NAME
    App::MFILE::WWW - Generic web front-end with demo app

VERSION
    Version 0.088

LICENSE
    This software is distributed under the "BSD 3-Clause" license, the text
    of which can be found in the file named `COPYING' in the top-level
    distro directory. The license text is also reprodued at the top of each
    source file.

DESCRIPTION
    This distro contains a generic framework for developing web front-ends
    to REST resources. The framework consists of a web server based on Plack
    and Web::Machine, CSS and HTML for the "app frame" (on-screen area where
    the application's "screens" are displayed), and "widgets" for defining
    the application's login dialog, menus, forms, and actions.

    For illustration, the distro contains a demo app that authenticates
    against App::Dochazka::REST and contains a single menu, a simple form,
    and a sample action.

INTRODUCTION
    The full stack, of which App::MFILE::WWW is a part, consists of the
    following components:

    * Database engine
        For storing application data.

    * Perl DBI
        For interfacing between the Perl code and the database engine.

    * REST server
        A REST server, such as App::Dochazka::REST, implements a data model
        and provides a HTTP interface to that model.

    * optional CLI client/frontend
        An optional Command Line Interface (frontend) can provide a command
        line interface to the REST server.

    * WWW client/frontend
        The WWW frontend, built based on this distro, is a web server that
        serves HTML, CSS, and JavaScript code to users to provide them with
        a menu-driven "browser experience" of the application.

    Conceptually, the clients act as proxies between the user and the REST
    server. Taking this one step further, the REST server itself is a proxy
    between the client and the database engine.

    The philosophy behind this RESTful design is that you, the user, have
    the freedom and the flexibility to write your own client, on any
    platform, in any language -- however you see fit. From a technical
    perspective, the strict separation between the server and clients makes
    the application as a whole more robust.

REQUEST-RESPONSE CYCLE
    The HTTP request-response cycle is implemented as follows:

    * nginx listens for incoming connections on port 80/443 of the server
    * When a connection comes in, nginx decrypts it and forwards it to a
    high-numbered port where a PSGI-compatible HTTP server (such as Starman)
    is listening
    * The HTTP server takes the connection and passes it to the Plack
    middleware. The key middleware component is Plack::Middleware::Session,
    which assigns an ID to the session, stores whatever data the server-side
    code needs to associate with the session, links the session to the
    user's browser via a cookie, and provides the application a hook (in the
    Plack environment stored in the HTTP request) to access the session data
    * if the connection is asking for static content (defined as anything in
    `images/', `css/', or `js/'), that content is served immediately and the
    request doesn't even make it into our Perl code
    * any other path is considered dynamic content and is passed to
    Web::Machine for processing -- Web::Machine implements the HTTP standard
    as a state machine
    * the Web::Machine state machine takes the incoming request and runs it
    through several functions that are overlayed in
    App::MFILE::WWW::Resource - an appropriate HTTP error code is returned
    if the request doesn't make it through the state machine. Along the way,
    log messages are written to the log.
    * as part of the state machine, all incoming requests are subject to
    "authorization" (in the HTTP sense, which actually means
    authentication). First, the session data is examined to determine if the
    request belongs to an existing authorized session. If it doesn't, the
    request is treated as a login/logout attempt -- the session is cleared
    and control passes to the JavaScript side, which, lacking a currentUser
    object, displays the login dialog.
    * once an authorized session is established, there are two types of
    requests: GET and POST
    * incoming GET requests happen whenever the page is reloaded - in an
    authorized session, this causes the main menu to be displayed, but all
    static content (CSS and JavaScript modules) are reloaded for a "clean
    slate", as if the user had just logged in.
    * Note that App::MFILE::WWW pays no attention to the URI - if the user
    enters a path (e.g. http://mfile.site/some/bogus/path), this will be
    treated like any other page (re)load and the path is simply ignored.
    * if the session is expired or invalid, any incoming GET request will
    cause the login dialog to be displayed.
    * well-formed POST requests are assumed to be AJAX calls and are
    directed to the `process_post' routine, which first examines the request
    body, which must adhere to a simple structure:
            { method: "GET", path: "employee/current", body: { ... } }

        where 'method' is any HTTP method accepted by the REST server,
        'path' is a valid path to a REST server resource, and 'body' is the
        content body to be sent in the HTTP request to the REST server.
        Provided the request is properly authorized and the body is
        well-formed, the request is forwarded to the REST server via the
        App::MFILE package's `rest_req' routine and the REST server's
        response is sent back to the user's browser, where it is processed
        by the JavaScript code.

    * under ordinary operation, the user will spend 99% of her time
    interacting with the JavaScript code running in her browser, which will
    communicate asynchronously as needed with the REST server via AJAX
    calls.

  Development notes
    UTF-8
    In conformance with the JSON standard, all data passing to and from the
    server are assumed to be encoded in UTF-8. Users who need to use
    non-ASCII characters should check their browser's settings.

  Deployment
    To minimize latency, App::MFILE::WWW can be deployed on the same server
    as the back-end (e.g. App::Dochazka::REST), but this is not required.

PACKAGE VARIABLES
    For convenience, the following variables are declared with package
    scope:

FUNCTIONS
  init
    Initialization routine - run from `bin/mfile-www', the server startup
    script. This routine loads configuration parameters from files in the
    distro and site configuration directories, and sets up logging.

