Annotation of loncom/LondConnection.pm, revision 1.2

1.2     ! albertel    1: #   This module defines and implements a class that represents
        !             2: #   a connection to a lond daemon.
        !             3: #
        !             4: # $Id: gplheader.pl,v 1.1 2001/11/29 18:19:27 www Exp $
        !             5: #
        !             6: # Copyright Michigan State University Board of Trustees
        !             7: #
        !             8: # This file is part of the LearningOnline Network with CAPA (LON-CAPA).
        !             9: #
        !            10: # LON-CAPA is free software; you can redistribute it and/or modify
        !            11: # it under the terms of the GNU General Public License as published by
        !            12: # the Free Software Foundation; either version 2 of the License, or
        !            13: # (at your option) any later version.
        !            14: #
        !            15: # LON-CAPA is distributed in the hope that it will be useful,
        !            16: # but WITHOUT ANY WARRANTY; without even the implied warranty of
        !            17: # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
        !            18: # GNU General Public License for more details.
        !            19: #
        !            20: # You should have received a copy of the GNU General Public License
        !            21: # along with LON-CAPA; if not, write to the Free Software
        !            22: # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
        !            23: #
        !            24: # /home/httpd/html/adm/gpl.txt
        !            25: #
        !            26: # http://www.lon-capa.org/
1.1       foxr       27: #
                     28: package LondConnection;
                     29: 
                     30: use IO::Socket;
                     31: use IO::Socket::INET;
                     32: use IO::Handle;
                     33: use IO::File;
                     34: use Fcntl;
                     35: use POSIX;
                     36: use Crypt::IDEA;
                     37: use LONCAPA::Configuration;
                     38: use LONCAPA::HashIterator;
                     39: 
                     40: my $DebugLevel=4;
                     41: 
                     42: #   Read the configuration file for apache to get the perl
                     43: #   variable set.
                     44: 
                     45: my $perlvarref = LONCAPA::Configuration::read_conf('loncapa.conf');
                     46: my %perlvar    = %{$perlvarref};
                     47: my $hoststab   = 
                     48:     LONCAPA::Configuration::read_hosts(
                     49:             "$perlvar{'lonTabDir'}/hosts.tab") || 
                     50:     die "Can't read host table!!";
                     51: my %hostshash  = %{$hoststab};
                     52: 
                     53: close(CONFIG);
                     54: 
                     55: sub Debug {
                     56:     my $level   = shift;
                     57:     my $message = shift;
                     58:     if ($level < $DebugLevel) {
                     59: 	print($message."\n");
                     60:     }
                     61: }
                     62: =pod 
                     63:    Dump the internal state of the object: For debugging purposes.
                     64: =cut
                     65: 
                     66: sub Dump {
                     67:     my $self   = shift;
                     68:     print "Dumping LondConnectionObject:\n";
                     69:     while(($key, $value) = each %$self) {
                     70: 	print "$key -> $value\n";
                     71:     }
                     72:     print "-------------------------------\n";
                     73: }
                     74: 
                     75: =pod
                     76:   Local function to do a state transition.  If the state transition callback
                     77:     is defined it is called with two parameters:  the self and the old state.
                     78: =cut
                     79: sub Transition {
                     80:     my $self     = shift;
                     81:     my $newstate = shift;
                     82:     my $oldstate = $self->{State};
                     83:     $self->{State} = $newstate;
                     84:     $self->{TimeoutRemaining} = $self->{TimeoutValue};
                     85:     if($self->{TransitionCallback}) {
                     86: 	($self->{TransitionCallback})->($self, $oldstate); 
                     87:     }
                     88: }
                     89: 
                     90: =pod
                     91:   Construct a new lond connection.
                     92:   Parameters (besides the class name) include:
                     93: =item hostname - host the remote lond is on. 
                     94:     This host is a host in the hosts.tab file
                     95: =item port     - port number the remote lond is listening on.
                     96: =cut
                     97: sub new {
                     98:     my $class    = shift;	# class name.
                     99:     my $Hostname = shift;	# Name of host to connect to.
                    100:     my $Port     = shift;	# Port to connect 
                    101:     &Debug(4,$class."::new( ".$Hostname.",".$Port.")\n");
                    102: 
                    103:     # The host must map to an entry in the hosts table:
                    104:     #  We connect to the dns host that corresponds to that
                    105:     #  system and use the hostname for the encryption key 
                    106:     #  negotion.  In the objec these become the Host and
                    107:     #  LoncapaHim fields of the object respectively.
                    108:     #
                    109:     if (!exists $hostshash{$Hostname}) {
                    110: 	return undef;		# No such host!!!
                    111:     }
                    112:     my @ConfigLine = @{$hostshash{$Hostname}};
                    113:     my $DnsName    = $ConfigLine[3]; # 4'th item is dns of host.
                    114:     Debug(5, "Connecting to ".$DnsName);
                    115:     # Now create the object...
                    116:     my $self     = { Host               => $DnsName,
                    117: 		     LoncapaHim         => $Hostname,
                    118: 	             Port               => $Port,
                    119: 	             State              => "Initialized",
                    120: 	             TransactionRequest => "",
                    121: 	             TransactionReply   => "",
                    122: 	             InformReadable     => 0,
                    123: 	             InformWritable     => 0,
                    124: 		     TimeoutCallback    => undef,
                    125: 		     TransitionCallback => undef,
                    126: 	             Timeoutable        => 0,
                    127: 	             TimeoutValue       => 60,
                    128:              TimeoutRemaining   => 0,
                    129: 		     CipherKey          => "",
                    130: 		     Cipher             => undef};
                    131:     bless($self, $class);
                    132:     unless ($self->{Socket} = IO::Socket::INET->new(PeerHost => $self->{Host},
                    133: 					       PeerPort => $self->{Port},
                    134: 					       Type     => SOCK_STREAM,
                    135: 					       Proto    => "tcp")) {
                    136: 	return undef;		# Inidicates the socket could not be made.
                    137:     }
                    138:     #
                    139:     # We're connected.  Set the state, and the events we'll accept:
                    140:     #
                    141:     $self->Transition("Connected");
                    142:     $self->{InformWritable}     = 1;    # When  socket is writable we send init
                    143:     $self->{TransactionRequest} = "init\n";
                    144:     
                    145:     #
                    146:     # Set socket to nonblocking I/O.
                    147:     #
                    148:     my $socket = $self->{Socket};
                    149:     $flags    = fcntl($socket->fileno, F_GETFL,0);
                    150:     if($flags == -1) {
                    151: 	$socket->close;
                    152: 	return undef;
                    153:     }
                    154:     if(fcntl($socket, F_SETFL, $flags | O_NONBLOCK) == -1) {
                    155: 	$socket->close;
                    156: 	return undef;
                    157:     }
                    158: 
                    159:     # return the object :
                    160: 
                    161:     return $self;
                    162: }
                    163: =pod
                    164:    This member should be called when the Socket becomes readable.
                    165:    Until the read completes,  action is state independet. Data are accepted
                    166:     into the TransactionReply until a newline character is received.  At that
                    167:    time actionis state dependent:
                    168: =item Connected: in this case we received challenge, the state changes
                    169:     to ChallengeReceived, and we initiate a send with the challenge response.
                    170: =item ReceivingReply: In this case a reply has been received for a transaction,
                    171:     the state goes to Idle and we disable write and read notification.
                    172: =item ChallengeReeived: we just got what should be an ok\n and the
                    173:     connection can now handle transactions.
                    174: 
                    175: =cut
                    176: sub Readable {
                    177:     my $self    = shift;
                    178:     my $socket  = $self->{Socket};
                    179:     my $data    = '';
                    180:     my $rv      = $socket->recv($data, POSIX::BUFSIZ,  0);
                    181:     my $errno   = $! + 0;	             # Force numeric context.
                    182: 
                    183:     unless (defined($rv) && length($data)) { # Read failed,
                    184: 	if(($errno == POSIX::EWOULDBLOCK)   ||
                    185: 	   ($errno == POSIX::EAGAIN)        ||
                    186: 	   ($errno == POSIX::EINTR)         ||
                    187: 	   ($errno == 0)) {
                    188: 	    return 0;
                    189: 	}
                    190: 
                    191: 	# Connection likely lost.
                    192: 	&Debug(4, "Connection lost");
                    193: 	$self->{TransactionRequest} = '';
                    194: 	$socket->close();
                    195: 	$self->Transition("Disconnected");
                    196: 	return -1;
                    197:     }
                    198:     #  Append the data to the buffer.  And figure out if the read is done:
                    199: 
                    200:     &Debug(9,"Received from host: ".$data);
                    201:     $self->{TransactionReply} .= $data;
                    202:     if($self->{TransactionReply} =~ /(.*\n)/) {
                    203: 	&Debug(8,"Readable End of line detected");
                    204: 	if ($self->{State}  eq "Initialized") { # We received the challenge:
                    205: 	    if($self->{TransactionReply} eq "refused") {	# Remote doesn't have
                    206: 		
                    207: 		$self->Transition("Disconnected"); # in host tables.
                    208: 		$socket->close();
                    209: 		return -1;
                    210: 	    }
                    211: 
                    212: 	    &Debug(8," Transition out of Initialized");
                    213: 	    $self->{TransactionRequest} = $self->{TransactionReply};
                    214: 	    $self->{InformWritable}     = 1;
                    215: 	    $self->{InformReadable}     = 0;
                    216: 	    $self->Transition("ChallengeReceived");
                    217: 	    $self->{TimeoutRemaining}   = $self->{TimeoutValue};
                    218: 	    return 0;
                    219: 	} elsif ($self->{State} eq "ChallengeReplied") { # should be ok.
                    220: 	    if($self->{TransactionReply} != "ok\n") {
                    221: 		$self->Transition("Disconnected");
                    222: 		$socket->close();
                    223: 		return -1;
                    224: 	    }
                    225: 	    $self->Transition("RequestingKey");
                    226: 	    $self->{InformReadable}  = 0;
                    227: 	    $self->{InformWritable}  = 1;
                    228: 	    $self->{TransactionRequest} = "ekey\n";
                    229: 	    return 0;
                    230: 	} elsif ($self->{State}  eq "ReceivingKey") {
                    231: 	    my $buildkey = $self->{TransactionReply};
                    232: 	    my $key = $self->{LoncapaHim}.$perlvar{'lonHostID'};
                    233: 	    $key=~tr/a-z/A-Z/;
                    234: 	    $key=~tr/G-P/0-9/;
                    235: 	    $key=~tr/Q-Z/0-9/;
                    236: 	    $key=$key.$buildkey.$key.$buildkey.$key.$buildkey;
                    237: 	    $key=substr($key,0,32);
                    238: 	    my $cipherkey=pack("H32",$key);
                    239: 	    $self->{Cipher} = new IDEA $cipherkey;
                    240: 	    if($self->{Cipher} == undef) {
                    241: 		$self->Transition("Disconnected");
                    242: 		$socket->close();
                    243: 		return -1;
                    244: 	    } else {
                    245: 		$self->Transition("Idle");
                    246: 		$self->{InformWritable}  =  0;
                    247: 		$self->{InformReadable}  =  0;
                    248: 		$self->{Timeoutable}     = 0;
                    249: 		return 0;
                    250: 	    }
                    251: 	} elsif ($self->{State}  eq "ReceivingReply") {
                    252: 
                    253: 	    # If the data are encrypted, decrypt first.
                    254: 
                    255: 	    my $answer = $self->{TransactionReply};
                    256: 	    if($answer =~ /^enc\:/) {
                    257: 		$answer = $self->Decrypt($answer);
                    258: 		$self->{TransactionReply} = $answer;
                    259: 	    }
                    260: 
                    261: 	    # finish the transaction
                    262: 
                    263: 	    $self->{InformWritable}     = 0;
                    264: 	    $self->{InformReadable}     = 0;
                    265: 	    $self->{Timeoutable}        = 0;
                    266: 	    $self->Transition("Idle");
                    267: 	    return 0;
                    268: 	} elsif ($self->{State} eq "Disconnected") { # No connection.
                    269: 	    return -1;
                    270: 	} else {			# Internal error: Invalid state.
                    271: 	    $self->Transition("Disconnected");
                    272: 	    $socket->close();
                    273: 	    return -1;
                    274: 	}
                    275:     }
                    276: 
                    277:     return 0;
                    278:     
                    279: }
                    280: 
                    281: 
                    282: =pod
                    283:   This member should be called when the Socket becomes writable.
                    284: The action is state independent. An attempt is made to drain the contents of
                    285: the TransactionRequest member.  Once this is drained, we mark the  object
                    286: as waiting for readability.
                    287: 
                    288: Returns  0 if successful, or -1 if not.
                    289:   
                    290: =cut
                    291: sub Writable {
                    292:     my $self     = shift;		# Get reference to the object.
                    293:     my $socket   = $self->{Socket};
                    294:     my $nwritten = $socket->send($self->{TransactionRequest}, 0);
                    295:     my $errno    = $! + 0;
                    296:     unless (defined $nwritten) {
                    297: 	if($errno != POSIX::EINTR) {
                    298: 	    $self->Transition("Disconnected");
                    299: 	    return -1;
                    300: 	}
                    301:       
                    302:     }
                    303:     if (($rv >= 0)                        ||
                    304:         ($errno == POSIX::EWOULDBLOCK)    ||
                    305: 	($errno == POSIX::EAGAIN)         ||
                    306: 	($errno == POSIX::EINTR)          ||
                    307: 	($errno ==  0)) {
                    308: 	substr($self->{TransactionRequest}, 0, $nwritten) = ""; # rmv written part
                    309: 	if(length $self->{TransactionRequest} == 0) {
                    310: 	    $self->{InformWritable} = 0;
                    311: 	    $self->{InformReadable} = 1;
                    312: 	    $self->{TransactionReply} = '';
                    313: 	    #
                    314: 	    # Figure out the next state:
                    315: 	    #
                    316: 	    if($self->{State} eq "Connected") {
                    317: 		$self->Transition("Initialized");
                    318: 	    } elsif($self->{State} eq "ChallengeReceived") {
                    319: 		$self->Transition("ChallengeReplied");
                    320: 	    } elsif($self->{State} eq "RequestingKey") {
                    321: 		$self->Transition("ReceivingKey");
                    322: 		$self->{InformWritable} = 0;
                    323: 		$self->{InformReadable} = 1;
                    324: 		$self->{TransactionReply} = '';
                    325: 	    } elsif ($self->{State} eq "SendingRequest") {
                    326: 		$self->Transition("ReceivingReply");
                    327: 		$self->{TimeoutRemaining} = $self->{TimeoutValue};
                    328: 	    } elsif ($self->{State} eq "Disconnected") {
                    329: 		return -1;
                    330: 	    }
                    331: 	    return 0;
                    332: 	}
                    333:     } else {			# The write failed (e.g. partner disconnected).
                    334: 	$self->Transition("Disconnected");
                    335: 	$socket->close();
                    336: 	return -1;
                    337:     }
                    338: 	
                    339: }
                    340: =pod
                    341:    Tick is called every time unit by the event framework.  It
                    342:    1. decrements the remaining timeout.
                    343:    2. If the timeout is zero, calls TimedOut indicating that the 
                    344:       current operation timed out.
                    345: 
                    346: =cut
                    347:     
                    348: sub Tick {
                    349:     my $self = shift;
                    350:     $self->{TimeoutRemaining}--;
                    351:     if ($self->{TimeoutRemaining} < 0) {
                    352: 	$self->TimedOut();
                    353:     }
                    354: }
                    355: =pod
                    356:   TimedOut - called on a timeout.  If the timeout callback is defined,
                    357:   it is called with $self as  its parameters.
                    358: 
                    359: =cut  
                    360: sub TimedOut  {
                    361: 
                    362:     my $self = shift;
                    363:     if($self->{TimeoutCallback}) {
                    364: 	my $callback = $self->{TimeoutCallback};
                    365: 	my @args = ( $self);
                    366: 	&$callback(@args);
                    367:     }
                    368: }
                    369: =pod
                    370:     Called to initiate a transaction.  A transaction can only be initiated
                    371:     when the object is idle... otherwise an error is returned.
                    372:     A transaction consists of a request to the server that will have a reply.
                    373:     This member sets the request data in the TransactionRequest member,
                    374:     makes the state SendingRequest and sets the data to allow a timout,
                    375:     and to request writability notification.  
                    376: =cut
                    377: sub InitiateTransaction {
                    378:     my $self   = shift;
                    379:     my $data   = shift;
                    380: 
                    381:     if($self->{State} ne "Idle") {
                    382: 	return -1;		# Error indicator.
                    383:     }
                    384:     # if the transaction is to be encrypted encrypt the data:
                    385: 
                    386:     if($data =~ /^encrypt\:/) {
                    387: 	$data = $self->Encrypt($data);
                    388:     }
                    389: 
                    390:     # Setup the trasaction
                    391: 
                    392:     $self->{TransactionRequest} = $data;
                    393:     $self->{TransactionReply}   = "";
                    394:     $self->{InformWritable}     = 1;
                    395:     $self->{InformReadable}     = 0;
                    396:     $self->{Timeoutable}        = 1;
                    397:     $self->{TimeoutRemaining}   = $self->{TimeoutValue};
                    398:     $self->Transition("SendingRequest");
                    399: }
                    400: 
                    401: 
                    402: =pod
                    403:     Sets a callback for state transitions.  Returns a reference to any
                    404:     prior established callback, or undef if there was none:
                    405: =cut
                    406: sub SetStateTransitionCallback {
                    407:     my $self        = shift;
                    408:     my $oldCallback = $self->{TransitionCallback};
                    409:     $self->{TransitionCallback} = shift;
                    410:     return $oldCallback;
                    411: }
                    412: =pod
                    413:    Sets the timeout callback.  Returns a reference to any prior established 
                    414:    callback or undef if there was none.
                    415: =cut
                    416: sub SetTimeoutCallback {
                    417:     my $self                 = shift;
                    418:     my $callback             = shift;
                    419:     my $oldCallback          = $self->{TimeoutCallback};
                    420:     $self->{TimeoutCallback} = $callback;
                    421:     return $oldCallback;
                    422: }
                    423: 
                    424: =pod
                    425:    GetState - selector for the object state.
                    426: =cut
                    427: sub GetState {
                    428:     my $self = shift;
                    429:     return $self->{State};
                    430: }
                    431: =pod
                    432:    GetSocket - selector for the object socket.
                    433: =cut
                    434: sub GetSocket {
                    435:     my $self  = shift;
                    436:     return $self->{Socket};
                    437: }
                    438: =pod
                    439:    Return the state of the flag that indicates the object wants to be
                    440:     called when readable.
                    441: =cut
                    442: sub WantReadable {
                    443:     my   $self = shift;
                    444: 
                    445:     return $self->{InformReadable};
                    446: }
                    447: =pod
                    448:    Return the state of the flag that indicates the object wants write
                    449:     notification.
                    450: =cut
                    451: sub WantWritable {
                    452:     my $self = shift;
                    453:     return $self->{InformWritable};
                    454: }
                    455: =pod
                    456:   return the state of the flag that indicates the object wants to be informed
                    457:    of timeouts.
                    458: =cut
                    459: sub WantTimeout {
                    460:     my $self = shift;
                    461:     return $self->{Timeoutable};
                    462: }
                    463: 
                    464: =pod
                    465:   Returns the reply from the last transaction.
                    466: =cut
                    467: sub GetReply {
                    468:     my $self = shift;
                    469:     return $self->{TransactionReply};
                    470: }
                    471: 
                    472: =pod
                    473:   Returns the encrypted version of the command string.
                    474:   The command input string is of the form:
                    475:   encrypt:command
                    476:   The output string can be directly sent to lond as it's of the form:
                    477:   enc:length:<encodedrequest>
                    478: '
                    479: =cut
                    480: sub Encrypt {
                    481:     my $self    = shift;		# Reference to the object.
                    482:     my $request = shift;	        # Text to send.
                    483: 
                    484:    
                    485:     # Split the encrypt: off the request and figure out it's length.
                    486:     # the cipher works in blocks of 8 bytes.
                    487: 
                    488:     my $cmd = $request;
                    489:     $cmd    =~ s/^encrypt\://;	# strip off encrypt:
                    490:     chomp($cmd);		# strip off trailing \n
                    491:     my     $length=length($cmd);	# Get the string length.
                    492:     $cmd .= "         ";	# Pad with blanks so we can fill out a block.
                    493: 
                    494:     # encrypt the request in 8 byte chunks to create the encrypted
                    495:     # output request.
                    496: 
                    497:     my $Encoded = '';
                    498:     for(my $index = 0; $index <= $length; $index += 8) {
                    499: 	$Encoded .= 
                    500: 	    unpack("H16", 
                    501: 		   $self->{Cipher}->encrypt(substr($cmd, 
                    502: 						   $index, 8)));
                    503:     }
                    504: 
                    505:     # Build up the answer as enc:length:$encrequest.
                    506: 
                    507:     $request = "enc:$length:$Encoded\n";
                    508:     return $request;
                    509:     
                    510:     
                    511: }
                    512: =pod 
                    513:     Decrypt
                    514:     Decrypt a response from the server.  The response is in the form:
                    515:   enc:<length>:<encrypted data>
                    516: =cut
                    517: sub Decrypt {
                    518:     my $self      = shift;	# Recover reference to object
                    519:     my $encrypted = shift;	# This is the encrypted data.
                    520: 
                    521:     #  Bust up the response into length, and encryptedstring:
                    522: 
                    523:     my ($enc, $length, $EncryptedString) = split(/:/,$encrypted);
                    524:     chomp($EncryptedString);
                    525: 
                    526:     # Decode the data in 8 byte blocks.  The string is encoded
                    527:     # as hex digits so there are two characters per byte:
                    528: 
                    529:     $decrpyted = "";
                    530:     for(my $index = 0; $index < length($EncryptedString);
                    531: 	$index += 16) {
                    532: 	$decrypted .= $self->{Cipher}->decrypt(
                    533: 				    pack("H16",
                    534: 					 substr($EncryptedString,
                    535: 						$index, 
                    536: 						16)));
                    537:     }
                    538:     #  the answer may have trailing pads to fill out a block.
                    539:     #  $length tells us the actual length of the decrypted string:
                    540: 
                    541:     $decrypted = substr($decrypted, 0, $length);
                    542: 
                    543:     return $decrypted;
                    544: 
                    545: }
                    546: 
                    547: =pod
                    548: =head GetHostIterator
                    549: 
                    550: Returns a hash iterator to the host information.  Each get from 
                    551: this iterator returns a reference to an array that contains 
                    552: information read from the hosts configuration file.  Array elements
                    553: are used as follows:
                    554: 
                    555: [0]   - LonCapa host name.
                    556: [1]   - LonCapa domain name.
                    557: [2]   - Loncapa role (e.g. library or access).
                    558: [3]   - DNS name server hostname.
                    559: [4]   - IP address (result of e.g. nslooup [3]).
                    560: [5]   - Maximum connection count.
                    561: [6]   - Idle timeout for reducing connection count.
                    562: [7]   - Minimum connection count.
                    563: 
                    564: 
                    565: =cut
                    566: sub GetHostIterator {
                    567: 
                    568:     return HashIterator->new(\%hostshash);    
                    569: }
                    570: 
                    571: 1;
                    572: 
                    573: =pod
                    574: =head1 Theory
                    575:    The lond object is a state machine.  It lives through the following states:
                    576: 
                    577: =item Connected: a TCP connection has been formed, but the passkey has not yet
                    578:     been negotiated.
                    579: =item Initialized: "init" sent.
                    580: =item ChallengeReceived: lond sent its challenge to us.
                    581: =item ChallengeReplied:  We replied to lond's challenge waiting for lond's ok.
                    582: =item RequestingKey:    We are requesting an encryption key.
                    583: =item ReceivingKey:     We are receiving an encryption key.
                    584: =item Idle:  Connection was negotiated but no requests are active.
                    585: =item SendingRequest: A request is being sent to the peer.
                    586: =item ReceivingReply: Waiting for an entire reply from the peer.
                    587: =item Disconnected:   For whatever reason, the connection was dropped.
                    588: 
                    589:   When we need to be writing data, we have a writable
                    590: event. When we need to be reading data, a readable event established.
                    591: Events dispatch through the class functions Readable and Writable, and the
                    592: watcher contains a reference to the associated object to allow object context
                    593: to be reached.
                    594: 
                    595: =head2 Member data.
                    596: Host   - Host socket is connected to.
                    597: Port   - The port the remote lond is listening on.
                    598: Socket - Socket open on the connection.
                    599: State  - The current state.
                    600: TransactionRequest - The request being transmitted.
                    601: TransactionReply   - The reply being received from the transaction.
                    602: InformReadable     - True if we want to be called when socket is readable.
                    603: InformWritable     - True if we want to be informed if the socket is writable.
                    604: Timeoutable        - True if the current operation is allowed to timeout.
                    605: TimeoutValue       - Number of seconds in the timeout.
                    606: TimeoutRemaining   - Number of seconds left in the timeout.
                    607: CipherKey          - The key that was negotiated with the peer.
                    608: Cipher             - The cipher obtained via the key.
                    609: 
                    610: 
                    611: 
                    612: =head2 The following are callback like members:
                    613: =item Tick: Called in response to a timer tick. Used to managed timeouts etc.
                    614: =item Readable: Called when the socket becomes readable.
                    615: =item Writable: Called when the socket becomes writable.
                    616: =item TimedOut: Called when a timed operation timed out.
                    617: 
                    618: =head2 The following are operational member functions.
                    619: =item InitiateTransaction: Called to initiate a new transaction
                    620: =item SetStateTransitionCallback: Called to establish a function that is called
                    621:     whenever the object goes through a state transition.  This is used by
                    622:     The client to manage the work flow for the object.
                    623: =item SetTimeoutCallback -Set a function to be called when a transaction times
                    624:     out.  The function will be called with the object as its sole parameter.
                    625: =item Encrypt - Encrypts a block of text according to the cipher negotiated
                    626:        with the peer (assumes the text is a command).
                    627: =item Decrypt - Decrypts a block of text according to the cipher negotiated
                    628:        with the peer (assumes the block was a reply.
                    629: 
                    630: =head2 The following are selector member functions:
                    631: 
                    632: =item GetState: Returns the current state
                    633: =item GetSocket: Gets the socekt open on the connection to lond.
                    634: =item WantReadable: true if the current state requires a readable event.
                    635: =item WantWritable: true if the current state requires a writable event.
                    636: =item WantTimeout: true if the current state requires timeout support.
                    637: =item GetHostIterator: Returns an iterator into the host file hash.
                    638: =cut

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