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CGI::Push(3)	      User Contributed Perl Documentation	  CGI::Push(3)

NAME
       CGI::Push - Simple Interface to Server Push

SYNOPSIS
	   use strict;
	   use warnings;

	   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;
	       ....
	   }

	   sub last_page {
	       my($q,$counter) = @_;
	       return ...
	   }

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 =	CGI::Push->new;
	   $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;
		   ...
	       }

	   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
	       ....
	   }

       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
	       ...
	   }

	   sub my_last_page {
	       return header(-refresh=>'5; URL=http://somewhere.else/finished.html',
			     -type=>'text/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
       The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is
       distributed under the Artistic License 2.0. It is currently maintained
       by Lee Johnson with help	from many contributors.

       Address bug reports and comments	to:
       https://github.com/leejo/CGI.pm/issues

       The original bug	tracker	can be found at:
       https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm

       When sending bug	reports, please	provide	the version of CGI.pm, the
       version of Perl,	the name and version of	your Web server, and the name
       and version of the operating system you are using.  If the problem is
       even remotely browser dependent,	please provide information about the
       affected	browsers as well.  Copyright 1995-1998,	Lincoln	D. Stein.  All
       rights reserved.

BUGS
       This section intentionally left blank.

SEE ALSO
       CGI::Carp, CGI

perl v5.32.0			  2020-06-22			  CGI::Push(3)

NAME | SYNOPSIS | DESCRIPTION | USING CGI::Push | INSTALLING CGI::Push SCRIPTS | AUTHOR INFORMATION | BUGS | SEE ALSO

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