completely k.i.s.s technique to do realtime log tailing in a live rails' app from the browser

tail-f.rb

### blogged @ http://dojo4.com/blog/easy-cheasy-realtime-log-tailing-in-a-rails-admin-view



### the su controller action


  def logs
    log = File.join(Rails.root, "log", "#{ Rails.env }.log")
    @lines = `tail -1024 #{ log }`.split(/\n/).reverse
    respond_to do |wants|
      wants.html{ render }
      wants.json{ render(:json => @lines) }
    end
  end


### the su view

<<-TEH_VIEW

  <%= link_to 'Stop', 'javascript:void("stop")', :id => :stop %>
  <%= link_to 'Start', 'javascript:void("start")', :id => :start, :style => 'display:none' %>
  <br />
  <hr />

  <pre id='logs'>
    <%= @lines.join("\n") %>
  </pre>

  <script>
    jq(function(){
      var start = jq('#start');
      var stop = jq('#stop');

      var milliseconds = 1024;
      var id = null;

      var update = function(){
        id = setInterval(function(){
          var lines = App.ajax('logs?silence=logger');
          jq('#logs').html(lines.join("\n"));
        }, milliseconds);
      };

      start.click(function(){ start.toggle(); stop.toggle(); update(); });
      stop.click(function(){ stop.toggle(); start.toggle(); clearInterval(id); });

      update();
    });
  </script>


TEH_VIEW


### the neat-o logger that let's us bludgeon the lame ass rails' logger for certain requests


# inspired by
#
#   http://dennisreimann.de/blog/silencing-the-rails-log-on-a-per-action-basis/
#
# and
#
#   http://stackoverflow.com/questions/6312448/how-to-disable-logging-of-asset-pipeline-sprockets-messages-in-rails-3-1
#
# file: ./config/initializers/silenceable_logger.rb
#
# then, in some crazy js polling action use
#
#   ajax('/poll?silence=logger')
#
  NullLogger = Logger.new('/dev/null')

  Rails::Rack::Logger.class_eval do
    def call_with_silenced_logger(env = {})
      silence = (
        env['QUERY_STRING'] =~ %r[silence=logger]iomx ||
        env['PATH_INFO'] =~ %r[(^/assets\b)|(^/su/logs\b)]iomx
      )

      if silence
        begin
          a = Rails.logger
          b = ActionController::Base.logger
          Rails.logger = NullLogger
          ActionController::Base.logger =  NullLogger
          call_without_silenced_logger(env)
        ensure
          Rails.logger = a
          ActionController::Base.logger = b
        end
      else
        call_without_silenced_logger(env)
      end
    end

    alias_method_chain(:call, :silenced_logger)
  end

  Rails.application.assets.logger = NullLogger




### finally, the required configuration to use the above logger selectively

    class Application < Rails::Application
      config.autoload_paths += %w( lib app app/presenters )

      require File.join(Rails.root, 'lib/silenceable_logger.rb')
      config.middleware.swap(Rails::Rack::Logger, SilenceableLogger)