NAME

       CGI::Push - Simple Interface to Server Push

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;
           }

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.

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:

       -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 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.

       -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.

       -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 homogeneous 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.

       -delay
           This indicates the delay, in seconds, between frames.  Smaller delays refresh the page
           faster.  Fractional values are allowed.

           If not specified, -delay will default to 1 second

       -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).

   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;
           }

   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.

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.

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

BUGS

       This section intentionally left blank.

SEE ALSO

       CGI::Carp, CGI