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CGI::Application::DispUser:Contributed PerlCGI::Application::Dispatch::PSGI(3)

NAME
       CGI::Application::Dispatch::PSGI	- Dispatch requests to
       CGI::Application	based objects using PSGI

SYNOPSIS
   Out of Box
       Under mod_perl:

	 # change "Apache1" to "Apache2" as needed.

	 <Location />
	 SetHandler perl-script
	 PerlHandler Plack::Handler::Apache1
	 PerlSetVar psgi_app /path/to/app.psgi
	 </Location>

	 <Perl>
	 use Plack::Handler::Apache1;
	 Plack::Handler::Apache1->preload("/path/to/app.psgi");
	 </Perl>

       Under CGI:

       This would be the instance script for your application, such as
       /cgi-bin/dispatch.cgi:

	   ### in your dispatch.psgi:
	   # ( in a persistent environment, use	FindBin::Real instead. )
	   use FindBin 'Bin';
	   use lib "$Bin/../perllib';
	   use Your::Application::Dispatch;
	   Your::Application::Dispatch->as_psgi;

	   ### In Your::Application::Dispatch;
	   package Your::Application::Dispatch;
	   use base 'CGI::Application::Dispatch::PSGI';

   With	a dispatch table
	   package MyApp::Dispatch;
	   use base 'CGI::Application::Dispatch::PSGI';

	   sub dispatch_args {
	       return {
		   prefix  => 'MyApp',
		   table   => [
		       ''		 => { app => 'Welcome',	rm => 'start' },
		       ':app/:rm'	 => { },
		       'admin/:app/:rm'	 => { prefix   => 'MyApp::Admin' },
		   ],
	       };
	   }

       The ".psgi" file	is constructed as above.

   With	a custom query object
       If you want to supply your own PSGI object, something like this in your
       .psgi file will work:

	   sub {
	       my $env = shift;
	       my $app = CGI::Application::Dispatch::PSGI->as_psgi(
		   table => [
		       '/:rm'	 =>    { app =>	'TestApp' }
		   ],
		   args_to_new => {
		       QUERY	=> CGI::PSGI->new($env)
		   }
	       );
	       return $app->($env);
	   }

DESCRIPTION
       This module provides a way to look at the path (as returned by
       "$env->{PATH_INFO}") of the incoming request, parse off the desired
       module and its run mode,	create an instance of that module and run it.

       It will translate a URI like this (in a persistent environment)

	   /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
   as_psgi(%args)
       This is the primary method used during dispatch.

	   #!/usr/bin/perl
	   use strict;
	   use CGI::Application::Dispatch::PSGI;

	   CGI::Application::Dispatch::PSGI->as_psgi(
	       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.

       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_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 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::PSGI->require_module('MyApp::Module::Name');

DISPATCH TABLE
       Sometimes it's easiest to explain with an example, so here you go:

	 CGI::Application::Dispatch::PSGI->as_psgi(
	   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 as_psgi 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 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. The run
	       mode can	be optional, as	noted below. Example:

		   /foo/:rm?

	       If no run mode is found,	it will	default	to using the
	       "start_mode()", just like invoking CGI::Application directly.
	       Both of these URLs would	end up dispatching to the start	mode
	       associated with /foo:

		   /foo/
		   /foo

       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 "$env->{PATH_INFO}".

   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.

Exception Handling
       A CGI::Application object can throw an exception	up to
       "CGI::Application::Dispatch::PSGI" if no	"error_mode()" is implemented
       or if the error_mode itself throws an exception.	In these cases we
       generally return	a generic "500"	response, and log some details for the
       developer with a	warning.

       However,	we will	check to see if	the exception thrown is	an
       HTTP::Exception object. If that's the case, we will rethrow it, and you
       can handle it yourself using something like
       Plack::Middleware::HTTPExceptions.

MISC NOTES
       o       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::PSGI
	       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.

AUTHORS
       Mark Stosberg <mark@summersault.com>

       Heavily based on	CGI::Application::Dispatch, written by Michael Peters
       <mpeters@plusthree.com> and others

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/>

SOURCE CODE REPOSITORY
       A public	source code repository for this	project	is hosted here:

       https://github.com/markstos/CGI--Application--Dispatch

SECURITY
       Since C::A::Dispatch::PSGI 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.

Backwards Compatibility
       Versions	0.2 and	earlier	of this	module injected	the "as_psgi" method
       into CGI::Application::Dispatch,	creating a syntax like this:

	  ### in your dispatch.psgi:
	  use Your::Application::Dispatch;
	  use CGI::Application::Dispatch::PSGI;
	  Your::Application::Dispatch->as_psgi;

	  ### In Your::Application::Dispatch;
	  use base 'CGI::Application::Dispatch::PSGI';

       In the current design, the "as_pgsi" method is directly in this module,
       so a couple of lines of code need to be changed:

	  ### in your dispatch.psgi:
	  use Your::Application::Dispatch;
	  Your::Application::Dispatch->as_psgi;

	  ### In Your::Application::Dispatch;
	  use base 'CGI::Application::Dispatch::PSGI';

Differences with CGI::Application::Dispatch
       dispatch()
	   Use "as_psgi()" instead.

	   Note	that the "error_document" key is not supported here. Use the
	   Plack::Middleware::ErrorDocument or another PSGI solution instead.

       dispatch_path()
	   The dispatch_path() method is not supported.	The alternative	is to
	   reference "$env->{PATH_INFO}" which is available per	the PSGI spec.

       handler()
	   This	provided an Apache-specific handler. Other PSGI	components
	   like	Plack::Handler::Apache2	provide	Apache handlers	now instead.

       _http_method()
	   This	method has been	eliminated. Check "$env->{REQUEST_METHOD}"
	   directly instead.

       _parse_path()
	   The private _parse_path() method now	accepts	an additional
	   argument, the PSGI $env hash.

       _run_app()
	   The private _run_app() method now accepts an	additional argument,
	   the PSGI $env hash.

       _r()
	   This	method has been	eliminated. It does not	apply in PSGI.

SEE ALSO
       CGI::Application, Apache::Dispatch

COPYRIGHT & LICENSE
       Copyright Michael Peters	and Mark Stosberg 2008-2010, all rights
       reserved.

       This library is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

perl v5.32.0			  2020-08-2CGI::Application::Dispatch::PSGI(3)

NAME | SYNOPSIS | DESCRIPTION | METHODS | DISPATCH TABLE | Path Parsing | Exception Handling | MISC NOTES | CLEAN URLS WITH MOD_REWRITE | SUBCLASSING | AUTHORS | COMMUNITY | SOURCE CODE REPOSITORY | SECURITY | Backwards Compatibility | Differences with CGI::Application::Dispatch | SEE ALSO | COPYRIGHT & LICENSE

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