Rails browser based log file tail-er

admin_controller.rb

class AdminController < ApplicationController
  layout 'admin'

  def logs
    log = File.join(Rails.root, "log", "#{Rails.env}.log")
    @lines = `tail -1024 #{log}`.split(/\n/)
  end
end

log.rake

require 'open3'

namespace :log do
  task :tail => [:environment] do
    log = File.join(Rails.root, "log", "#{ Rails.env }.log")

    Open3.popen3("tail -f #{log}") do |stdin, stdout, stderr, wait_thr|
      begin
        stdout.each do |s|
          if s =~ /^Started/
            s = "<span class='request-start'>#{s}</span>"
          elsif s =~ /^Completed/
            s = "<span class='request-end'>#{s}</span>"
          end
          s = "#{s}<br/>"
          WebsocketRails[:log].trigger 'update', s
        end
      rescue Exception => ex
        Rails.logger.info ex.message
        Rails.logger.info ex.backtrace
      ensure
        stdin.close
      end

      exit_status = wait_thr.value
    end
  end
end

logs.css.scss

#logs{
  font-family: monospace;
  
  .request-start{
    color: blue;
    font-weight: bold;
  }

  .request-end{
    color: green;
    font-weight: bold;
  }
}

logs.html.erb

<%= javascript_include_tag "admin/logs" %>
<%= stylesheet_link_tag "admin/logs" %>

<div id='logs'>
  <% @lines.each do |line| %>
    <% if line =~ /^Started/ %>
      <span class='request-start'><%= line %></span>
    <% elsif line =~ /^Completed/ %>
      <span class='request-end'><%= line %></span>
    <% else %>
      <%= line %>
    <% end %>
    <br/>
  <% end %>
</div>

logs.js.coffee

class Logs
  constructor: ->
    @scroll()
    
    logChannel = window.dispatcher.subscribe 'log'
    logChannel.bind 'update', (data) =>
      $('#logs').append data
      unless (window.scrollY + window.innerHeight) < $("#logs")[0].scrollHeight
        @scroll()

  scroll: ->
    $(document).scrollTop($("#logs")[0].scrollHeight)

$ ->
  new Logs()