CGI::Push - Simple Interface to Server Push
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;
}
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.
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;
$q->do_push(-next_page=>\&draw_a_page);
-or-
use CGI::Push qw(:standard);
do_push(-next_page=>\&draw_a_page);
Parameters are as follows:
do_push(-next_page=>\&my_draw_routine);
This required parameter points to a reference to a subroutine responsible for drawing each new page. The subroutine should expect two parameters consisting of the CGI object and a counter indicating the number of times the subroutine has been called. It should return the contents of the page as an array of one or more items to print. It can return a false value (or an empty array) in order to abort the redrawing loop and print out the final page (if any)
sub my_draw_routine {
my($q,$counter) = @_;
return undef if $counter > 100;
return start_html('testing'),
h1('testing'),
"This page called $counter times";
}
You are of course free to refer to create and use global variables within your draw routine in order to achieve special effects.
If not specified, -delay will default to 1 second
Ordinarily all pages displayed by CGI::Push share a common
MIME type. However by providing a value of ``heterogeneous'' or ``dynamic'' in the
do_push() -type parameter, you can specify the
MIME type of each page on a case-by-case basis.
If you use this option, you will be responsible for producing the HTTP header for each page. Simply modify your draw routine to look like this:
sub my_draw_routine {
my($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 {
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;
}
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.
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.
This is a new module. It hasn't been extensively tested.
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.
Address bug reports and comments to: lstein@genome.wi.mit.edu
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