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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
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SEE ALSO
CGI::Carp, CGI
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