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   1  package CGI::Push;
   2  
   3  # See the bottom of this file for the POD documentation.  Search for the
   4  # string '=head'.
   5  
   6  # You can run this file through either pod2man or pod2html to produce pretty
   7  # documentation in manual or html file format (these utilities are part of the
   8  # Perl 5 distribution).
   9  
  10  # Copyright 1995-2000, Lincoln D. Stein.  All rights reserved.
  11  # It may be used and modified freely, but I do request that this copyright
  12  # notice remain attached to the file.  You may modify this module as you 
  13  # wish, but if you redistribute a modified version, please attach a note
  14  # listing the modifications you have made.
  15  
  16  # The most recent version and complete docs are available at:
  17  #   http://stein.cshl.org/WWW/software/CGI/
  18  
  19  $CGI::Push::VERSION='1.04';
  20  use CGI;
  21  use CGI::Util 'rearrange';
  22  @ISA = ('CGI');
  23  
  24  $CGI::DefaultClass = 'CGI::Push';
  25  $CGI::Push::AutoloadClass = 'CGI';
  26  
  27  # add do_push() and push_delay() to exported tags
  28  push(@{$CGI::EXPORT_TAGS{':standard'}},'do_push','push_delay');
  29  
  30  sub do_push {
  31      my ($self,@p) = CGI::self_or_default(@_);
  32  
  33      # unbuffer output
  34      $| = 1;
  35      srand;
  36      my ($random) = sprintf("%08.0f",rand()*1E8);
  37      my ($boundary) = "----=_NeXtPaRt$random";
  38  
  39      my (@header);
  40      my ($type,$callback,$delay,$last_page,$cookie,$target,$expires,$nph,@other) = rearrange([TYPE,NEXT_PAGE,DELAY,LAST_PAGE,[COOKIE,COOKIES],TARGET,EXPIRES,NPH],@p);
  41      $type = 'text/html' unless $type;
  42      $callback = \&simple_counter unless $callback && ref($callback) eq 'CODE';
  43      $delay = 1 unless defined($delay);
  44      $self->push_delay($delay);
  45      $nph = 1 unless defined($nph);
  46  
  47      my(@o);
  48      foreach (@other) { push(@o,split("=")); }
  49      push(@o,'-Target'=>$target) if defined($target);
  50      push(@o,'-Cookie'=>$cookie) if defined($cookie);
  51      push(@o,'-Type'=>"multipart/x-mixed-replace;boundary=\"$boundary\"");
  52      push(@o,'-Server'=>"CGI.pm Push Module") if $nph;
  53      push(@o,'-Status'=>'200 OK');
  54      push(@o,'-nph'=>1) if $nph;
  55      print $self->header(@o);
  56  
  57      $boundary = "$CGI::CRLF--$boundary";
  58  
  59      print "WARNING: YOUR BROWSER DOESN'T SUPPORT THIS SERVER-PUSH TECHNOLOGY.$boundary}$CGI::CRLF";
  60  
  61      my (@contents) = &$callback($self,++$COUNTER);
  62  
  63      # now we enter a little loop
  64      while (1) {
  65          print "Content-type: $type}$CGI::CRLF$CGI::CRLF" unless $type =~ /^dynamic|heterogeneous$/i;
  66          print @contents;
  67          @contents = &$callback($self,++$COUNTER);
  68          if ((@contents) && defined($contents[0])) {
  69              print "$boundary}$CGI::CRLF";
  70              do_sleep($self->push_delay()) if $self->push_delay();
  71          } else {
  72              if ($last_page && ref($last_page) eq 'CODE') {
  73                  print "$boundary}$CGI::CRLF";
  74                  do_sleep($self->push_delay()) if $self->push_delay();
  75                  print "Content-type: $type}$CGI::CRLF$CGI::CRLF" unless $type =~ /^dynamic|heterogeneous$/i;
  76                  print  &$last_page($self,$COUNTER);
  77              }
  78              print "$boundary}--$CGI::CRLF";
  79              last;
  80          }
  81      }
  82      print "WARNING: YOUR BROWSER DOESN'T SUPPORT THIS SERVER-PUSH TECHNOLOGY.$CGI::CRLF";
  83  }
  84  
  85  sub simple_counter {
  86      my ($self,$count) = @_;
  87      return $self->start_html("CGI::Push Default Counter"),
  88             $self->h1("CGI::Push Default Counter"),
  89             "This page has been updated ",$self->strong($count)," times.",
  90             $self->hr(),
  91             $self->a({'-href'=>'http://www.genome.wi.mit.edu/ftp/pub/software/WWW/cgi_docs.html'},'CGI.pm home page'),
  92             $self->end_html;
  93  }
  94  
  95  sub do_sleep {
  96      my $delay = shift;
  97      if ( ($delay >= 1) && ($delay!~/\./) ){
  98          sleep($delay);
  99      } else {
 100          select(undef,undef,undef,$delay);
 101      }
 102  }
 103  
 104  sub push_delay {
 105      my ($self,$delay) = CGI::self_or_default(@_);
 106      return defined($delay) ? $self->{'.delay'} = 
 107          $delay : $self->{'.delay'};
 108  }
 109  
 110  1;
 111  
 112  =head1 NAME
 113  
 114  CGI::Push - Simple Interface to Server Push
 115  
 116  =head1 SYNOPSIS
 117  
 118      use CGI::Push qw(:standard);
 119  
 120      do_push(-next_page=>\&next_page,
 121              -last_page=>\&last_page,
 122              -delay=>0.5);
 123  
 124      sub next_page {
 125          my($q,$counter) = @_;
 126          return undef if $counter >= 10;
 127          return start_html('Test'),
 128                 h1('Visible'),"\n",
 129                 "This page has been called ", strong($counter)," times",
 130                 end_html();
 131      }
 132  
 133      sub last_page {
 134          my($q,$counter) = @_;
 135          return start_html('Done'),
 136                 h1('Finished'),
 137                 strong($counter - 1),' iterations.',
 138                 end_html;
 139      }
 140  
 141  =head1 DESCRIPTION
 142  
 143  CGI::Push is a subclass of the CGI object created by CGI.pm.  It is
 144  specialized for server push operations, which allow you to create
 145  animated pages whose content changes at regular intervals.
 146  
 147  You provide CGI::Push with a pointer to a subroutine that will draw
 148  one page.  Every time your subroutine is called, it generates a new
 149  page.  The contents of the page will be transmitted to the browser
 150  in such a way that it will replace what was there beforehand.  The
 151  technique will work with HTML pages as well as with graphics files, 
 152  allowing you to create animated GIFs.
 153  
 154  Only Netscape Navigator supports server push.  Internet Explorer
 155  browsers do not.
 156  
 157  =head1 USING CGI::Push
 158  
 159  CGI::Push adds one new method to the standard CGI suite, do_push().
 160  When you call this method, you pass it a reference to a subroutine
 161  that is responsible for drawing each new page, an interval delay, and
 162  an optional subroutine for drawing the last page.  Other optional
 163  parameters include most of those recognized by the CGI header()
 164  method.
 165  
 166  You may call do_push() in the object oriented manner or not, as you
 167  prefer:
 168  
 169      use CGI::Push;
 170      $q = new CGI::Push;
 171      $q->do_push(-next_page=>\&draw_a_page);
 172  
 173          -or-
 174  
 175      use CGI::Push qw(:standard);
 176      do_push(-next_page=>\&draw_a_page);
 177  
 178  Parameters are as follows:
 179  
 180  =over 4
 181  
 182  =item -next_page
 183  
 184      do_push(-next_page=>\&my_draw_routine);
 185  
 186  This required parameter points to a reference to a subroutine responsible for
 187  drawing each new page.  The subroutine should expect two parameters
 188  consisting of the CGI object and a counter indicating the number
 189  of times the subroutine has been called.  It should return the
 190  contents of the page as an B<array> of one or more items to print.  
 191  It can return a false value (or an empty array) in order to abort the
 192  redrawing loop and print out the final page (if any)
 193  
 194      sub my_draw_routine {
 195          my($q,$counter) = @_;
 196          return undef if $counter > 100;
 197          return start_html('testing'),
 198                 h1('testing'),
 199                 "This page called $counter times";
 200      }
 201  
 202  You are of course free to refer to create and use global variables
 203  within your draw routine in order to achieve special effects.
 204  
 205  =item -last_page
 206  
 207  This optional parameter points to a reference to the subroutine
 208  responsible for drawing the last page of the series.  It is called
 209  after the -next_page routine returns a false value.  The subroutine
 210  itself should have exactly the same calling conventions as the
 211  -next_page routine.
 212  
 213  =item -type
 214  
 215  This optional parameter indicates the content type of each page.  It
 216  defaults to "text/html".  Normally the module assumes that each page
 217  is of a homogenous MIME type.  However if you provide either of the
 218  magic values "heterogeneous" or "dynamic" (the latter provided for the
 219  convenience of those who hate long parameter names), you can specify
 220  the MIME type -- and other header fields -- on a per-page basis.  See 
 221  "heterogeneous pages" for more details.
 222  
 223  =item -delay
 224  
 225  This indicates the delay, in seconds, between frames.  Smaller delays
 226  refresh the page faster.  Fractional values are allowed.
 227  
 228  B<If not specified, -delay will default to 1 second>
 229  
 230  =item -cookie, -target, -expires, -nph
 231  
 232  These have the same meaning as the like-named parameters in
 233  CGI::header().
 234  
 235  If not specified, -nph will default to 1 (as needed for many servers, see below).
 236  
 237  =back
 238  
 239  =head2 Heterogeneous Pages
 240  
 241  Ordinarily all pages displayed by CGI::Push share a common MIME type.
 242  However by providing a value of "heterogeneous" or "dynamic" in the
 243  do_push() -type parameter, you can specify the MIME type of each page
 244  on a case-by-case basis.  
 245  
 246  If you use this option, you will be responsible for producing the
 247  HTTP header for each page.  Simply modify your draw routine to
 248  look like this:
 249  
 250      sub my_draw_routine {
 251          my($q,$counter) = @_;
 252          return header('text/html'),   # note we're producing the header here
 253                 start_html('testing'),
 254                 h1('testing'),
 255                 "This page called $counter times";
 256      }
 257  
 258  You can add any header fields that you like, but some (cookies and
 259  status fields included) may not be interpreted by the browser.  One
 260  interesting effect is to display a series of pages, then, after the
 261  last page, to redirect the browser to a new URL.  Because redirect() 
 262  does b<not> work, the easiest way is with a -refresh header field,
 263  as shown below:
 264  
 265      sub my_draw_routine {
 266          my($q,$counter) = @_;
 267          return undef if $counter > 10;
 268          return header('text/html'),   # note we're producing the header here
 269                 start_html('testing'),
 270                 h1('testing'),
 271                 "This page called $counter times";
 272      }
 273  
 274      sub my_last_page {
 275          return header(-refresh=>'5; URL=http://somewhere.else/finished.html',
 276                        -type=>'text/html'),
 277                 start_html('Moved'),
 278                 h1('This is the last page'),
 279                 'Goodbye!'
 280                 hr,
 281                 end_html; 
 282      }
 283  
 284  =head2 Changing the Page Delay on the Fly
 285  
 286  If you would like to control the delay between pages on a page-by-page
 287  basis, call push_delay() from within your draw routine.  push_delay()
 288  takes a single numeric argument representing the number of seconds you
 289  wish to delay after the current page is displayed and before
 290  displaying the next one.  The delay may be fractional.  Without
 291  parameters, push_delay() just returns the current delay.
 292  
 293  =head1 INSTALLING CGI::Push SCRIPTS
 294  
 295  Server push scripts must be installed as no-parsed-header (NPH)
 296  scripts in order to work correctly on many servers.  On Unix systems,
 297  this is most often accomplished by prefixing the script's name with "nph-".  
 298  Recognition of NPH scripts happens automatically with WebSTAR and 
 299  Microsoft IIS.  Users of other servers should see their documentation
 300  for help.
 301  
 302  Apache web server from version 1.3b2 on does not need server
 303  push scripts installed as NPH scripts: the -nph parameter to do_push()
 304  may be set to a false value to disable the extra headers needed by an
 305  NPH script.
 306  
 307  =head1 AUTHOR INFORMATION
 308  
 309  Copyright 1995-1998, Lincoln D. Stein.  All rights reserved.  
 310  
 311  This library is free software; you can redistribute it and/or modify
 312  it under the same terms as Perl itself.
 313  
 314  Address bug reports and comments to: lstein@cshl.org
 315  
 316  =head1 BUGS
 317  
 318  This section intentionally left blank.
 319  
 320  =head1 SEE ALSO
 321  
 322  L<CGI::Carp>, L<CGI>
 323  
 324  =cut
 325