1CGI::Push(3) User Contributed Perl Documentation CGI::Push(3)
2
6 CGI::Push - Simple Interface to Server Push
7
9 use strict;
10 use warnings;
11 use CGI::Push qw(:standard);
13 do_push(
15 -next_page => \&next_page,
16 -last_page => \&last_page,
17 -delay => 0.5
18 );
19 sub next_page {
21 my($q,$counter) = @_;
22 return undef if $counter >= 10;
23 ....
24 }
25 sub last_page {
27 my($q,$counter) = @_;
28 return ...
29 }
30
32 CGI::Push is a subclass of the CGI object created by CGI.pm. It is
33 specialized for server push operations, which allow you to create
34 animated pages whose content changes at regular intervals.
35 You provide CGI::Push with a pointer to a subroutine that will draw one
37 page. Every time your subroutine is called, it generates a new page.
38 The contents of the page will be transmitted to the browser in such a
39 way that it will replace what was there beforehand. The technique will
40 work with HTML pages as well as with graphics files, allowing you to
41 create animated GIFs.
42 Only Netscape Navigator supports server push. Internet Explorer
44 browsers do not.
45
47 CGI::Push adds one new method to the standard CGI suite, do_push().
48 When you call this method, you pass it a reference to a subroutine that
49 is responsible for drawing each new page, an interval delay, and an
50 optional subroutine for drawing the last page. Other optional
51 parameters include most of those recognized by the CGI header() method.
52 You may call do_push() in the object oriented manner or not, as you
54 prefer:
55 use CGI::Push;
57 $q = CGI::Push->new;
58 $q->do_push(-next_page=>\&draw_a_page);
59 -or-
61 use CGI::Push qw(:standard);
63 do_push(-next_page=>\&draw_a_page);
64 Parameters are as follows:
66 -next_page
68 do_push(-next_page=>\&my_draw_routine);
69 This required parameter points to a reference to a subroutine
71 responsible for drawing each new page. The subroutine should
72 expect two parameters consisting of the CGI object and a counter
73 indicating the number of times the subroutine has been called. It
74 should return the contents of the page as an array of one or more
75 items to print. It can return a false value (or an empty array) in
76 order to abort the redrawing loop and print out the final page (if
77 any)
78 sub my_draw_routine {
80 my($q,$counter) = @_;
81 return undef if $counter > 100;
82 ...
83 }
84 You are of course free to refer to create and use global variables
86 within your draw routine in order to achieve special effects.
87 -last_page
89 This optional parameter points to a reference to the subroutine
90 responsible for drawing the last page of the series. It is called
91 after the -next_page routine returns a false value. The subroutine
92 itself should have exactly the same calling conventions as the
93 -next_page routine.
94 -type
96 This optional parameter indicates the content type of each page.
97 It defaults to "text/html". Normally the module assumes that each
98 page is of a homogeneous MIME type. However if you provide either
99 of the magic values "heterogeneous" or "dynamic" (the latter
100 provided for the convenience of those who hate long parameter
101 names), you can specify the MIME type -- and other header fields --
102 on a per-page basis. See "heterogeneous pages" for more details.
103 -delay
105 This indicates the delay, in seconds, between frames. Smaller
106 delays refresh the page faster. Fractional values are allowed.
107 If not specified, -delay will default to 1 second
109 -cookie, -target, -expires, -nph
111 These have the same meaning as the like-named parameters in
112 CGI::header().
113 If not specified, -nph will default to 1 (as needed for many
115 servers, see below).
116 Heterogeneous Pages
118 Ordinarily all pages displayed by CGI::Push share a common MIME type.
119 However by providing a value of "heterogeneous" or "dynamic" in the
120 do_push() -type parameter, you can specify the MIME type of each page
121 on a case-by-case basis.
122 If you use this option, you will be responsible for producing the HTTP
124 header for each page. Simply modify your draw routine to look like
125 this:
126 sub my_draw_routine {
128 my($q,$counter) = @_;
129 return header('text/html'), # note we're producing the header here
130 ....
131 }
132 You can add any header fields that you like, but some (cookies and
134 status fields included) may not be interpreted by the browser. One
135 interesting effect is to display a series of pages, then, after the
136 last page, to redirect the browser to a new URL. Because redirect()
137 does b<not> work, the easiest way is with a -refresh header field, as
138 shown below:
139 sub my_draw_routine {
141 my($q,$counter) = @_;
142 return undef if $counter > 10;
143 return header('text/html'), # note we're producing the header here
144 ...
145 }
146 sub my_last_page {
148 return header(-refresh=>'5; URL=http://somewhere.else/finished.html',
149 -type=>'text/html'),
150 ...
151 }
152 Changing the Page Delay on the Fly
154 If you would like to control the delay between pages on a page-by-page
155 basis, call push_delay() from within your draw routine. push_delay()
156 takes a single numeric argument representing the number of seconds you
157 wish to delay after the current page is displayed and before displaying
158 the next one. The delay may be fractional. Without parameters,
159 push_delay() just returns the current delay.
160
162 Server push scripts must be installed as no-parsed-header (NPH) scripts
163 in order to work correctly on many servers. On Unix systems, this is
164 most often accomplished by prefixing the script's name with "nph-".
165 Recognition of NPH scripts happens automatically with WebSTAR and
166 Microsoft IIS. Users of other servers should see their documentation
167 for help.
168 Apache web server from version 1.3b2 on does not need server push
170 scripts installed as NPH scripts: the -nph parameter to do_push() may
171 be set to a false value to disable the extra headers needed by an NPH
172 script.
173
175 The CGI.pm distribution is copyright 1995-2007, Lincoln D. Stein. It is
176 distributed under the Artistic License 2.0. It is currently maintained
177 by Lee Johnson with help from many contributors.
178 Address bug reports and comments to:
180 https://github.com/leejo/CGI.pm/issues
181 The original bug tracker can be found at:
183 https://rt.cpan.org/Public/Dist/Display.html?Queue=CGI.pm
184 When sending bug reports, please provide the version of CGI.pm, the
186 version of Perl, the name and version of your Web server, and the name
187 and version of the operating system you are using. If the problem is
188 even remotely browser dependent, please provide information about the
189 affected browsers as well. Copyright 1995-1998, Lincoln D. Stein. All
190 rights reserved.
191
193 This section intentionally left blank.
194
196 CGI::Carp, CGI
197perl v5.32.0 2020-07-28 CGI::Push(3)