Railsで特定のURLのときだけログファイルを分ける

versions

• rails (5.2.1)
• request_store (1.4.1)

code

gem 'request_store'

config/initializers/foo_logger.rb

class FooLogger < ActiveSupport::Logger
  PATH = "#{Rails.root}/log/#{Rails.env}_foo.log"

  # LEVEL = Logger::UNKNOWN
  # LEVEL = Logger::FATAL
  # LEVEL = Logger::ERROR
  # LEVEL = Logger::WARN
  LEVEL = Logger::INFO
  # LEVEL = Logger::DEBUG

  def self.logger
    @logger ||= \
      new(PATH).tap do |l|
        l.level     = LEVEL
        l.formatter = Rails.logger.formatter
      end
  end

  def self.activate
    RequestStore.store[:FooLogger_active] = true
  end

  def active?
    !!RequestStore.store[:FooLogger_active]
  end

  def add(severity, message = nil, progname = nil, &block)
    return true unless active?
    super
  end
end

Rails.logger.extend ActiveSupport::Logger.broadcast(FooLogger.logger)

config/initializers/foo_loggable.rb

module FooLoggable
  def call(env)
    if env['PATH_INFO'] =~ Regexp.new('/foo')
      HostLogger.activate
    end
    super
  end
end

Rails::Rack::Logger.prepend FooLoggable