NAME
CGI::Push - Simple Interface to Server Push
SYNOPSIS
use CGI::Push qw(:standard);
dopush(-nextpage=>\&nextpage,
-lastpage=>\&lastpage,
-delay=>0.5);
sub nextpage {my($q,$counter) = @;
return undef if $counter >= 10;
return starthtml('Test'), h1('Visible'),"\n","This page has been called ", strong($counter)," times",
endhtml(); } sub lastpage {my($q,$counter) = @;
return starthtml('Done'), h1('Finished'),strong($counter - 1),' iterations.',
endhtml; }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 ani-
mated 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. UUSSIINNGG CCGGII::::PPuusshhCGI::Push adds one new method to the standard CGI suite, dopush().
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 anoptional subroutine for drawing the last page. Other optional parame-
ters include most of those recognized by the CGI header() method. You may call dopush() in the object oriented manner or not, as you prefer:use CGI::Push;
$q = new CGI::Push;
$q->dopush(-nextpage=>\&drawapage);
-or-
use CGI::Push qw(:standard);
dopush(-nextpage=>\&drawapage);
Parameters are as follows:-nextpage
dopush(-nextpage=>\&mydrawroutine);
This required parameter points to a reference to a subroutine responsible for drawing each new page. The subroutine should expect two parameters consisting of the CGI object and a counter indicating the number of times the subroutine has been called. It should return the contents of the page as an aarrrraayy of one or more items to print. It can return a false value (or an empty array) in order to abort the redrawing loop and print out the final page (if any) sub mydrawroutine {my($q,$counter) = @;
return undef if $counter > 100;
return starthtml('testing'), h1('testing'),"This page called $counter times";
} You are of course free to refer to create and use global variables within your draw routine in order to achieve special effects.-lastpage
This optional parameter points to a reference to the subroutine responsible for drawing the last page of the series. It is calledafter the -nextpage routine returns a false value. The subroutine
itself should have exactly the same calling conventions as the-nextpage routine.
-type
This optional parameter indicates the content type of each page. It defaults to "text/html". Normally the module assumes that each page is of a homogenous MIME type. However if you provide eitherof the magic values "heterogeneous" or "dynamic" (the latter pro-
vided for the convenience of those who hate long parameter names),you can specify the MIME type - and other header fields - on a
per-page basis. See "heterogeneous pages" for more details.
-delay
This indicates the delay, in seconds, between frames. Smaller delays refresh the page faster. Fractional values are allowed.IIff nnoott ssppeecciiffiieedd,, -ddeellaayy wwiillll ddeeffaauulltt ttoo 11 sseeccoonndd
-cookie, -target, -expires, -nph
These have the same meaning as the like-named parameters in
CGI::header().If not specified, -nph will default to 1 (as needed for many
servers, see below). HHeetteerrooggeenneeoouuss PPaaggeessOrdinarily all pages displayed by CGI::Push share a common MIME type.
However by providing a value of "heterogeneous" or "dynamic" in thedopush() -type parameter, you can specify the MIME type of each page
on a case-by-case basis.
If you use this option, you will be responsible for producing the HTTP header for each page. Simply modify your draw routine to look like this: sub mydrawroutine {my($q,$counter) = @;
return header('text/html'), # note we're producing the header here
starthtml('testing'), h1('testing'),"This page called $counter times";
}You can add any header fields that you like, but some (cookies and sta-
tus fields included) may not be interpreted by the browser. One inter-
esting effect is to display a series of pages, then, after the last page, to redirect the browser to a new URL. Because redirect() doesb
below: sub mydrawroutine {work, the easiest way is with a -refresh header field, as shown my($q,$counter) = @;
return undef if $counter > 10;
return header('text/html'), # note we're producing the header here
starthtml('testing'), h1('testing'),"This page called $counter times";
} sub mylastpage {return header(-refresh=>'5; URL=http://somewhere.else/finished.html',
-type=>'text/html'),
starthtml('Moved'), h1('This is the last page'), 'Goodbye!' hr, endhtml; } CChhaannggiinngg tthhee PPaaggee DDeellaayy oonn tthhee FFllyyIf you would like to control the delay between pages on a page-by-page
basis, call pushdelay() from within your draw routine. pushdelay() 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, pushdelay() just returns the current delay. IINNSSTTAALLLLIINNGG CCGGII::::PPuusshh SSCCRRIIPPTTSSServer push scripts must be installed as no-parsed-header (NPH) scripts
in order to work correctly on many servers. On Unix systems, this ismost 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 pushscripts installed as NPH scripts: the -nph parameter to dopush() may
be set to a false value to disable the extra headers needed by an NPH script. AUTHOR INFORMATIONCopyright 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.orgBUGS
This section intentionally left blank.SEE ALSO
CGI::Carp, CGIperl v5.8.8 2001-09-21 CGI::Push(3pm)