Annotation of loncom/LONCAPA.pm, revision 1.34

1.1       albertel    1: # The LearningOnline Network
                      2: # Base routines
                      3: #
1.34    ! raeburn     4: # $Id: LONCAPA.pm,v 1.33 2011/11/07 20:05:52 www Exp $
1.1       albertel    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/
                     27: #
                     28: ###
                     29: 
1.25      jms        30: 
                     31: 
1.1       albertel   32: package LONCAPA;
                     33: 
                     34: use strict;
1.2       www        35: use lib '/home/httpd/lib/perl/';
                     36: use LONCAPA::Configuration;
                     37: use Fcntl qw(:flock);
                     38: use GDBM_File;
                     39: use POSIX;
1.32      foxr       40: #use Apache::lonnet;
1.2       www        41: 
                     42: my $loncapa_max_wait_time = 13;
                     43: 
1.14      albertel   44: 
1.32      foxr       45: #--------------------------------------------------------------------------
                     46: #
                     47: #   The  constant definnitions below probably should really be in 
                     48: #   a configuration file somewhere (loncapa.conf?) and loaded so that they can be 
                     49: #   modified without requring source code changes:
                     50: #
                     51: #   COURSE_CACHE_TIME - Number of minutes after which an unaccessed
                     52: #                       course.db or course_param.db file is considered
                     53: #                       to be a stale cache of this info.
                     54: #
                     55: #   LONCAPA_TEMPDIR   - Place loncapa puts temporary files
                     56: #
                     57: 
                     58: my  $COURSE_CACHE_TIME =  60;	# minutes course cache file is considered valid. 
                     59: my  $LONCAPA_TEMPDIR   =  '/tmp/'; # relative to configuration{'lonTabDir'}.
                     60: 
1.14      albertel   61: use vars qw($match_domain   $match_not_domain
                     62: 	    $match_username $match_not_username
1.16      albertel   63: 	    $match_courseid $match_not_courseid
1.29      raeburn    64:             $match_community
1.16      albertel   65: 	    $match_name
1.23      albertel   66:             $match_lonid
1.14      albertel   67: 	    $match_handle   $match_not_handle);
                     68: 
1.1       albertel   69: require Exporter;
                     70: our @ISA = qw (Exporter);
1.14      albertel   71: our @EXPORT = qw(&add_get_param    &escape            &unescape       
                     72: 		 &tie_domain_hash  &untie_domain_hash &tie_user_hash
1.32      foxr       73: 		 &untie_user_hash  &propath &tie_course);
1.14      albertel   74: our @EXPORT_OK = qw($match_domain   $match_not_domain
                     75: 		    $match_username $match_not_username
1.16      albertel   76: 		    $match_courseid $match_not_courseid
1.29      raeburn    77:                     $match_community
1.16      albertel   78: 		    $match_name
1.23      albertel   79: 		    $match_lonid
1.32      foxr       80: 		    $match_handle   $match_not_handle &tie_course);
1.14      albertel   81: our %EXPORT_TAGS = ( 'match' =>[qw($match_domain   $match_not_domain
                     82: 				   $match_username $match_not_username
1.16      albertel   83: 				   $match_courseid $match_not_courseid
1.29      raeburn    84:                                    $match_community
1.16      albertel   85: 				   $match_name
1.23      albertel   86: 				   $match_lonid
1.14      albertel   87: 				   $match_handle   $match_not_handle)],);
1.2       www        88: my %perlvar;
1.1       albertel   89: 
1.8       foxr       90: 
1.32      foxr       91: #
                     92: # If necessary fetch and tie a user's image of the course hash 
                     93: # to the specified hash
                     94: # Parameters:
                     95: #   domain   - User's domain
                     96: #   user     - Name of user.
                     97: #   course   - Course number.
                     98: #   cdom     - Domain that is home to the course
                     99: #   hash     - reference to the has to tie.
                    100: #
                    101: # Side effects:
                    102: #   a gdbm file and it's associated lock file will be created in the 
                    103: #   tmp directory tree.
                    104: #
                    105: # Returns:
                    106: #   0 - failure.
                    107: #   1 - success.
                    108: #
                    109: #  Note:
                    110: #     It's possible the required user's db file is already present in the tempdir.
                    111: #     in that case a decision must be made about whether or not to just tie to it
                    112: #     or to fetch it again. Remember this sub could be called in the context of a user
                    113: #     other than the one whose data are being fetched.  We don't know if that user already
                    114: #     has a live session on this server.  What we'll do is only re-fetch if the hash atime.
                    115: #     is older than COURSE_CACHE_TIME...that is if it's been accessed relatively recently
                    116: #     where COURSE_CACHE_TIME defines the caching time.
                    117: #
                    118: #     The database files this function creates are of the form:
                    119: #     $user@$domain_$course@$cdom.{db,lock}
                    120: #     This differs from the prior filenames.  Therefore if a module does its own
                    121: #     caching (That's a coding no-no) and does not use this centralized sub,
                    122: #     multiple cache files for the same course/user will be created. 
                    123: #  
                    124: sub tie_course {
                    125:     my ($domain, $user, $course, $cdom, $hash) = @_;
                    126: 
                    127:     #
                    128:     #  See if we need to re-fetch the course data
                    129:     #
                    130: 
                    131:     
                    132: }
                    133: 
                    134: # Return a string that is the path in which loncapa puts temp files:
                    135: 
                    136: sub tempdir {
                    137:     my $result =  $perlvar{'lonDaemons'}.$LONCAPA_TEMPDIR; # to allow debugging.
                    138:     return $result;
                    139: }
                    140: 
1.34    ! raeburn   141: # Return the Linux distro where this LON-CAPA instance is running
        !           142: 
        !           143: sub distro {
        !           144:     my $distro;
        !           145:     if (open(PIPE,"/home/httpd/perl/distprobe |")) {
        !           146:         $distro = <PIPE>;
        !           147:         close(PIPE);
        !           148:     }
        !           149:     return $distro;
        !           150: }
1.32      foxr      151: 
                    152: #----------------------------------------------------------------------
                    153: #
                    154: #  some of these subs need a bit of documentation
                    155: 
1.1       albertel  156: sub add_get_param {
                    157:     my ($url,$form_data) = @_;
                    158:     my $needs_question_mark = ($url !~ /\?/);
                    159: 
                    160:     while (my ($name,$value) = each(%$form_data)) {
                    161: 	if ($needs_question_mark) {
                    162: 	    $url.='?';
                    163: 	    $needs_question_mark = 0;
                    164: 	} else { 
                    165: 	    $url.='&';
                    166: 	}
                    167: 	$url.=$name.'='.&escape($form_data->{$name});
                    168:     }
                    169:     return $url;
                    170: }
                    171: 
                    172: # -------------------------------------------------------- Escape Special Chars
                    173: 
                    174: sub escape {
                    175:     my $str=shift;
                    176:     $str =~ s/(\W)/"%".unpack('H2',$1)/eg;
                    177:     return $str;
                    178: }
                    179: 
                    180: # ----------------------------------------------------- Un-Escape Special Chars
                    181: 
                    182: sub unescape {
                    183:     my $str=shift;
                    184:     $str =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;
                    185:     return $str;
                    186: }
                    187: 
1.33      www       188: $LONCAPA::assess_re = qr{\.(problem|exam|quiz|assess|survey|form|library|task)$};
                    189: $LONCAPA::assess_page_re = qr{\.(problem|exam|quiz|assess|survey|form|library|task|page)$};
                    190: $LONCAPA::assess_page_seq_re = qr{\.(problem|exam|quiz|assess|survey|form|library|task|sequence|page)$};
                    191: $LONCAPA::parse_re = qr{\.(problem|exam|quiz|assess|survey|form|library|page|xml|html|htm|xhtml|xhtm)$};
                    192: $LONCAPA::parse_page_re = qr{\.(problem|exam|quiz|assess|survey|form|library|page|xml|html|htm|xhtml|xhtm|page)$};
                    193: $LONCAPA::parse_page_sty_re = qr{\.(problem|exam|quiz|assess|survey|form|library|page|xml|html|htm|xhtml|xhtm|page|sty)$};
                    194: 
                    195: 
1.30      raeburn   196: $match_domain     = $LONCAPA::domain_re     = qr{[[:alnum:]\-.]+};
                    197: $match_not_domain = $LONCAPA::not_domain_re = qr{[^[:alnum:]\-.]+};
1.14      albertel  198: sub clean_domain {
                    199:     my ($domain) = @_;
                    200:     $domain =~ s/$match_not_domain//g;
                    201:     return $domain;
                    202: }
                    203: 
1.24      albertel  204: $match_username     = $LONCAPA::username_re     = qr{\w[\w\-.@]+};
                    205: $match_not_username = $LONCAPA::not_username_re = qr{[^\w\-.@]+};
1.14      albertel  206: sub clean_username {
                    207:     my ($username) = @_;
1.21      albertel  208:     $username =~ s/^\W+//;
1.14      albertel  209:     $username =~ s/$match_not_username//g;
                    210:     return $username;
                    211: }
                    212: 
1.16      albertel  213: 
                    214: $match_courseid     = $LONCAPA::courseid_re     = qr{\d[\w\-.]+};
1.29      raeburn   215: $match_community    =$LONCAPA::community_re     = qr{0[\w\-.]+};
1.16      albertel  216: $match_not_courseid = $LONCAPA::not_courseid_re = qr{[^\w\-.]+};
1.22      albertel  217: sub clean_courseid {
                    218:     my ($courseid) = @_;
                    219:     $courseid =~ s/^\D+//;
                    220:     $courseid =~ s/$match_not_courseid//g;
                    221:     return $courseid;
                    222: }
1.16      albertel  223: 
1.22      albertel  224: $match_name         = $LONCAPA::name_re = qr{$match_username|$match_courseid};
1.16      albertel  225: sub clean_name {
                    226:     my ($name) = @_;
                    227:     $name =~ s/$match_not_username//g;
                    228:     return $name;
                    229: }
                    230: 
1.23      albertel  231: $match_lonid     = $LONCAPA::lonid_re     = qr{[\w\-.]+};
                    232: 
1.16      albertel  233: sub split_courseid {
                    234:     my ($courseid) = @_;
                    235:     my  ($domain,$coursenum) = 
                    236: 	($courseid=~m{^/($match_domain)/($match_courseid)});
                    237:     return ($domain,$coursenum);
                    238: }
                    239: 
1.24      albertel  240: $match_handle     = $LONCAPA::handle_re     = qr{[\w\-.@]+};
                    241: $match_not_handle = $LONCAPA::not_handle_re = qr{[^\w\-.@]+};
1.14      albertel  242: sub clean_handle {
                    243:     my ($handle) = @_;
                    244:     $handle =~ s/$match_not_handle//g;
                    245:     return $handle;
                    246: }
                    247: 
1.31      raeburn   248: #
                    249: # -- Ensure another process for same filesystem action is not running.
                    250: #    lond uses for: apachereload; loncron uses for: lciptables
                    251: #
                    252: 
                    253: sub try_to_lock {
                    254:     my ($lockfile)=@_;
                    255:     my $currentpid;
                    256:     my $lastpid;
                    257:     # Do not manipulate lock file as root
                    258:     if ($>==0) {
                    259:         return 0;
                    260:     }
                    261:     # Try to generate lock file.
                    262:     # Wait 3 seconds.  If same process id is in
                    263:     # lock file, then assume lock file is stale, and
                    264:     # go ahead.  If process id's fluctuate, try
                    265:     # for a maximum of 10 times.
                    266:     for (0..10) {
                    267:         if (-e $lockfile) { 
                    268:             open(LOCK,"<$lockfile");
                    269:             $currentpid=<LOCK>;
                    270:             close LOCK;
                    271:             if ($currentpid==$lastpid) {
                    272:                 last;
                    273:             }
                    274:             sleep 3;
                    275:             $lastpid=$currentpid;
                    276:         } else {
                    277:             last;
                    278:         }
                    279:         if ($_==10) {
                    280:             return 0;
                    281:         }
                    282:     }
                    283:     open(LOCK,">$lockfile");
                    284:     print LOCK $$;
                    285:     close LOCK;
                    286:     return 1;
                    287: }
                    288: 
1.2       www       289: # -------------------------------------------- Return path to profile directory
                    290: 
                    291: sub propath {
                    292:     my ($udom,$uname)=@_;
1.14      albertel  293:     $udom = &clean_domain($udom);
1.16      albertel  294:     $uname= &clean_name($uname);
1.2       www       295:     my $subdir=$uname.'__';
                    296:     $subdir =~ s/(.)(.)(.).*/$1\/$2\/$3/;
                    297:     my $proname="$perlvar{'lonUsersDir'}/$udom/$subdir/$uname";
                    298:     return $proname;
1.29      raeburn   299: }
1.2       www       300: 
                    301: sub tie_domain_hash {
                    302:     my ($domain,$namespace,$how,$loghead,$logtail) = @_;
                    303:     
                    304:     # Filter out any whitespace in the domain name:
                    305:     
1.14      albertel  306:     $domain = &clean_domain($domain);
1.2       www       307:     
                    308:     # We have enough to go on to tie the hash:
                    309:     
                    310:     my $user_top_dir   = $perlvar{'lonUsersDir'};
                    311:     my $domain_dir     = $user_top_dir."/$domain";
                    312:     my $resource_file  = $domain_dir."/$namespace";
                    313:     return &_locking_hash_tie($resource_file,$namespace,$how,$loghead,$logtail);
                    314: }
                    315: 
                    316: sub untie_domain_hash {
                    317:     return &_locking_hash_untie(@_);
                    318: }
1.25      jms       319: 
                    320: 
1.2       www       321: sub tie_user_hash {
                    322:     my ($domain,$user,$namespace,$how,$loghead,$what) = @_;
                    323: 
1.15      albertel  324:     $namespace=~s{/}{_}g;	# / -> _
                    325:     $namespace     = &clean_username($namespace);
                    326:     my $proname    = &propath($domain, $user);
1.2       www       327:     my $file_prefix="$proname/$namespace";
                    328:     return &_locking_hash_tie($file_prefix,$namespace,$how,$loghead,$what);
                    329: }
                    330: 
                    331: sub untie_user_hash {
                    332:     return &_locking_hash_untie(@_);
                    333: }
                    334: 
1.6       www       335: 
                    336: sub locking_hash_tie {
                    337:     my ($filename,$how)=@_;
                    338:     my ($file_prefix,$namespace)=&db_filename_parts($filename);
1.7       albertel  339:     if ($namespace eq '') { return undef; }
1.6       www       340:     return &_locking_hash_tie($file_prefix,$namespace,$how);
                    341: }
                    342: 
                    343: sub locking_hash_untie {
                    344:     return &_locking_hash_untie(@_);
                    345: }
                    346: 
                    347: sub db_filename_parts {
                    348:     my ($filename)=@_;
                    349:     my ($file_path,$namespace)=($filename=~/^(.*)\/([^\/]+)\.db$/);
1.7       albertel  350:     if ($namespace eq '') { return undef; }
1.6       www       351:     return ($file_path.'/'.$namespace,$namespace);
                    352: }
                    353: 
1.2       www       354: # internal routines that handle the actual tieing and untieing process
                    355: 
                    356: sub _do_hash_tie {
                    357:     my ($file_prefix,$namespace,$how,$loghead,$what) = @_;
                    358:     my %hash;
                    359:     if(tie(%hash, 'GDBM_File', "$file_prefix.db", $how, 0640)) {
                    360: 	# If this is a namespace for which a history is kept,
                    361: 	# make the history log entry:    
                    362: 	if (($namespace !~/^nohist\_/) && (defined($loghead))) {
                    363: 	    my $hfh = IO::File->new(">>$file_prefix.hist"); 
                    364: 	    if($hfh) {
1.5       albertel  365: 		my $now = time();
                    366: 		print $hfh ("$loghead:$now:$what\n");
1.2       www       367: 	    }
                    368: 	    $hfh->close;
                    369: 	}
                    370: 	return \%hash;
                    371:     } else {
                    372: 	return undef;
                    373:     }
                    374: }
                    375: 
                    376: sub _do_hash_untie {
                    377:     my ($hashref) = @_;
                    378:     my $result = untie(%$hashref);
                    379:     return $result;
                    380: }
                    381: 
                    382: {
                    383:     my $sym;
1.10      albertel  384:     my @pushed_syms;
1.11      albertel  385: 
                    386:     sub clean_sym {
                    387: 	undef($sym);
                    388:     }
1.10      albertel  389:     sub push_locking_hash_tie {
                    390: 	if (!defined($sym)) {
                    391: 	    die("Invalid used of push_locking_hash_tie, should only be called after a lock has occurred and before and unlock.");
                    392: 	}
                    393: 	push(@pushed_syms,$sym);
                    394: 	undef($sym);
                    395:     }
                    396: 
                    397:     sub pop_locking_hash_tie {
                    398: 	if (defined($sym)) {
                    399: 	    die("Invalid nested used of pop_locking_hash_tie, should only be called after a unlock has occurred.");
                    400: 	}
                    401: 	$sym = pop(@pushed_syms);
                    402:     }
1.2       www       403: 
                    404:     sub _locking_hash_tie {
                    405: 	my ($file_prefix,$namespace,$how,$loghead,$what) = @_;
1.9       albertel  406: 	if (defined($sym)) {
1.11      albertel  407: 	    die('Nested locking attempted without proper use of push_locking_hash_tie, this is unsupported');
1.9       albertel  408: 	}
                    409: 
1.2       www       410:         my $lock_type=LOCK_SH;
                    411: # Are we reading or writing?
                    412:         if ($how eq &GDBM_READER()) {
                    413: # We are reading
                    414:            if (!open($sym,"$file_prefix.db.lock")) {
                    415: # We don't have a lock file. This could mean
                    416: # - that there is no such db-file
                    417: # - that it does not have a lock file yet
                    418:                if ((! -e "$file_prefix.db") && (! -e "$file_prefix.db.gz")) {
                    419: # No such file. Forget it.                
                    420:                    $! = 2;
1.11      albertel  421: 		   &clean_sym();
1.2       www       422:                    return undef;
                    423:                }
                    424: # Apparently just no lock file yet. Make one
                    425:                open($sym,">>$file_prefix.db.lock");
                    426:            }
                    427: # Do a shared lock
1.9       albertel  428:            if (!&flock_sym(LOCK_SH)) { 
1.11      albertel  429: 	       &clean_sym();
1.9       albertel  430: 	       return undef; 
                    431: 	   } 
1.2       www       432: # If this is compressed, we will actually need an exclusive lock
                    433: 	   if (-e "$file_prefix.db.gz") {
1.9       albertel  434: 	       if (!&flock_sym(LOCK_EX)) {
1.11      albertel  435: 		   &clean_sym();
1.9       albertel  436: 		   return undef;
                    437: 	       }
1.2       www       438: 	   }
                    439:         } elsif ($how eq &GDBM_WRCREAT()) {
                    440: # We are writing
                    441:            open($sym,">>$file_prefix.db.lock");
                    442: # Writing needs exclusive lock
1.9       albertel  443:            if (!&flock_sym(LOCK_EX)) {
1.11      albertel  444: 	       &clean_sym();
1.9       albertel  445: 	       return undef;
                    446: 	   }
1.2       www       447:         } else {
1.5       albertel  448:            die("Unknown method $how for $file_prefix");
1.2       www       449:         }
                    450: # The file is ours!
                    451: # If it is archived, un-archive it now
                    452:        if (-e "$file_prefix.db.gz") {
                    453:            system("gunzip $file_prefix.db.gz");
                    454: 	   if (-e "$file_prefix.hist.gz") {
                    455: 	       system("gunzip $file_prefix.hist.gz");
                    456: 	   }
                    457:        }
                    458: # Change access mode to non-blocking
                    459:        $how=$how|&GDBM_NOLOCK();
                    460: # Go ahead and tie the hash
1.13      albertel  461:       	my $result = 
                    462: 	    &_do_hash_tie($file_prefix,$namespace,$how,$loghead,$what);
                    463: 	if (!$result) {
                    464: 	    &clean_sym();
                    465: 	}
                    466: 	return $result;
1.2       www       467:     }
                    468: 
                    469:     sub flock_sym {
                    470:         my ($lock_type)=@_;
                    471: 	my $failed=0;
                    472: 	eval {
                    473: 	    local $SIG{__DIE__}='DEFAULT';
                    474: 	    local $SIG{ALRM}=sub {
                    475: 		$failed=1;
                    476: 		die("failed lock");
                    477: 	    };
                    478: 	    alarm($loncapa_max_wait_time);
                    479: 	    flock($sym,$lock_type);
                    480: 	    alarm(0);
                    481: 	};
                    482: 	if ($failed) {
                    483: 	    $! = 100; # throwing error # 100
                    484: 	    return undef;
                    485: 	} else {
                    486: 	    return 1;
                    487: 	}
                    488:     }
                    489: 
                    490:     sub _locking_hash_untie {
                    491: 	my ($hashref) = @_;
                    492: 	my $result = untie(%$hashref);
                    493: 	flock($sym,LOCK_UN);
                    494: 	close($sym);
1.11      albertel  495: 	&clean_sym();
1.2       www       496: 	return $result;
                    497:     }
                    498: }
                    499: 
1.32      foxr      500: 
1.2       www       501: BEGIN {
1.4       albertel  502:     %perlvar=%{&LONCAPA::Configuration::read_conf('loncapa.conf')};
1.2       www       503: }
                    504: 
1.1       albertel  505: 1;
                    506: 
                    507: __END__
                    508: 
1.28      raeburn   509: =pod
1.1       albertel  510: 
1.27      jms       511: =head1 NAME
                    512: 
                    513: Apache::LONCAPA
                    514: 
                    515: LONCAPA - Basic routines
                    516: 
                    517: =head1 SYNOPSIS
                    518: 
                    519: Generally useful routines
                    520: 
                    521: =head1 EXPORTED SUBROUTINES
                    522: 
                    523: =over
                    524: 
                    525: =item escape()
                    526: 
                    527: unpack non-word characters into CGI-compatible hex codes
                    528: 
                    529: =item unescape()
                    530: 
                    531:  pack CGI-compatible hex codes into actual non-word ASCII character
                    532: 
                    533: =item  add_get_param()
1.28      raeburn   534: 
                    535: Append escaped form elements (name=value etc.) to a url.
1.27      jms       536:  
                    537:  Inputs:  url (with or without exit GET from parameters), hash ref of
                    538:               form name => value pairs
                    539: 
1.28      raeburn   540:  Return: url with form name elements and values appended to the 
                    541:          the url, doing proper escaping of the values and joining with ? or &
1.27      jms       542:          as needed
                    543: 
                    544: =item clean_handle()
                    545: 
                    546: =item propath()
                    547: 
                    548: =item untie_domain_hash()
                    549: 
                    550: =item tie_domain_hash()
                    551: 
                    552: Manipulation of hash based databases (factoring out common code
                    553: for later use as we refactor.
                    554: 
                    555:  Ties a domain level resource file to a hash.
                    556:  If requested a history entry is created in the associated hist file.
                    557: 
                    558:  Parameters:
                    559:     domain    - Name of the domain in which the resource file lives.
                    560:     namespace - Name of the hash within that domain.
                    561:     how       - How to tie the hash (e.g. GDBM_WRCREAT()).
                    562:     loghead   - Optional parameter, if present a log entry is created
                    563:                 in the associated history file and this is the first part
                    564:                  of that entry.
                    565:     logtail   - Goes along with loghead,  The actual logentry is of the
                    566:                 form $loghead:<timestamp>:logtail.
                    567: Returns:
                    568:    Reference to a hash bound to the db file or alternatively undef
                    569:    if the tie failed.
                    570: 
                    571: =item tie_user_hash()
                    572: 
                    573:   Ties a user's resource file to a hash.  
                    574:   If necessary, an appropriate history
                    575:   log file entry is made as well.
                    576:   This sub factors out common code from the subs that manipulate
                    577:   the various gdbm files that keep keyword value pairs.
                    578: Parameters:
                    579:   domain       - Name of the domain the user is in.
                    580:   user         - Name of the 'current user'.
                    581:   namespace    - Namespace representing the file to tie.
                    582:   how          - What the tie is done to (e.g. GDBM_WRCREAT().
                    583:   loghead      - Optional first part of log entry if there may be a
                    584:                  history file.
                    585:   what         - Optional tail of log entry if there may be a history
                    586:                  file.
                    587: Returns:
                    588:   hash to which the database is tied.  It's up to the caller to untie.
                    589:   undef if the has could not be tied.
                    590: 
1.32      foxr      591: =item tie_course
                    592: 
                    593: Caches the course database into the temp directory in the context of a specific
                    594: user and ties it to a hash.
                    595: Parameters:
                    596:    domain    - Domain the user is in.
                    597:    user      - Username of the user.
                    598:    course    - Course specification
                    599:    cdom      - The course domain.
                    600:    hash      - Reference to the hash to tie.
                    601: 
                    602: Returns:
                    603:     1        - Success
                    604:     0        - Failure.
                    605: 
                    606: =item tie_course_params
                    607: 
                    608: Caches the course parameter database into the temp directory in the context
                    609: of a specific user and ties it to a hash.
                    610: Parameters:
                    611:    domain   - Domain the user is in.
                    612:    user     - Username of the user.
                    613:    course   - course specification.
                    614:    cdom     - The course domain.
                    615:    hash     - reference to the hash to tie.
                    616: 
                    617: Returns:
                    618:    1        - Success.
                    619:    0        - Failure./
                    620: 
                    621: 
1.27      jms       622: =item locking_hash_tie()
                    623: 
                    624: routines if you just have a filename return tied hashref or undef
                    625: 
                    626: =item locking_hash_untie()
                    627: 
                    628: =item db_filename_parts()
                    629: 
1.32      foxr      630: =back
                    631: 
                    632: =item tempdir()
                    633: 
                    634: Returns the file system path to the place loncapa temporary files should be placed/found.
                    635: 
                    636: 
1.27      jms       637: =head1 INTERNAL SUBROUTINES
                    638: 
1.32      foxr      639: =over 
                    640: 
1.27      jms       641: =item _do_hash_tie()
                    642: 
                    643: =item _do_hash_untie()
                    644: 
                    645: =back
                    646: 
                    647: =cut
                    648: 

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