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CGI::Push(3)	 Perl Programmers Reference Guide    CGI::Push(3)

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),' 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.

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:

16/Sep/1999	       perl 5.005, patch 03			1

CGI::Push(3)	 Perl Programmers Reference Guide    CGI::Push(3)

	   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 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

16/Sep/1999	       perl 5.005, patch 03			2

CGI::Push(3)	 Perl Programmers Reference Guide    CGI::Push(3)

	   "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
	   These have the same meaning as the like-named
	   parameters in CGI::header().

       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:

16/Sep/1999	       perl 5.005, patch 03			3

CGI::Push(3)	 Perl Programmers Reference Guide    CGI::Push(3)

	   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 {
	       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 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.

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
       the CGI::Carp manpage, the CGI manpage

16/Sep/1999	       perl 5.005, patch 03			4

CGI::Push(3)	 Perl Programmers Reference Guide    CGI::Push(3)

16/Sep/1999	       perl 5.005, patch 03			5

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