fail.rb

require 'rubygems'
require 'sinatra/base'

class Fail < Sinatra::Base
  error do
    "Failed"
  end

  get "/" do
    raise "OMG"
  end
end

if __FILE__ == $0
  Fail.run! :host => 'localhost', :port => 4567
end

# This is incorrect:
#
# $ ruby fail.rb 
# == Sinatra/0.9.4 has taken the stage on 4567 for development with backup from Thin
# >> Thin web server (v1.2.4 codename Flaming Astroboy)
# >> Maximum connections set to 1024
# >> Listening on localhost:4567, CTRL+C to stop
# !! Unexpected error while processing request: OMG
# !! Unexpected error while processing request: OMG
# !! Unexpected error while processing request: OMG
# 
# ...and the page is not at all friendly: in firefox it's empty, and in Safari it says "Safari can’t open the page “http://localhost:4567/” because the server unexpectedly dropped the connection."

fail_ok.rb

require 'rubygems'
require 'sinatra'

error do
  "Failed"
end

get "/" do
  raise "OMG"
end

# This is correct behavior:
#
# $ ruby fail_ok.rb 
# == Sinatra/0.9.4 has taken the stage on 4567 for development with backup from Thin
# >> Thin web server (v1.2.4 codename Flaming Astroboy)
# >> Maximum connections set to 1024
# >> Listening on 0.0.0.0:4567, CTRL+C to stop
# RuntimeError - OMG:
#  fail_ok.rb:9:in `GET /'
#  fail_ok.rb:8RuntimeError: OMG
#   fail_ok.rb:9:in `GET /'
#   /Library/Ruby/Gems/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:779:in `call'
#   /Library/Ruby/Gems/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:779:in `route'
#   /Library/Ruby/Gems/1.8/gems/sinatra-0.9.4/lib/sinatra/base.rb:474:in `instance_eval'
# ...