CGI::Push(3) Perl Programmers Reference Guide CGI::Push(3)NAMECGI::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;
}
DESCRIPTIONCGI::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::PushCGI::Push adds one new method to the standard CGI suite,
do_push(). When you call this method, you pass it a ref
erence to a subroutine that is responsible for drawing
each new page, an interval delay, and an optional subrou
tine 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 $counter times";
}
You are of course free to refer to create and use
global variables within your draw routine in order to
achieve special effects.
-last_page
This optional parameter points to a reference to the
subroutine responsible for drawing the last page of
the series. It is called after the -next_page routine
returns a false value. The subroutine itself should
have exactly the same calling conventions as the
-next_page routine.
-type
This optional parameter indicates the content type of
each page. It defaults to "text/html". Normally the
module assumes that each page is of a homogenous MIME
type. However if you provide either of the magic val
ues "heterogeneous" or "dynamic" (the latter provided
for the convenience of those who hate long parameter
names), you can specify the MIME type -- and other
header fields -- on a per-page basis. See "heteroge
neous pages" for more details.
-delay
This indicates the delay, in seconds, between frames.
Smaller delays refresh the page faster. Fractional
values are allowed.
If not specified, -delay will default to 1 second
-cookie, -target, -expires, -nph
These have the same meaning as the like-named parame
ters in CGI:\fIs0:header().
If not specified, -nph will default to 1 (as needed
for many servers, see below).
Heterogeneous Pages
Ordinarily all pages displayed by CGI::Push share a common
MIME type. However by providing a value of "heteroge
neous" or "dynamic" in the do_push()-type parameter, you
can specify the MIME type of each page on a case-by-case
basis.
If you use this option, you will be responsible for pro
ducing the HTTP header for each page. Simply modify your
draw routine to look like this:
sub my_draw_routine {
my($q,$counter) = @_;
return header('text/html'), # note we're producing the header here
start_html('testing'),
h1('testing'),
"This page called $counter times";
}
You can add any header fields that you like, but some
(cookies and status fields included) may not be inter
preted by the browser. One interesting effect is to dis
play a series of pages, then, after the last page, to
redirect the browser to a new URL. Because redirect()
does b<not> work, the easiest way is with a -refresh
header field, as shown below:
sub my_draw_routine {
my($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 argu
ment 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 pre
fixing 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 dis
able 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
the CGI::Carp manpage, the CGI manpage
2001-02-22 perl v5.6.1 CGI::Push(3)
