Hanami provides a built-in logger that is used by default as a general-purpose logger and, if you’re building a web application, a Rack request logger too.

You can tweak its configuration in your App class, but typically, the defaults should serve you well. Hanami sets up its logger differently depending on the environments:

• In development environment logger logs to $stdout in :debug mode
• In test environment logger logs to logs/test.log in :debug mode
• In production environment logger logs to $stdout in :info mode using :json formatter

Changing default config

The logger configuration is namespaced as config.logger and you can access it in your App class. If you change these settings, they will be set for all environments by default.

Here’s how you could set :json formatter for all environments:

# config/app.rb
require "hanami"
module Bookshelf
  class App < Hanami::App
    # This would change formatter for all environments to `:json`
    config.logger.formatter = :json
  end
end

You can fine-tune your logger on a per-environment basis using the convenient environment method:

# config/app.rb
require "hanami"
module Bookshelf
  class App < Hanami::App
    environment(:development) do
      config.logger.stream = root.join("log").join("development.log")
    end
  end
end

Log filters

In order to avoid having sensitive information leak to your log streams, Hanami configures log filtering to filter out the following keys:

• _csrf
• password
• password_confirmation

If you want to add more keys, you can simply do it like this:

# config/app.rb
require "hanami"
module Bookshelf
  class App < Hanami::App
    config.logger.filters = config.logger.filters + ["token"]
  end
end

Colorized output

If you want colorized log levels in your output, you can do so via colorize option:

# config/app.rb
require "hanami"
module Bookshelf
  class App < Hanami::App
    environment(:development) do
      config.logger.options[:colorize] = true
    end
  end
end

You can also customize text log template to use custom colors:

require "hanami"
module Bookshelf
  class App < Hanami::App
    environment(:development) do
      config.logger.options[:colorize] = true
      config.logger.template = <<~TMPL
        [<blue>%<progname>s</blue>] [%<severity>s] [<green>%<time>s</green>] %<message>s %<payload>s
      TMPL
    end
  end
end

Customizing logging destinations

You may want to handle certain type of log entries in a special way. One example of this could be logging unexpected crashes to a special file to be able to see them more easily when running tests. You can achieve this by adding a dedicated logging backend.

Here’s what you could add to your spec_helper.rb to have any exception that’s being logged while tests are running go to log/exceptions.log file:

# spec/spec_helper.rb
Hanami.logger.add_backend(
  stream: Hanami.app.root.join("log").join("exceptions.log"), log_if: :exception?
)
begin
  raise "Oh noez"
rescue => e
  Hanami.logger.error(e)
end