1CGI::Push(3)          User Contributed Perl Documentation         CGI::Push(3)
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NAME

6       CGI::Push - Simple Interface to Server Push
7

SYNOPSIS

9           use CGI::Push qw(:standard);
10
11           do_push(-next_page=>\&next_page,
12                   -last_page=>\&last_page,
13                   -delay=>0.5);
14
15           sub next_page {
16               my($q,$counter) = @_;
17               return undef if $counter >= 10;
18               return start_html('Test'),
19                      h1('Visible'),"\n",
20                      "This page has been called ", strong($counter)," times",
21                      end_html();
22           }
23
24           sub last_page {
25               my($q,$counter) = @_;
26               return start_html('Done'),
27                      h1('Finished'),
28                      strong($counter - 1),' iterations.',
29                      end_html;
30           }
31

DESCRIPTION

33       CGI::Push is a subclass of the CGI object created by CGI.pm.  It is
34       specialized for server push operations, which allow you to create
35       animated pages whose content changes at regular intervals.
36
37       You provide CGI::Push with a pointer to a subroutine that will draw one
38       page.  Every time your subroutine is called, it generates a new page.
39       The contents of the page will be transmitted to the browser in such a
40       way that it will replace what was there beforehand.  The technique will
41       work with HTML pages as well as with graphics files, allowing you to
42       create animated GIFs.
43
44       Only Netscape Navigator supports server push.  Internet Explorer
45       browsers do not.
46

USING CGI::Push

48       CGI::Push adds one new method to the standard CGI suite, do_push().
49       When you call this method, you pass it a reference to a subroutine that
50       is responsible for drawing each new page, an interval delay, and an
51       optional subroutine for drawing the last page.  Other optional
52       parameters include most of those recognized by the CGI header() method.
53
54       You may call do_push() in the object oriented manner or not, as you
55       prefer:
56
57           use CGI::Push;
58           $q = new CGI::Push;
59           $q->do_push(-next_page=>\&draw_a_page);
60
61               -or-
62
63           use CGI::Push qw(:standard);
64           do_push(-next_page=>\&draw_a_page);
65
66       Parameters are as follows:
67
68       -next_page
69               do_push(-next_page=>\&my_draw_routine);
70
71           This required parameter points to a reference to a subroutine
72           responsible for drawing each new page.  The subroutine should
73           expect two parameters consisting of the CGI object and a counter
74           indicating the number of times the subroutine has been called.  It
75           should return the contents of the page as an array of one or more
76           items to print.  It can return a false value (or an empty array) in
77           order to abort the redrawing loop and print out the final page (if
78           any)
79
80               sub my_draw_routine {
81                   my($q,$counter) = @_;
82                   return undef if $counter > 100;
83                   return start_html('testing'),
84                          h1('testing'),
85                          "This page called $counter times";
86               }
87
88           You are of course free to refer to create and use global variables
89           within your draw routine in order to achieve special effects.
90
91       -last_page
92           This optional parameter points to a reference to the subroutine
93           responsible for drawing the last page of the series.  It is called
94           after the -next_page routine returns a false value.  The subroutine
95           itself should have exactly the same calling conventions as the
96           -next_page routine.
97
98       -type
99           This optional parameter indicates the content type of each page.
100           It defaults to "text/html".  Normally the module assumes that each
101           page is of a homogeneous MIME type.  However if you provide either
102           of the magic values "heterogeneous" or "dynamic" (the latter
103           provided for the convenience of those who hate long parameter
104           names), you can specify the MIME type -- and other header fields --
105           on a per-page basis.  See "heterogeneous pages" for more details.
106
107       -delay
108           This indicates the delay, in seconds, between frames.  Smaller
109           delays refresh the page faster.  Fractional values are allowed.
110
111           If not specified, -delay will default to 1 second
112
113       -cookie, -target, -expires, -nph
114           These have the same meaning as the like-named parameters in
115           CGI::header().
116
117           If not specified, -nph will default to 1 (as needed for many
118           servers, see below).
119
120   Heterogeneous Pages
121       Ordinarily all pages displayed by CGI::Push share a common MIME type.
122       However by providing a value of "heterogeneous" or "dynamic" in the
123       do_push() -type parameter, you can specify the MIME type of each page
124       on a case-by-case basis.
125
126       If you use this option, you will be responsible for producing the HTTP
127       header for each page.  Simply modify your draw routine to look like
128       this:
129
130           sub my_draw_routine {
131               my($q,$counter) = @_;
132               return header('text/html'),   # note we're producing the header here
133                      start_html('testing'),
134                      h1('testing'),
135                      "This page called $counter times";
136           }
137
138       You can add any header fields that you like, but some (cookies and
139       status fields included) may not be interpreted by the browser.  One
140       interesting effect is to display a series of pages, then, after the
141       last page, to redirect the browser to a new URL.  Because redirect()
142       does b<not> work, the easiest way is with a -refresh header field, as
143       shown below:
144
145           sub my_draw_routine {
146               my($q,$counter) = @_;
147               return undef if $counter > 10;
148               return header('text/html'),   # note we're producing the header here
149                      start_html('testing'),
150                      h1('testing'),
151                      "This page called $counter times";
152           }
153
154           sub my_last_page {
155               return header(-refresh=>'5; URL=http://somewhere.else/finished.html',
156                             -type=>'text/html'),
157                      start_html('Moved'),
158                      h1('This is the last page'),
159                      'Goodbye!'
160                      hr,
161                      end_html;
162           }
163
164   Changing the Page Delay on the Fly
165       If you would like to control the delay between pages on a page-by-page
166       basis, call push_delay() from within your draw routine.  push_delay()
167       takes a single numeric argument representing the number of seconds you
168       wish to delay after the current page is displayed and before displaying
169       the next one.  The delay may be fractional.  Without parameters,
170       push_delay() just returns the current delay.
171

INSTALLING CGI::Push SCRIPTS

173       Server push scripts must be installed as no-parsed-header (NPH) scripts
174       in order to work correctly on many servers.  On Unix systems, this is
175       most often accomplished by prefixing the script's name with "nph-".
176       Recognition of NPH scripts happens automatically with WebSTAR and
177       Microsoft IIS.  Users of other servers should see their documentation
178       for help.
179
180       Apache web server from version 1.3b2 on does not need server push
181       scripts installed as NPH scripts: the -nph parameter to do_push() may
182       be set to a false value to disable the extra headers needed by an NPH
183       script.
184

AUTHOR INFORMATION

186       Copyright 1995-1998, Lincoln D. Stein.  All rights reserved.
187
188       This library is free software; you can redistribute it and/or modify it
189       under the same terms as Perl itself.
190
191       Address bug reports and comments to: lstein@cshl.org
192

BUGS

194       This section intentionally left blank.
195

SEE ALSO

197       CGI::Carp, CGI
198
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200
201perl v5.12.2                      2011-01-05                      CGI::Push(3)
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