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 will only allow access from localhost. You can however specify a list of allowed hosts or nil (to allow access from everywhere). But that will still not protect you from somebody reading the data as it goes through the net.

A good approach for getting security and remote access 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 www.rubygarden.org/ruby?DrbTutorial

Security considerations

Usually you will be fine when using the default druby:// URI and the default access control list. However, if you are sitting on a machine where there are local users that you likely can not trust (this is the case for example on most web hosts which have multiple users sitting on the same physical machine) you will be better off by doing client/server communication through a unix socket. This can be accomplished by calling with a drbunix:/ style URI, e.g. Breakpoint.activate_drb(‘drbunix:/tmp/breakpoint_server’). This will only work on Unix based platforms.

[Source]

     # File lib/breakpoint.rb, line 374
374:   def activate_drb(uri = nil, allowed_hosts = ['localhost', '127.0.0.1', '::1'],
375:     ignore_collisions = false)
376: 
377:     return false if @use_drb
378: 
379:     uri ||= 'druby://localhost:42531'
380: 
381:     if allowed_hosts then
382:       acl = ["deny", "all"]
383: 
384:       Array(allowed_hosts).each do |host|
385:         acl += ["allow", host]
386:       end
387: 
388:       DRb.install_acl(ACL.new(acl))
389:     end
390: 
391:     @use_drb = true
392:     @drb_service = DRbService.new
393:     did_collision = false
394:     begin
395:       @service = DRb.start_service(uri, @drb_service)
396:     rescue Errno::EADDRINUSE
397:       if ignore_collisions then
398:         nil
399:       else
400:         # The port is already occupied by another
401:         # Breakpoint service. We will try to tell
402:         # the old service that we want its port.
403:         # It will then forward that request to the
404:         # user and retry.
405:         unless did_collision then
406:           DRbObject.new(nil, uri).collision
407:           did_collision = true
408:         end
409:         sleep(10)
410:         retry
411:       end
412:     end
413: 
414:     return true
415:   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.

[Source]

     # File lib/breakpoint.rb, line 248
248:   def assert(context = nil, &condition)
249:     return if Breakpoint.optimize_asserts and not $DEBUG
250:     return if yield
251: 
252:     callstack = caller
253:     callstack.slice!(0, 3) if callstack.first["assert"]
254:     file, line, method = *callstack.first.match(/^(.+?):(\d+)(?::in `(.*?)')?/).captures
255: 
256:     message = "Assert failed at #{file}:#{line}#{" in `#{method}'" if method}."
257: 
258:     if Breakpoint.asserts_cause_exceptions and not $DEBUG then
259:       raise(Breakpoint::FailedAssertError, message)
260:     end
261: 
262:     message += " Executing implicit breakpoint."
263: 
264:     if context then
265:       return handle_breakpoint(context, message, file, line)
266:     end
267: 
268:     Binding.of_caller do |context|
269:       handle_breakpoint(context, message, file, line)
270:     end
271:   end

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 = name, age
      breakpoint("Person#initialize")
    end

    attr_reader :age
    def name
      breakpoint("Person#name") { @name }
    end
  end

  person = Person.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=23, @name="Random Person">
  irb(#<Person:0x292fbe8>):005:0> @age += 1; self
  => #<Person:0x292fbe8 @age=24, @name="Random 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.

[Source]

     # File lib/breakpoint.rb, line 110
110:   def breakpoint(id = nil, context = nil, &block)
111:     callstack = caller
112:     callstack.slice!(0, 3) if callstack.first["breakpoint"]
113:     file, line, method = *callstack.first.match(/^(.+?):(\d+)(?::in `(.*?)')?/).captures
114: 
115:     message = "Executing break point " + (id ? "#{id.inspect} " : "") +
116:               "at #{file}:#{line}" + (method ? " in `#{method}'" : "")
117: 
118:     if context then
119:       return handle_breakpoint(context, message, file, line, &block)
120:     end
121: 
122:     Binding.of_caller do |binding_context|
123:       handle_breakpoint(binding_context, message, file, line, &block)
124:     end
125:   end

Deactivates a running Breakpoint service.

[Source]

     # File lib/breakpoint.rb, line 418
418:   def deactivate_drb
419:     Thread.exclusive do
420:       @service.stop_service unless @service.nil?
421:       @service = nil
422:       @use_drb = false
423:       @drb_service = nil
424:     end
425:   end

Returns true when Breakpoints are used over DRb. Breakpoint.activate_drb causes this to be true.

[Source]

     # File lib/breakpoint.rb, line 429
429:   def use_drb?
430:     @use_drb == true
431:   end