NAME

CGI::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),' iterations.',
                end_html;
     }

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.

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 = 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";
    }

-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''. Currently, server push of heterogeneous document types is not supported.

-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

These have the same meaning as the like-named parameters in CGI::header().

INSTALLING CGI::Push SCRIPTS

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.

CAVEATS

This is a new module. It hasn't been extensively tested.

AUTHOR INFORMATION

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

BUGS

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