citizen

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Node.js MVC web application framework. Includes routing, serving, caching, session management, and other helpful tools.

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// repository documentation

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# citizen

citizen is an MVC-based web application framework designed for people interested in quickly building fast, scalable web sites instead of digging around Node's guts or cobbling together a wobbly Jenga tower made out of 50 different packages.

Use citizen as the foundation for a traditional server-side web application, a modular single-page application (SPA), or a RESTful API.

**There were numerous breaking changes in the transition from 0.9.x to 1.0.x.** Please consult the changelog for an itemized list and review this updated documentation thoroughly.

## Benefits

- Convention over configuration, but still flexible
- Zero-configuration server-side routing with SEO-friendly URLs
- Server-side session management
- Key/value store: cache requests, controller actions, objects, and static files
- Simple directives for managing cookies, sessions, redirects, caches, and more
- Powerful code reuse options via includes (components) and chaining
- HTML, JSON, JSONP, and plain text served from the same pattern
- ES module and Node (CommonJS) module support
- Hot module replacement in development mode
- View rendering using template literals or any engine supported by [consolidate](https://github.com/ladjs/consolidate)
- Few direct dependencies

Clearly, this is way more content than any NPM/Github README should contain. I'm working on a site for this documentation.

## Is it production ready?

I use citizen on [my personal site](https://jaysylvester.com) and [originaltrilogy.com](https://originaltrilogy.com). OT.com handles a moderate amount of traffic (a few hundred thousand views each month) on a $30 cloud hosting plan running a single instance of citizen, where the app/process runs for months at a time without crashing. It's very stable.

## Quick Start

These commands will create a new directory for your web app, install citizen, use its scaffolding utility to create the app's skeleton, and start the web server:

```bash
$ mkdir myapp && cd myapp
$ npm install citizen
$ node node_modules/citizen/util/scaffold skeleton
$ node app/start.js
```

If everything went well, you'll see confirmation in the console that the web server is running. Go to http://127.0.0.1:3000 in your browser and you'll see a bare index template.

citizen uses [template literals](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals) in its default template engine. You can install [consolidate](https://github.com/ladjs/consolidate), update the [template config](#config-settings), and modify the default view templates accordingly.

For configuration options, see [Configuration](#configuration). For more utilities to help you get started, see [Utilities](#utilities).

<!-- ### Demo App

Check out [model-citizen](https://github.com/jaysylvester/model-citizen), a basic responsive web site built with citizen that demonstrates some of the framework's functionality. -->

### App Directory Structure

```
app/
  config/             // These files are all optional
    citizen.json      // Default config file
    local.json        // Examples of environment configs
    qa.json
    prod.json
  controllers/
    hooks/            // Application event hooks (optional)
      application.js
      request.js
      response.js
      session.js
    routes/           // Public route controllers
      index.js
  helpers/            // Utility modules (optional)
  models/             // Models (optional)
    index.js
  views/
    error/            // Default error views
      404.html
      500.html
      ENOENT.html
      error.html
    index.html        // Default index view
  start.js
logs/                 // Log files
  access.log
  error.log
web/                  // public static assets
```

### Initializing citizen and starting the web server

Import citizen and start your app:

```js
// start.js
import citizen from 'citizen'
    
global.app = citizen
app.start()
```

Run from the terminal:

```bash
$ node start.js
```

### Configuration

You can configure your citizen app with a config file, startup options, and/or custom controller configurations.

The config directory is optional and contains configuration files in JSON format that drive both citizen and your app. You can have multiple citizen configuration files within this directory, allowing different configurations based on environment. citizen builds its configuration based on the following hierarchy:

1. If citizen finds a config directory, it parses each JSON file looking for a `host` key that matches the machine's hostname, and if it finds one, extends the default configuration with the file config.
2. If citizen can't find a matching `host` key, it looks for a file named citizen.json and loads that configuration.
3. citizen then extends the config with your [optional startup config](#startup-configuration).
4. Individual route controllers and and actions can have [their own custom config](#controller-configuration) that further extends the app config.

Let's say you want to run citizen on port 8080 in your local dev environment and you have a local database your app will connect to. You could create a config file called local.json (or dev.json, whatever you want) with the following:

```js
{
  "host":       "My-MacBook-Pro.local",
  "citizen": {
    "mode":     "development",
    "http": {
      "port":   8080
    }
  },
  "db": {
    "server":   "localhost",  // app.config.db.server
    "username": "dbuser",     // app.config.db.username
    "password": "dbpassword"  // app.config.db.password
  }
}
```

This config would extend the default configuration only when running on your local machine. Using this method, you can commit multiple config files from different environments to the same repository.

The database settings would be accessible anywhere within your app via `app.config.db`. The `citizen` and `host` nodes are reserved for the framework; create your own node(s) to store your custom settings.

#### Startup configuration

You can set your app's configuration at startup through `app.start()`. If there is a config file, the startup config will extend the config file. If there's no config file, the startup configuration extends the default citizen config.

```js
// Start an HTTPS server with a PFX file
app.start({
  citizen: {
    http: {
      enabled: false
    },
    https: {
      enabled: true,
      pfx:    '/absolute/path/to/site.pfx'
    }
  }
})
```

#### Controller configuration

To set custom configurations at the route controller level, export a `config` object (more on route controllers and actions in the [route controllers](#route-controllers) section).

```js
export const config = {
  // The "controller" property sets a configuration for all actions in this controller
  controller: {
    contentTypes: [ 'application/json' ]
  }

// The "submit" property is only for the submit() controller action
  submit: {
    form: {
      maxPayloadSize: 1000000
    }
  }
}
```

#### Default configuration

The following represents citizen's default configuration, which is extended by your configuration:

```js
{
  host                 : '',
  citizen: {
    mode               : process.env.NODE_ENV || 'production',
    global             : 'app',
    http: {
      enabled          : true,
      hostname         : '127.0.0.1',
      port             : 80
    },
    https: {
      enabled          : false,
      hostname         : '127.0.0.1',
      port             : 443,
      secureCookies    : true
    },
    connectionQueue    : null,
    templateEngine     : 'templateLiterals',
    compression: {
      enabled          : false,
      force            : false,
      mimeTypes        : [
                          'application/javascript',
                          'application/x-javascript',
                          'application/xml',
                          'application/xml+rss',
                          'image/svg+xml',
                          'text/css',
                          'text/html',
                          'text/javascript',
                          'text/plain',
                          'text/xml'
                          ]
    },
    sessions: {
      enabled          : false,
      lifespan         : 20 // minutes
    },
    layout: {
      controller       : '',
      view             : ''
    },
    contentTypes       : [
                          'text/html',
                          'text/plain',
                          'application/json',
                          'application/javascript'
                          ],
    forms: {
      enabled          : true,
      maxPayloadSize   : 524288 // 0.5MB
    },
    cache: {
      application: {
        enabled        : true,
        lifespan       : 15, // minutes
        resetOnAccess  : true,
        encoding       : 'utf-8',
        synchronous    : false
      },
      static: {
        enabled        : false,
        lifespan       : 15, // minutes
        resetOnAccess  : true
      },
      invalidUrlParams : 'warn',
      control          : {}
    },
    errors             : 'capture',
    logs: {
      access           : false, // performance-intensive, opt-in only
      error: {
        client         : true, // 400 errors
        server         : true // 500 errors
      },
      debug            : false,
      maxFileSize      : 10000,
      watcher: {
        interval       : 60000
      }
    },
    development: {
      debug: {
        scope: {
          config       : true,
          context      : true,
          cookie       : true,
          form         : true,
          payload      : true,
          route        : true,
          session      : true,
          url          : true,
        },
        depth          : 4,
        showHidden     : false,
        view           : false
      },
      watcher: {
        custom         : [],
        killSession    : false,
        ignored        : /(^|[/\\])\../ // Ignore dotfiles
      }
    },
    urlPath            : '/',
    directories: {
      app              : <appDirectory>,
      controllers      : <appDirectory> + '/controllers',
      helpers          : <appDirectory> + '/helpers',
      models           : <appDirectory> + '/models',
      views            : <appDirectory> + '/views',
      logs             : new URL('../../../logs', import.meta.url).pathname
      web              : new URL('../../../web', import.meta.url).pathname
    }
  }
}
```

#### Config settings

Here's a complete rundown of citizen's settings and what they do.

When starting a server, in addition to citizen's `http` and `https` config options, you can provide the same options as Node's [http.createServer()](https://nodejs.org/api/http.html#httpcreateserveroptions-requestlistener) and [https.createServer()](https://nodejs.org/api/https.html#httpscreateserveroptions-requestlistener).

The only difference is how you pass key files. As you can see in the examples above, you pass citizen the file paths for your key files. citizen reads the files for you.

<table>
  <caption>citizen config options</caption>
  <thead>
    <tr>
      <th>
        Setting
      </th>
      <th>
        Type
      <th>
        Default Value
      </th>
      <th>
        Description
      </th>
    </tr>
  </thead>
  <tr>
    <td>
      <code>host</code>
    </td>
    <td>
        String
    </td>
    <td>
      <code>''</code>
    </td>
    <td>
      To load different config files in different environments, citizen relies upon the server's hostname as a key. At startup, if citizen finds a config file with a <code>host</code> key that matches the server's hostname, it chooses that config file. This is not to be confused with the HTTP server <code>hostname</code> (see below).
    </td>
  </tr>
  <tr>
    <td colspan="4">
      citizen
    </td>
  </tr>
  <tr>
    <td>
      <code>mode</code>
    </td>
    <td>
      String
    </td>
    <td>
      Checks <code>NODE_ENV</code> first, otherwise <code>production</code>
    </td>
    <td>
      The application mode determines certain runtime behaviors. Possible values are <code>production</code> and <code>development</code> Production mode silences console logs. Development mode enables verbose console logs, URL debug options, and hot module replacement.
    </td>
  </tr>
  <tr>
    <td>
      <code>global</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>app</code>
    </td>
    <td>
      The convention for initializing citizen in the start file assigns the framework to a global variable. The default, which you'll see referenced throughout the documentation, is <code>app</code>. You can change this setting if you want to use another name.
    </td>
  </tr>
  <tr>
    <td>
      <code>contentTypes</code>
    </td>
    <td>
      Array
    </td>
    <td>
      <code>
        [
          'text/html',
          'text/plain',
          'application/json',
          'application/javascript'
        ]
      </code>
    </td>
    <td>
      An allowlist of response formats for each request, based on the client's <code>Accept</code> request header. When configuring available formats for individual route controllers or actions, the entire array of available formats must be provided.
    </td>
  </tr>
  <tr>
    <td>
      <code>errors</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>capture</code>
    </td>
    <td>
      When your application throws an error, the default behavior is for citizen to try to recover from the error and keep the application running. Setting this option to <code>exit</code> tells citizen to log the error and exit the process instead.
    </td>
  </tr>
  <tr>
    <td>
      <code>templateEngine</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>templateLiterals</code>
    </td>
    <td>
      citizen uses [template literal](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals) syntax for view rendering by default. Optionally, you can install <a href="https://github.com/tj/consolidate.js">consolidate</a> and use any engine it supports (for example, install Handlebars and set <code>templateEngine</code> to <code>handlebars</code>).
    </td>
  </tr>
  <tr>
    <td>
      <code>urlPath</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>/</code>
    </td>
    <td>
      Denotes the URL path leading to your app. If you want your app to be accessible via http://yoursite.com/my/app and you're not using another server as a front end to proxy the request, this setting should be <code>/my/app</code> (don't forget the leading slash). This setting is required for the router to work.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      http
    </td>
  </tr>
  <tr>
    <td>
      <code>enabled</code>
    </td>
    <td>
        Boolean
    </td>
    <td>
      <code>true</code>
    </td>
    <td>
      Enables the HTTP server.
    </td>
  </tr>
  <tr>
    <td>
      <code>hostname</code>
    </td>
    <td>
        String
    </td>
    <td>
      <code>127.0.0.1</code>
    </td>
    <td>
      The hostname at which your app can be accessed via HTTP. You can specify an empty string to accept requests at any hostname.
    </td>
  </tr>
  <tr>
    <td>
      <code>port</code>
    </td>
    <td>
        Number
    </td>
    <td>
      <code>3000</code>
    </td>
    <td>
      The port number on which citizen's HTTP server listens for requests.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      https
    </td>
  </tr>
  <tr>
    <td>
      <code>enabled</code>
    </td>
    <td>
        Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Enables the HTTPS server.
    </td>
  </tr>
  <tr>
    <td>
      <code>hostname</code>
    </td>
    <td>
        String
    </td>
    <td>
      <code>127.0.0.1</code>
    </td>
    <td>
      The hostname at which your app can be accessed via HTTPS. The default is localhost, but you can specify an empty string to accept requests at any hostname.
    </td>
  </tr>
  <tr>
    <td>
      <code>port</code>
    </td>
    <td>
        Number
    </td>
    <td>
      <code>443</code>
    </td>
    <td>
      The port number on which citizen's HTTPS server listens for requests.
    </td>
  </tr>
  <tr>
    <td>
      <code>secureCookies</code>
    </td>
    <td>
        Boolean
    </td>
    <td>
      <code>true</code>
    </td>
    <td>
      By default, all cookies set within an HTTPS request are secure. Set this option to <code>false</code> to override that behavior, making all cookies insecure and requiring you to manually set the <code>secure</code> option in the cookie directive.
    </td>
  </tr>
  <tr>
    <td>
      <code>connectionQueue</code>
    </td>
    <td>
        Integer
    </td>
    <td>
      <code>null</code>
    </td>
    <td>
      The maximum number of incoming requests to queue. If left unspecified, the operating system determines the queue limit.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      sessions
    </td>
  </tr>
  <tr>
    <td>
      <code>enabled</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Enables the user session scope, which assigns each visitor a unique ID and allows you to store data associated with that ID within the application server.
    </td>
  </tr>
  <tr>
    <td>
      <code>lifespan</code>
    </td>
    <td>
      Positive Integer
    </td>
    <td>
      <code>20</code>
    </td>
    <td>
      If sessions are enabled, this number represents the length of a user's session, in minutes. Sessions automatically expire if a user has been inactive for this amount of time.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      layout
    </td>
  </tr>
  <tr>
    <td>
      <code>controller</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>''</code>
    </td>
    <td>
      If you use a global layout controller, you can specify the name of that controller here instead of using the <code>next</code> directive in all your controllers.
    </td>
  </tr>
  <tr>
    <td>
      <code>view</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>''</code>
    </td>
    <td>
      By default, the layout controller will use the default layout view, but you can specify a different view here. Use the file name without the file extension.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      forms
    </td>
  </tr>
  <tr>
    <td>
      <code>enabled</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>true</code>
    </td>
    <td>
      citizen provides basic payload processing for simple forms. If you prefer to use a separate form package, set this to <code>false</code>.
    </td>
  </tr>
  <tr>
    <td>
      <code>maxPayloadSize</code>
    </td>
    <td>
      Positive Integer
    </td>
    <td>
      <code>524288</code>
    </td>
    <td>
      Maximum form payload size, in bytes. Set a max payload size to prevent your server from being overloaded by form input data.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      compression
    </td>
  </tr>
  <tr>
    <td>
      <code>enabled</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Enables gzip and deflate compression for rendered views and static assets.
    </td>
  </tr>
  <tr>
    <td>
      <code>force</code>
    </td>
    <td>
      Boolean or String
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Forces gzip or deflate encoding for all clients, even if they don't report accepting compressed formats. Many proxies and firewalls break the Accept-Encoding header that determines gzip support, and since all modern clients support gzip, it's usually safe to force it by setting this to <code>gzip</code>, but you can also force <code>deflate</code>.
    </td>
  </tr>
  <tr>
    <td>
      <code>mimeTypes</code>
    </td>
    <td>
      Array
    </td>
    <td>
      <p>See default config above.</p>
    </td>
    <td>
      An array of MIME types that will be compressed if compression is enabled. See the sample config above for the default list. If you want to add or remove items, you must replace the array in its entirety.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      cache
    </td>
  </tr>
  <tr>
    <td>
      <code>control</code>
    </td>
    <td>
      Object containing key/value pairs
    </td>
    <td>
      <code>{}</code>
    </td>
    <td>
      Use this setting to set Cache-Control headers for route controllers and static assets. The key is the pathname of the asset, and the value is the Cache-Control header. See <a href="#client-side-caching">Client-Side Caching</a> for details.
    </td>
  </tr>
  <tr>
    <td>
      <code>invalidUrlParams</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>warn</code>
    </td>
    <td>
      The route cache option can specify valid URL parameters to prevent bad URLs from being cached, and <code>invalidUrlParams</code> determines whether to log a warning when encountering bad URLs or throw a client-side error. See <a href="#caching-requests-and-controller-actions">Caching Requests and Controller Actions</a> for details.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      cache.application
    </td>
  </tr>
  <tr>
    <td>
      <code>enabled</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>true</code>
    </td>
    <td>
      Enables the in-memory cache, accessed via the <code>cache.set()</code> and <code>cache.get()</code> methods.
    </td>
  </tr>
  <tr>
    <td>
      <code>lifespan</code>
    </td>
    <td>
      Number
    </td>
    <td>
      <code>15</code>
    </td>
    <td>
      The length of time a cached application asset remains in memory, in minutes.
    </td>
  </tr>
  <tr>
    <td>
      <code>resetOnAccess</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>true</code>
    </td>
    <td>
      Determines whether to reset the cache timer on a cached asset whenever the cache is accessed. When set to <code>false</code>, cached items expire when the <code>lifespan</code> is reached.
    </td>
  </tr>
  <tr>
    <td>
      <code>encoding</code>
    </td>
    <td>
      String
    </td>
    <td>
      <code>utf-8</code>
    </td>
    <td>
      When you pass a file path to cache.set(), the encoding setting determines what encoding should be used when reading the file.
    </td>
  </tr>
  <tr>
    <td>
      <code>synchronous</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      When you pass a file path to cache.set(), this setting determines whether the file should be read synchronously or asynchronously. By default, file reads are asynchronous.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      cache.static
    </td>
  </tr>
  <tr>
    <td>
      <code>enabled</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      When serving static files, citizen normally reads the file from disk for each request. You can speed up static file serving considerably by setting this to <code>true</code>, which caches file buffers in memory.
    </td>
  </tr>
  <tr>
    <td>
      <code>lifespan</code>
    </td>
    <td>
      Number
    </td>
    <td>
      <code>15</code>
    </td>
    <td>
      The length of time a cached static asset remains in memory, in minutes.
    </td>
  </tr>
  <tr>
    <td>
      <code>resetOnAccess</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>true</code>
    </td>
    <td>
      Determines whether to reset the cache timer on a cached static asset whenever the cache is accessed. When set to <code>false</code>, cached items expire when the <code>lifespan</code> is reached.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      logs
    </td>
  </tr>
  <tr>
    <td>
      <code>access</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Enables HTTP access log files. Disabled by default because access logs can explode quickly and ideally it should be handled by a web server.
    </td>
  </tr>
  <tr>
    <td>
      <code>debug</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Enables debug log files. Useful for debugging production issues, but extremely verbose (the same logs you would see in the console in development mode).
    </td>
  </tr>
  <tr>
    <td>
      <code>maxFileSize</code>
    </td>
    <td>
      Number
    </td>
    <td>
      <code>10000</code>
    </td>
    <td>
      Determines the maximum file size of log files, in kilobytes. When the limit is reached, the log file is renamed with a time stamp and a new log file is created.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      logs.error
    </td>
  </tr>
  <tr>
    <td>
      <code>client</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>true</code>
    </td>
    <td>
      Enables logging of 400-level client errors.
    </td>
  </tr>
  <tr>
    <td>
      <code>server</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Enables logging of 500-level server/application errors.
    </td>
  </tr>
  <tr>
    <td>
      <code>status</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Controls whether status messages should be logged to the console when in production mode. (Development mode always logs to the console.)
    </td>
  </tr>
  <tr>
    <td colspan="4">
      logs.watcher
    </td>
  </tr>
  <tr>
    <td>
      <code>interval</code>
    </td>
    <td>
      Number
    </td>
    <td>
      <code>60000</code>
    </td>
    <td>
      For operating systems that don't support file events, this timer determines how often log files will be polled for changes prior to archiving, in milliseconds.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      development
    </td>
  </tr>
  <tr>
    <td colspan="4">
      development.debug
    </td>
  </tr>
  <tr>
    <td>
      <code>scope</code>
    </td>
    <td>
      Object
    </td>
    </td>
    <td>
    <td>
      This setting determines which scopes are logged in the debug output in development mode. By default, all scopes are enabled.
    </td>
  </tr>
  <tr>
    <td>
      <code>depth</code>
    </td>
    <td>
      Positive integer
    </td>
    <td>
      <code>3</code>
    </td>
    <td>
      When citizen dumps an object in the debug content, it inspects it using Node's util.inspect. This setting determines the depth of the inspection, meaning the number of nodes that will be inspected and displayed. Larger numbers mean deeper inspection and slower performance.
    </td>
  </tr>
  <tr>
    <td>
      <code>view</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Set this to true to dump debug info directly into the HTML view.
    </td>
  </tr>
  <tr>
    <td>
      <code>enableCache</code>
    </td>
    <td>
      Boolean
    </td>
    <td>
      <code>false</code>
    </td>
    <td>
      Development mode disables the cache. Change this setting to <code>true</code> to enable the cache in development mode.
    </td>
  </tr>
  <tr>
    <td colspan="4">
      development.watcher
    </td>
  </tr>
  <tr>
    <td>
      <code>custom</code>
    </td>
    <td>
      Array
    </td>
    </td>
    <td>
    <td>
      You can tell citizen's hot module replacement to watch your own custom modules. This array can contain objects with <code>watch</code> (relative directory path to your modules within the app directory) and <code>assign</code> (the variable to which you assign these modules) properties. Example:
      <br><br>
      <code>[ { "watch": "/util", "assign": "app.util" } ]</code>
    </td>
  </tr>
</table>

citizen uses [chokidar](https://www.npmjs.com/package/chokidar) as its file watcher, so `watcher` option for both logs and development mode also accepts any option allowed by chokidar.

These settings are exposed publicly via `app.config.host` and `app.config.citizen`.

This documentation assumes your global app variable name is `app`. Adjust accordingly.

### citizen exports

<table>
  <tr>
    <td>
      <code>app.start()</code>
    </td>
    <td>
      Starts a citizen web application server.
    </td>
  </tr>
  <tr>
    <td>
      <code>app.config</code>
    </td>
    <td>
      The configuration settings you supplied at startup. citizen's settings are within <code>app.config.citizen</code>.
    </td>
  </tr>
  <tr>
    <td>
      <code>app.controllers</code><br />
      <code>app.models</code><br />
      <code>app.views</code>
    </td>
    <td>
      It's unlikely you'll need to access controllers and views directly, but referencing <code>app.models</code> instead of importing your models manually benefits from citizen's built-in <a href="#hot-module-replacement">hot module replacement</a>.
    </td>
  </tr>
  <tr>
    <td>
      <code>app.helpers</code>
    </td>
    <td>
      All <a href="#helpers">helper/utility modules</a> placed in <code>app/helpers/</code> are imported into the helpers object.
    </td>
  </tr>
  <tr>
    <td>
      <code>app.cache.set()</code><br />
      <code>app.cache.get()</code><br />
      <code>app.cache.exists()</code><br />
      <code>app.cache.clear()</code>
    </td>
    <td>
      <a href="#object-caching">Application cache</a> and key/value store used internally by citizen, also available for your app.
    </td>
  </tr>
  <tr>
    <td>
      <code>app.log()</code>
    </td>
    <td>
      Basic <a href="#logs">console and file logging</a> used by citizen, exported for your use.
    </td>
  </tr>
</table>

## Routing and URLs

The citizen URL structure determines which route controller and action to fire, passes URL parameters, and makes a bit of room for SEO-friendly content that can double as a unique identifier. The structure looks like this:

```
http://www.site.com/controller/seo-content/action/myAction/param/val/param2/val2
```

For example, let's say your site's base URL is:

```
http://www.cleverna.me
```

The default route controller is `index`, and the default action is `handler()`, so the above is the equivalent of the following:

```
http://www.cleverna.me/index/action/handler
```

If you have an `article` route controller, you'd request it like this:

```
http://www.cleverna.me/article
```

Instead of query strings, citizen passes URL parameters consisting of name/value pairs. If you had to pass an article ID of 237 and a page number of 2, you'd append name/value pairs to the URL:

```
http://www.cleverna.me/article/id/237/page/2
```

Valid parameter names may contain letters, numbers, underscores, and dashes, but must start with a letter or underscore.

The default controller action is `handler()`, but you can specify alternate actions with the `action` parameter (more on this later):

```
http://www.cleverna.me/article/action/edit
```

citizen also lets you optionally insert relevant content into your URLs, like so:

```
http://www.cleverna.me/article/My-Clever-Article-Title/page/2
```

This SEO content must always follow the controller name and precede any name/value pairs, including the controller action. You can access it generically via `route.descriptor` or within the `url` scope (`url.article` in this case), which means you can use it as a unique identifier (more on URL parameters in the [Route Controllers section](#route-controllers)).

### Reserved words

The URL parameters `action` and `direct` are reserved for the framework, so don't use them for your app.

## MVC Patterns

citizen relies on a simple model-view-controller convention. The article pattern mentioned above might use the following structure:

```
app/
  controllers/
    routes/
      article.js
  models/
    article.js    // Optional, name it whatever you want
  views/
    article.html  // The default view file name should match the controller name
```

At least one route controller is required for a given URL, and a route controller's default view file must share its name. Models are optional.

All views for a given route controller can exist in the `app/views/` directory, or they can be placed in a directory whose name matches that of the controller for cleaner organization:

```
app/
  controllers/
    routes/
      article.js
    models/
      article.js
    views/
      article/
        article.html  // The default view
        edit.html     // Alternate article views
        delete.html
```

More on views in the [Views section](#views).

Models and views are optional and don't necessarily need to be associated with a particular controller. If your route controller is going to pass its output to another controller for further processing and final rendering, you don't need to include a matching view (see the [controller next directive](#controller-chaining)).

### Route Controllers

A citizen route controller is just a JavaScript module. Each route controller requires at least one export to serve as an action for the requested route. The default action should be named `handler()`, which is called by citizen when no action is specified in the URL.

```js
// Default route controller action

export const handler = async (params, request, response, context) => {

// Do some stuff

return {
    // Send content and directives to the server
  }
}
```

The citizen server calls `handler()` after it processes the initial request and passes it 4 arguments: a `params` object containing the parameters of the request, the Node.js `request` and `response` objects, and the current request's context.

<table>
  <caption>Properties of the <code>params</code> object</caption>
  <tr>
    <td><code>config</code></td>
    <td>Your app's configuration, including any <a href="#controller-configuration">customizations</a> for the current controller action</td>
  </tr>
  <tr>
    <td><code>route</code></td>
    <td>Details of the requested route, such as the URL and the name of the route controller</td>
  </tr>
  <tr>
    <td><code>url</code></td>
    <td>Any parameters derived from the URL</td>
  </tr>
  <tr>
    <td><code>form</code></td>
    <td>Data collected from a POST</td>
  </tr>
  <tr>
    <td><code>payload</code></td>
    <td>The raw request payload</td>
  </tr>
  <tr>
    <td><code>cookie</code></td>
    <td>Cookies sent with the request</td>
  </tr>
  <tr>
    <td><code>session</code></td>
    <td>Session variables, if sessions are enabled</td>
  </tr>
</table>

In addition to having access to these objects within your controller, they are also included in your view context automatically so you can reference them within your view templates as local variables (more details in the <a href="#views">Views section</a>).

For example, based on the previous article URL...

```
http://www.cleverna.me/article/My-Clever-Article-Title/id/237/page/2
```

...you'll have the following `params.url` object passed to your controller:

```js
{
  article: 'My-Clever-Article-Title',
  id: '237',
  page: '2'
}
```

The controller name becomes a property in the URL scope that references the descriptor, which makes it well-suited for use as a unique identifier. It's also available in the `params.route` object as `params.route.descriptor`.

The `context` argument contains any data or directives that have been generated by previous controllers in the chain using their `return` statement.

To return the results of the controller action, include a `return` statement with any data and [directives](#controller-directives) you want to pass to citizen.

Using the above URL parameters, I can retrieve the article content from the model and pass it back to the server:

```js
// article controller

export const handler = async (params) => {
  // Get the article
  const article = await app.models.article.get({
    article: params.url.article,
    page: params.url.page
  })
  const author = await app.models.article.getAuthor({
    author: article.author
  })

// Any data you want available to the view should be placed in the local directive
  return {
    local: {
      article: article,
      author: author
    }
  }
}
```

Alternate actions can be requested using the `action` URL parameter. For example, maybe we want a different action and view to edit an article:

```js
// http://www.cleverna.me/article/My-Clever-Article-Title/id/237/page/2/action/edit

// article controller

// Return the article for view rendering using the local directive
  return {
    local: {
      article: article,
      author: author
    }
  }
}

export const edit = async (params) => {
  // Get the article
  const article = await app.models.article.get({
    article: params.url.article,
    page: params.url.page
  })

// Use the /views/article/edit.html view for this action
  return {
    local: {
      article: article
    },
    view: 'edit'
  }
}
```

You place any data you want to pass back to citizen within the `return` statement. All the data you want to render in your view should be passed to citizen within an object called `local`, as shown above. Additional objects can be passed to citizen to set directives that provide instructions to the server (see [Controller Directives](#controller-directives)). You can even add your own objects to the context and pass them from controller to controller (more in the [Controller Chaining section](#controller-chaining).)

### Models

Models are optional modules and their structure is completely up to you. citizen doesn't talk to your models directly; it only stores them in `app.models` for your convenience. You can also import them manually into your controllers if you prefer.

The following function, when placed in `app/models/article.js`, will be accessible in your app via `app.models.article.get()`:

```js
// app.models.article.get()
export const get = async (id) => {

let article = // do some stuff to retrieve the article from the db using the provided ID, then...

return article
}
```

### Views

citizen uses [template literals](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals) for view rendering by default. You can install [consolidate.js](https://github.com/tj/consolidate.js) and use any supported template engine. Just update the `templateEngine` config setting accordingly.

In `article.html`, you can reference variables you placed within the `local` object passed into the route controller's return statement. citizen also injects properties from the `params` object into your view context automatically, so you have access to those objects as local variables (such as the `url` scope):

```html

<!doctype html>
<html>
  <body>
    <main>
      <h1>
        ${local.article.title} — Page ${url.page}
      </h1>
      <h2>${local.author.name}, ${local.article.published}</h2>
      <p>
        ${local.article.summary}
      </p>
      <section>
        ${local.article.text}
      </section>
    </main>
  </body>
</html>
```

#### Rendering alternate views

By default, the server renders the view whose name matches that of the controller. To render a different view, [use the `view` directive in your return statement](#alternate-views).

All views go in `/app/views`. If a controller has multiple views, you can organize them within a directory named after that controller.

```
app/
  controllers/
    routes/
      article.js
      index.js
  views/
    article/
      article.html  // Default article controller view
      edit.html
    index.html      // Default index controller view
```

#### JSON and JSON-P

You can tell a route controller to return its local variables as JSON or JSON-P by setting the appropriate HTTP `Accept` header in your request, letting the same resource serve both a complete HTML view and JSON for AJAX requests and RESTful APIs.

The article route controller `handler()` action would return:

```json
{
  "article": {
    "title": "My Clever Article Title",
    "summary": "Am I not terribly clever?",
    "text": "This is my article text."
  },
  "author": {
    "name": "John Smith",
    "email": "jsmith@cleverna.me"
  }
}
```

Whatever you've added to the controller's return statement `local` object will be returned.

For JSONP, use `callback` in the URL:

```
http://www.cleverna.me/article/My-Clever-Article-Title/callback/foo
```

Returns:

```js
foo({
  "article": {
    "title": "My Clever Article Title",
    "summary": "Am I not terribly clever?",
    "text": "This is my article text."
  },
  "author": {
    "name": "John Smith",
    "email": "jsmith@cleverna.me"
  }
});
```

### Forcing a Content Type

To force a specific content type for a given request, set `response.contentType` in the route controller to your desired output:

```js
export const handler = async (params, request, response) => {
  // Every request will receive a JSON response regardless of the Accept header
  response.contentType = 'application/json'
}
```

You can force a global response type across all requests within an [event hook](#application-event-hooks).

## Helpers

Helpers are optional utility modules and their structure is completely up to you. They're stored in `app.helpers` for your convenience. You can also import them manually into your controllers and models if you prefer.

The following function, when placed in `app/helpers/validate.js`, will be accessible in your app via `app.helpers.validate.email()`:

```js
// app.helpers.validate.email()
export const email = (address) => {
  const emailRegex = new RegExp(/[a-z0-9!##$%&''*+/=?^_`{|}~-]+(?:\.[a-z0-9!##$%&''*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?/i)

return emailRegex.test(address)
}
```

## Hot Module Replacement

citizen stores all modules in the `app` scope not just for easy retrieval, but to support hot module replacement (HMR). When you save changes to any module or view in development mode, citizen clears the existing module import and re-imports that module in real time.

You'll see a console log noting the affected file, and your app will continue to run. No need to restart.

## Error Handling

citizen does its best to handle errors gracefully without exiting the process. The following controller action will throw an error, but the server will respond with a 500 and keep running:

```js
export const handler = async (params) => {
  // app.models.article.foo() doesn't exist, so this action will throw an error
  const foo = await app.models.article.foo(params.url.article)

return {
    local: foo
  }
}
```

You can also throw an error manually and customize the error message:

```js
export const handler = async (params) => {
  // Get the article
  const article = await app.models.article.get({
    article: params.url.article,
    page: params.url.page
  })

// If the article exists, return it
  if ( article ) {
    return {
      local: {
        article: article
      }
    }
  // If the article doesn't exist, throw a 404
  } else {
    // Error messages default to the standard HTTP Status Code response, but you can customize them.
    let err = new Error('The requested article does not exist.')

// The HTTP status code defaults to 500, but you can specify your own
    err.statusCode = 404

throw err
  }
}
```

Note that `params.route.controller` is updated from the requested controller to `error`, so any references in your app to the requested controller should take this into account.

Errors are returned in the format requested by the route. If you request [JSON](#json-and-json-p) and the route throws an error, citizen will return the error in JSON format.

The app skeleton created by the [scaffold utility](#scaffold) includes optional error view templates for common client and server errors, but you can create templates for any HTTP error code.

### Capture vs. Exit

citizen's default error handling method is `capture`, which attempts graceful recovery. If you'd prefer to exit the process after an error, change `config.citizen.errors` to `exit`.

```js
// config file: exit the process after an error
{
  "citizen": {
    "errors": "exit"
  }
}
```

After the application error handler fires, citizen will exit the process.

### Error Views

To create custom error views for server errors, create a directory called `/app/views/error` and populate it with templates named after the HTTP response code or Node error code.

```
app/
  views/
    error/
      500.html      // Displays any 500-level error
      404.html      // Displays 404 errors specifically
      ENOENT.html   // Displays bad file read operations
      error.html    // Displays any error without its own template
```

## Controller Directives

In addition to view data, the route controller action's return statement can also pass directives to render alternate views, set cookies and session variables, initiate redirects, call and render includes, cache route controller actions/views (or entire requests), and hand off the request to another controller for further processing.

### Alternate Views

By default, the server renders the view whose name matches that of the controller. To render a different view, use the `view` directive in your return statement:

```js
// article controller

export const edit = async (params) => {
  const article = await app.models.article.get({
    article: params.url.article,
    page: params.url.page
  })

return {
    local: article,
    // This tells the server to render app/views/article/edit.html
    view: 'edit'
  }
}
```

### Cookies

You set cookies by returning a `cookie` object within the controller action.

```js
export const handler = async (params) => {
  return {
    cookie: {
      // Cookie shorthand sets a cookie called username using the default cookie properties
      username: params.form.username,

// Sets a cookie called last_active that expires in 20 minutes
      last_active: {
        value: new Date().toISOString(),
        expires: 20
      }
    }
  }
}
```

Here's an example of a complete cookie object's default settings:

```js
myCookie = {
  value: 'myValue',

// Valid expiration options are:
  // 'now' - deletes an existing cookie
  // 'never' - current time plus 30 years, so effectively never
  // 'session' - expires at the end of the browser session (default)
  // [time in minutes] - expires this many minutes from now
  expires: 'session',

path: '/',

// citizen's cookies are accessible via HTTP/HTTPS only by default. To access a
  // cookie via JavaScript, set this to false.
  httpOnly: true,

// Cookies are insecure when set over HTTP and secure when set over HTTPS.
  // You can override that behavior globally with the https.secureCookies setting
  // in your config or on a case-by-case basis with this setting.
  secure: false
}
```

Once cookies are set on the client, they're available in `params.cookie` within controllers and simply `cookie` within the view:

```html
<!doctype html>
<html>
  <body>
    <section>
      Welcome, ${cookie.username}.
    </section>
  </body>
</html>
```

Cookie variables you set within your controller aren't immediately available within the `params.cookie` scope. citizen has to receive the context from the controller and send the response to the client first, so use a local instance of the variable if you need to access it during the same request.

#### Reserved Words

All cookies set by citizen start with the `ctzn_` prefix to avoid collisions. Don't start your cookie names with `ctzn_` and you should have no problems.

#### Proxy Header

If you use citizen behind a proxy, such as NGINX or Apache, make sure you have an HTTP `Forwarded` header in your server configuration so citizen's handling of secure cookies works correctly.

Here's an example of how you might set this up in NGINX:

```
location / {
  proxy_set_header Forwarded         "for=$remote_addr;host=$host;proto=$scheme;";
  proxy_pass                          http://127.0.0.1:8080;
}
```

### Session Variables

If sessions are enabled, you can access session variables via `params.session` in your controller or simply `session` within views. These local scopes reference the current user's session without having to pass a session ID.

By default, a session has four properties: `id`, `started`, `expires`, and `timer`. The session ID is also sent to the client as a cookie called `ctzn_session_id`.

Setting session variables is pretty much the same as setting cookie variables:

```js
return {
  session: {
    username: 'Danny',
    nickname: 'Doc'
  }
}
```

Like cookies, session variables you've just assigned aren't available during the same request within the `params.session` scope, so use a local instance if you need to access this data right away.

Sessions expire based on the `sessions.lifespan` config property, which represents the length of a session in minutes. The default is 20 minutes. The `timer` is reset with each request from the user. When the `timer` runs out, the session is deleted. Any client requests after that time will generate a new session ID and send a new session ID cookie to the client.

To forcibly clear and expire the current user's session:

```js
return {
  session: {
    expires: 'now'
  }
}
```

#### Reserved Words

All session variables set by citizen start with the `ctzn_` prefix to avoid collisions. Don't start your session variable names with `ctzn_` and you should have no problems.

### Redirects

You can pass redirect instructions to the server that will be initiated after the controller action is processed.

The `redirect` object takes a URL string in its shorthand version, or three options: `statusCode`, `url`, and `refresh`. If you don't provide a status code, citizen uses 302 (temporary redirect). The `refresh` option determines whether the redirect uses a [Location header](http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.30) or the non-standard [Refresh header](https://en.wikipedia.org/wiki/List_of_HTTP_header_fields#Refresh).

```js
// Initiate a temporary redirect using the Location header
return {
  redirect: '/login'
}

// Initiate a permanent redirect using the Refresh header, delaying the redirect by 5 seconds
return {
  redirect: {
    url: '/new-url',
    statusCode: 301,
    refresh: 5
  }
}
```

Unlike the Location header, if you use the `refresh` option, citizen will send a rendered view to the client because the redirect occurs client-side.

Using the Location header breaks (in my opinion) the Referer header because the Referer ends up being not the resource that initiated the redirect, but the resource prior to the page that initiated it. To get around this problem, citizen stores a session variable called `ctzn_referer` that contains the URL of the resource that initiated the redirect, which you can use to redirect users properly. For example, if an unauthenticated user attempts to access a secure page and you redirect them to a login form, the address of the secure page will be stored in `ctzn_referer` so you can send them there instead of the previous page.

If you haven't enabled sessions, citizen falls back to creating a cookie named `ctzn_referer` instead.

#### Proxy Header

If you use citizen behind a proxy, such as NGINX or Apache, make sure you have an HTTP `Forwarded` header in your server configuration so `ctzn_referer` works correctly.

Here's an example of how you might set this up in NGINX:

```
location / {
  proxy_set_header Forwarded         "for=$remote_addr;host=$host;proto=$scheme;";
  proxy_pass                          http://127.0.0.1:8080;
}
```

### HTTP Headers

You can set HTTP headers using the `header` directive:

```js
return {
  header: {
    'Cache-Control':  'max-age=86400',
    'Date':           new Date().toISOString()
  }
}
```

You can also set headers directly using Node's `response.setHeader()` method, but using citizen's `header` directive preserves those headers in the [request cache](#caching-requests-and-controller-actions), so they'll be applied whenever that controller action is pulled from the cache.

### Includes (Components)

citizen lets you use complete MVC patterns as includes, which are citizen's version of components. Each has its own route controller, model, and view(s). Includes can be used to perform an action or return a complete rendered view. Any route controller can be an include.

Let's say our article pattern's template has the following contents. The head section contains dynamic meta data, and the header's content changes depending on whether the user is logged in or not:

```html
<!doctype html>
<html>
  <head>
    <title>${local.metaData.title}</title>
    <meta name="description" content="${local.metaData.description}">
    <meta name="keywords" content="${local.metaData.keywords}">
    <link rel="stylesheet" type="text/css" href="site.css">
  </head>
  <body>
    <header>
      ${ cookie.username ? '<p>Welcome, ' + cookie.username + '</p>' : '<a href="/login">Login</a>' }
    </header>
    <main>
      <h1>${local.article.title} — Page ${url.page}</h1>
      <p>${local.article.summary}</p>
      <section>${local.article.text}</section>
    </main>
  </body>
</html>
```

It probably makes sense to use includes for the head section and header because you'll use that code everywhere, but rather than simple partials, you can create citizen includes. The head section can use its own model for populating the meta data, and since the header is different for authenticated users, let's pull that logic out of the view and put it in the header's controller. I like to follow the convention of starting partials with an underscore, but that's up to you:

```
app/
  controllers/
    routes/
      _head.js
      _header.js
      article.js
  models/
    _head.js
    article.js
  views/
    _head.html
    _header/
      _header.html
      _header-authenticated.html  // A different header for logged in users
    article.html
```

When the article controller is fired, it has to tell citizen which includes it needs. We do that with the `include` directive:

```js
// article controller

export const handler = async (params) => {
  // Get the article
  const article = await app.models.article.get({
    article: params.url.article,
    page: params.url.page
  })

return {
    local: {
      article: article
    },
    include: {
      // Include shorthand is a string containing the pathname to the desired route controller
      _head: '/_head/action/article',

// Long-form include notation can explicitly define a route controller, action, and view
      _header: {
        controller: '_header',

// If the username cookie exists, use the authenticated action. If not, use the default action.
        action: params.cookie.username ? 'authenticated' : 'handler'
      }
    }
  }
}
```

citizen include patterns have the same requirements as regular patterns, including a controller with a public action. The `include` directive above tells citizen to call the `_head` and `_header` controllers, pass them the same arguments that were passed to the `article` controller (params, request, response, context), render their respective views, and add the resulting views to the view context.

Here's what our head section controller might look like:

```js
// _head controller

export const article = async (params) => {
  let metaData = await app.models._head({ article: params.url.article })

return {
    local: {
      metaData: metaData
    }
  }
}
```

And the head section view:

```html
<head>
  <title>${local.metaData.title}</title>
  <meta name="description" content="${local.metaData.description}">
  <meta name="keywords" content="${local.metaData.keywords}">
  <link rel="stylesheet" type="text/css" href="site.css">
</head>
```

Here's what our header controller might look like:

```js
// _header controller

// No need for a return statement, and no need to specify the view
// because handler() renders the default view.
//
// Every route controller needs at least one action, even if it's empty.
export const handler = () => {}

export const authenticated = () => {
  return {
    view: '_header-authenticated'
  }
}
```

And the header views:

```html

<header>
  <a href="/login">Login</a>
</header>
```

&nbsp;

```html

<header>
  <p>Welcome, ${cookie.username}</p>
</header>
```

The rendered includes are stored in the `include` scope:

```html

<!doctype html>
<html>
  ${include._head}
  <body>
    ${include._header}
    <main>
      <h1>${local.title} — Page ${url.page}</h1>
      <p>${local.summary}</p>
      <section>${local.text}</section>
    </main>
  </body>
</html>
```

citizen includes are self-contained and delivered to the calling controller as a fully-rendered view. While they receive the same data (URL parameters, form inputs, request context, etc.) as the calling controller, data generated inside an include isn't passed back to the caller.

A pattern meant to be used as an include can be accessed via HTTP just like any other route controller. You could request the `_header` controller like so and receive a chunk of HTML or JSON as a response:

```
http://cleverna.me/_header
```

This is great for handling the first request server-side and then updating content with a client-side library.

#### Should I use a citizen include or a view partial?

citizen includes provide rich functionality, but they do have limitations and can be overkill in certain situations.

* **Do you only need to share a chunk of markup across different views?** Use a standard view partial as defined by whatever template engine you're using. The syntax is easy and you don't have to create a full MVC pattern like you would with a citizen include.
* **Do you need to loop over a chunk of markup to render a data set?** The server processes citizen includes and returns them as fully-rendered HTML (or JSON), not compiled templates. You can't loop over them and inject data like you can with view partials. However, you can build an include that returns a complete data set and view.
* **Do you need the ability to render different includes based on logic?** citizen includes can have multiple actions and views because they're full MVC patterns. Using a citizen include, you can call different actions and views based on logic and keep that logic in the controller where it belongs. Using view partials would require registering multiple partials and putting the logic in the view template.
* **Do you want the include to be accessible from the web?** Since a citizen include has a route controller, you can request it via HTTP like any other controller and get back HTML, JSON, or JSONP, which is great for AJAX requests and client-side rendering.

### Controller Chaining

citizen allows you to chain multiple route controllers together in series from a single request using the `next` directive. The requested controller passes its data and rendered view to a subsequent controller, adding its own data and rendering its own view.

You can string as many route controllers together in a single request as you'd like. Each route controller will have its data and view output stored in the `params.route.chain` object.

```js
// The index controller accepts the initial request and hands off execution to the article controller
export const handler = async (params) => {
  let user = await app.models.user.getUser({ userID: params.url.userID })

return {
    local: {
      user: user
    },

// Shorthand for next is a string containing the pathname to the route controller.
    // URL paramaters in this route will be parsed and handed to the next controller.
    next: '/article/My-Article/id/5'

// Or, you can be explicit, but without parameters
    next: {
      // Pass this request to app/controllers/routes/article.js
      controller: 'article',

// Specifying the action is optional. The next controller will use its default action, handler(), unless you specify a different action here.
      action: 'handler',

// Specifying the view is optional. The next controller will use its default view unless you tell it to use a different one.
      view: 'article'
    }

// You can also pass custom directives and data.
    doSomething: true
  }
}
```

Each controller in the chain has access to the previous controller's context and views. The last controller in the chain provides the final rendered view. A layout controller with all your site's global elements is a common use for this.

```js
// The article controller does its thing, then hands off execution to the _layout controller
export const handler = async (params, request, response, context) => {
  let article = await getArticle({ id: params.url.id })

// The context from the previous controller is available to you in the current controller.
  if ( context.doSomething ) {  // Or, params.route.chain.index.context
    await doSomething()
  }

return {
    local: {
      article: article
    },
    next: '/_layout'
  }
}
```

The rendered view of each controller in the chain is stored in the `route.chain` object:

```html

<h1>Welcome, ${local.user.username}!</h1>

<h1>${local.article.title}</h1>
<p>${local.article.summary}</p>
<section>${local.article.text}</section>
```

The layout controller handles the includes and renders its own view. Because it's the last controller in the chain, this rendered view is what will be sent to the client.

```js
// _layout controller

export const handler = async (params) => {
  return {
    include: {
      _head: '/_head',
      _header: {
        controller: '_header',
        action: params.cookie.username ? 'authenticated' : 'handler'
      },
      _footer: '/_footer
    }
  }
}
```

&nbsp;

```html

<!doctype html>
<html>
  ${include._head}
  <body>
    ${include._header}
    <main>
      
      ${route.chain.index.output}
      ${route.chain.article.output}

${Object.keys(route.chain).map( controller => { return route.chain[controller].output }).join('')}
    </main>
    ${include._footer}
  </body>
</html>
```

You can skip rendering a controller's view in the chain by setting the `view` directive to false:

```js
// This controller action won't render a view
export const handler = async () => {
  return {
    view: false,
    next: '/_layout'
  }
}
```

To bypass `next` in a request, add `/direct/true` to the URL.

```
http://cleverna.me/index/direct/true
```

The requested route controller's `next` directive will be ignored and its view will be returned to the client directly.

### Default Layout

As mentioned in the config section at the beginning of this document, you can specify a default layout controller in your config so you don't have to insert it at the end of every controller chain:

```json
{
  "citizen": {
    "layout": {
      "controller": "_layout",
      "view":       "_layout"
    }
  }
}
```

If you use this method, there's no need to use `next` for the layout. The last controller in the chain will always hand the request to the layout controller for final rendering.

## Performance

citizen provides several ways for you to improve your app's performance, most of which come at the cost of system resources (memory or CPU).

### Caching Requests and Controller Actions

In many cases, a requested URL or route controller action will generate the same view every time based on the same input parameters, so it doesn't make sense to run the controller chain and render the view from scratch for each request. citizen provides flexible caching capabilities to speed up your server side rendering via the `cache` directive.

#### cache.request

If a given request (URL) will result in the exact same rendered view with every request, you can cache that request with the `request` property. This is the fastest cache option because it pulls a fully rendered view from memory and skips all controller processing.

Let's say you chain the index, article, and layout controllers like we did above. If you put the following cache directive in your index controller, the requested URL's response will be cached and subsequent requests will skip the index, article, and layout controllers entirely.

```js
return {
  next: '/article',
  cache: {
    request: true
  }
}
```

For the request cache directive to work, it must be placed in the first controller in the chain; in other words, the original requested route controller (index in this case). It will be ignored in any subsequent controllers.

The URL serves as the cache key, so each of the following URLs would generate its own cache item:

http://cleverna.me/article

http://cleverna.me/article/My-Article

http://cleverna.me/article/My-Article/page/2

The example above is shorthand for default cache settings. The `cache.request` directive can also be an object with options:

```js
// Cache the requested route with some additional options
return {
  cache: {
    request: {
      // Optional. This setting lets the server respond with a 304 Not Modified
      // status if the cache content hasn't been updated since the client last
      // accessed the route. Defaults to the current time if not specified.
      lastModified: new Date().toISOString(),

// Optional. List of valid URL parameters that protects against accidental
      // caching of malformed URLs.
      urlParams: ['article', 'page'],

// Optional. Life of cached item in minutes. Default is 15 minutes.
      // For no expiration, set to 'application'.
      lifespan: 15,

// Optional. Reset the cached item's expiration timer whenever the item is
      // accessed, keeping it in the cache until traffic subsides. Default is true.
      resetOnAccess: true
    }
  }
}
```

#### cache.action

If a given route chain will vary across requests, you can still cache individual controller actions to speed up rendering using the `action` property.

```js
// Cache this controller action using the default settings
return {
  cache: {
    action: true
  }
}

// Cache this controller with additional options
return {
  cache: {
    action: {
      // These options function the same as request caching (see above)
      urlParams: ['article', 'page'],
      lifespan: 15,
      resetOnAccess: true
    }
  }
}
```

When you cache controller actions, their context is also cached. Setting a cookie or session variable in a cached controller action means all future requests for that action will set the same cookie or session variable—probably not something you want to do with user data.

#### cache.request and cache.action options

##### `lastModified`

This setting lets the server respond with a faster `304 Not Modified` response if the content of the request cache hasn't changed since the client last accessed it. By default, it's set to the time at which the request was cached, but you can specify a custom date in ISO format that reflects the last modification to the request's content.

```js
return {
  next: '/_layout',
  cache: {
    request: {
      // Use toISOString() to format your date appropriately
      lastModified: myDate.toISOString()   // 2015-03-05T08:59:51.491Z
    }
  }
}
```

##### `urlParams`

The `urlParams` property helps protect against invalid cache items (or worse: an attack meant to flood your server's resources by overloading the cache).

```js
return {
  next: '/_layout',
  cache: {
    request: {
      urlParams: ['article', 'page']
    }
  }
}
```

If we used the example above in our article controller, the following URLs would be cached because the "article" and "page" URL parameters are permitted:

http://cleverna.me/article

http://cleverna.me/article/My-Article-Title

http://cleverna.me/article/My-Article-Title/page/2

The following URLs wouldn't be cached, which is a good thing because it wouldn't take long for an attacker's script to loop over a URL and flood the cache:

http://cleverna.me/article/My-Article-Title/dosattack/1

http://cleverna.me/article/My-Article-Title/dosattack/2

http://cleverna.me/article/My-Article-Title/page/2/dosattack/3

The server logs a warning when invalid URL parameters are present, but continues processing without caching the result.

##### `lifespan`

This setting determines how long the request or controller action should remain in the cache, in minutes.

```js
return {
  cache: {
    request: {
      // This cached request will expire in 10 minutes
      lifespan: 10
    }
  }
}
```

##### `resetOnAccess`

Used with the `lifespan` setting, `resetOnAccess` will reset the timer of the route or controller cache whenever it's accessed, keeping it in the cache until traffic subsides. Defaults to `true`.

```js
return {
  cache: {
    request: {
      // This cached request will expire in 10 minutes, but if a request accesses it
      // before then, the cache timer will be reset to 10 minutes from now
      lifespan: 10,
      resetOnAccess: true
    }
  }
}
```

#### Cache Limitations and Warnings

In most cases, you'll probably want to choose between caching an entire request (URL) or caching individual controller actions, but not both.

When caching an include controller action, the route pathname pointing to that include is used as the cache key. If you use logic to render different views using the same controller action, the first rendered view will be cached. You can pass an additional URL parameter in such cases to get past this limitation and create a unique cache item for different include views.

```js
export const handler = async (context) => {
  return: {
    // Two different versions of the _header include will be cached becaues the URLs are unique
    include: context.authenticated ? '/_header/authenticated/true' : '/_header'
  }
}
```

citizen's cache is a RAM cache stored in the V8 heap, so be careful with your caching strategy. Use the `lifespan` and `resetOnAccess` options so URLs that receive a lot of traffic stay in the cache, while less popular URLs naturally fall out of the cache over time.

### Caching Static Assets

By caching static assets in memory, you speed up file serving considerably. To enable static asset caching for your app's public (web) directory, set `cache.static.enabled` to `true` in your config:

```json
{
  "citizen": {
    "cache": {
      "static": {
        "enabled": true
      }
    }
  }
}
```

citizen handles response headers automatically (ETags, 304 status codes, etc.) using each file's last modified date. Note that if a file changes after it's been cached, you'll need to clear the file cache using [cache.clear()](#clear-options) or restart the app.

To clear a file from the cache in a running app:

```js
app.cache.clear({ file: '/absolute/path/to/file.jpg' })
```

With static caching enabled, all static files citizen serves will be cached in the V8 heap, so keep an eye on your app's memory usage to make sure you're not using too many resources.

### Client-Side Caching

citizen automatically sets ETag headers for cached requests and static assets. You don't need to do anything to make them work. The Cache-Control header is entirely manual, however.

To set the Cache-Control header for static assets, use the `cache.control` setting in your config:

```json
{
  "citizen": {
    "cache": {
      "static":             true,
      "control": {
        "/css/global.css":  "max-age=86400",
        "/css/index.css":   "max-age=86400",
        "/js/global.js":    "max-age=86400",
        "/js/index.js":     "max-age=86400",
        "/images/logo.png": "max-age=31536000"
      }
    }
  }
}
```

The key name is the pathname that points to the static asset in your web directory. If your app's URL path is `/my/app`, then this value should be something like `/my/app/styles.css`. The value is the Cache-Control header value you want to assign to that asset.

You can use strings that match the exact pathname like above, or you can also use wildcards. Mixing the two is fine:

```json
{
  "citizen": {
    "cache": {
      "static":             true,
      "control": {
        "/css/*":           "max-age=86400",
        "/js/*":            "max-age=86400",
        "/images/logo.png": "max-age=31536000"
      }
    }
  }
}
```

Here's [a great tutorial on client-side caching](https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching) to help explain ETag and Cache-Control headers.

### Compression

Both dynamic routes and static assets can be compressed before sending them to the browser. To enable compression for clients that support it:

```json
{
  "citizen": {
    "compression": {
      "enabled": true
    }
  }
}
```

Proxies, firewalls, and other network circumstances can strip the request header that tells the server to provide compressed assets. You can force gzip or deflate for all clients like this:

```json
{
  "citizen": {
    "compression": {
      "enabled": true,
      "force":  "gzip"
    }
  }
}
```

If you have [request caching](#caching-requests-and-controller-actions) enabled, both the original (identity) and compressed (gzip and deflate) versions of the request will be cached, so your cache's memory utilization will increase.

## Forms

citizen includes basic request payload parsing. When a user submits a form, the parsed form data is available in your controller via `params.form`. If you want to use a third-party package to parse the form data yourself, you can disable form parsing in the config and access the raw payload via `request.payload`.

```js
// login controller

export const handler = (params) => {
  // Set some defaults for the login view
  params.form.username = ''
  params.form.password = ''
  params.form.remember = false
}

// Using a separate action in your controller for form submissions is probably a good idea
export const submit = async (params) => {
  let authenticate = await app.models.user.authenticate({
        username: params.form.username,
        password: params.form.password
      }),
      cookies = {}

if ( authenticate.success ) {
    if ( params.form.remember ) {
      cookies.username: authenticate.username
    }

return {
      cookies: cookies,
      redirect: '/'
    }
  } else {
    return {
      local: {
        message: 'Login failed.'
      }
    }
  }
}
```

If it's a multipart form containing a file, the form object passed to your controller will look something like this:

```js
{
  field1: 'bar',
  field2: 'buzz',
  fileField1: {
    filename    : 'file.png',
    contentType : 'image/png',
    binary      : <binary data>
  }
}
```

File contents are presented in binary format, so you'll need to use `Buffer.from(fileField1.binary, 'binary')` to create the actual file for storage.

You can pass global form settings via `citizen.form` in the config or at the controller action level via controller config (see below).

Use the `maxPayloadSize` config to limit form uploads. The following config sets the `maxFieldsSize` to 512k:

```js
{
  "citizen": {
    "forms": {
      "maxPayloadSize": 500000  // 0.5MB
    }
  }
}
```

The `maxPayloadSize` option includes text inputs and files in a multipart form in its calculations. citizen throws an error if form data exceeds this amount.

## Application Event Hooks

Certain events will occur throughout the life of your citizen application, or within each request. You can act on these  events, execute functions, set directives, and pass the results to the next event or controller via the `context` argument. For example, you might set a cookie at the beginning of every new session, or check for cookies at the beginning of every request and redirect the user to a login page if they're not authenticated.

To take advantage of these events, include a directory called "hooks" in your app with any or all of following modules and exports:

```
app/
  controllers/
    hooks/
      application.js  // exports start() and error()
      request.js      // exports start() and end()
      response.js     // exports start() and end()
      session.js      // exports start() and end()
```

`request.start()`, `request.end()`, and `response.start()` are called before your controller is fired, so the output from those events is passed from each one to the next, and ultimately to your controller via the `context` argument. Exactly what actions they perform and what they output—content, citizen directives, custom directives—is up to you.

All files and exports are optional. citizen parses them at startup and only calls them if they exist. For example, you could have only a request.js module that exports `start()`.

Here's an example of a request module that checks for a username cookie at the beginning of every request and redirects the user to the login page if it doesn't exist. We also avoid a redirect loop by making sure the requested controller isn't the login controller:

```js
// app/controllers/hooks/request.js

export const start = (params) => {
  if ( !params.cookie.username && params.route.controller !== 'login' ) {
    return {
      redirect = '/login'
    }
  }
}
```

`session.end` is slightly different in terms of the arguments it receives, which consists only of a copy of the expired session (no longer active):

```js
// app/controllers/hooks/session.js

export const end = (expiredSession) => {
  // do something whenever a session ends
}
```

## Cross-Origin Resource Sharing (CORS)

By default, all controllers respond to requests from the host only. citizen supports cross-domain HTTP requests via access control headers.

To enable cross-domain access for individual controller actions, add a `cors` object with the necessary headers to your controller's exports:

```js
export const config = {
  // Each controller action can have its own CORS headers
  handler: {
    cors: {
      'Access-Control-Allow-Origin': 'http://www.foreignhost.com',
      'Access-Control-Expose-Headers': 'X-My-Custom-Header, X-Another-Custom-Header',
      'Access-Control-Max-Age': 600,
      'Access-Control-Allow-Credentials': 'true',
      'Access-Control-Allow-Methods': 'OPTIONS, PUT',
      'Access-Control-Allow-Headers': 'Content-Type',
      'Vary': 'Origin'
    }
  }
}
```

Why not just use the [HTTP Headers](#http-headers) directive or set them manually with `response.setHeader()`? When citizen receives a request from an origin other than the host, it checks for the `cors` export in your controller to provide a preflight response without you having to write your own logic within the controller action. You can of course check `request.method` and write logic to handle this manually if you prefer.

For more details on CORS, check out [the W3C spec](http://www.w3.org/TR/cors/) and [the Mozilla Developer Network](https://developer.mozilla.org/en-US/docs/HTTP/Access_control_CORS).

### Proxy Header

If you use citizen behind a proxy, such as NGINX or Apache, make sure you have a `Forwarded` header in your server configuration so citizen handles CORS requests correctly. Different protocols (HTTPS on your load balancer and HTTP in your citizen app) will cause CORS requests to fail without these headers.

Here's an example of how you might set this up in NGINX:

```
location / {
  proxy_set_header Forwarded  "for=$remote_addr;host=$host;proto=$scheme;";
  proxy_pass                  http://127.0.0.1:3000;
}
```

## Object Caching

citizen has a built-in application cache where you can store basically anything: strings, objects, buffers, static files, etc.

### cache.set(options)

You can store any object in citizen's cache. The benefits of using `cache` over storing content in your own global app variables are built-in cache expiration and extension, as well as wrappers for reading, parsing, and storing file content.

citizen's default cache time is 15 minutes, which you can change in the config (see [Configuration](#configuration)). Cached item lifespans are extended whenever they're accessed unless you pass `resetOnAccess: false` or change that setting in the config.

```js
// Cache a string in the default app scope for 15 minutes (default). Keys
// must be unique within a given scope.
app.cache.set({
  key: 'welcome-message',
  value: 'Welcome to my site.'
})

// Cache a string under a custom scope, which is used for retrieving or clearing
// multiple cache items at once. Keys must be unique within a given scope.
// Reserved scope names are "app", "routes", and "files".
app.cache.set({
  key: 'welcome-message',
  scope: 'site-messages',
  value: 'Welcome to our site.'
})

// Cache a string for the life of the application.
app.cache.set({
  key: 'welcome-message',
  value: 'Welcome to my site.',
  lifespan: 'application'
})

// Cache a file buffer using the file path as the key. This is a wrapper for
// fs.readFile and fs.readFileSync paired with citizen's cache function.
// Optionally, tell citizen to perform a synchronous file read operation and
// use an encoding different from the default (UTF-8).
app.cache.set({
  file: '/path/to/articles.txt',
  synchronous: true,
  encoding: 'CP-1252'
})

// Cache a file with a custom key. Optionally, parse the JSON and store the
// parsed object in the cache instead of the raw buffer. Expire the cache
// after 10 minutes, regardless of whether the cache is accessed or not.
app.cache.set({
  file: '/path/to/articles.json',
  key: 'articles',
  parseJSON: true,
  lifespan: 10,
  resetOnAccess: false
})
```

`app`, `routes`, and `files` are reserved scope names, so you can't use them for your own custom scopes.

### cache.exists(options)

This is a way to check for the existence of a given key or scope in the cache without resetting the cache timer on that item. Returns `false` if a match isn't found.

```js
// Check for the existence of the specified key
let keyExists = app.cache.exists({ key: 'welcome-message' })          // keyExists is true
let keyExists = app.cache.exists({ file: '/path/to/articles.txt' })   // keyExists is true
let keyExists = app.cache.exists({ file: 'articles' })                // keyExists is true
let keyExists = app.cache.exists({ key: 'foo' })                      // keyExists is false

// Check the specified scope for the specified key
let keyExists = app.cache.exists({
  scope: 'site-messages',
  key: 'welcome-message'
})
// keyExists is true

// Check if the specified scope exists and contains items
let scopeExists = app.cache.exists({
  scope: 'site-messages'
})
// scopeExists is true

// Check if the route cache has any instances of the specified route
let controllerExists = app.cache.exists({
  route: '/article'
})
```

### cache.get(options)

Retrieve an individual key or an entire scope. Returns `false` if the requested item doesn't exist. If `resetOnAccess` was true when the item was cached, using retrieve() will reset the cache clock and extend the life of the cached item. If a scope is retrieved, all items in that scope will have their cache timers reset.

Optionally, you can override the `resetOnAccess` attribute when retrieving a cache item by specifying it inline.

```js
// Retrieve the specified key from the default (app) scope
let welcomeMessage = app.cache.get({
  key: 'welcome-message'
})

// Retrieve the specified key from the specified scope and reset its cache timer
// even if resetOnAccess was initially set to false when it was stored
let welcomeMessage = app.cache.get({
  scope: 'site-messages',
  key: 'welcome-message',
  resetOnAccess: true
})

// Retrieve all keys from the specified scope
let siteMessages = app.cache.get({
  scope: 'site-messages'
})

// Retrieve a cached file
let articles = app.cache.get({
  file: '/path/to/articles.txt'
})

// Retrieve a cached file with its custom key
let articles = app.cache.get({
  file: 'articles'
})
```

### cache.clear(options)

Clear a cache object using a key or a scope.

```js
// Store some cache items

app.cache.set({
  key: 'welcome-message',
  scope: 'site-messages',
  value: 'Welcome to our site.'
})

app.cache.set({
  key: 'goodbye-message',
  scope: 'site-messages',
  value: 'Thanks for visiting!'
})

app.cache.set({
  file: '/path/to/articles.txt',
  synchronous: true
})

// Clear the welcome message from its custom scope cache
app.cache.clear({ scope: 'site-messages', key: 'welcome-message' })

// Clear all messages from the cache using their custom scope
app.cache.clear({ scope: 'site-messages' })

// Clear the articles cache from the file scope
app.cache.clear({ file: '/path/to/articles.txt' })
```

`cache.clear()` can also be used to delete cached requests and controller actions.

```js
app.cache.clear({
  route: '/article/My-Article/page/2'
})

// Clear the entire route scope
app.cache.clear({ scope: 'routes' })

// Clear the entire file scope
app.cache.clear({ scope: 'files' })

// Clear the entire cache
app.cache.clear()
```

## Logs

citizen's `log()` function is exposed for use in your app via `app.log()`.

### log(options)

Makes it easy to log comments to either the console or a file (or both) in a way that's dependent on the mode of the framework.

When citizen is in production mode, `log()` does nothing by default. In development mode, `log()` will log whatever you pass to it. This means you can place it throughout your application's code and it will only write to the log in development mode. You can override this behavior globally with the log settings in your config file or inline with the `console` or `file` options when calling `log()`.

```js
app.log({
  // Optional. Valid settings are "status" (default) or "error".
  type: 'status',

// Optional string. Applies a label to your log item.
  label: 'Log output',

// The content of your log. If it's anything other than a string or
  // number, log() will run util.inspect on it and dump the contents.
  contents: someObject,

// Optional. Enables console logs.
  console: true,

// Optional. Enables file logging.
  file: false,

// Optional. File name you'd like to write your log to.
  file: 'my-log-file.log',

// Optional. Disables the timestamp that normally appears in front of the log
  timestamp: false
})
```

Log files appear in the directory you specify in `config.citizen.directories.logs`.

## Debugging

**Warning: `development` mode is inherently insecure. Don't use it in a production environment.**

If you set `"mode": "development"` in your config file, citizen dumps all major operations to the console.

You can also dump the request context to the view by setting `development.debug.view` in your config file to `true`, or use the `ctzn_debug` URL parameter on a per-request basis:

```js
// config file: always dumps debug output in the view
{
  "citizen": {
    "development": {
      "debug": {
        "view": true
      }
    }
  }
}
```

By default, citizen dumps the pattern's complete context. You can specify the exact object to debug with the `ctzn_inspect` URL parameter:

```
// Dumps the server params object
http://www.cleverna.me/article/id/237/page/2/ctzn_debug/true/ctzn_inspect/params

// Dumps the user's session scope
http://www.cleverna.me/article/id/237/page/2/ctzn_debug/true/ctzn_inspect/params.session
```

The debug output traverses objects 4 levels deep by default. To display deeper output, use the `development.debug.depth` setting in your config file or append `ctzn_debugDepth` to the URL. Debug rendering will take longer the deeper you go.

```js
// config file: debug 4 levels deep
{
  "citizen": {
    "development": {
      "debug": {
        "depth": 6
      }
    }
  }
}

// URL
// http://www.cleverna.me/article/id/237/page/2/ctzn_debug/true/ctzn_debugDepth/4
```

In `development` mode, you must specify the `ctzn_debug` URL parameter to display debug output. Debug output is disabled in production mode.

## Utilities

The util directory within the citizen package has some helpful utilities.

### scaffold

#### skeleton

Creates a complete skeleton of a citizen app with a functional index pattern and error templates.

```bash
$ node node_modules/citizen/util/scaffold skeleton
```

Resulting file structure:

```
app/
  config/
    citizen.json
  controllers/
    hooks/
      application.js
      request.js
      response.js
      session.js
    routes/
      index.js
  models/
    index.js
  views/
    error/
      404.html
      500.html
      ENOENT.html
      error.html
    index.html
  start.js
web/
```

Run `node node_modules/citizen/util/scaffold skeleton -h` for options.

#### pattern

Creates a complete citizen MVC pattern. The pattern command takes a pattern name and options:

```bash
$ node node_modules/citizen/util/scaffold pattern [options] [pattern]
```

For example, `node scaffold pattern article` will create the following pattern:

```
app/
  controllers/
    routes/
      article.js
  models/
    article.js
  views/
    article/
      article.html
```

Use `node node_modules/citizen/util/scaffold pattern -h` to see all available options for customizing your patterns.

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