NAME
    AtomMQ - An atompub server that supports the message queue/bus model.

VERSION
    version 0.0301

SYNOPSIS
        #!/usr/bin/perl
        use AtomMQ;
        my $db_info = { dsn => 'dbi:SQLite:dbname=/path/to/foo.db' };
        my $server = AtomMQ->new(feed => 'MyCoolFeed', db_info => $db_info);
        $server->run;

DESCRIPTION
    AtomMQ is an atompub server that supports the message queue/bus model.
    Throughout this document, I will use the term message when refering to
    an atom feed entry, since the point of this module is to use atompub for
    messaging. AtomMQ extends Inoue's Atompub::Server which extends
    Miyagawa's XML::Atom::Server. Can you feel the love already?

    To get started, just copy the code from the "SYNOPSIS" to a file. You
    now have a shiny new atompub server with a feed named MyCoolFeed. You
    can configure your web server to run it via CGI or as a mod_perl
    handler. My recommendation is to run it in a PSGI environment. See the
    "PSGI" section for directions. To create more feeds, just copy that file
    and change 'MyCoolFeed' to 'MyOtherFeed'.

    To publish a message to AtomMQ, make a HTTP POST request:

        $ curl -d '<entry> <title>allo</title> <content type="xhtml">
          <div xmlns="http://www.w3.org/1999/xhtml" >an important message</div>
          </content> </entry>' http://localhost/cgi-bin/mycoolfeed

    To retrieve messages, make a HTTP GET request:

        $ curl http://localhost/cgi-bin/mycoolfeed

    That will get all the messages since the feed was created. Lets say you
    are running a client that polls the feed and processes messages. If this
    client dies, you will not want it to process all the messages again when
    it comes back up. So clients are responsible for maintaining and
    persisting the id of the last message they processed. This allows a
    client to request only messages that came after the message with the
    given id. They can do this by passing a Xlastid header:

        $ curl -H 'Xlastid: 42' http://localhost/cgi-bin/mycoolfeed

    That will return only messages that came after the message that had id
    42.

METHODS
  new
    Arguments: $feed, $db_info, $auto_create_db

    This is the AtomMQ constructor. The required arguments are $feed and
    $db_info. $feed is the name of the feed. $db_info is a hashref
    containing the database connection info as described in "connect_info"
    in DBIx::Class::Storage::DBI. It must at least contain a dsn entry.
    $auto_create_db defaults to 1. Set it to 0 if you don't want AtomMQ to
    attempt to create the db table for you. You can leave it set to 1 even
    if the db table already exists. Setting it to 0 improves performance
    slightly. See "DATABASE" for more info. Example:

        my $server = AtomMQ->new(feed => 'MyCoolFeed', db_info => {
            dsn      => 'dbi:SQLite:dbname=/path/to/foo.db',
            user     => 'joe',
            password => 'momma',
        });

  run
    Arguments: None

    Call this method to start the server.

DATABASE
    AtomMQ depends on a database to store its data. The db_info you pass to
    the constructor must point to a database which you have write privileges
    to. Only one table named atommq_entry is required. This table will be
    created automagically for you if it doesn't already exist. Of course for
    that to work, you will need create table privileges. You can also create
    the table yourself if you like. Here is an example sql command for
    creating the table in sqlite:

        CREATE TABLE atommq_entry (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            feed TEXT NOT NULL,
            title TEXT NOT NULL,
            content TEXT NOT NULL
        );

    The feed, title and content columns can be of type TEXT or VARCHAR and
    can be any size you want. All databases supported by DBIx::Class are
    supported, which are most major databases including postgresql, sqlite,
    mysql and oracle.

PSGI
    If you have the need for speed, then this section is for you. AtomMQ can
    be run in a persistent PSGI environment via Plack. This is the
    recommended way to run AtomMQ, but it takes slightly more work. You will
    need to have Plack and CGI::Emulate::PSGI installed. Copy the following
    to mycoolfeed.fcgi:

        #!/usr/bin/perl
        use AtomMQ;
        use CGI::Emulate::PSGI;
        my $app = CGI::Emulate::PSGI->handler(sub {
            my $db_info = { dsn => 'dbi:SQLite:dbname=/path/to/foo.db' };
            my $server = AtomMQ->new(feed => 'MyCoolFeed', db_info => $db_info);
            $server->run
        });

    Then you can run:

        plackup -p 5000 mycoolfeed.fcgi

    Now AtomMQ is running on port 5000 via the HTTP::Server::PSGI web
    server. If you want to run in a FastCGI environment using your favorite
    web server, then you can run:

        plackup -s FCGI --listen /tmp/fcgi.sock mycoolfeed.fcgi

    Then configure your web server accordingly. Here is an example lighttpd
    configuration:

        fastcgi.server += (
            ".fcgi" => (( "socket" => "/tmp/fcgi.sock" ))
        )

MOTIVATION
    I am a big fan of messaging systems because they make it so easy to
    create scalable systems. Existing message brokers are great for creating
    message queues. But once a consumer reads a message off of a queue, it
    is gone. I needed a system to publish events such that multiple
    heterogeneous services could subscribe to them. So I really needed a
    message bus, not a message queue. I know for example I could have used
    something called topics in ActiveMQ, but they are extremely flakey in my
    experience. Actually, I have found ActiveMQ to be broken in general. An
    instance I manage has to be restarted at least twice a week. AtomMQ on
    the other hand will be extremely stable, because it is so simple. It is
    in essence just an interface to a database. As long as your database and
    web server are up, AtomMQ will be there for you. She will not let you
    down. And there are all sorts of ways to add redundancy to databases and
    web heads. Another advantage of using AtomMQ is that atompub is an RFC
    standard. Everyone already has a client for it, their browser. Aren't
    standards great! By the way, if you just need message queues, try
    POE::Component::MessageQueue. It rocks. If you need a message bus, give
    AtomMQ a shot.

AUTHOR
    Naveed Massjouni <naveed.massjouni@rackspace.com>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2010 by Naveed Massjouni.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

