CGI::Application::DispUser(Contributed Perl DocumCGI::Application::Dispatch(3)NAMECGI::Application::Dispatch - Dispatch requests to CGI::Application
based objects
SYNOPSIS
Out of Box
Under mod_perl:
<Location /app>
SetHandler perl-script
PerlHandler CGI::Application::Dispatch
</Location>
Under normal cgi:
This would be the instance script for your application, such as
/cgi-bin/dispatch.cgi:
#!/usr/bin/perl
use FindBin::Real 'Bin';
use lib Bin() . '/../../rel/path/to/my/perllib';
use CGI::Application::Dispatch;
CGI::Application::Dispatch->dispatch();
With a dispatch table
package MyApp::Dispatch;
use base 'CGI::Application::Dispatch';
sub dispatch_args {
return {
prefix => 'MyApp',
table => [
'' => { app => 'Welcome', rm => 'start' },
':app/:rm' => { },
'admin/:app/:rm' => { prefix => 'MyApp::Admin' },
],
};
}
Under mod_perl:
<Location /app>
SetHandler perl-script
PerlHandler MyApp::Dispatch
</Location>
Under normal cgi:
This would be the instance script for your application, such as
/cgi-bin/dispatch.cgi:
#!/usr/bin/perl
use FindBin::Real 'Bin';
use lib Bin() . '/../../rel/path/to/my/perllib';
use MyApp::Dispatch;
MyApp::Dispatch->dispatch();
DESCRIPTION
This module provides a way (as a mod_perl handler or running under
vanilla CGI) to look at the path (as returned by dispatch_path) of the
incoming request, parse off the desired module and its run mode, create
an instance of that module and run it.
It currently supports both generations of mod_perl (1.x and 2.x).
Although, for simplicity, all examples involving Apache configuration
and mod_perl code will be shown using mod_perl 1.x. This may change as
mp2 usage increases.
It will translate a URI like this (under mod_perl):
/app/module_name/run_mode
or this (vanilla cgi)
/app/index.cgi/module_name/run_mode
into something that will be functionally similar to this
my $app = Module::Name->new(..);
$app->mode_param(sub {'run_mode'}); #this will set the run mode
METHODS
dispatch(%args)
This is the primary method used during dispatch. Even under mod_perl,
the handler method uses this under the hood.
#!/usr/bin/perl
use strict;
use CGI::Application::Dispatch;
CGI::Application::Dispatch->dispatch(
prefix => 'MyApp',
default => 'module_name',
);
This method accepts the following name value pairs:
default
Specify a value to use for the path if one is not available. This
could be the case if the default page is selected (eg: "/" ).
prefix
This option will set the string that will be prepended to the name
of the application module before it is loaded and created. So to
use our previous example request of
/app/index.cgi/module_name/run_mode
This would by default load and create a module named
'Module::Name'. But let's say that you have all of your application
specific modules under the 'My' namespace. If you set this option
to 'My' then it would instead load the 'My::Module::Name'
application module instead.
args_to_new
This is a hash of arguments that are passed into the "new()"
constructor of the application.
table
In most cases, simply using Dispatch with the "default" and
"prefix" is enough to simplify your application and your URLs, but
there are many cases where you want more power. Enter the dispatch
table. Since this table can be slightly complicated, a whole
section exists on its use. Please see the "DISPATCH TABLE" section.
debug
Set to a true value to send debugging output for this module to
STDERR. Off by default.
error_document
This string is similar to Apache ErrorDocument directive. If this
value is not present, then Dispatch will return a NOT FOUND error
either to the browser with simple hardcoded message (under CGI) or
to Apache (under mod_perl).
This value can be one of the following:
A string with error message - if it starts with a single double-
quote character ("""). This double-quote character will be trimmed
from final output.
A file with content of error document - if it starts with greater-
than sign ("<"). First character will be excluded as well. Path of
this file should be relative to server DOCUMENT_ROOT.
A URI to which the application will be redirected - if no leading
""" or "<" will be found.
Custom messages will be displayed in non mod_perl environment only.
(Under mod_perl, please use ErrorDocument directive in Apache
configuration files.) This value can contain %s placeholder for
sprintf Perl function. This placeholder will be replaced with
numeric HTTP error code. Currently CGI::Application::Dispatch uses
three HTTP errors:
400 Bad Request - If there are invalid characters in module name
(parameter :app) or runmode name (parameter :rm).
404 Not Found - When the path does not match anything in the
"DISPATCH TABLE", or module could not be found in @INC, or run mode
did not exist.
500 Internal Server Error - If application error occurs.
Examples of using error_document (assume error 404 have been
returned):
# return in browser 'Opss... HTTP Error #404'
error_document => '"Opss... HTTP Error #%s'
# return contents of file $ENV{DOCUMENT_ROOT}/errors/error404.html
error_document => '</errors/error%s.html'
# internal redirect to /errors/error404.html
error_document => '/errors/error%s.html'
# external redirect to http://host.domain/cgi-bin/errors.cgi?error=404
error_document => 'http://host.domain/cgi-bin/errors.cgi?error=%s'
auto_rest
This tells Dispatch that you are using REST by default and that you
care about which HTTP method is being used. Dispatch will append
the HTTP method name (upper case by default) to the run mode that
is determined after finding the appropriate dispatch rule. So a GET
request that translates into "MyApp::Module-"foo> will become
"MyApp::Module-"foo_GET>.
This can be overridden on a per-rule basis in a custom dispatch
table.
auto_rest_lc
In combinaion with auto_rest this tells Dispatch that you prefer
lower cased HTTP method names. So instead of "foo_POST" and
"foo_GET" you'll have "foo_post" and "foo_get".
dispatch_path()
This method returns the path that is to be processed.
By default it returns the value of $ENV{PATH_INFO} (or "$r->path_info"
under mod_perl) which should work for most cases. It allows the
ability for subclasses to override the value if they need to do
something more specific.
handler()
This method is used so that this module can be run as a mod_perl
handler. When it creates the application module it passes the $r
argument into the PARAMS hash of new()
<Location /app>
SetHandler perl-script
PerlHandler CGI::Application::Dispatch
PerlSetVar CGIAPP_DISPATCH_PREFIX MyApp
PerlSetVar CGIAPP_DISPATCH_DEFAULT /module_name
</Location>
The above example would tell apache that any url beginning with /app
will be handled by CGI::Application::Dispatch. It also sets the prefix
used to create the application module to 'MyApp' and it tells
CGI::Application::Dispatch that it shouldn't set the run mode but that
it will be determined by the application module as usual (through the
query string). It also sets a default application module to be used if
there is no path. So, a url of "/app/module_name" would create an
instance of "MyApp::Module::Name".
Using this method will add the "Apache-"request> object to your
application's "PARAMS" as 'r'.
# inside your app
my $request = $self->param('r');
If you need more customization than can be accomplished with just
prefix and default, then it would be best to just subclass
CGI::Application::Dispatch and override dispatch_args since "handler()"
uses dispatch to do the heavy lifting.
package MyApp::Dispatch;
use base 'CGI::Application::Dispatch';
sub dispatch_args {
return {
prefix => 'MyApp',
table => [
'' => { app => 'Welcome', rm => 'start' },
':app/:rm' => { },
'admin/:app/:rm' => { prefix => 'MyApp::Admin' },
],
args_to_new => {
PARAMS => {
foo => 'bar',
baz => 'bam',
},
}
};
}
1;
And then in your httpd.conf
<Location /app>
SetHandler perl-script
PerlHandler MyApp::Dispatch
</Location>
dispatch_args()
Returns a hashref of args that will be passed to dispatch(). It will
return the following structure by default.
{
prefix => '',
args_to_new => {},
table => [
':app' => {},
':app/:rm' => {},
],
}
This is the perfect place to override when creating a subclass to
provide a richer dispatch table.
When called, it receives 1 argument, which is a reference to the hash
of args passed into dispatch.
translate_module_name($input)
This method is used to control how the module name is translated from
the matching section of the path (see "Path Parsing". The main reason
that this method exists is so that it can be overridden if it doesn't
do exactly what you want.
The following transformations are performed on the input:
The text is split on '_'s (underscores) and each word has its first
letter capitalized. The words are then joined back together and each
instance of an underscore is replaced by '::'.
The text is split on '-'s (hyphens) and each word has its first letter
capitalized. The words are then joined back together and each instance
of a hyphen removed.
Here are some examples to make it even clearer:
module_name => Module::Name
module-name => ModuleName
admin_top-scores => Admin::TopScores
require_module($module_name)
This class method is used internally by CGI::Application::Dispatch to
take a module name (supplied by get_module_name) and require it in a
secure fashion. It is provided as a public class method so that if you
override other functionality of this module, you can still safely
require user specified modules. If there are any problems requiring the
named module, then we will "croak".
CGI::Application::Dispatch->require_module('MyApp::Module::Name');
DISPATCH TABLE
Sometimes it's easiest to explain with an example, so here you go:
CGI::Application::Dispatch->dispatch(
prefix => 'MyApp',
args_to_new => {
TMPL_PATH => 'myapp/templates'
},
table => [
'' => { app => 'Blog', rm => 'recent'},
'posts/:category' => { app => 'Blog', rm => 'posts' },
':app/:rm/:id' => { app => 'Blog' },
'date/:year/:month?/:day?' => {
app => 'Blog',
rm => 'by_date',
args_to_new => { TMPL_PATH => "events/" },
},
]
);
So first, this call to dispatch sets the prefix and passes a
"TMPL_PATH" into args_to_new. Next it sets the table.
VOCABULARY
Just so we all understand what we're talking about....
A table is an array where the elements are gouped as pairs (similar to
a hash's key-value pairs, but as an array to preserve order). The first
element of each pair is called a "rule". The second element in the pair
is called the rule's "arg list". Inside a rule there are slashes "/".
Anything set of characters between slashes is called a "token".
URL MATCHING
When a URL comes in, Dispatch tries to match it against each rule in
the table in the order in which the rules are given. The first one to
match wins.
A rule consists of slashes and tokens. A token can one of the following
types:
literal
Any token which does not start with a colon (":") is taken to be a
literal string and must appear exactly as-is in the URL in order to
match. In the rule
'posts/:category'
"posts" is a literal token.
variable
Any token which begins with a colon (":") is a variable token.
These are simply wild-card place holders in the rule that will
match anything in the URL that isn't a slash. These variables can
later be referred to by using the "$self->param" mechanism. In the
rule
'posts/:category'
":category" is a variable token. If the URL matched this rule, then
you could retrieve the value of that token from whithin your
application like so:
my $category = $self->param('category');
There are some variable tokens which are special. These can be used
to further customize the dispatching.
:app
This is the module name of the application. The value of this
token will be sent to the translate_module_name method and then
prefixed with the prefix if there is one.
:rm This is the run mode of the application. The value of this
token will be the actual name of the run mode used.
optional-variable
Any token which begins with a colon (":") and ends with a question
mark (<?>) is considered optional. If the rest of the URL matches
the rest of the rule, then it doesn't matter whether it contains
this token or not. It's best to only include optional-variable
tokens at the end of your rule. In the rule
'date/:year/:month?/:day?'
":month?" and ":day?" are optional-variable tokens.
Just like with variable tokens, optional-variable tokens' values
can also be retrieved by the application, if they existed in the
URL.
if( defined $self->param('month') ) {
...
}
wildcard
The wildcard token "*" allows for partial matches. The token MUST
appear at the end of the rule.
'posts/list/*'
By default, the "dispatch_url_remainder" param is set to the
remainder of the URL matched by the *. The name of the param can be
changed by setting "*" argument in the "ARG LIST".
'posts/list/*' => { '*' => 'post_list_filter' }
method
You can also dispatch based on HTTP method. This is similar to
using auto_rest but offers more fine grained control. You include
the method (case insensitive) at the end of the rule and enclose it
in square brackets.
':app/news[post]' => { rm => 'add_news' },
':app/news[get]' => { rm => 'news' },
':app/news[delete]' => { rm => 'delete_news' },
The main reason that we don't use regular expressions for dispatch
rules is that regular expressions provide no mechanism for named back
references, like variable tokens do.
ARG LIST
Each rule can have an accompanying arg-list. This arg list can contain
special arguments that override something set higher up in dispatch for
this particular URL, or just have additional args passed available in
"$self->param()"
For instance, if you want to override prefix for a specific rule, then
you can do so.
'admin/:app/:rm' => { prefix => 'MyApp::Admin' },
Path Parsing
This section will describe how the application module and run mode are
determined from the path if no "DISPATCH TABLE" is present, and what
options you have to customize the process. The value for the path to
be parsed is retrieved from the dispatch_path method, which by default
uses the "PATH_INFO" environment variable.
Getting the module name
To get the name of the application module the path is split on
backslahes ("/"). The second element of the returned list (the first
is empty) is used to create the application module. So if we have a
path of
/module_name/mode1
then the string 'module_name' is used. This is passed through the
translate_module_name method. Then if there is a "prefix" (and there
should always be a prefix) it is added to the beginning of this new
module name with a double colon "::" separating the two.
If you don't like the exact way that this is done, don't fret you do
have a couple of options. First, you can specify a "DISPATCH TABLE"
which is much more powerful and flexible (in fact this default behavior
is actually implemented internally with a dispatch table). Or if you
want something a little simpler, you can simply subclass and extend the
translate_module_name method.
Getting the run mode
Just like the module name is retrieved from splitting the path on
slashes, so is the run mode. Only instead of using the second element
of the resulting list, we use the third as the run mode. So, using the
same example, if we have a path of
/module_name/mode2
Then the string 'mode2' is used as the run mode.
MISC NOTES
· CGI query strings
CGI query strings are unaffected by the use of "PATH_INFO" to
obtain the module name and run mode. This means that any other
modules you use to get access to you query argument (ie, CGI,
Apache::Request) should not be affected. But, since the run
mode may be determined by CGI::Application::Dispatch having a
query argument named 'rm' will be ignored by your application
module.
CLEAN URLS WITH MOD_REWRITE
With a dispatch script, you can fairly clean URLS like this:
/cgi-bin/dispatch.cgi/module_name/run_mode
However, including "/cgi-bin/dispatch.cgi" in ever URL doesn't add any
value to the URL, so it's nice to remove it. This is easily done if you
are using the Apache web server with "mod_rewrite" available. Adding
the following to a ".htaccess" file would allow you to simply use:
/module_name/run_mode
If you have problems with mod_rewrite, turn on debugging to see exactly
what's happening:
RewriteLog /home/project/logs/alpha-rewrite.log
RewriteLogLevel 9
mod_rewrite related code in the dispatch script.
This seemed necessary to put in the dispatch script to make mod_rewrite
happy. Perhaps it's specific to using "RewriteBase".
# mod_rewrite alters the PATH_INFO by turning it into a file system path,
# so we repair it.
$ENV{PATH_INFO} =~ s/^$ENV{DOCUMENT_ROOT}// if defined $ENV{PATH_INFO};
Simple Apache Example
RewriteEngine On
# You may want to change the base if you are using the dispatcher within a
# specific directory.
RewriteBase /
# If an actual file or directory is requested, serve directly
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Otherwise, pass everything through to the dispatcher
RewriteRule ^(.*)$ /cgi-bin/dispatch.cgi/$1 [L,QSA]
More complex rewrite: dispatching "/" and multiple developers
Here is a more complex example that dispatches "/", which would
otherwise be treated as a directory, and also supports multiple
developer directories, so "/~mark" has its own separate dispatching
system beneath it.
Note that order matters here! The Location block for "/" needs to come
before the user blocks.
<Location />
RewriteEngine On
RewriteBase /
# Run "/" through the dispatcher
RewriteRule ^home/project/www/$ /cgi-bin/dispatch.cgi [L,QSA]
# Don't apply this rule to the users sub directories.
RewriteCond %{REQUEST_URI} !^/~.*$
# If an actual file or directory is requested, serve directly
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Otherwise, pass everything through to the dispatcher
RewriteRule ^(.*)$ /cgi-bin/dispatch.cgi/$1 [L,QSA]
</Location>
<Location /~mark>
RewriteEngine On
RewriteBase /~mark
# Run "/" through the dispatcher
RewriteRule ^/home/mark/www/$ /~mark/cgi-bin/dispatch.cgi [L,QSA]
# Otherwise, if an actual file or directory is requested, serve directly
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
# Otherwise, pass everything through to the dispatcher
RewriteRule ^(.*)$ /~mark/cgi-bin/dispatch.cgi/$1 [L,QSA]
# These examples may also be helpful, but are unrelated to dispatching.
SetEnv DEVMODE mark
SetEnv PERL5LIB /home/mark/perllib:/home/mark/config
ErrorDocument 404 /~mark/errdocs/404.html
ErrorDocument 500 /~mark/errdocs/500.html
</Location>
SUBCLASSING
While Dispatch tries to be flexible, it won't be able to do everything
that people want. Hopefully we've made it flexible enough so that if it
doesn't do The Right Thing you can easily subclass it.
AUTHOR
Michael Peters <mpeters@plusthree.com>
Thanks to Plus Three, LP (http://www.plusthree.com) for sponsoring my
work on this module
COMMUNITY
This module is a part of the larger CGI::Application community. If you
have questions or comments about this module then please join us on the
cgiapp mailing list by sending a blank message to
"cgiapp-subscribe@lists.erlbaum.net". There is also a community wiki
located at http://www.cgi-app.org/ <http://www.cgi-app.org/>
SOURCE CODE REPOSITORY
A public source code repository for this project is hosted here:
http://code.google.com/p/cgi-app-modules/source/checkout
CONTRIBUTORS
· Shawn Sorichetti
· Timothy Appnel
· dsteinbrunner
· ZACKSE
· Stew Heckenberg
· Drew Taylor <drew@drewtaylor.com>
· James Freeman <james.freeman@smartsurf.org>
· Michael Graham <magog@the-wire.com>
· Cees Hek <ceeshek@gmail.com>
· Mark Stosberg <mark@summersault.com>
· Viacheslav Sheveliov <slavash@aha.ru>
SECURITY
Since C::A::Dispatch will dynamically choose which modules to use as
the content generators, it may give someone the ability to execute
random modules on your system if those modules can be found in you
path. Of course those modules would have to behave like
CGI::Application based modules, but that still opens up the door more
than most want. This should only be a problem if you don't use a
prefix. By using this option you are only allowing Dispatch to pick
from a namespace of modules to run.
SEE ALSO
CGI::Application, Apache::Dispatch
COPYRIGHT & LICENSE
Copyright Michael Peters and Mark Stosberg 2008, all rights reserved.
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
perl v5.14.1 2011-07-21 CGI::Application::Dispatch(3)
