package CGI::Push;# See the bottom of this file for the POD documentation.  Search for the# string '=head'.# You can run this file through either pod2man or pod2html to produce pretty# documentation in manual or html file format (these utilities are part of the# Perl 5 distribution).# Copyright 1995-2000, Lincoln D. Stein.  All rights reserved.# It may 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.# The most recent version and complete docs are available at:#   http://stein.cshl.org/WWW/software/CGI/$CGI::Push::VERSION='1.04';use CGI;use CGI::Util 'rearrange';@ISA = ('CGI');$CGI::DefaultClass = 'CGI::Push';$CGI::Push::AutoloadClass = 'CGI';# add do_push() and push_delay() to exported tagspush(@{$CGI::EXPORT_TAGS{':standard'}},'do_push','push_delay');sub do_push {    my ($self,@p) = CGI::self_or_default(@_);    # unbuffer output    $| = 1;    srand;    my ($random) = sprintf("%08.0f",rand()*1E8);    my ($boundary) = "----=_NeXtPaRt$random";    my (@header);    my ($type,$callback,$delay,$last_page,$cookie,$target,$expires,$nph,@other) = rearrange([TYPE,NEXT_PAGE,DELAY,LAST_PAGE,[COOKIE,COOKIES],TARGET,EXPIRES,NPH],@p);    $type = 'text/html' unless $type;    $callback = \&simple_counter unless $callback && ref($callback) eq 'CODE';    $delay = 1 unless defined($delay);    $self->push_delay($delay);    $nph = 1 unless defined($nph);    my(@o);    foreach (@other) { push(@o,split("=")); }    push(@o,'-Target'=>$target) if defined($target);    push(@o,'-Cookie'=>$cookie) if defined($cookie);    push(@o,'-Type'=>"multipart/x-mixed-replace;boundary=\"$boundary\"");    push(@o,'-Server'=>"CGI.pm Push Module") if $nph;    push(@o,'-Status'=>'200 OK');    push(@o,'-nph'=>1) if $nph;    print $self->header(@o);    $boundary = "$CGI::CRLF--$boundary";    print "WARNING: YOUR BROWSER DOESN'T SUPPORT THIS SERVER-PUSH TECHNOLOGY.${boundary}$CGI::CRLF";    my (@contents) = &$callback($self,++$COUNTER);    # now we enter a little loop    while (1) {        print "Content-type: ${type}$CGI::CRLF$CGI::CRLF" unless $type =~ /^dynamic|heterogeneous$/i;        print @contents;        @contents = &$callback($self,++$COUNTER);        if ((@contents) && defined($contents[0])) {            print "${boundary}$CGI::CRLF";            do_sleep($self->push_delay()) if $self->push_delay();        } else {            if ($last_page && ref($last_page) eq 'CODE') {                print "${boundary}$CGI::CRLF";                do_sleep($self->push_delay()) if $self->push_delay();                print "Content-type: ${type}$CGI::CRLF$CGI::CRLF" unless $type =~ /^dynamic|heterogeneous$/i;                print  &$last_page($self,$COUNTER);            }            print "${boundary}--$CGI::CRLF";            last;        }    }    print "WARNING: YOUR BROWSER DOESN'T SUPPORT THIS SERVER-PUSH TECHNOLOGY.$CGI::CRLF";}sub simple_counter {    my ($self,$count) = @_;    return $self->start_html("CGI::Push Default Counter"),           $self->h1("CGI::Push Default Counter"),           "This page has been updated ",$self->strong($count)," times.",           $self->hr(),           $self->a({'-href'=>'http://www.genome.wi.mit.edu/ftp/pub/software/WWW/cgi_docs.html'},'CGI.pm home page'),           $self->end_html;}sub do_sleep {    my $delay = shift;    if ( ($delay >= 1) && ($delay!~/\./) ){        sleep($delay);    } else {        select(undef,undef,undef,$delay);    }}sub push_delay {    my ($self,$delay) = CGI::self_or_default(@_);    return defined($delay) ? $self->{'.delay'} =         $delay : $self->{'.delay'};}1;=head1 NAMECGI::Push - Simple Interface to Server Push=head1 SYNOPSIS    use CGI::Push qw(:standard);    do_push(-next_page=>\&next_page,            -last_page=>\&last_page,            -delay=>0.5);    sub next_page {        my($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;    }=head1 DESCRIPTIONCGI::Push is a subclass of the CGI object created by CGI.pm.  It isspecialized for server push operations, which allow you to createanimated pages whose content changes at regular intervals.You provide CGI::Push with a pointer to a subroutine that will drawone page.  Every time your subroutine is called, it generates a newpage.  The contents of the page will be transmitted to the browserin such a way that it will replace what was there beforehand.  Thetechnique will work with HTML pages as well as with graphics files, allowing you to create animated GIFs.Only Netscape Navigator supports server push.  Internet Explorerbrowsers do not.=head1 USING CGI::PushCGI::Push adds one new method to the standard CGI suite, do_push().When you call this method, you pass it a reference to a subroutinethat is responsible for drawing each new page, an interval delay, andan optional subroutine for drawing the last page.  Other optionalparameters include most of those recognized by the CGI header()method.You may call do_push() in the object oriented manner or not, as youprefer:    use CGI::Push;    $q = new CGI::Push;    $q->do_push(-next_page=>\&draw_a_page);        -or-    use CGI::Push qw(:standard);    do_push(-next_page=>\&draw_a_page);Parameters are as follows:=over 4=item -next_page    do_push(-next_page=>\&my_draw_routine);This required parameter points to a reference to a subroutine responsible fordrawing each new page.  The subroutine should expect two parametersconsisting of the CGI object and a counter indicating the numberof times the subroutine has been called.  It should return thecontents of the page as an B<array> of one or more items to print.  It can return a false value (or an empty array) in order to abort theredrawing loop and print out the final page (if any)    sub my_draw_routine {        my($q,$counter) = @_;        return undef if $counter > 100;        return start_html('testing'),               h1('testing'),               "This page called $counter times";    }You are of course free to refer to create and use global variableswithin your draw routine in order to achieve special effects.=item -last_pageThis optional parameter points to a reference to the subroutineresponsible for drawing the last page of the series.  It is calledafter the -next_page routine returns a false value.  The subroutineitself should have exactly the same calling conventions as the-next_page routine.=item -typeThis optional parameter indicates the content type of each page.  Itdefaults to "text/html".  Normally the module assumes that each pageis of a homogenous MIME type.  However if you provide either of themagic values "heterogeneous" or "dynamic" (the latter provided for theconvenience of those who hate long parameter names), you can specifythe MIME type -- and other header fields -- on a per-page basis.  See "heterogeneous pages" for more details.=item -delayThis indicates the delay, in seconds, between frames.  Smaller delaysrefresh the page faster.  Fractional values are allowed.B<If not specified, -delay will default to 1 second>=item -cookie, -target, -expires, -nphThese have the same meaning as the like-named parameters inCGI::header().If not specified, -nph will default to 1 (as needed for many servers, see below).=back=head2 Heterogeneous PagesOrdinarily all pages displayed by CGI::Push share a common MIME type.However by providing a value of "heterogeneous" or "dynamic" in thedo_push() -type parameter, you can specify the MIME type of each pageon a case-by-case basis.  If you use this option, you will be responsible for producing theHTTP header for each page.  Simply modify your draw routine tolook like this:    sub my_draw_routine {        my($q,$counter) = @_;        return header('text/html'),   # note we're producing the header here               start_html('testing'),               h1('testing'),               "This page called $counter times";    }You can add any header fields that you like, but some (cookies andstatus fields included) may not be interpreted by the browser.  Oneinteresting effect is to display a series of pages, then, after thelast page, to redirect the browser to a new URL.  Because redirect() does b<not> work, the easiest way is with a -refresh header field,as shown below:    sub my_draw_routine {        my($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;     }=head2 Changing the Page Delay on the FlyIf you would like to control the delay between pages on a page-by-pagebasis, call push_delay() from within your draw routine.  push_delay()takes a single numeric argument representing the number of seconds youwish to delay after the current page is displayed and beforedisplaying the next one.  The delay may be fractional.  Withoutparameters, push_delay() just returns the current delay.=head1 INSTALLING CGI::Push SCRIPTSServer 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 documentationfor help.Apache web server from version 1.3b2 on does not need serverpush 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 anNPH script.=head1 AUTHOR INFORMATIONCopyright 1995-1998, Lincoln D. Stein.  All rights reserved.  This library is free software; you can redistribute it and/or modifyit under the same terms as Perl itself.Address bug reports and comments to: lstein@cshl.org=head1 BUGSThis section intentionally left blank.=head1 SEE ALSOL<CGI::Carp>, L<CGI>=cut