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App-MFILE-WWW-0.136
River stage one • 1 direct dependent • 1 total dependent
/ App::MFILE::WWW

NAME

App::MFILE::WWW - Web UI development toolkit with prototype demo app

VERSION

Version 0.136

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.

SYNOPSIS

    $ man mfile-www
    $ mfile-www
    $ firefox http://localhost:5001

DESCRIPTION

This distro contains a foundation/framework/toolkit for developing the "front end" portion of web applications.

App::MFILE::WWW is a Plack application that provides a HTTP request-response handler (based on Web::Machine), CSS and HTML source code for an in-browser "screen", and JavaScript code for displaying various "widgets" (menus, forms, etc.) in that screen and for processing user input from within those widgets.

In addition, infrastructure is included (but need not be used) for user authentication, session management, and communication with a backend server via AJAX calls.

Front ends built with App::MFILE::WWW will typicaly be menu-driven, consisting exclusively of fixed-width Unicode text, and capable of being controlled from the keyboard, without the use of a mouse. The overall look-and-feel is reminiscent of the text terminal era.

The distro comes with a prototype (demo) application to illustrate how the various widgets are used.

QUICK START (DEMO)

App::MFILE::WWW can be run as a standalone HTTP server providing a self-contained demo application.

Assuming App::MFILE::WWW has been installed properly, this mode of operation can be started by running mfile-www, as a normal user (even 'nobody'), with no arguments or options:

    $ mfile-www

The start-up script will write information about its state to the standard output. This includes the location of its log file, the port where the HTTP server is listening (default is 5001), etc. For a detailed description of what happens when the start-up script is run, see the POD of mfile-www itself - e.g. "man mfile-www".

WRITING A DERIVED CLIENT

Now that you have the demo running, you probably want to roll up your sleeves and start using this to write your own application. Now is a good time to read about the basic architecture of applications based on App::MFILE::WWW.

Stack

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 an 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 from 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 frontends (or "clients") act as proxies between the user and the REST server in this setup. Taking this one step further, the REST server itself is a proxy between the client and the database engine.

Strict separation between backend (REST server) and frontend (clients) is a technical measure that makes the application as a whole more robust.

DERIVED WWW CLIENTS

When you write your own web frontend using this distro, from App::MFILE::WWW's perspective it is a "derived client" and will be reffered to as such in this document.

Derived client operation

In a derived-client scenario, App::MFILE::WWW is basically used as a library, or framework, upon which the "real" application is built.

The derived-client handling is triggered by providing the --ddist command-line option, i.e.

    $ mfile-www --ddist=App-Dochazka-WWW

Where 'App-Dochazka-WWW' refers to the Perl module App::Dochazka::WWW, which is assumed to contain the derived client source code.

So, in the first place it is necessary to create such a Perl module. It should have a sharedir configured and present. One such derived client, App::Dochazka::WWW, is available on CPAN.

IMPLEMENTATION DETAILS

HTTP 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

The App::MFILE::WWW codebase has two parts, or "sides": the "Perl side" and the "JavaScript side". Control passes from the Perl side to the JavaScript side

  • synchronously whenever the user (re)loads the page

  • asynchronously whenever the user triggers an AJAX call

JavaScript side

Modular (RequireJS)

The JavaScript code is modular. Each code module has its own file and modules are loaded asynchronously by RequireJS.

Unit testing (QUnit)

The JavaScript code included in this package is set up for unit testing using the QUnit http://qunitjs.com/ library.

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.