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J. D. wrote:

> What is the best way to debug fastcgi scripts?

Remote breakpoints might be a good option here -- they let you connect 
an irb shell to any given point of your application meaning you can just 
use Ruby's regular introspection facilities to have a look at local 
variables, instance variables, call traces, methods and modify Object 
altogether. Attached to this mail you will find the latest mostly stable 
version which will turn into a release soon. If everything goes well 
this should be merged back into dev-utils and be available in Ruby On 
Rails with a few nice goodies (a link to  launch a breakpoint from the 
error page you get in your browser when an uncaught exception of your 
application occurs) very soon.


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 nameinding_of_caller.rb"
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 filenameinding_of_caller.rb"

begin
  require 'simplecc'
rescue LoadError
  def Continuation.create(*args, &block)
    cc  il; result  allcc {|c| cc  ; block.call(cc) if block and args.empty?}
    result || rgs
    return *[cc, *result]
  end
end

# This method returns the binding of the method that called your
# method. It will raise an Exception when you're not inside a method.
#
# It's used like this:
#   def inc_counter(amount  )
#     Binding.of_caller do |binding|
#       # Create a lambda that will increase the variable 'counter'
#       # in the caller of this method when called.
#       inc  val("lambda { |arg| counter + rg }", binding)
#       # We can refer to amount from inside this block safely.
#       inc.call(amount)
#     end
#     # No other statements can go here. Put them inside the block.
#   end
#   counter  
#   2.times { inc_counter }
#   counter # 2
#
# Binding.of_caller must be the last statement in the method.
# This means that you will have to put everything you want to
# do after the call to Binding.of_caller into the block of it.
# This should be no problem however, because Ruby has closures.
# If you don't do this an Exception will be raised. Because of
# the way that Binding.of_caller is implemented it has to be
# done this way.
def Binding.of_caller(&block)
  old_critical  hread.critical
  Thread.critical  rue
  count  
  cc, result, error, extra_data  ontinuation.create(nil, nil)
  error.call if error

  tracer  ambda do |*args|
    type, context, extra_data  rgs[0], args[4], args
    if type "return"
      count + 
      # First this method and then calling one will return --
      # the trace event of the second event gets the context
      # of the method which called the method that called this
      # method.
      if count 2
        # It would be nice if we could restore the trace_func
        # that was set before we swapped in our own one, but
        # this is impossible without overloading set_trace_func
        # in current Ruby.
        set_trace_func(nil)
        cc.call(eval("binding", context), nil, extra_data)
      end
    elsif type "line" then
      nil
    elsif type "c-return" and extra_data[3] :set_trace_func then
      nil
    else
      set_trace_func(nil)
      error_msg  Binding.of_caller used in non-method context or " +
        "trailing statements of method using it aren't in the block."
      cc.call(nil, lambda { raise(ArgumentError, error_msg) }, nil)
    end
  end

  unless result
    set_trace_func(tracer)
    return nil
  else
    Thread.critical  ld_critical
    case block.arity
      when 1 then yield(result)
      else yield(result, extra_data)        
    end
  end
end

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 namereakpoint.rb"
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 filenamereakpoint.rb"

# The Breakpoint library provides the convenience of
# being able to inspect and modify state, diagnose
# bugs all via IRB by simply setting breakpoints in
# your applications by the call of a method.
#
# This library was written and is supported by me,
# Florian Gross. I can be reached at flgr / ccan.de
# and enjoy getting feedback about my libraries.
#
# The whole library (including breakpoint_client.rb
# and binding_of_caller.rb) is licensed under the
# same license that Ruby uses. (Which is currently
# either the GNU General Public License or a custom
# one that allows for commercial usage.) If you for
# some good reason need to use this under another
# license please contact me.

require 'irb'
require 'binding_of_caller'
require 'drb'
require 'drb/acl'

module Breakpoint
  extend self

  # This will pop up an interactive ruby session at a
  # pre-defined break point in a Ruby application. In
  # this session you can examine the environment of
  # the break point.
  #
  # You can get a list of variables in the context using
  # local_variables via +local_variables+. You can then
  # examine their values by typing their names.
  #
  # You can have a look at the call stack via +caller+.
  #
  # The source code around the location where the breakpoint
  # was executed can be examined via +source_lines+. Its
  # argument specifies how much lines of context to display.
  # The default amount of context is 5 lines. Note that
  # the call to +source_lines+ can raise an exception when
  # it isn't able to read in the source code.
  #
  # breakpoints can also return a value. They will execute
  # a supplied block for getting a default return value.
  # A custom value can be returned from the session by doing
  # +throw(:debug_return, value)+.
  #
  # You can also give names to break points which will be
  # used in the message that is displayed upon execution 
  # of them.
  #
  # Here's a sample of how breakpoints should be placed:
  #
  #   class Person
  #     def initialize(name, age)
  #       @name, @age  ame, age
  #       breakpoint("Person#initialize")
  #     end
  #
  #     attr_reader :age
  #     def name
  #       breakpoint("Person#name") { @name }
  #     end
  #   end
  #
  #   person  erson.new("Random Person", 23)
  #   puts "Name: #{person.name}"
  #
  # And here is a sample debug session:
  #
  #   Executing break point "Person#initialize" at file.rb:4 in `initialize'
  #   irb(#<Person:0x292fbe8>):001:0> local_variables
  #   ["name", "age", "_", "__"]
  #   irb(#<Person:0x292fbe8>):002:0> [name, age]
  #   ["Random Person", 23]
  #   irb(#<Person:0x292fbe8>):003:0> [@name, @age]
  #   ["Random Person", 23]
  #   irb(#<Person:0x292fbe8>):004:0> self
  #   #<Person:0x292fbe8 @age#, @nameandom Person">
  #   irb(#<Person:0x292fbe8>):005:0> @age + ; self
  #   #<Person:0x292fbe8 @age$, @nameandom Person">
  #   irb(#<Person:0x292fbe8>):006:0> exit
  #   Executing break point "Person#name" at file.rb:9 in `name'
  #   irb(#<Person:0x292fbe8>):001:0> throw(:debug_return, "Overriden name")
  #   Name: Overriden name
  #
  # Breakpoint sessions will automatically have a few
  # convenience methods available. See Breakpoint::CommandBundle
  # for a list of them.
  #
  # Breakpoints can also be used remotely over sockets.
  # This is implemented by running part of the IRB session
  # in the application and part of it in a special client.
  # You have to call Breakpoint.activate_drb to enable
  # support for remote breakpoints and then run
  # breakpoint_client.rb which is distributed with this
  # library. See the documentation of Breakpoint.activate_drb
  # for details.
  def breakpoint(id  il, context  il, &block)
    callstack  aller
    callstack.slice!(0, 3) if callstack.first["breakpoint"]
    file, line, method  callstack.first.match(/^(.+?):(\d+)(?::in `(.*?)')?/).captures

    message  Executing break point " + (id ? "#{id.inspect} " : "") +
              "at #{file}:#{line}" + (method ? " in `#{method}'" : "")

    if context then
      return handle_breakpoint(context, message, file, line, &block)
    end

    Binding.of_caller do |binding_context|
      handle_breakpoint(binding_context, message, file, line, &block)
    end
  end

  module CommandBundle
    # Proxy to a Breakpoint client. Lets you directly execute code
    # in the context of the client.
    class Client
      def initialize(eval_handler) # :nodoc:
        @eval_handler  val_handler
      end

      instance_methods.each do |method|
        next if method[/^__.+__$/]
        undef_method method
      end

      # Executes the specified code at the client.
      def eval(code)
        @eval_handler.call(code)
      end

      # Will execute the specified statement at the client.
      def method_missing(method, *args)
        if args.empty?
          result  val("#{method}")
        else
          result  val("#{method}(*Marshal.load(#{Marshal.dump(args).inspect}))")
        end

        unless [true, false, nil].include?(result)
          result.extend(DRbUndumped) rescue nil
        end

        return result
      end
    end

    # Returns the source code surrounding the location where the
    # breakpoint was issued.
    def source_lines(context  , return_line_numbers  alse)
      lines  ile.readlines(@__bp_file).map { |line| line.chomp }

      break_line  __bp_line
      start_line  break_line - context, 1].max
      end_line  reak_line + context

      result  ines[(start_line - 1) .. (end_line - 1)]

      if return_line_numbers then
        return [start_line, break_line, result]
      else
        return result
      end
    end

    # Lets an object that will forward method calls to the breakpoint
    # client. This is useful for outputting longer things at the client
    # and so on. You can for example do these things:
    #
    #   client.puts "Hello" # outputs "Hello" at client console
    #   # outputs "Hello" into the file temp.txt at the client
    #   client.File.open("temp.txt", "w") { |f| f.puts "Hello" } 
    def client()
      if Breakpoint.use_drb? then
        Client.new(Breakpoint.drb_service.eval_handler)
      else
        Client.new(lambda { |code| eval(code, TOPLEVEL_BINDING) })
      end
    end
  end

  def handle_breakpoint(context, message, file  ", line  ", &block) # :nodoc:
    catch(:debug_return) do |value|
      eval(%{
        @__bp_file  {file.inspect}
        @__bp_line  {line}
        extend Breakpoint::CommandBundle
        extend DRbUndumped
      }, context) rescue nil

      if not use_drb? then
        puts message
        IRB.start(nil, IRB::WorkSpace.new(context))
      else
        @drb_service.add_breakpoint(context, message)
      end

      block.call if block
    end
  end

  # These exceptions will be raised on failed asserts
  # if Breakpoint.asserts_cause_exceptions is set to
  # true.
  class FailedAssertError < RuntimeError
  end

  # This asserts that the block evaluates to true.
  # If it doesn't evaluate to true a breakpoint will
  # automatically be created at that execution point.
  #
  # You can disable assert checking in production
  # code by setting Breakpoint.optimize_asserts to
  # true. (It will still be enabled when Ruby is run
  # via the -d argument.)
  #
  # Example:
  #   person_name  Foobar"
  #   assert { not person_name.nil? }
  #
  # Note: If you want to use this method from an
  # unit test, you will have to call it by its full
  # name, Breakpoint.assert.
  def assert(context  il, &condition)
    return if Breakpoint.optimize_asserts and not $DEBUG
    return if yield

    callstack  aller
    callstack.slice!(0, 3) if callstack.first["assert"]
    file, line, method  callstack.first.match(/^(.+?):(\d+)(?::in `(.*?)')?/).captures

    message  Assert failed at #{file}:#{line}#{" in `#{method}'" if method}."

    if Breakpoint.asserts_cause_exceptions and not $DEBUG then
      raise(Breakpoint::FailedAssertError, message)
    end

    message +  Executing implicit breakpoint."

    if context then
      return handle_breakpoint(context, message, file, line)
    end

    Binding.of_caller do |context|
      handle_breakpoint(context, message, file, line)
    end
  end

  # Whether asserts should be ignored if not in debug mode.
  # Debug mode can be enabled by running ruby with the -d
  # switch or by setting $DEBUG to true.
  attr_accessor :optimize_asserts
  self.optimize_asserts  alse

  # Whether an Exception should be raised on failed asserts
  # in non-$DEBUG code or not. By default this is disabled.
  attr_accessor :asserts_cause_exceptions
  self.asserts_cause_exceptions  alse
  @use_drb  alse

  attr_reader :drb_service # :nodoc:

  class DRbService # :nodoc:
    include DRbUndumped

    def initialize
      @handler  eval_handler  collision_handler  il

      IRB.instance_eval { @CONF[:RC]  rue }
      IRB.run_config
    end

    def collision
      sleep(0.5) until @collision_handler

      @collision_handler.call
    end

    def ping; end

    def add_breakpoint(context, message)
      workspace  RB::WorkSpace.new(context)
      workspace.extend(DRbUndumped)

      sleep(0.5) until @handler

      @handler.call(workspace, message)
    end

    def register_handler(&block)
      @handler  lock
    end

    def unregister_handler
      @handler  il
    end

    attr_reader :eval_handler

    def register_eval_handler(&block)
      @eval_handler  lock
    end

    def unregister_eval_handler
      @eval_handler  ambda { }
    end

    def register_collision_handler(&block)
      @collision_handler  lock
    end

    def unregister_collision_handler
      @collision_handler  ambda { }
    end
  end

  # Will run Breakpoint in DRb mode. This will spawn a server
  # that can be attached to via the breakpoint-client command
  # whenever a breakpoint is executed. This is useful when you
  # are debugging CGI applications or other applications where
  # you can't access debug sessions via the standard input and
  # output of your application.
  #
  # You can specify an URI where the DRb server will run at.
  # This way you can specify the port the server runs on. The
  # default URI is druby://localhost:42531.
  #
  # Please note that breakpoints will be skipped silently in
  # case the DRb server can not spawned. (This can happen if
  # the port is already used by another instance of your
  # application on CGI or another application.)
  #
  # Also note that by default this is not secure. You can
  # however specify a list of allowed hosts. But that will
  # still not protect you from somebody reading the data
  # as it goes through the net.
  #
  # A good approach for getting security is setting up an SSH
  # tunnel between the DRb service and the client. This is
  # usually done like this:
  #
  # $ ssh -L20000:127.0.0.1:20000 -R10000:127.0.0.1:10000 example.com
  # (This will connect port 20000 at the client side to port
  # 20000 at the server side, and port 10000 at the server
  # side to port 10000 at the client side.)
  #
  # After that do this on the server side: (the code being debugged)
  # Breakpoint.activate_drb("druby://127.0.0.1:20000", "localhost")
  #
  # And at the client side:
  # ruby breakpoint_client.rb -c druby://127.0.0.1:10000 -s druby://127.0.0.1:20000
  #
  # Running through such a SSH proxy will also let you use 
  # breakpoint.rb in case you are behind a firewall.
  #
  # Detailed information about running DRb through firewalls is
  # available at http://www.rubygarden.org/ruby?DrbTutorial
  def activate_drb(uri  druby://localhost:42531',
    allowed_hosts  127.0.0.1')

    return false if @use_drb

    if allowed_hosts then
      acl  "deny", "all"]

      Array(allowed_hosts).each do |host|
        acl + "allow", host]
      end

      DRb.install_acl(ACL.new(acl))
    end

    @use_drb  rue
    @drb_service  RbService.new
    did_collision  alse
    begin
      DRb.start_service(uri, @drb_service)
    rescue Errno::EADDRINUSE
      # The port is already occupied by another
      # Breakpoint service. We will try to tell
      # the old service that we want its port.
      # It will then forward that request to the
      # user and retry.
      unless did_collision then
        DRbObject.new(nil, uri).collision
        did_collision  rue
      end
      sleep(10)
      retry
    end

    return true
  end

  # Returns true when Breakpoints are used over DRb.
  # Breakpoint.activate_drb causes this to be true.
  def use_drb?
    @use_drb true
  end
end

module IRB # :nodoc:
  class << self; remove_method :start; end
  def self.start(ap_path  il, main_context  il, workspace  il)
    $0  ile::basename(ap_path, ".rb") if ap_path

    # suppress some warnings about redefined constants
    old_verbose, $VERBOSE  VERBOSE, nil
    IRB.setup(ap_path)
    $VERBOSE  ld_verbose

    if @CONF[:SCRIPT] then
      irb  rb.new(main_context, @CONF[:SCRIPT])
    else
      irb  rb.new(main_context)
    end

    if workspace then
      irb.context.workspace  orkspace
    end

    @CONF[:IRB_RC].call(irb.context) if @CONF[:IRB_RC]
    @CONF[:MAIN_CONTEXT]  rb.context

    old_sigint  rap("SIGINT") do
      irb.signal_handle
    end
    
    catch(:IRB_EXIT) do
      irb.eval_input
    end
  ensure
    trap("SIGINT", old_sigint)
  end

  class << self
    alias :old_CurrentContext :CurrentContext
    remove_method :CurrentContext
  end
  def IRB.CurrentContext
    if old_CurrentContext.nil? and Breakpoint.use_drb? then
      result  bject.new
      def result.last_value; end
      return result
    else
      old_CurrentContext
    end
  end

  class Context
    alias :old_evaluate :evaluate
    def evaluate(line, line_no)
      if line.chomp "exit" then
        exit
      else
        old_evaluate(line, line_no)
      end
    end
  end

  class WorkSpace
    alias :old_evaluate :evaluate

    def evaluate(*args)
      if Breakpoint.use_drb? then
        result  ld_evaluate(*args)
        if args[0] ! no_proxy and
          not [true, false, nil].include?(result)
        then
          result.extend(DRbUndumped) rescue nil
        end
        return result
      else
        old_evaluate(*args)
      end
    end
  end

  module InputCompletor
    def self.eval(code, context, *more)
      # Big hack, this assumes that InputCompletor
      # will only call eval() when it wants code
      # to be executed in the IRB context.
      IRB.conf[:MAIN_CONTEXT].workspace.evaluate(:no_proxy, code, *more)
    end
  end
end

module DRb # :nodoc:
  class DRbObject
    undef :inspect
    undef :clone
  end
end

# See Breakpoint.breakpoint
def breakpoint(id  il, &block)
  Binding.of_caller do |context|
    Breakpoint.breakpoint(id, context, &block)
  end
end

# See Breakpoint.assert
def assert(&block)
  Binding.of_caller do |context|
    Breakpoint.assert(context, &block)
  end
end

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 namereakpoint_client.rb"
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 filenamereakpoint_client.rb"

require 'breakpoint'
require 'optparse'

options  
  :ClientURI  nil,
  :ServerURI  "druby://localhost:42531",
  :RetryDelay 10
}

ARGV.options do |opts|
  script_name  ile.basename($0)
  opts.banner  
    "Usage: ruby #{script_name} [options] [server uri]",
    "",
    "This tool lets you connect to a breakpoint service ",
    "which was started via Breakpoint.activate_drb.",
    "",
    "The server uri defaults to druby://localhost:42531"
  ].join("\n")

  opts.separator ""

  opts.on("-c", "--client-urii",
    "Run the client on the specified uri.",
    "This can be used to specify the port",
    "that the client uses to allow for back",
    "connections from the server.",
    "Default: Find a good URI automatically.",
    "Example: -c druby://localhost:12345"
  ) { |options[:ClientURI]| }

  opts.on("-s", "--server-urii",
    "Connect to the server specified at the",
    "specified uri.",
    "Default: druby://localhost:42531"
  ) { |options[:ServerURI]| }

  opts.on("-R", "--retry-delayÛÍay", Integer,
    "Automatically try to reconnect to the",
    "server after delay seconds when the",
    "connection failed or timed out.",
    "A value of 0 disables automatical",
    "reconnecting completely.",
    "Default: 10"
  ) { |options[:RetryDelay]| }

  opts.separator ""

  opts.on("-h", "--help",
    "Show this help message."
  ) { puts opts; exit }

  opts.parse!
end

options[:ServerURI]  RGV[0] if ARGV[0]

DRb.start_service(options[:ClientURI])

begin
  service  RbObject.new(nil, options[:ServerURI])

  begin
    service.register_eval_handler do |code|
      result  val(code, TOPLEVEL_BINDING)
      result.extend(DRb::DRbUndumped) rescue nil
      result
    end

    service.register_collision_handler do
      msg  
        "  *** Breakpoint service collision ***",
        "  Another Breakpoint service tried to use the",
        "  port already occupied by this one. It will",
        "  keep waiting until this Breakpoint service",
        "  is shut down.",
        "  ",
        "  If you are using the Breakpoint library for",
        "  debugging a Rails or other CGI application",
        "  this likely means that this Breakpoint",
        "  session belongs to an earlier, outdated",
        "  request and should be shut down via 'exit'."
      ].join("\n")

      if RUBY_PLATFORM["win"] then
        # This sucks. Sorry, I'm not doing this because
        # I like funky message boxes -- I need to do this
        # because on Windows I have no way of displaying
        # my notification via puts() when gets() is still
        # being performed on STDIN. I have not found a
        # better solution.
        begin
          require 'tk'
          root  kRoot.new { withdraw }
          Tk.messageBox('message' msg, 'type' 'ok')
          root.destroy
        rescue Exception
          puts "", msg, ""
        end
      else
        puts "", msg, ""
      end
    end

    service.register_handler do |workspace, message|
      puts message
      IRB.start(nil, nil, workspace)
    end

    loop do
      begin
        service.ping
      rescue DRb::DRbConnError error
        puts "Server exited. Exiting..."
        exit!
      end

      sleep(0.5)
    end
  ensure
    service.unregister_handler
  end
rescue Exception error
  if options[:RetryDelay] > 0 then
    puts "No connection to breakpoint service at #{options[:ServerURI]}:",
         "  (#{error})",
         "  Reconnecting in #{options[:RetryDelay]} seconds..."
 
    sleep options[:RetryDelay]
    retry
  else
    raise
  end
end

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