loggability

home	hg.sr.ht/~ged/Loggability
code	hg.sr.ht/~ged/Loggability/browse
docs	deveiate.org/code/loggability
github	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 that use Loggability
require 'strelka'
require 'inversion'
require 'treequel'
require 'loggability'

# Set up our own library
module MyProject
    extend Loggability
    log_as :my_project

    class Server
        extend Loggability
        log_to :my_project

        def initialize
            self.log.debug "Listening."
        end
    end

end

# 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 2.4+

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 and log clients. A log host is an object that contains a Logger instance that will be used to log stuff. A log client is an object that will write logging messages to a particular log host’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.

Setting Up A ‘Log Client’

To add an object that will log to your log host, after you extend Loggability, 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 #log 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 log host itself as the argument to log_to:

class MyProject::Client
    extend Loggability
    log_to MyProject
end

Aggregate Logging

If you have several log hosts, 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" )

Temporarily Overriding Logging Behavior

Sometimes you want to log one particular chunk of code at a different level, or to a different destination, and then restore everything back to the way it was afterwards.

Loggability has a few ways of doing that:

# Log only fatal errors...
Loggability.with_level( :fatal ) do
    ...
end

# Log everything to an array for the block
logs = []
Loggability.outputting_to( logs ) do
    ...
end

# Log using the HTML formatter
Loggability.formatted_with( :html ) do
    ...
end

# Or chain them together:
Loggability.with_level( :debug ).outputting_to( $stderr ).formatted_with( :color ) do
    Client.connect!
end

You can also make the override only apply to the loggers for a subset of log hosts:

# Log only fatal errors on the loggers for the specified two classes
Loggability.with_level( :fatal ).for_loggers( ACME::Model, ACME::Adapter ) do
  ACME.start_up
end

# Debug a particular class:
Loggability.with_level( :debug ).for_logger( ACME::Server ) do
  ACME.start_up
end

Configurability

Loggability has support for the Configurability library, which does the same thing for configuration that Loggability does for logging.

You can configure all registered loggers from the ‘logging’ section of the config:

logging:
  __default__: warn STDERR
  mongrel2: info STDOUT (html)
  strelka: debug (html)
  inversion: error /var/log/templating.log (default)

The format of the value of each logger is:

SEVERITY [TARGET] [(FORMAT)]

where:

SEVERITY	The log level; one of: debug, info, warn, error, or fatal
TARGET	The destination for log messages. This can be the path to a log file, or one of 'STDOUT' or 'STDERR', which get mapped to the equivalent filehandle. Optional.
FORMAT	The name of one of the formatters. Loggability comes with default (plaintext), color (ANSI colored text), and html formatters. Optional.

If the special key default is included, its config will be used to set global defaults before the individual configs are applied.

If either of the optional values is unspecified, it is left unchanged from what it was before configuration.

RSpec Helpers

Loggability includes a couple of helper functions for RSpec that allow you to control log levels for particular specs.

To use it, require loggability/spechelpers in your specs (we put it in the spec helpers file) and then include the helpers from your RSpec config:

require 'loggability/spechelpers'
RSpec.configure do |c|
  # ...
  c.include( Loggability::SpecHelpers )
end

This will install a before and after :all hook to set the logging levels before each example group and then reset it before moving on to the next group.

You can also access the bodies of those hooks manually:

setup_logging( level=:fatal ) reset_logging()

The helpers also allow you to set logging levels for a whole example group, for particular contexts, or even for individual examples using RSpec’s metadata hash syntax:

# Set logging to ‘error’ level for each example in this group describe MyClass, logging: :error do

# ...but for examples in this context, set it to 'fatal'
context 'created with a target', log: :fatal do

  # ...except for this one, which logs at 'debug' level
  it "does something to it", logging: :debug do

  end

  it "does some other stuff, too"

end

end

The setup_logging helper also provides support for displaying the logs inline with spec formatters for which outputting the logs to STDERR isn’t optimal. The only one that’s currently uses it is the ‘webkit’ formatter, but it should be easy to adapt to other HTML displays as well.

It looks for either an HTML_LOGGING environment variable, or for the TM_FILENAME variable to be set to a filename that ends with ‘_spec.rb’ (for Textmate’s rspec runner). In either of those conditions, it will set up logging output to go to a thread-local Array called ‘logger-output’, log using the ‘html’ formatter, and set the log level to ‘debug’.

This can be used to append logs to each example when the formatter builds the output.

Contributing

You can check out the current development source with Mercurial, or if you prefer Git, via its Github mirror.

Author

• Michael Granger ged@faeriemud.org

License

Copyright © 2012-2020, 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.