,v 1.1 2002/05/28 05:12:09 harris41 Exp $

# This is derived from LON-CAPA's lonc.

use lib '/home/httpd/lib/perl/';
use LONCAPA::Configuration;

use POSIX;
use IO::Socket;
use IO::Select;
use IO::File;
use Socket;
use Fcntl;
use Tie::RefHash;
use Crypt::IDEA;
#use Net::Ping;
use LWP::UserAgent();

$status='';
$lastlog='';
$conserver='SHELL';
$DEBUG = 0;			# Set to 1 for annoyingly complete logs.

# -------------------------------- Set signal handlers to record abnormal exits

&status("Init exception handlers");
$SIG{QUIT}=\&catchexception;
$SIG{__DIE__}=\&catchexception;

# ---------------------------------- Read loncapa_apache.conf and loncapa.conf
&status("Read loncapa_apache.conf and loncapa.conf");
my $perlvarref=LONCAPA::Configuration::read_conf('loncapa_apache.conf',
                                                 'loncapa.conf');
my %perlvar=%{$perlvarref};
undef $perlvarref;

# ----------------------------- Make sure this process is running from user=www
&status("Check user ID");
my $wwwid=getpwnam('www');
if ($wwwid!=$<) {
   $emailto="$perlvar{'lonAdmEMail'},$perlvar{'lonSysEMail'}";
   $subj="LON: $perlvar{'lonHostID'} User ID mismatch";
   system("echo 'User ID mismatch.  lonc must be run as user www.' |\
 mailto $emailto -s '$subj' > /dev/null");
   exit 1;
}

# --------------------------------------------- Check if other instance running

my $pidfile="$perlvar{'lonDaemons'}/logs/lonc.pid";

if (-e $pidfile) {
   my $lfh=IO::File->new("$pidfile");
   my $pide=<$lfh>;
   chomp($pide);
   if (kill 0 => $pide) { die "already running"; }
}

# ------------------------------------------------------------- Read hosts file

open (CONFIG,"$perlvar{'lonTabDir'}/hosts.tab") || die "Can't read host file";

while ($configline=<CONFIG>) {
    my ($id,$domain,$role,$name,$ip)=split(/:/,$configline);
    chomp($ip);
    if ($ip) {
     $hostip{$id}=$ip;
     $hostname{$id}=$name;
    }
}

close(CONFIG);

# -------------------------------------------------------- Routines for forking

%children               = ();       # keys are current child process IDs,
                                    # values are hosts
%childpid               = ();       # the other way around

%childatt               = ();       # number of attempts to start server
                                    # for ID

$childmaxattempts=5;

# ---------------------------------------------------- Fork once and dissociate
&status("Fork and dissociate");
$fpid=fork;
exit if $fpid;
die "Couldn't fork: $!" unless defined ($fpid);

POSIX::setsid() or die "Can't start new session: $!";

$conserver='PARENT';

# ------------------------------------------------------- Write our PID on disk
&status("Write PID");
$execdir=$perlvar{'lonDaemons'};
open (PIDSAVE,">$execdir/logs/lonc.pid");
print PIDSAVE "$$\n";
close(PIDSAVE);
&logthis("<font color=red>CRITICAL: ---------- Starting ----------</font>");

# ----------------------------- Ignore signals generated during initial startup
$SIG{HUP}=$SIG{USR1}='IGNORE';
# ------------------------------------------------------- Now we are on our own
    
# Fork off our children, one for every server

&status("Forking ...");

foreach $thisserver (keys %hostip) {
    #if (&online($hostname{$thisserver})) {
       make_new_child($thisserver);
    #}
}

&logthis("Done starting initial servers");
# ----------------------------------------------------- Install signal handlers


$SIG{INT}  = $SIG{TERM} = \&HUNTSMAN;
$SIG{HUP}  = \&HUPSMAN;
$SIG{USR1} = \&USRMAN;

# And maintain the population.
while (1) {
    my $deadpid = wait;		# Wait for the next child to die.
                                # See who died and start new one
                                # or a signal (e.g. USR1 for restart).
                                # if a signal, the wait will fail
                                # This is ordinarily detected by
                                # checking for the existence of the
                                # pid index inthe children hash since
                                # the return value from a failed wait is -1
                                # which is an impossible PID.
    &status("Woke up");
    my $skipping='';

    if(exists($children{$deadpid})) {

	$thisserver = $children{$deadpid}; # Look name of dead guy's peer.

	delete($children{$deadpid}); # Get rid of dead hash entry.

	if($childatt{$thisserver} < $childmaxattempts) {
	    $childatt{$thisserver}++;
	    &logthis(
	       "<font color=yellow>INFO: Trying to reconnect for $thisserver "
            ."($childatt{$thisserver} of $childmaxattempts attempts)</font>"); 
	    make_new_child($thisserver);
	
	}
	else {
	    $skipping .= $thisserver.' ';
	}
	if($skipping) {
	    &logthis("<font color=blue>WARNING: Skipped $skipping</font>");
  
	}
    }

}



sub make_new_child {
   
    $newserver=shift;
    my $pid;
    my $sigset;
    &logthis("Attempting to start child for server $newserver");
    # block signal for fork
    $sigset = POSIX::SigSet->new(SIGINT);
    sigprocmask(SIG_BLOCK, $sigset)
        or die "Can't block SIGINT for fork: $!\n";
    
    die "fork: $!" unless defined ($pid = fork);
    
    if ($pid) {
        # Parent records the child's birth and returns.
        sigprocmask(SIG_UNBLOCK, $sigset)
            or die "Can't unblock SIGINT for fork: $!\n";
        $children{$pid} = $newserver;
        $childpid{$newserver} = $pid;
        return;
    } else {
        $conserver=$newserver;
        # Child can *not* return from this subroutine.
        $SIG{INT} = 'DEFAULT';      # make SIGINT kill us as it did before
        $SIG{USR1}= \&logstatus;
   
        # unblock signals
        sigprocmask(SIG_UNBLOCK, $sigset)
            or die "Can't unblock SIGINT for fork: $!\n";

# ----------------------------- This is the modified main program of non-forker

$port = "$perlvar{'lonSockDir'}/$conserver";

unlink($port);

# -------------------------------------------------------------- Open other end

&openremote($conserver);
	&logthis("<font color=green> Connection to $conserver open </font>");
# ----------------------------------------- We're online, send delayed messages
    &status("Checking for delayed messages");

    my @allbuffered;
    my $path="$perlvar{'lonSockDir'}/delayed";
    opendir(DIRHANDLE,$path);
    @allbuffered=grep /\.$conserver$/, readdir DIRHANDLE;
    closedir(DIRHANDLE);
    my $dfname;
    foreach (@allbuffered) {
        &status("Sending delayed: $_");
        $dfname="$path/$_";
        if($DEBUG) { &logthis('Sending '.$dfname); }
        my $wcmd;
        {
         my $dfh=IO::File->new($dfname);
         $cmd=<$dfh>;
        }
        chomp($cmd);
        my $bcmd=$cmd;
        if ($cmd =~ /^encrypt\:/) {
	    my $rcmd=$cmd;
            $rcmd =~ s/^encrypt\://;
            chomp($rcmd);
            my $cmdlength=length($rcmd);
            $rcmd.="         ";
            my $encrequest='';
            for (my $encidx=0;$encidx<=$cmdlength;$encidx+=8) {
                $encrequest.=
                    unpack("H16",$cipher->encrypt(substr($rcmd,$encidx,8)));
            }
            $cmd="enc:$cmdlength:$encrequest\n";
        }
	$answer = londtransaction($remotesock, $cmd, 60);
	chomp($answer);

        if (($answer ne '') && ($@!~/timeout/)) {
	    unlink("$dfname");
            &logthis("Delayed $cmd: >$answer<");
            &logperm("S:$conserver:$bcmd");
        }        
    }
	if($DEBUG) { &logthis("<font color=green> Delayed transactions sent"); }

# ------------------------------------------------------- Listen to UNIX socket
&status("Opening socket");
unless (
  $server = IO::Socket::UNIX->new(Local  => $port,
                                  Type   => SOCK_STREAM,
                                  Listen => 10 )
   ) { 
       my $st=120+int(rand(240));
       &logthis(
         "<font color=blue>WARNING: ".
         "Can't make server socket ($st secs):  .. exiting</font>");
       sleep($st);
       exit; 
     };
   
# -----------------------------------------------------------------------------

&logthis("<font color=green>$conserver online</font>");

# -----------------------------------------------------------------------------
# begin with empty buffers
%inbuffer  = ();
%outbuffer = ();
%ready     = ();
%servers   = ();	# To be compatible with make filevector.  indexed by
			# File ids, values are sockets.
			# note that the accept socket is omitted.

tie %ready, 'Tie::RefHash';

# nonblock($server);
# $select = IO::Select->new($server);

# Main loop: check reads/accepts, check writes, check ready to process

status("Main loop");
while (1) {
    my $client;
    my $rv;
    my $data;

    my $infdset;		# bit vec of fd's to select on input.

    my $outfdset;		# Bit vec of fd's to select on output.


    $infdset = MakeFileVector(\%servers);
    $outfdset= MakeFileVector(\%outbuffer);
    vec($infdset, $server->fileno, 1) = 1;
    if($DEBUG) {
	&logthis("Adding ".$server->fileno.
		 " to input select vector (listner)".
		 unpack("b*",$infdset)."\n");
    }
    DoSelect(\$infdset, \$outfdset); # Wait for input.
    if($DEBUG) {
	&logthis("Doselect completed!");
	&logthis("ins = ".unpack("b*",$infdset)."\n");
	&logthis("outs= ".unpack("b*",$outfdset)."\n");
		 
    }

    # Checkfor new connections:
    if (vec($infdset, $server->fileno, 1)) {
	if($DEBUG) {
	    &logthis("New connection established");
	}
	# accept a new connection
	&status("Accept new connection: $conserver");
	$client = $server->accept();
	if($DEBUG) {
	    &logthis("New client fd = ".$client->fileno."\n");
	}
	$servers{$client->fileno} = $client;
	nonblock($client);
    }
    HandleInput($infdset, \%servers, \%inbuffer, \%outbuffer, \%ready);
    HandleOutput($outfdset, \%servers, \%outbuffer, \%inbuffer,
		 \%ready);
# -------------------------------------------------------- Wow, connection lost

}
   
    }
}

# ------------------------------------------------------- End of make_new_child


#
#  Make a vector of file descriptors to wait for in a select.
#  parameters:
#     \%fdhash  -reference to a hash which has IO::Socket's as indices.  
#                We only care about the indices, not the values.
#  A select vector is created from all indices of the hash.

sub MakeFileVector
{
    my $fdhash = shift;
    my $selvar = "";

    foreach $socket (keys %$fdhash) {
	if($DEBUG) {
	    &logthis("Adding  ".$socket.
		     "to select vector. (client)\n");
	}
	vec($selvar, $socket, 1) = 1;
    }
    return $selvar;
}


#
#  HandleOutput:
#    Processes output on a buffered set of file descriptors which are
#    ready to be read.
#  Parameters:
#    $selvector - Vector of file descriptors which are writable.
#    \%sockets  - Vector of socket references indexed by socket.
#    \%buffers  - Reference to a hash containing output buffers.
#                 Hashes are indexed by sockets.  The file descriptors of some
#                 of those sockets will be present in $selvector.
#                 For each one of those, we will attempt to write the output
#                 buffer to the socket.  Note that we will assume that
#                 the sockets are being run in non blocking mode.
#   \%inbufs    - Reference to hash containing input buffers.
#   \%readys    - Reference to hash containing flags for items with complete
#                 requests.
#
sub HandleOutput
{
    my $selvector = shift;
    my $sockets   = shift;
    my $buffers   = shift;
    my $inbufs    = shift;
    my $readys    = shift;
    my $sock;

    if($DEBUG) {
	&logthis("HandleOutput entered\n");
    }

    foreach $sock (keys %$sockets) {
	my $socket = $sockets->{$sock};
	if(vec($selvector, $sock, 1)) { # $socket is writable.
	    if($DEBUG) {
		&logthis("Sending $buffers->{$sock} \n");
	    }
	    my $rv = $socket->send($buffers->{$sock}, 0);
	    $errno = $!;
	    unless ($buffers->{$sock} eq "con_lost\n") {
		unless (defined $rv) { # Write failed... could be EINTR
		    unless ($errno == POSIX::EINTR) {
			&logthis("Write failed on writable socket");
		    }		# EINTR is not an error .. just retry.
		    next;
		}
		if( ($rv == length $buffers->{$sock})    ||
		    ($errno == POSIX::EWOULDBLOCK)       ||
		    ($errno == POSIX::EAGAIN)            || # same as above.
		    ($errno == POSIX::EINTR)             || # signal during IO
		    ($errno == 0)) {
		    substr($buffers->{$sock}, 0, $rv)=""; # delete written part
		    delete $buffers->{$sock} unless length $buffers->{$sock};
		} else {
		    # For some reason the write failed with an error code
		    # we didn't look for.  Shutdown the socket.
		    &logthis("Unable to write data with ".$errno.": ".
			     "Dropping data: ".length($buffers->{$sock}).
			     ", $rv");
		    #
		    # kill off the buffers in the hash:

		    delete $buffers->{$sock};
		    delete $inbufs->{$sock};
		    delete $readys->{$sock};

		    close($socket); # Close the client socket.
		    next;
		}
	    } else {		# Kludgy way to mark lond connection lost.
		&logthis(
		 "<font color=red>CRITICAL lond connection lost</font>");
		status("Connection lost");
		$remotesock->shutdown(2);
		&logthis("Attempting to open a new connection");
		&openremote($conserver);
	    }
		   
	}
    }

}
#
#   HandleInput - Deals with input on client sockets.
#                 Each socket has an associated input buffer.
#                 For each readable socket, the currently available
#                 data is appended to this buffer.
#                 If necessary, the buffer is created.
#                 On various failures, we may shutdown the client.
#  Parameters:
#     $selvec   - Vector of readable sockets.
#     \%sockets - Refers to the  Hash of sockets indexed by sockets.  
#                 Each of these may or may not have it's fd bit set 
#                 in the $selvec.
#     \%ibufs   - Refers to the hash of input buffers indexed by socket.
#     \%obufs   - Hash of output buffers indexed by socket. 
#     \%ready   - Hash of ready flags indicating the existence of a completed
#                 Request.
sub HandleInput 
{

    # Marshall the parameters.   Note that the hashes are actually
    # references not values.

    my $selvec  = shift;
    my $sockets = shift;
    my $ibufs   = shift;
    my $obufs   = shift;
    my $ready   = shift;
    my $sock;

    if($DEBUG) {
	&logthis("Entered HandleInput\n");
    }
    foreach $sock (keys %$sockets) {
	my $socket = $sockets->{$sock};
	if(vec($selvec, $sock, 1)) { # Socket which is readable.

	    #  Attempt to read the data and do error management.
	    my $data = '';
	    my $rv = $socket->recv($data, POSIX::BUFSIZ, 0);
	    if($DEBUG) {
		&logthis("Received $data from socket");
	    }
	    unless (defined($rv) && length $data) {

		# Read an end of file.. this is a disconnect from the peer.

		delete $sockets->{$sock};
		delete $ibufs->{$sock};
		delete $obufs->{$sock};
		delete $ready->{$sock};

		status("Idle");
		close $socket;
		next;
	    }
	    #  Append the read data to the input buffer. If the buffer
	    # now contains a \n the request is complete and we can 
	    # mark this in the $ready hash (one request for each \n.)

	    $ibufs->{$sock} .= $data;
	    while($ibufs->{$sock} =~ s/(.*\n)//) {
		push(@{$ready->{$sock}}, $1);
	    }
	    
	}
    }
    #  Now handle any requests which are ready:

    foreach $client (keys %ready) {
	handle($client);
    }
}

# DoSelect:  does a select with no timeout.  On signal (errno == EINTR), 
#            the select is retried until there are items in the returned
#            vectors.  
#
# Parameters:
#   \$readvec   - Reference to a vector of file descriptors to 
#                 check for readability.
#   \$writevec  - Reference to a vector of file descriptors to check for
#                 writability.
#  On exit, the referents are modified with vectors indicating which 
#  file handles are readable/writable.
#
sub DoSelect {
    my $readvec = shift;
    my $writevec= shift;
    my $outs;
    my $ins;

    while (1) {
	my $nfds = select( $ins = $$readvec, $outs = $$writevec, undef, undef);
	if($nfds) {
	    if($DEBUG) {
		&logthis("select exited with ".$nfds." fds\n");
		&logthis("ins = ".unpack("b*",$ins).
			 " readvec = ".unpack("b*",$$readvec)."\n");
		&logthis("outs = ".unpack("b*",$outs).
			 " writevec = ".unpack("b*",$$writevec)."\n");
	    }
	    $$readvec  = $ins;
	    $$writevec = $outs;
	    return;
	} else {
	    if($DEBUG) {
		&logthis("Select exited with no bits set in mask\n");
	    }
	    die "Select failed" unless $! == EINTR;
	}
    }
}

# handle($socket) deals with all pending requests for $client
#
sub handle {
    # requests are in $ready{$client}
    # send output to $outbuffer{$client}
    my $client = shift;
    my $request;
    foreach $request (@{$ready{$client}}) {
# ============================================================= Process request
        # $request is the text of the request
        # put text of reply into $outbuffer{$client}
# ------------------------------------------------------------ Is this the end?
	chomp($request);
	if($DEBUG) {
     &logthis("<font color=green> Request $request processing starts</font>");
        }
        if ($request eq "close_connection_exit\n") {
	    &status("Request close connection");
           &logthis(
     "<font color=red>CRITICAL: Request Close Connection ... exiting</font>");
           $remotesock->shutdown(2);
           $server->close();
           exit;
        }
# -----------------------------------------------------------------------------
        if ($request =~ /^encrypt\:/) {
	    my $cmd=$request;
            $cmd =~ s/^encrypt\://;
            chomp($cmd);
            my $cmdlength=length($cmd);
            $cmd.="         ";
            my $encrequest='';
            for (my $encidx=0;$encidx<=$cmdlength;$encidx+=8) {
                $encrequest.=
                    unpack("H16",$cipher->encrypt(substr($cmd,$encidx,8)));
            }
            $request="enc:$cmdlength:$encrequest";
        }
# --------------------------------------------------------------- Main exchange
	$answer = londtransaction($remotesock, $request, 300);

	if($DEBUG) { 
	    &logthis("<font color=green> Request data exchange complete");
	}
	if ($@=~/timeout/) { 
	    $answer='';
	    &logthis(
		     "<font color=red>CRITICAL: Timeout: $request</font>");
	}  


        if ($answer) {
	   if ($answer =~ /^enc/) {
               my ($cmd,$cmdlength,$encinput)=split(/:/,$answer);
               chomp($encinput);
	       $answer='';
               for (my $encidx=0;$encidx<length($encinput);$encidx+=16) {
                  $answer.=$cipher->decrypt(
                   pack("H16",substr($encinput,$encidx,16))
                  );
	       }
	      $answer=substr($answer,0,$cmdlength);
	      $answer.="\n";
	   }
	   if($DEBUG) {
	       &logthis("sending $answer to client\n");
	   }
           $outbuffer{$client} .= $answer;
        } else {
           $outbuffer{$client} .= "con_lost\n";
        }

     &status("Completed: $request");
	if($DEBUG) {
	    &logthis("<font color=green> Request processing complete</font>");
	}
# ===================================================== Done processing request
    }
    delete $ready{$client};
# -------------------------------------------------------------- End non-forker
    if($DEBUG) {
	&logthis("<font color=green> requests for child handled</font>");
    }
}
# ---------------------------------------------------------- End make_new_child

# nonblock($socket) puts socket into nonblocking mode
sub nonblock {
    my $socket = shift;
    my $flags;

    
    $flags = fcntl($socket, F_GETFL, 0)
            or die "Can't get flags for socket: $!\n";
    fcntl($socket, F_SETFL, $flags | O_NONBLOCK)
            or die "Can't make socket nonblocking: $!\n";
}


sub openremote {
# ---------------------------------------------------- Client to network server

    my $conserver=shift;

&status("Opening TCP");
    my $st=120+int(rand(240)); # Sleep before opening:

unless (
  $remotesock = IO::Socket::INET->new(PeerAddr => $hostip{$conserver},
                                      PeerPort => $perlvar{'londPort'},
                                      Proto    => "tcp",
                                      Type     => SOCK_STREAM)
   ) { 

       &logthis(
"<font color=blue>WARNING: Couldn't connect to $conserver ($st secs): </font>");
       sleep($st);
       exit; 
     };
# ----------------------------------------------------------------- Init dialog

&logthis("<font color=green>INFO Connected to $conserver, initing </font>");
&status("Init dialogue: $conserver");

    $answer = londtransaction($remotesock, "init", 60);
    chomp($answer);
    $answer = londtransaction($remotesock, $answer, 60);
    chomp($answer);
 
     if ($@=~/timeout/) {
	 &logthis("Timed out during init.. exiting");
         exit;
     }

if ($answer ne 'ok') {
       &logthis("Init reply: >$answer<");
       my $st=120+int(rand(240));
       &logthis(
"<font color=blue>WARNING: Init failed ($st secs)</font>");
       sleep($st);
       exit; 
}

sleep 5;
&status("Ponging");
print $remotesock "pong\n";
$answer=<$remotesock>;
chomp($answer);
if ($answer!~/^$conserver/) {
   &logthis("Pong reply: >$answer<");
}
# ----------------------------------------------------------- Initialize cipher

&status("Initialize cipher");
print $remotesock "ekey\n";
my $buildkey=<$remotesock>;
my $key=$conserver.$perlvar{'lonHostID'};
$key=~tr/a-z/A-Z/;
$key=~tr/G-P/0-9/;
$key=~tr/Q-Z/0-9/;
$key=$key.$buildkey.$key.$buildkey.$key.$buildkey;
$key=substr($key,0,32);
my $cipherkey=pack("H32",$key);
if ($cipher=new IDEA $cipherkey) {
   &logthis("Secure connection initialized");
} else {
   my $st=120+int(rand(240));
   &logthis(
     "<font color=blue>WARNING: ".
     "Could not establish secure connection ($st secs)!</font>");
   sleep($st);
   exit;
}
    &logthis("<font color=green> Remote open success </font>");
}



# grabs exception and records it to log before exiting
sub catchexception {
    my ($signal)=@_;
    $SIG{QUIT}='DEFAULT';
    $SIG{__DIE__}='DEFAULT';
    chomp($signal);
    &logthis("<font color=red>CRITICAL: "
     ."ABNORMAL EXIT. Child $$ for server [$wasserver] died through "
     ."\"$signal\" with parameter </font>");
    die("Signal abend");
}

# -------------------------------------- Routines to see if other box available

#sub online {
#    my $host=shift;
#    &status("Pinging ".$host);
#    my $p=Net::Ping->new("tcp",20);
#    my $online=$p->ping("$host");
#    $p->close();
#    undef ($p);
#    return $online;
#}

sub connected {
    my ($local,$remote)=@_;
    &status("Checking connection $local to $remote");
    $local=~s/\W//g;
    $remote=~s/\W//g;

    unless ($hostname{$local}) { return 'local_unknown'; }
    unless ($hostname{$remote}) { return 'remote_unknown'; }

    #unless (&online($hostname{$local})) { return 'local_offline'; }

    my $ua=new LWP::UserAgent;
    
    my $request=new HTTP::Request('GET',
      "http://".$hostname{$local}.'/cgi-bin/ping.pl?'.$remote);

    my $response=$ua->request($request);

    unless ($response->is_success) { return 'local_error'; }

    my $reply=$response->content;
    $reply=(split("\n",$reply))[0];
    $reply=~s/\W//g;
    if ($reply ne $remote) { return $reply; }
    return 'ok';
}



sub hangup {
    foreach (keys %children) {
        $wasserver=$children{$_};
        &status("Closing $wasserver");
        &logthis('Closing '.$wasserver.': '.&subreply('exit',$wasserver));
        &status("Kill PID $_ for $wasserver");
	kill ('INT',$_);
    }
}

sub HUNTSMAN {                      # signal handler for SIGINT
    local($SIG{CHLD}) = 'IGNORE';   # we're going to kill our children
    &hangup();
    my $execdir=$perlvar{'lonDaemons'};
    unlink("$execdir/logs/lonc.pid");
    &logthis("<font color=red>CRITICAL: Shutting down</font>");
    exit;                           # clean up with dignity
}

sub HUPSMAN {                      # signal handler for SIGHUP
    local($SIG{CHLD}) = 'IGNORE';  # we're going to kill our children
    &hangup();
    &logthis("<font color=red>CRITICAL: Restarting</font>");
    unlink("$execdir/logs/lonc.pid");
    my $execdir=$perlvar{'lonDaemons'};
    exec("$execdir/lonc");         # here we go again
}

sub checkchildren {
    &initnewstatus();
    &logstatus();
    &logthis('Going to check on the children');
    foreach (sort keys %children) {
	sleep 1;
        unless (kill 'USR1' => $_) {
	    &logthis ('<font color=red>CRITICAL: Child '.$_.' is dead</font>');
            &logstatus($$.' is dead');
        } 
    }
}

sub USRMAN {
    &logthis("USR1: Trying to establish connections again");
    #
    #  It is really important not to just clear the childatt hash or we will
    #  lose all memory of the children.  What we really want to do is this:
    #  For each index where childatt is >= $childmaxattempts
    #  Zero the associated counter and do a make_child for the host.
    #  Regardles, the childatt entry is zeroed:
    my $host;
    foreach $host (keys %childatt) {
	if ($childatt{$host} >= $childmaxattempts) {
	    $childatt{$host} = 0;
	    &logthis("<font color=green>INFO: Restarting child for server: "
		     .$host."</font>\n");
	    make_new_child($host);
	}
	else {
	    $childatt{$host} = 0;
	}
    }
    &checkchildren();		# See if any children are still dead...
}

# -------------------------------------------------- Non-critical communication
sub subreply { 
 my ($cmd,$server)=@_;
 my $answer='';
 if ($server ne $perlvar{'lonHostID'}) { 
    my $peerfile="$perlvar{'lonSockDir'}/$server";
    my $sclient=IO::Socket::UNIX->new(Peer    =>"$peerfile",
                                      Type    => SOCK_STREAM,
                                      Timeout => 10)
       or return "con_lost";


    $answer = londtransaction($sclient, $cmd, 10);

    if ((!$answer) || ($@=~/timeout/)) { $answer="con_lost"; }
    $SIG{ALRM}='DEFAULT';
    $SIG{__DIE__}=\&catchexception;
 } else { $answer='self_reply'; }
 return $answer;
}

# --------------------------------------------------------------------- Logging

sub logthis {
    my $message=shift;
    my $execdir=$perlvar{'lonDaemons'};
    my $fh=IO::File->new(">>$execdir/logs/lonc.log");
    my $now=time;
    my $local=localtime($now);
    $lastlog=$local.': '.$message;
    print $fh "$local ($$) [$conserver] [$status]: $message\n";
}

#--------------------------------------  londtransaction:
#  
#  Performs a transaction with lond with timeout support.
#    result = londtransaction(socket,request,timeout)
#
sub londtransaction {
    my ($socket, $request, $tmo) = @_;

    if($DEBUG) {
	&logthis("londtransaction request: $request");
    }

    # Set the signal handlers: ALRM for timeout and disble the others.

    $SIG{ALRM} = sub { die "timeout" };
    $SIG{__DIE__} = 'DEFAULT';
    
    # Disable all but alarm so that only that can interupt the
    # send /receive.
    #
    my $sigset = POSIX::SigSet->new(QUIT, USR1, HUP, INT, TERM);
    my $priorsigs = POSIX::SigSet->new;
    unless (defined sigprocmask(SIG_BLOCK, $sigset, $priorsigs)) {
	&logthis("<font color=red> CRITICAL -- londtransaction ".
		"failed to block signals </font>");
	die "could not block signals in londtransaction";
    }
    $answer = '';
    #
    #  Send request to lond.
    #
    eval { 
	alarm($tmo);
	print $socket "$request\n";
	alarm(0);
    };
    #  If request didn't timeout, try for the response.
    #

    if ($@!~/timeout/) {
	eval {
	    alarm($tmo);
	    $answer = <$socket>;
	    if($DEBUG) {
		&logthis("Received $answer in londtransaction");
	    }
	    alarm(0);
	};
    } else {
	if($DEBUG) {
	    &logthis("Timeout on send in londtransaction");
	}
    }
    if( ($@ =~ /timeout/)  && ($DEBUG)) {
	&logthis("Timeout on receive in londtransaction");
    }
    #
    # Restore the initial sigmask set.
    #
    unless (defined sigprocmask(SIG_UNBLOCK, $priorsigs)) {
	&logthis("<font color=red> CRITICAL -- londtransaction ".
		"failed to re-enable signal processing. </font>");
	die "londtransaction failed to re-enable signals";
    }
    #
    # go back to the prior handler set.
    #
    $SIG{ALRM} = 'DEFAULT';
    $SIG{__DIE__} = \&cathcexception;

    #    chomp $answer;
    if ($DEBUG) {
	&logthis("Returning $answer in londtransaction");
    }
    return $answer;

}

sub logperm {
    my $message=shift;
    my $execdir=$perlvar{'lonDaemons'};
    my $now=time;
    my $local=localtime($now);
    my $fh=IO::File->new(">>$execdir/logs/lonnet.perm.log");
    print $fh "$now:$message:$local\n";
}
# ------------------------------------------------------------------ Log status

sub logstatus {
    my $docdir=$perlvar{'lonDocRoot'};
    my $fh=IO::File->new(">>$docdir/lon-status/loncstatus.txt");
    print $fh $$."\t".$conserver."\t".$status."\t".$lastlog."\n";
}

sub initnewstatus {
    my $docdir=$perlvar{'lonDocRoot'};
    my $fh=IO::File->new(">$docdir/lon-status/loncstatus.txt");
    my $now=time;
    my $local=localtime($now);
    print $fh "LONC status $local - parent $$\n\n";
}

# -------------------------------------------------------------- Status setting

sub status {
    my $what=shift;
    my $now=time;
    my $local=localtime($now);
    $status=$local.': '.$what;
}



# ----------------------------------- POD (plain old documentation, CPAN style)

=head1 NAME

lonc - LON TCP-MySQL-Server Daemon for handling database requests.

=head1 SYNOPSIS

Usage: B<gatewayc>

Should only be run as user=www.  This is a command-line script which
is invoked by B<loncron>.  There is no expectation that a typical user
will manually start B<lonc> from the command-line.  (In other words,
DO NOT START B<lonc> YOURSELF.)

=head1 DESCRIPTION

Provides persistent TCP connections to the other servers in the network
through multiplexed domain sockets

B<lonc> forks off children processes that correspond to the other servers
in the network.  Management of these processes can be done at the
parent process level or the child process level.

  After forking off the children, B<lonc> the B<parent> 
executes a main loop which simply waits for processes to exit.
As a process exits, a new process managing a link to the same
peer as the exiting process is created.  

B<logs/lonc.log> is the location of log messages.

The process management is now explained in terms of linux shell commands,
subroutines internal to this code, and signal assignments:

=over 4

=item *

PID is stored in B<logs/gatewayc.pid>

This is the process id number of the parent B<gatewayc> process.

=item *

SIGTERM and SIGINT

Parent signal assignment:
 $SIG{INT}  = $SIG{TERM} = \&HUNTSMAN;

Child signal assignment:
 $SIG{INT}  = 'DEFAULT'; (and SIGTERM is DEFAULT also)
(The child dies and a SIGALRM is sent to parent, awaking parent from slumber
 to restart a new child.)

Command-line invocations:
 B<kill> B<-s> SIGTERM I<PID>
 B<kill> B<-s> SIGINT I<PID>

Subroutine B<HUNTSMAN>:
 This is only invoked for the B<lonc> parent I<PID>.
This kills all the children, and then the parent.
The B<lonc.pid> file is cleared.

=item *

SIGHUP

Current bug:
 This signal can only be processed the first time
on the parent process.  Subsequent SIGHUP signals
have no effect.

Parent signal assignment:
 $SIG{HUP}  = \&HUPSMAN;

Child signal assignment:
 none (nothing happens)

Command-line invocations:
 B<kill> B<-s> SIGHUP I<PID>

Subroutine B<HUPSMAN>:
 This is only invoked for the B<lonc> parent I<PID>,
This kills all the children, and then the parent.
The B<lonc.pid> file is cleared.

=item *

SIGUSR1

Parent signal assignment:
 $SIG{USR1} = \&USRMAN;

Child signal assignment:
 $SIG{USR1}= \&logstatus;

Command-line invocations:
 B<kill> B<-s> SIGUSR1 I<PID>

Subroutine B<USRMAN>:
 When invoked for the B<lonc> parent I<PID>,
SIGUSR1 is sent to all the children, and the status of
each connection is logged.


=back

=head1 PREREQUISITES

POSIX
IO::Socket
IO::Select
IO::File
Socket
Fcntl
Tie::RefHash
Crypt::IDEA

=head1 COREQUISITES

=head1 OSNAMES

linux

=head1 SCRIPT CATEGORIES

Server/Process

=cut

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