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+package CGI::Push;
+
+# See the bottom of this file for the POD documentation. Search for the
+# string '=head'.
+
+# You can run this file through either pod2man or pod2html to produce pretty
+# documentation in manual or html file format (these utilities are part of the
+# Perl 5 distribution).
+
+# Copyright 1995-2000, Lincoln D. Stein. All rights reserved.
+# It may be used and modified freely, but I do request that this copyright
+# notice remain attached to the file. You may modify this module as you
+# wish, but if you redistribute a modified version, please attach a note
+# listing the modifications you have made.
+
+# The most recent version and complete docs are available at:
+# http://stein.cshl.org/WWW/software/CGI/
+
+$CGI::Push::VERSION='1.04';
+use CGI;
+use CGI::Util 'rearrange';
+@ISA = ('CGI');
+
+$CGI::DefaultClass = 'CGI::Push';
+$CGI::Push::AutoloadClass = 'CGI';
+
+# add do_push() and push_delay() to exported tags
+push(@{$CGI::EXPORT_TAGS{':standard'}},'do_push','push_delay');
+
+sub do_push {
+ my ($self,@p) = CGI::self_or_default(@_);
+
+ # unbuffer output
+ $| = 1;
+ srand;
+ my ($random) = sprintf("%08.0f",rand()*1E8);
+ my ($boundary) = "----=_NeXtPaRt$random";
+
+ my (@header);
+ my ($type,$callback,$delay,$last_page,$cookie,$target,$expires,$nph,@other) = rearrange([TYPE,NEXT_PAGE,DELAY,LAST_PAGE,[COOKIE,COOKIES],TARGET,EXPIRES,NPH],@p);
+ $type = 'text/html' unless $type;
+ $callback = \&simple_counter unless $callback && ref($callback) eq 'CODE';
+ $delay = 1 unless defined($delay);
+ $self->push_delay($delay);
+ $nph = 1 unless defined($nph);
+
+ my(@o);
+ foreach (@other) { push(@o,split("=")); }
+ push(@o,'-Target'=>$target) if defined($target);
+ push(@o,'-Cookie'=>$cookie) if defined($cookie);
+ push(@o,'-Type'=>"multipart/x-mixed-replace;boundary=\"$boundary\"");
+ push(@o,'-Server'=>"CGI.pm Push Module") if $nph;
+ push(@o,'-Status'=>'200 OK');
+ push(@o,'-nph'=>1) if $nph;
+ print $self->header(@o);
+
+ $boundary = "$CGI::CRLF--$boundary";
+
+ print "WARNING: YOUR BROWSER DOESN'T SUPPORT THIS SERVER-PUSH TECHNOLOGY.${boundary}$CGI::CRLF";
+
+ my (@contents) = &$callback($self,++$COUNTER);
+
+ # now we enter a little loop
+ while (1) {
+ print "Content-type: ${type}$CGI::CRLF$CGI::CRLF" unless $type =~ /^dynamic|heterogeneous$/i;
+ print @contents;
+ @contents = &$callback($self,++$COUNTER);
+ if ((@contents) && defined($contents[0])) {
+ print "${boundary}$CGI::CRLF";
+ do_sleep($self->push_delay()) if $self->push_delay();
+ } else {
+ if ($last_page && ref($last_page) eq 'CODE') {
+ print "${boundary}$CGI::CRLF";
+ do_sleep($self->push_delay()) if $self->push_delay();
+ print "Content-type: ${type}$CGI::CRLF$CGI::CRLF" unless $type =~ /^dynamic|heterogeneous$/i;
+ print &$last_page($self,$COUNTER);
+ }
+ print "${boundary}--$CGI::CRLF";
+ last;
+ }
+ }
+ print "WARNING: YOUR BROWSER DOESN'T SUPPORT THIS SERVER-PUSH TECHNOLOGY.$CGI::CRLF";
+}
+
+sub simple_counter {
+ my ($self,$count) = @_;
+ return $self->start_html("CGI::Push Default Counter"),
+ $self->h1("CGI::Push Default Counter"),
+ "This page has been updated ",$self->strong($count)," times.",
+ $self->hr(),
+ $self->a({'-href'=>'http://www.genome.wi.mit.edu/ftp/pub/software/WWW/cgi_docs.html'},'CGI.pm home page'),
+ $self->end_html;
+}
+
+sub do_sleep {
+ my $delay = shift;
+ if ( ($delay >= 1) && ($delay!~/\./) ){
+ sleep($delay);
+ } else {
+ select(undef,undef,undef,$delay);
+ }
+}
+
+sub push_delay {
+ my ($self,$delay) = CGI::self_or_default(@_);
+ return defined($delay) ? $self->{'.delay'} =
+ $delay : $self->{'.delay'};
+}
+
+1;
+
+=head1 NAME
+
+CGI::Push - Simple Interface to Server Push
+
+=head1 SYNOPSIS
+
+ use CGI::Push qw(:standard);
+
+ do_push(-next_page=>\&next_page,
+ -last_page=>\&last_page,
+ -delay=>0.5);
+
+ sub next_page {
+ my($q,$counter) = @_;
+ return undef if $counter >= 10;
+ return start_html('Test'),
+ h1('Visible'),"\n",
+ "This page has been called ", strong($counter)," times",
+ end_html();
+ }
+
+ sub last_page {
+ my($q,$counter) = @_;
+ return start_html('Done'),
+ h1('Finished'),
+ strong($counter - 1),' iterations.',
+ end_html;
+ }
+
+=head1 DESCRIPTION
+
+CGI::Push is a subclass of the CGI object created by CGI.pm. It is
+specialized for server push operations, which allow you to create
+animated pages whose content changes at regular intervals.
+
+You provide CGI::Push with a pointer to a subroutine that will draw
+one page. Every time your subroutine is called, it generates a new
+page. The contents of the page will be transmitted to the browser
+in such a way that it will replace what was there beforehand. The
+technique will work with HTML pages as well as with graphics files,
+allowing you to create animated GIFs.
+
+Only Netscape Navigator supports server push. Internet Explorer
+browsers do not.
+
+=head1 USING CGI::Push
+
+CGI::Push adds one new method to the standard CGI suite, do_push().
+When you call this method, you pass it a reference to a subroutine
+that is responsible for drawing each new page, an interval delay, and
+an optional subroutine for drawing the last page. Other optional
+parameters include most of those recognized by the CGI header()
+method.
+
+You may call do_push() in the object oriented manner or not, as you
+prefer:
+
+ use CGI::Push;
+ $q = new CGI::Push;
+ $q->do_push(-next_page=>\&draw_a_page);
+
+ -or-
+
+ use CGI::Push qw(:standard);
+ do_push(-next_page=>\&draw_a_page);
+
+Parameters are as follows:
+
+=over 4
+
+=item -next_page
+
+ do_push(-next_page=>\&my_draw_routine);
+
+This required parameter points to a reference to a subroutine responsible for
+drawing each new page. The subroutine should expect two parameters
+consisting of the CGI object and a counter indicating the number
+of times the subroutine has been called. It should return the
+contents of the page as an B<array> of one or more items to print.
+It can return a false value (or an empty array) in order to abort the
+redrawing loop and print out the final page (if any)
+
+ sub my_draw_routine {
+ my($q,$counter) = @_;
+ return undef if $counter > 100;
+ return start_html('testing'),
+ h1('testing'),
+ "This page called $counter times";
+ }
+
+You are of course free to refer to create and use global variables
+within your draw routine in order to achieve special effects.
+
+=item -last_page
+
+This optional parameter points to a reference to the subroutine
+responsible for drawing the last page of the series. It is called
+after the -next_page routine returns a false value. The subroutine
+itself should have exactly the same calling conventions as the
+-next_page routine.
+
+=item -type
+
+This optional parameter indicates the content type of each page. It
+defaults to "text/html". Normally the module assumes that each page
+is of a homogenous MIME type. However if you provide either of the
+magic values "heterogeneous" or "dynamic" (the latter provided for the
+convenience of those who hate long parameter names), you can specify
+the MIME type -- and other header fields -- on a per-page basis. See
+"heterogeneous pages" for more details.
+
+=item -delay
+
+This indicates the delay, in seconds, between frames. Smaller delays
+refresh the page faster. Fractional values are allowed.
+
+B<If not specified, -delay will default to 1 second>
+
+=item -cookie, -target, -expires, -nph
+
+These have the same meaning as the like-named parameters in
+CGI::header().
+
+If not specified, -nph will default to 1 (as needed for many servers, see below).
+
+=back
+
+=head2 Heterogeneous Pages
+
+Ordinarily all pages displayed by CGI::Push share a common MIME type.
+However by providing a value of "heterogeneous" or "dynamic" in the
+do_push() -type parameter, you can specify the MIME type of each page
+on a case-by-case basis.
+
+If you use this option, you will be responsible for producing the
+HTTP header for each page. Simply modify your draw routine to
+look like this:
+
+ sub my_draw_routine {
+ my($q,$counter) = @_;
+ return header('text/html'), # note we're producing the header here
+ start_html('testing'),
+ h1('testing'),
+ "This page called $counter times";
+ }
+
+You can add any header fields that you like, but some (cookies and
+status fields included) may not be interpreted by the browser. One
+interesting effect is to display a series of pages, then, after the
+last page, to redirect the browser to a new URL. Because redirect()
+does b<not> work, the easiest way is with a -refresh header field,
+as shown below:
+
+ sub my_draw_routine {
+ my($q,$counter) = @_;
+ return undef if $counter > 10;
+ return header('text/html'), # note we're producing the header here
+ start_html('testing'),
+ h1('testing'),
+ "This page called $counter times";
+ }
+
+ sub my_last_page {
+ return header(-refresh=>'5; URL=http://somewhere.else/finished.html',
+ -type=>'text/html'),
+ start_html('Moved'),
+ h1('This is the last page'),
+ 'Goodbye!'
+ hr,
+ end_html;
+ }
+
+=head2 Changing the Page Delay on the Fly
+
+If you would like to control the delay between pages on a page-by-page
+basis, call push_delay() from within your draw routine. push_delay()
+takes a single numeric argument representing the number of seconds you
+wish to delay after the current page is displayed and before
+displaying the next one. The delay may be fractional. Without
+parameters, push_delay() just returns the current delay.
+
+=head1 INSTALLING CGI::Push SCRIPTS
+
+Server push scripts must be installed as no-parsed-header (NPH)
+scripts in order to work correctly on many servers. On Unix systems,
+this is most often accomplished by prefixing the script's name with "nph-".
+Recognition of NPH scripts happens automatically with WebSTAR and
+Microsoft IIS. Users of other servers should see their documentation
+for help.
+
+Apache web server from version 1.3b2 on does not need server
+push scripts installed as NPH scripts: the -nph parameter to do_push()
+may be set to a false value to disable the extra headers needed by an
+NPH script.
+
+=head1 AUTHOR INFORMATION
+
+Copyright 1995-1998, Lincoln D. Stein. All rights reserved.
+
+This library is free software; you can redistribute it and/or modify
+it under the same terms as Perl itself.
+
+Address bug reports and comments to: lstein@cshl.org
+
+=head1 BUGS
+
+This section intentionally left blank.
+
+=head1 SEE ALSO
+
+L<CGI::Carp>, L<CGI>
+
+=cut
+
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