Michael Graham

NAME

CGI::Application::Plugin::Config::Context - Hierarchical, context-based configuration support for CGI::Application

VERSION

Version 0.18

SYNOPSIS

Simple Access to Configuration

In your CGI::Application-based module:

    use base 'CGI::Application';
    use CGI::Application::Plugin::Config::Context;

    sub cgiapp_init {
        my $self = shift;

        # Set config file and other options
        $self->conf->init(
            file   => 'app.conf',
            driver => 'ConfigGeneral',
        );
    }

    sub my_run_mode {
        my $self = shift;

        # get entire configuration
        my %conf = $self->conf->context;

        # get entire configuration (as a reference)
        my $conf = $self->conf->context;

        # get single config parameter
        my $value = $self->conf->param('some_value');

        # get raw configuraion (pre-context-matching)
        my $raw_config = $self->conf->raw;
        my %raw_config = $self->conf->raw;
    }

Configuration Based on URL or Module

You can match a configuration section to the request URL, or to the module name. For instance, given the following configuration file:

    admin_area    = 0

    <AppMatch ^MyApp::Admin>
        admin_area = 1
        title      = Admin Area
    </AppMatch>

    <Location /cgi-bin/feedback.cgi>
        title      = Feedback Form
    </Location>

The configuration will depend on how the script is called:

    # URL:      /cgi-bin/feedback.cgi?rm=add
    # Module:   MyApp::Feedback

    print $self->conf->param('admin_area');  # 0
    print $self->conf->param('title');       # 'Feedback Form'

    # URL:      /cgi-bin/admin/users.cgi
    # Module:   MyApp::Admin::Users

    print $self->conf->param('admin_area');  # 1
    print $self->conf->param('title');       # 'Admin Area'

Matching Configuration based on a Virtual Host

This module can also pick a configuration section based on the current virtual-host:

    # httpd.conf
    <VirtualHost _default_:8080>
        SetEnv SITE_NAME REDSITE
    </VirtualHost>

    # in app.conf
    <Site BLUESITE>
        background = blue
        foreground = white
    </Site>

    <Site REDSITE>
        background = red
        foreground = pink
    </Site>

    <Site GREENSITE>
        background = darkgreen
        foreground = lightgreen
    </Site>

Multiple configuration formats

Supports any configuration format supported by Config::Context. As of this writing, that includes the following formats:

Apache-style syntax, via Config::General:

    <AppMatch ^MyApp::Admin>
        admin_area = 1
        title      = Admin Area
    </AppMatch>

    <Location /cgi-bin/feedback.cgi>
        title      = Feedback Form
    </Location>

XML, via XML::Simple:

    <AppMatch name="^MyApp::Admin">
        <admin_area>1</admin_area>
        <title>Admin Area</title>
    </AppMatch>

    <Location name="/cgi-bin/feedback.cgi">
        <title>Feedback Form</title>
    </Location>

Config::Scoped syntax:

    AppMatch '^MyApp::Admin' {
        admin_area = 1
        title      = Admin Area
    }

    Location '/cgi-bin/feedback.cgi' {
        title      = Feedback Form
    }

Most of the examples in this document are in Config::General syntax, but can be translated into the other formats fairly easily. For more information, see the Config::Context docs.

DESCRIPTION

This module allows you to easily access configuration data stored in any of the formats supported by Config::Context: Config::General (Apache style), XML::Simple and Config::Scoped.

You can also automatically match configuration sections to the request URL, or to the module name. This is similar to how Apache dynamically selects a configuration by matching the request URL to (for instance) <Location> and <LocationMatch> sections.

You can also select configuration sections based on Virtual Host or by an environment variable you set in an .htaccess file. This allows you to share a configuration file and an application between many virtual hosts, each with its own unique configuration. This could be useful, for instance, in providing multiple themes for a single application.

Simple access to Configuration

This module provides a conf method to your CGI::Application object. First, you initialize the configuration system (typically in your cgiapp_init method):

    $self->conf->init(
        file   => 'app.conf',
        driver => 'ConfigGeneral',
    );

The configuration file is parsed at this point and the configuration is available from this moment on.

Then, within your run-modes you can retrieve configuration data:

    # get entire configuration
    my %conf = $self->conf->context;
    my $value = $conf{'some_value'};

    # get entire configuration (as a reference)
    my $conf = $self->conf->context;
    my $value = $conf->{'some_value'};

    # get single config parameter
    my $value = $self->conf->param('some_value');

The context method provides the configuration based on the context of your application, i.e. after matching configuration sections based on runtime data such as the current URL or package name.

But you can also access the raw configuration data from before the matching took place:

    # get raw configuration
    my %conf = $self->conf->raw;

    # get raw configuration (as a reference)
    my $conf = $self->conf->raw;

Multiple named Configurations

You can use more than one configuration by providing a name to the conf method:

    $self->conf('database')->init(
        file   => 'db.conf',
        driver => 'ConfigGeneral',
    );
    $self->conf('application')->init(
        file   => 'app.conf',
        driver => 'ConfigScoped',
    );

    ...

    my %db_config  = $self->conf('database')->context;
    my %app_config = $self->conf('application')->context;

Configuration based on URL or Module

Within your configuration file, you can provide different configurations depending on the current URL, or on the package name of your application.

<Site>

Matches against the SITE_NAME environment variable, using an exact match.

    # httpd.conf
    <VirtualHost _default_:8080>
        SetEnv SITE_NAME REDSITE
    </VirtualHost>

    # in app.conf
    <Site BLUESITE>
        background = blue
        foreground = white
    </Site>

    <Site REDSITE>
        background = red
        foreground = pink
    </Site>

    <Site GREENSITE>
        background = darkgreen
        foreground = lightgreen
    </Site>

You can name your sections something other than <Site>, and you can use a different environment variable than SITE_NAME. See "Notes on Site Matching", below.

<App>

Matches the Package name of your application module, for instance:

    <App ABC_Books::Admin>
        ...
    </App>

The match is performed hierarchically, like a filesystem path, except using :: as a delimiter, instead of /. The match is tied to the beginning of the package name, just like absolute paths. For instance, given the section:

    <App Site::Admin>
        ...
    </App>

the packages Site::Admin and Site::Admin::Users would match, but the packages My::Site::Admin and Site::Administrative would not.

<AppMatch>

Matches the package name of your application module, using a regular expression. The expression is not tied to the start of the string. For instance, given the section:

    <AppMatch Site::Admin>
        ...
    </AppMatch>

The following packages would all match: Site::Admin, Site::Admin::Users, My::Site::Admin, MySite::Admin, Site::Administrative.

<Location>

Matches hierarchically against the request URI, including the path and the PATH_INFO components, but excluding the scheme, host, port and query string.

So, for instance with the following URL:

    http://bookstore.example.com/cgi-bin/category.cgi/fiction/?rm=list

The Location would be:

    /cgi-bin/category.cgi/fiction/

Internally, the location is obtained by calling the url method of the query object (which is usually either a CGI or CGI::Simple object):

    $path = $webapp->query->url('-absolute' => 1, '-path_info' => 1);
<LocationMatch>

Matches against the request URI, using a regular expression.

Section Merge Order

The sections are matched in the following order:

    Site:         <Site>
    Package Name: <App>      and <AppMatch>
    URL:          <Location> and <LocationMatch>

When there is more than one matching section at the same level of priority (e.g. two <Location> sections, or both an <App> and an <AppMatch> section), then the sections are merged in the order of shortest match first.

Values in sections matched later override the values in sections matched earlier.

The idea is that the longer matches are more specific and should have priority, and that URIs are more specific than Module names.

Section Nesting

The sections can be nested inside each other. For instance:

    <Site BOOKSHOP>
        <Location /admin>
            admin_books = 1
        </Location>
    </Site>

    <Location /admin>
        <Site RECORDSHOP>
            admin_records = 1
        </Site>
    </Location>

    <App Bookshop::>
        <App Admin::>
        </App>
    </App>

By default, the sections can be nested up to two levels deep. This alows for Location sections within Site sections and vice versa. You can change this by setting the nesting_depth parameter to init.

Note: there is limited support for this kind of nesting when using Config::Scoped format files. See the documentation in Config::Context::ConfigScoped for details.

Merging Configuration Values into your Template

You can easily pass values from your configuration files directly to your templates. This allows you to associate HTML titles with URLs, or keep text like copyright notices in your config file instead of your templates:

    copyright_notice    =  Copyright (C) 1492 Christopher Columbus

    <Location /about>
        title = "Manifest Destiny, Inc. -  About Us"
    </Location>

    <Location /contact>
        title = "Manifest Destiny, Inc. - Contact Us"
    </Location>

If you use HTML::Template, you use the associate method when you load the template:

    $self->load_template(
        'template.tmpl',
        'associate' => $self->conf,
    );

If you use Template::Toolkit (via the CGI::Application::Plugin::TT module), you can accomplish the same thing by providing a custom tt_pre_process method:

    sub tt_pre_process {
        my $self            = shift;
        my $template        = shift;
        my $template_params = shift;

        my $config = $self->conf->context
        foreach (keys %$config) {
            unless (exists $template_params->{$_}) {
                $template_params->{$_} = $config->{$_};
            }
        }
    }

NOTE: If you plan to merge data directly from your config files to your templates, you should consider keeping your database passwords and other sensitive data in a separate configuration file, in order to avoid accidentally leaking these data into your web pages.

METHODS

init

Initializes the plugin. The only required parameter is the source of the configuration, either file, string or hash.

    $self->conf->init(
        file => 'app.conf',
    );

The other paramters are described below:

file

The path to the configuration file to be parsed.

string

A string containing configuration data to be parsed.

hash

A Perl data structure containing containing the pre-parsed config data.

driver

Which Config::Context driver should parse the config. Currently supported drivers are:

    driver            module name
    ------            -----------
    ConfigGeneral     Config::Context::ConfigGeneral
    ConfigScoped      Config::Context::ConfigScoped
    XMLSimple         Config::Context::XMLSimple

The default driver is ConfigGeneral.

driver_options

Options to pass directly on to the driver. This is a multi-level hash, where the top level keys are the driver names:

    my $conf = Config::Context->new(
        driver => 'ConfigScoped',
        driver_options => {
           ConfigGeneral => {
               -AutoLaunder => 1,
           },
           ConfigScoped = > {
               warnings => {
                   permissions  => 'off',
               }
           },
        },
    );

In this example the options under ConfigScoped will be passed to the ConfigScoped driver. (The options under ConfigGeneral will be ignored because driver is not set to 'ConfigGeneral'.)

cache_config_files

Whether or not to cache configuration files. Enabled, by default. This option is useful in a persistent environment such as mod_perl. See "Config File Caching" under "ADVANCED USAGE", below.

stat_config

If config file caching is enabled, this option controls how often the config files are checked to see if they have changed. The default is 60 seconds. This option is useful in a persistent environment such as mod_perl. See "Config File Caching" under ADVANCED USAGE, below.

site_section_name

Change the name of the <Site> section to something else. For instance, to use sections named <VirtualHost>, use:

    site_section_name => 'VirtualHost'
site_var

Change the name of the SITE_NAME environment variable used to match against <Site> sections. For instance To change this name to HTTP_HOST, use:

    site_var => 'HTTP_HOST',
nesting_depth

The number of levels deep that sections can be nested. The default is two levels deep.

See "Section Nesting", above.

You can initialize the plugin from within your instance CGI script:

    my $app = WebApp->new();
    $app->conf->init(file        => '../../config/app.conf');
    $app->run();

Or you can do so from within your cgiapp_init method within the application:

    sub cgiapp_init {
        my $self = shift;
        $self->conf->init(
            file => "$ENV{DOCUMENT_ROOT}/../config/app.conf"
        );
    }

context

Gets the entire configuration as a hash or hashref:

    my %config = $self->conf->context;  # as hash
    my $config = $self->conf->context;  # as hashref

raw

Gets the raw configuration as a hash or hashref:

    my %raw_config = $self->conf->raw;  # as hash
    my $raw_config = $self->conf->raw;  # as hashref

The raw configuration is the configuration before matching has taken place. It includes all the raw config with all of the <Location>, <App>, etc. sections intact.

param

Allows you to retrieve individual values from the configuration.

It behvaves like the param method in other classes, such as CGI, CGI::Application and HTML::Template:

    $value      = $self->conf->param('some_key');
    @all_keys   = $self->conf->param();

get_current_context ($name)

This is a class method which returns the current configuration object.

    my $conf = CGI::Application::Plugin::Config::Context->get_current_context;
    print $conf->{'title'};

    my %db_conf = CGI::Application::Plugin::Config::Context->get_current_context('db');
    print $db_conf{'username'};

This method is most useful in situations where you don't have access to the CGI::Application object, such within a Class::DBI class. See "Access to Configuration information from another Class" for an example.

get_current_raw_config ($name)

Same as get_current_context, but returns the raw configuration.

ADVANCED USAGE

Usage in a Persistent Environment such as mod_perl

The following sections describe some notes about running this module under mod_perl:

Config File Caching

Config::Context caches configuration files by default.

Each config file is read only once when the conf object is first initialized. Thereafter, on each init, the cached config is used.

This means that in a persistent environment like mod_perl, the config file is parsed on the first request, but not on subsequent requests.

If enough time has passed (sixty seconds by default) the config file is checked to see if it has changed. If it has changed, then the file is reread.

See the docs for Config::Context for details.

Notes on Site Matching

Renaming <Site> or SITE_NAME

Normally, the environment variable SITE_NAME is matched to <Site> section.

You can change these with the site_section_name and site_var parameters to init:

    $self->conf->init(
        file              => 'app.conf',
        site_section_name => 'Host',
        site_var          => 'MY_HOST',
    );

This will match the environment variable MY_HOST to the <Host> section.

Setting SITE_NAME from an .htaccess file or the CGI script

Since SITE_NAME is just an environment variable, you can set it anywhere you can set environment variables. For instance in an .htaccess file:

    # .htaccess
    SetEnv SITE_NAME bookshop

Or even the calling CGI script:

    #!/usr/bin/perl

    use MySite::WebApp;

    $ENV{'SITE_NAME'} = 'recordshop';
    my $app = MySite::WebApp->new();
    $app->run();

Access to Configuration information from another Class

You can also get at the current configuration settings from a completely unrelated Perl module. This can be useful for instance if you need to configure a set of Class::DBI classes, and you want them to be able to pick up their configuration on their own. For instance:

    # app.conf

    <database>
        connect_string = dbi:Pg:dbname=example
        username       = test
        password       = test

        <options>
            RaiseError = 1
            AutoCommit = 1
        </options>
    </database>


    # In your Class::DBI subclass
    package My::Class::DBI::Base;
    use base 'Class::DBI';

    sub db_Main {

        my $conf = CGI::Application::Plugin::Config::Context->get_current_context;

        my $dsn  = $conf->{'database'}{'connect_string'};
        my $user = $conf->{'database'}{'username'};
        my $pass = $conf->{'database'}{'password'};
        my $opts = $conf->{'database'}{'options'};

        return DBI->connect_cached($dsn, $user, $pass, $opts);
    }

For this example to work, you need to make sure you call $self->conf->init before you access the database through any of your Class::DBI objects.

You can also call get_current_raw_config to get access to the raw configuration.

Changing Parsing Behaviour Using Custom match_sections

Internally, this module uses Config::Context to parse its config files. If you want to change the parsing behaviour, you can pass your own match_sections list to init. For instance, if you want to allow only sections named <URL>, with no nesting, and have these matched exactly to the complete request path, you could do the following:

    # app.conf

    admin_area = 0
    user_area  = 0

    <URL /cgi-bin/admin.cgi>
        admin_area = 1
    </URL>

    <URL /cgi-bin/user.cgi>
        user_area = 1
    </URL>


    # in your cgiapp_init:
    $self->conf->init(
        file           => 'app.conf',
        nesting_depth  => 1,
        match_sections => [
            {
                name           => 'URL',
                match_type     => 'exact',
                merge_priority => 0,
                section_type   => 'path',
            },
        ]
    );

For reference, here is the default match_sections:

    [
        {
            name                => 'Site', # overridden by 'site_section_name'
            match_type          => 'exact',
            merge_priority      => 0,
            section_type        => 'env',
        },
        {
            name                => 'AppMatch',
            match_type          => 'regex',
            section_type        => 'module',
            merge_priority      => 1,
        },
        {
            name                => 'App',
            match_type          => 'path',
            path_separator      => '::',
            section_type        => 'module',
            merge_priority      => 1,
        },
        {
            name                => 'LocationMatch',
            match_type          => 'regex',
            section_type        => 'path',
            merge_priority      => 3,
        },
        {
            name                => 'Location',
            match_type          => 'path',
            section_type        => 'path',
            merge_priority      => 3,
        },
    ],

For each section, the section_type param indicates what runtime variable the section will be matched against. Here are the allowed values

    env:     matched to the environment variable SITE_NAME (overridden by site_name_var)
    module:  name of the Perl Module handling this request (e.g. MyApp::Users)
    path:    path of the request, including path_info (e.g. /cgi-bin/myapp/users.cgi/some/path)

You can use the above section_type values in your own custom match_sections.

For more information on the syntax of match_sections, see the docs for Config::Context.

Importing the 'conf' method, but using a different name.

If you want to access the features of this module using a method other than conf, you can do so via Anno Siegel's Exporter::Renaming module (available on CPAN).

    use Exporter::Renaming;
    use CGI::Application::Plugin::Config::Context Renaming => [ conf => custom_config_method];

    sub cgiapp_init {
        my $self = shift;

        # Set config file and other options
        $self->custom_config_method->init(
            file   => 'app.conf',
            driver => 'ConfigGeneral',
        );

        my $config = $self->custom_config_method->context;

        # ....

    }

AUTHOR

Michael Graham, <mag-perl@occamstoothbrush.com>

BUGS

Please report any bugs or feature requests to bug-cgi-application-plugin-config-general@rt.cpan.org, or through the web interface at http://rt.cpan.org. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

ACKNOWLEDGEMENTS

Thanks to the excellent examples provided by the other CGI::Application plugin authors: Mark Stosberg, Michael Peters, Cees Hek and others.

SEE ALSO

    CGI::Application
    Config::Context
    Config::Context::ConfigGeneral
    Config::Context::ConfigScoped
    Config::Context::XMLSimple
    CGI::Application::Plugin::Config::Simple
    CGI::Application::Plugin::ConfigAuto

    Exporter::Renaming

    CGI::Application::Plugin::TT
    Template::Toolkit
    HTML::Template

COPYRIGHT & LICENSE

Copyright 2005 Michael Graham, All Rights Reserved.

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




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