WebMCP 2.1.0 Documentation

WebMCP is a web development framework based on the Lua programming language (read more about Lua here).

Requirements

WebMCP has been developed on Linux and FreeBSD. Using it with Mac OS X is untested as of yet; Microsoft Windows is not supported. Beside the operating system, the only mandatory dependencies for WebMCP are the programming language Lua version 5.2 or 5.3, the Moonbridge Network Server for Lua Applications version 1.0.1 or higher, PostgreSQL version 8.2 or higher, and a C compiler.

Installation

After downloading the tar.gz package, unpack it, enter the unpacked directory and type make. If you use Mac OS X or if you experience problems during compilation, you need to edit the Makefile.options file prior to compilation. The framework itself will be available in the framework/ directory, while a demo application is available in the demo-app/ directory. The framework.precompiled/ and demo-app.precompiled/ directories will contain a version with all Lua files being byte-code pre-compiled, which can be used instead. You may copy these directories (with cp -L to follow links) to any other place you like. Don't forget to setup a database, and make the tmp/ directory of the application writable for user who executes WebMCP. Good luck and have fun!

Configuration, initializers, and request handling

WebMCP uses the Moonbridge Network Server to handle HTTP requests. The Moonbridge Network Server listens to a TCP port and passes control to WebMCP by calling request.handler(...) for each request. However, before each request is processed, WebMCP will initialize the environment. This initialization includes tasks such as

For each request, it is also possible to execute filters. Filters can be used to

Filters and initializers are created by adding files in the application's directory structure. The filename determins the execution order of otherwise equally ranked initializers and/or filters. It is a common idiom to start the filename of a filter or initializer with a two digit number to be easily able to change the execution order when desired. Filters and initializers are executed both before and after a request. Each file must contain a command execute.inner(). The part before that command is executed before the request, and the part after that command is executed after the request.

The Moonbridge server creates forks (i.e. clones) of the application server process (i.e. the whole Lua engine including all libraries and variables) in order to handle concurrent requests. Certain initializations may be performed before forking, other initializations must be performed after forking. For this purpose, WebMCP allows an application to provide so-called "pre-fork" and "post-fork" initializers. The application's configuration files as well as its pre-fork initializers are executed before forking. The application's post-fork initializers are executed after forking. In particular, any libraries that open file or network handles during initialization must not be loaded before the server process is forked. Opening database connections must be performed after forking as well. WebMCP follows the following execution order (directory structure is explained further down):

  1. Loading all WebMCP libraries except the "multirand" library (multirand opens /dev/urandom and thus must not be loaded prior to forking)
  2. Executing the selected configuration file: config/configuration_name.lua
  3. Executing all pre-fork initializers (both those in the app/_prefork/ and those in the app/application_name/_prefork/ directory) until call of execute.inner() within each initializer
  4. The Moonbridge Network Server forks the process (i.e. cloning the whole Lua machine)
    Note: no file handles or network connections must be opened prior to this point!
  5. Loading WebMCP's "multirand" library
  6. Executing all post-fork initializers (both those in the app/_postfork/ and those in the app/application_name/_postfork/ directory) until call of execute.inner() within each initializer
  7. For each request:
  8. Resuming execution of all post-fork initializers in reverse order from that position where execute.inner() had been called
  9. Resuming execution of all pre-fork initializers in reverse order from that position where execute.inner() had been called

As a minimum configuration, the used configuration file or pre-fork initializer should at least contain a listen{...} call, e.g.:

listen{
  { proto = "tcp", host = "::", port = 8080 },
  { proto = "tcp", host = "0.0.0.0", port = 8080 }
}
execute.inner()  -- only use this line if done in pre-fork initializer

Using the atom library

Lua itself has only very few built-in data types. The atom library gives support for extra data types. Currently the following extra data types are provided:

In addition the following pseudo-types are existent, corresponding to Lua's base types:

Both atom.integer and atom.number refer to Lua's base type “number”.

New values of atom data types are created by either calling atom.type:load(string_representation) or by calling atom.type{...}, e.g. atom.date{year=1970, month=1, day=1}. You can dump any atom value as a string by calling atom.dump(value) and later reload it with atom.type:load(string).

Using the Object-Relational Mapper “mondelefant”

The library “mondelefant” shipping with WebMCP can be used to access PostgreSQL databases. It also serves as an Object-Relational Mapper (ORM). The database connection is usually configured in the config file (e.g. in config/devel.lua):

config.db = { engine="postgresql", dbname="webmcp_demo" }

In addition to configuring the database, it must be opened within a post-fork initializer (e.g. in app/_postfork/01_database.lua):

_G.db = assert(mondelefant.connect(config.db))
function mondelefant.class_prototype:get_db_conn() return db end
execute.inner()

The parameters for mondelefant.connect are directly passed to PostgreSQL's client library libpq. See PostgreSQL's documentation on PQconnect for information about supported parameters.

To define a model to be used within a WebMCP application, create a file named with the name of the model and .lua as extension in the model/ directory of your application. The most basic definition of a model (named “movie” in this example) is:

Movie = mondelefant.new_class()
Movie.table = 'movie'

Note: Model classes are always written CamelCase, while the name of the file in model/ is written lower_case.

To select objects from the database, the mondelefant library provides a selector framework:

local s = Movie:new_selector()
s:add_where{ 'id = ?', param.get_id() }
s:single_object_mode()  -- return single object instead of list
local movie = s:exec()

A short form of the above query would be:

local movie = Movie:new_selector():add_where{ 'id = ?', param.get_id() }:single_object_mode():exec()

For more examples about how to use the model system, please take a look at the demo application.

The Model-View-Action (MVA) concept

As opposed to other web application frameworks, WebMCP does not use a Model-View-Controller (MVC) concept, but a Model-View-Action (MVA) concept.

Models

The models in MVA are like the models in MVC; they are used to access data, which is stored in a relational database (PostgreSQL), in an object oriented way. Methods provided by the corresponding classes be used to alter stored objects or execute any other associated program code. Models are usually defined in a file with a lowercase filename ending with ".lua" in the models/ directory of the application. The corresponding model name (i.e. class name) must be written in CamelCase, e.g. "models/my_model.lua" should define a model class named "MyModel". The simplest model is created by calling mondelefant.new_class() and subsequently setting the table attribute of the returned class.

-- filename: model/customer_receipt.lua
CustomerReceipt = mondelefant.new_class()
CustomerReceipt.table = "custreceipt"

Methods such as :add_reference(...) can be used to further modify or extend the class.

Views

The views in the MVA concept are different from the views in the MVC concept. As WebMCP has no controllers, the views are responsible for processing the GET/POST parameters from the webbrowser, fetching the data to be displayed, and creating the output by directly writing HTML to slots of a layout (see slot.select(...), slot.put(...), and slot.put_into(...) or by calling helper functions for the user interface (those functions beginning with "ui."). Views are stored in files with the file path "app/application_name/module_name/view_name.lua". When their corresponding URL, e.g. "http://hostname:port/module_name/view_name.html", is requested, the code in that file gets executed (after calling appropriate filters). After the execution of the view has finished (and after all filters have finished their execution too), the slot data will be inserted into placeholder sections in the selected layout file. The layout file defaults to app/application_name/_layout/default.html" but may be changed using the slot.set_layout(...) function.

Actions

Actions are similar to views, but supposed to change data in the database, hence only callable by HTTP POST requests. They are also responsible for processing the POST parameters from the webbrowser. They can modify the database, but instead of rendering a page to be displayed, they just return a status code string (via Lua's return statement, where true can also be used instead of "ok", and false instead of "error"). Depending on the status string there will be an internal forward or an HTTP 303 redirect to a view. When calling an action via a POST request, additional POST parameters, which are usually added by hidden form fields, determine the view to be displayed for each status string returned by the action. See the routing parameter to the ui.form{...} function for further details.

Layouts

Templates for HTML documents to be returned by views are stored at the path "app/application_name/_layout/layout_name.html", relative to the application base path. The default layout name is "default". For system errors, the layout name "system_error" is used. A sample layout is given as follows:

<!DOCTYPE HTML>
<html>
  <head>
    <title><!-- WEBMCP SLOTNODIV title --></title>
    <link rel="stylesheet" type="text/css" media="screen" href="__BASEURL__/static/style.css"/>
  </head>
  <body>
    <!-- WEBMCP SLOT content -->
  </body>
</html>

The following elements in a layout file get replaced automatically:

Internationalization/Localization

To translate certain strings in your application, simply use the underscore function. A language can be selected with locale.set{lang = "code"} where code is a language code. The translations for strings are expected to be contained in files "locale/translations.language_code.lua". These files should return a table that maps strings to their corresponding translation:

return{
["Are you sure?"] = "Bist Du sicher?";
["User '#{name}' created"] = "Benutzer '#{name}' created";
}

Such translation files can be automatically created with the langtool.lua program, found in the framework's bin/ directory.

Directory structure of a WebMCP application

Summarizing information from the previous section, we get the following directory structure for a WebMCP application:

Starting your application

Ensure that the moonbridge binary is within your system's search path and that the moonbridge_http.lua file is included in the LUA_PATH or linked into the framework's lib/ directory (alternatively the MOONBR_LUA_PATH option might be set accordingly at compile-time of the Moonbridge Network Server). To start an application, call the mcp.lua executable (found in framework/bin/mcp.lua) with the following arguments:

  1. Path of the WebMCP framework directory, e.g. ./framework
  2. Path of your application's directory, e.g. ./demo-app
  3. Name of your applicaiton (usually main)
  4. Name of configuration (e.g. devel to use config/devel.lua)

Automatically generated reference for the WebMCP environment