= loggability

home   :: http://deveiate.org/projects/loggability
code   :: http://bitbucket.org/ged/loggability
docs   :: http://deveiate.org/code/loggability
github :: http://github.com/ged/loggability


== Description

A composable logging system built on the standard Logger library.

You can add Loggability to large libraries and systems, then hook everything
up later when you know where you want logs to be written, at what level of
severity, and in which format.

An example:

    # Load a bunch of libraries
	require 'strelka'
	require 'inversion'
	require 'treequel'
	require 'loggability'

    # Now tell everything that's using Loggability to log to an HTML
	# log file at INFO level
	Loggability.write_to( '/usr/local/www/htdocs/log.html' )
	Loggability.format_as( :html )
	Loggability.level = :info


== Prerequisites

* Ruby 1.9.3 or better, Rubinius 2.0 or better

It will probably work under any other interpreter in which Logger works, but
it's only tested in the above.


== Installation

    $ gem install loggability


== Usage

Loggability is split up into two parts: {log hosts}[rdoc-ref:Loggability::LogHost]
and {log clients}[rdoc-ref:Loggability::LogClient]. A <b>log
host</b> is an object that contains a Logger instance that will be used to
log stuff. A <b>log client</b> is an object that will write logging messages to a
particular <b>log host</b>'s Logger.

Both parts require that you extend the object with Loggability.

=== Setting Up A 'Log Host'

To install a Logger into an object, you use the +log_as+ declaration with a
Symbol that will be used as the key for the object's Logger:

    module MyProject
        extend Loggability
        log_as :my_project
    end

After declaring itself as a log host, it will have an associated Loggability::Logger
object that's a wrapper around a Logger instance:

    MyProject.logger
    # => #<Loggability::Logger:0x4e0c :my_project ...>

Since it's still a Logger object, you can call all the regular Logger methods:

    MyProject.logger.level = Logger::WARN

    MyProject.logger.debug("Created logger")
    MyProject.logger.info("Program started")
    MyProject.logger.warn("Nothing to do!")

    begin
        File.each_line(path) do |line|
            unless line =~ /^(\w+) = (.*)$/
                MyProject.logger.error("Line in wrong format: #{line}")
            end
        end
    rescue => err
        MyProject.logger.fatal("Caught exception; exiting")
        MyProject.logger.fatal(err)
    end

or use a few new convenience methods for changing the logging level:

    MyProject.logger.level = :debug

...installing a different formatter:

    MyProject.logger.format_as( :html )

...changing the output destination:

    log_messages = []
    MyProject.logger.output_to( log_messages )

...{and more}[rdoc-ref:Loggability::Logger].


=== Setting Up A 'Log Client'

To add an object that will log to your log host, after you <tt>extend Loggability</tt>,
use the +log_to+ declaration to hook up the object (and instances of the object if
you use +log_to+ in a Class) to the log host you specify:

    class MyProject::Server
        extend Loggability
        log_to :my_project

        def initialize( config={} )
            self.log.debug "Creating a server with config: %p" % [ config ]
            #...
        end
    end

You can fetch any object's Logger through the Loggability object:

    Loggability[ MyProject ]
    # => #<Loggability::Logger:0x007f88ca3bf510 ...>

    Loggability[ MyProject::Server ]
    # => #<Loggability::Logger:0x007f88ca3bf510 ...>

Calling the object's <tt>#log</tt> method will return a Proxy for its host's Logger object that will include the object's name in the log messages 'progname'.

You can also use the <b>log host</b> itself as the argument to +log_to+:

    class MyProject::Client
        extend Loggability
        log_to MyProject
    end


=== Aggregate Logging

If you have several <b>log hosts</b>, and you want to affect them all simultaneously,
you can do that using the aggregate functions of Loggability. They're the same as the
methods on Loggability::Logger:

    # Set all logs to log at INFO level
    Loggability.level = :info
    
    # Write HTML logs
    Loggability.format_with( :html )
    
    # Log everything to the same logfile
    Loggability.output_to( "/tmp/my_project_log.html" )


== Contributing

You can check out the current development source with
Mercurial[http://bitbucket.org/ged/loggability], or if you prefer Git, via
{its Github mirror}[https://github.com/ged/loggability].

After checking out the source, run:

    $ rake newb

This task will install any missing dependencies, run the tests/specs,
and generate the API documentation.


== License

Copyright (c) 2012, Michael Granger
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice,
  this list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

* Neither the name of the author/s, nor the names of the project's
  contributors may be used to endorse or promote products derived from this
  software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.