remote debugger failing on first hit with puma

[kikonen]

Your environment

• ruby -v: 3.3.5
• rdbg -v: 1.9.2

Describe the bug
When hitting breakpoint via placing "debugger" into source code, and connecting with remote debugger, with sinatra controller and puma web server in local docker container, first time when "debugger" is hit will fail, as described below

For example,
Puma started freshly serving sinatra app in local docker container

    33|       def some_method_called_via_puma_via_sinatra_controller
=>  34|         debugger
    35|         some logic...
    37|       end
    38|
(rdbg:remote) n
# No sourcefile available for /usr/local/bundle/gems/puma-6.4.2/lib/puma/single.rb

Stop by SIGURG
(rdbg:remote) n
# it looks like it tries to step in code, but in reality context is lost
(rdbg:remote) n
[1, 7] in $(Gem)/rack-2.2.9/lib/rack/file.rb
     1| # frozen_string_literal: true
     2|
     3| require_relative 'files'
     4|
=>   5| module Rack
     6|   File = Files
     7| end
(rdbg:remote) c

Thus only way to end to proceed is to hit "continue", since control flow has jumped into some odd place, and now, after this failure when doing same request again, debugger works as espected (i.e. does not hit this "SIGURG" which seems to break thing).

Makes usage rather irritating since after every modify of code (and restart of web server thus), have to first hit debugger "cold", and failing, and hitting continue, and now it seems to be "hot", and can actually succeed.

To Reproduce

• Local docker container
• running sinatra app with puma on it
• setting up remote debugger
• adding breakpoint via placing "debugger" into code
• launching app on container
• performing some request hitting "debugger" put in code
• connect remote debugger to process
  => fails on first time, if hitting continue, and retrying request it works as expected

Expected behavior
It would not fail on first time, since it makes debugging few cases difficult.

Additional context
Issue has been there for a while, i.e. it has had this failure always for me with this debug gem

[ko1]

You mean that the "fail" is showing the "# No sourcefile available for /usr/local/bundle/gems/puma-6.4.2/lib/puma/single.rb
" message, right?

I'm not sure but /usr/local/bundle/gems/puma-6.4.2/lib/puma/single.rb is available on the container?

[kikonen]

I figured out that in order to make thing work is

1. add "debugger" statement into desired place
2. let "rerun" logic to restart app in container (thus any existing remote debugger session will be killed)
3. attach remote debugger to app in aonther shell
   => it opens debugger console
   => hit continue on it
4. Do relevant things to trigger breakpoint
   => when "debugger" is hit it activaves console session in remote debug session started in step (3)
   => it seems to work as expected

However, this sequence fails

1. add "debugger" statement into desired place
2. let "rerun" logic to restart app in container (thus any existing remote debugger session will be killed)
3. Do relevant things to trigger breakpoint
   => it tells that it's waiting for remote debugger in stdout of app
4. attach remote debugger to app in aonther shell
   => console opens
   => seems to be in right place
   => but after trying to do anything, it hits issue described in original description
   => thus does not actually work
   => hitting continue is only option possibly
5. Do relevant things to trigger breakpoint again
   => when "debugger" is hit it activaves console session in remote debug session started in step (4)
   => this time it seems to work as expected