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Erlang web MVC, now featuring Comet

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README.md

Chicago Boss: Start small, dream big

Build Status

Chicago Boss is a server framework inspired by Rails and written in Erlang. It offers all the conveniences of modern web development, including Comet. What sets Chicago Boss apart from other non-Erlang frameworks is that it can handle large amounts of traffic without any drop in performance. What sets Chicago Boss apart from other Erlang frameworks is that it is easy to set up and use.

WARNING: Chicago Boss does not work with Erlang R16B03 due to an error in erl_syntax

60-second Quickstart

After downloading and extracting, type

make
make app PROJECT=mynewproject
cd ../mynewproject
./init-dev.sh

For Windows, type

windows-make.bat
windows-make.bat app PROJECT=mynewproject
cd ..\mynewproject
start-server.bat

Then visit http://localhost:8001/ in your browser. Congratulations, you have a web server. There will be a lot of PROGRESS REPORTs on your console but everything should be running smoothly.

The project name should be a legal Erlang atom, i.e. start with a lowercase letter and contain only letters, digits, and underscores (for easy compatibility is recommended name the project dir and app name the same).

Dependencies

Admin Interface

You probably want to install the CB admin interface. Download it from

<https://github.com/ChicagoBoss/cb_admin>

Upgrades

Uprading used to be a pain but now it is easy. See README_UPGRADE

Database Setup

By default CB uses an in-memory database that needs no configuration. To start working with an actual database, See README_DATABASE

Philosophy and Features

Why another web framework? Because Rails apps are slow and Node apps are messy. Chicago Boss takes advantage of functional programming and under-the-hood compiler magic to provide clean, understandable controller logic, Django-style templates, and an ORM based on Erlang's parameterized modules. The best part is that the network I/O is 100% asynchronous so you can seamlessly integrate Comet endpoints into your app, and you never have to worry about a slow database query dragging down unrelated requests.

CB ships with all the tools you need to build a feature-ful website, including sessions, URL routing, filtering requests and post-processing responses, frameworks for sending and receiving email, JSON generation, Comet via long-poll and message queues, and internationalization (i18n). Read on for details.

Databases. Chicago Boss currently supports MySQL, PostgreSQL, Tokyo Tyrant, Mnesia, MongoDB, and Riak. In CB 0.5.4 and later, you can mix and match databases by configuring Boss to use vertical shards. For SQL databases, the conventions are similar to Rails (plural nouns for the table names, object_id for foreign keys, etc.).

BossRecords. Boss's take on ActiveRecord is called a BossRecord, which is an Erlang parameterized module on steroids. You instantiate a BossRecord like a regular parameterized module:

Article = article:new('id', "This is a title", "This is a body")

But then CB generates functions and attaches them to BossRecords, so you can write code like

{ok, SavedArticle} = Article:save()

Before saving to the database, the save() function will call a function called validation_tests(), where you can perform custom validation logic.

CB also generates getter functions which can be invoked directly in templates, so in your template you can write things like

{{ article.title }}

Speaking of which...

Templates. Chicago Boss uses ErlyDTL, an Erlang implentation of Django template language. In fact, Chicago Boss originated with a rewrite of ErlyDTL, and the same person maintains both projects so you always get the latest ErlyDTL features. Templates can access and loop over values stored in proplists, dictionaries, and BossRecords, so you can move data from the database to your templates with a minimum of massaging.

In addition, templates are tightly integrated with Boss's i18n machinery. The admin interface automatically parses templates for translatable strings, and Boss can choose which language to serve based on the request's Accept-Languages header and the calculated translation coverage for a particular page. Multi-language websites are easy to develop with Chicago Boss.

Controllers. Erlang's pattern-matching is a perfect fit for writing controller logic. Your controllers are passed the URL method (GET, POST) and a list of URL tokens, and just need to return a tuple telling Boss what to do, for example:

  • {ok, Variables} - render the default template with Variables
  • {render_other, Variables} - render another template
  • {redirect, URL} - redirect the request
  • {json, Proplist} - encode the Proplist as JSON and send to the client
  • {output, Data} - send Data to the client

If you come from Rails, you'll instantly notice the benefit of Erlang's language design: you don't need an ugly case request.method statement inside every action, you never have atrocities like render and return, and you can always see every variable that is in scope. In CB apps, controller logic is always concise and usually a pleasure to read.

Sessions. You can configure sessions to be stored in memory (ETS) or in an Mnesia database. The boss_session and boss_flash modules provide functions for storing and retrieving session information.

Routes. By default, Chicago Boss uses the same routing conventions as Ruby on Rails (/controller/action/id). You can customize the routes and provide a base URL in the priv/application.routes file. Of course, most routing occurs with the pattern-matching controller logic, e.g.

posts('GET', ["category", Category]) ->

You can then generate URLs to match controller patterns in your templates like so:

{% url action="posts" category="some category" %}

Email. Chicago Boss ships with a miniature MVC for sending multipart emails. Emails can be templated with ErlyDTL, and it is easy to provide plain-text and HTML versions of the same email. In testing environments, email can be sent directly to the recipient, or in production can be relayed to an SMTP server.

A Chicago Boss server can also receive email over SMTP. Each email address maps to a function in your incoming mail controller, so it is easy to write well-organized email applications. Your email controller has access to the exact same resources as your web controllers, including database requests, BossRecord instantiation, and the message queue; web and email are fully integrated.

Comet. It's simple to write a Comet endpoint in Chicago Boss. Unlike any other language, Erlang gives you the benefits of asynchronous network communcation without using callbacks. Here is a trivial example of a long-poll controller:

longpoll('GET', [Channel]) ->
    {ok, Timestamp, Messages} = boss_mq:pull(Channel, last),
    {json, [{timestamp, Timestamp}, {messages, Messages}]}.

The call to pull blocks until a message is received. Because processes are cheap in Erlang, the overhead of keeping alive a blocking request is very small (just a few kilobytes of memory, compared to megabytes in Rails). You can thus keep alive thousands of Comet request with just a few megabytes of memory. Also notice that the controller logic remains nice and clean (no callbacks). We can perform an arbitrary sequence of asynchronous network requests without increasing the scope level.

Events. An interesting feature of Chicago Boss is the events API called BossNews. With it, you can watch a record or a set of records for changes, then execute a callback when a change is witnessed. Combined with long-polling, you can provide a real-time view of your database on your website. Events can also be used to provide a clean separation of business logic and notification logic.

Tests. Chicago Boss has a kick-ass testing framework. Once you try it you won't go back. That's all I'll say for now.

Future Work

Most of Chicago Boss's planned features have been implemented at this point. It hasn't really been tested in a distributed environment, but it's already running on a few public-facing websites, and many more internal websites (or so I am told). It would be nice to add more databases (such as CouchDB and Oracle) and support horizontal sharding. The last main feature before 1.0 will be the ability to distribute apps written in Chicago Boss as standalone OTP applications.

Further Reading

See the FAQ and API files located at

http://www.chicagoboss.org/

If you need help getting started, check the new pdf tutorial:

http://www.chicagoboss.org/tutorial.pdf

Be sure to also check the wiki

https://github.com/ChicagoBoss/ChicagoBoss/wiki

There's also the mailing list:

http://groups.google.com/group/chicagoboss

If you want to contribute to CB

CODING_STANDARDS.md

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