Docker Container Debugging: File Not Found

[Finleth]

I'm running a docker container with Alpine running Ruby 3.1 and Rails 7.0 where the docker-compose.yml uses the following command to start the debug session:

sh -c "rm -f tmp/pids/server.pid && rdbg -O --host=0.0.0.0 --port=1234 -c -- bundle exec rails server -b 0.0.0.0 -p 3000"

When I run docker compose up I get the container up and running with a debugger ready for a connection to attach. In my VS Code launch.js I have the following configuration:

{
  "name": "Attach with rdbg",
  "type": "rdbg",
  "request": "attach",
  "debugPort": "1234",
}

When I start the debugger using the above configuration it launches the debugger and immediately stops on the bin/rails file. I can then continue/step through the process using VS Code's debugger tools but it doesn't actually show the debugger line in VS Code and instead says Unable to open '<file name>'. File not found.. It says that for every file that the debugger stops on.

In my docker-compose.yml I define the volumes for the application like so:

.:/app:cached

I'm not sure what I need to do in order to get the full integration of VS Code's debugger with a rails app running on a docker container.

Let me know what other information would be useful to diagnose my issue and I can add that. Thanks!

[ko1]

Thank you for the report. I need to prepare repro env...

[ko1]

I could repro this feature without Docker. I'm trying to fix, but it can be later version, I can fix.

[ko1]

ruby/debug#600 may solve this issue.

[Finleth]

Awesome! Thank you for this quick turnaround! Based off of that pull request does this mean I would be able to set the sourceReference in my launch.json to tell vscode where the debugger's file system is?

[ko1]

You don't need any configurations. Please try to use latest version of extension and debug.gem.

[Finleth]

I've updated the extension and gem to the latest versions and am getting some parts of it to work! Using the same configurations as I mentioned at the beginning of this issue I can now add a line with debugger which will cause a break when the code is run. However when this happens vscode opens a readonly of the file with the debugger line (which I assume is being sent from the docker container).
Is there a way to use path mappings to tell vscode to use the local files when displaying the debugging info?

Another thing that I'm seeing is when I add a vscode breakpoint (the red dot) then I see this error in my docker container output:

DEBUGGER: Debugger can attach via TCP/IP (0.0.0.0:1234)
DEBUGGER: wait for debugger connection...
DEBUGGER: Connected.
DEBUGGER: ReaderThreadError: No such file or directory @ rb_check_realpath_internal - /app/c:\Users\jpau\Documents\sites\fees\app\controllers\application_controller.rb
["/usr/local/bundle/gems/debug-1.5.0/lib/debug/session.rb:1600:in `realpath'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/session.rb:1600:in `resolve_path'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/session.rb:1373:in `clear_line_breakpoints'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server_dap.rb:233:in `process'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server.rb:72:in `block (3 levels) in activate'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server.rb:244:in `setup_interrupt'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server.rb:70:in `block (2 levels) in activate'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server.rb:419:in `block (2 levels) in accept'",
 "/usr/local/lib/ruby/3.1.0/socket.rb:810:in `block (2 levels) in accept_loop'",
 "/usr/local/lib/ruby/3.1.0/socket.rb:807:in `each'",
 "/usr/local/lib/ruby/3.1.0/socket.rb:807:in `block in accept_loop'",
 "/usr/local/lib/ruby/3.1.0/socket.rb:805:in `loop'",
 "/usr/local/lib/ruby/3.1.0/socket.rb:805:in `accept_loop'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server.rb:417:in `block in accept'",
 "/usr/local/lib/ruby/3.1.0/socket.rb:782:in `tcp_server_sockets'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server.rb:393:in `accept'",
 "/usr/local/bundle/gems/debug-1.5.0/lib/debug/server.rb:49:in `block in activate'"]
DEBUGGER: Disconnected.

The file on my local would be just:

c:\Users\jpau\Documents\sites\fees\app\controllers\application_controller.rb

And on the container would be:

/app/app/controllers/application_controller.rb

Is there anything I need to do so the built in vscode break points reference the correct the path mappings?

[firien]

#32 (comment)

I patched together a working demo of this extension in a remote vscode environment - with it debugging a dockerized rails app.

The issue I have now is that I want multiple mappings. The main rails directory is my working directory that I mapped to a docker volume. I can debug with breakpoints fine with my hack job mentioned in #32. But I also have a ruby gems docker volume that is handled by docker that I am more or less oblivious of. I would want the debugger to have a second read only mapping, something like:

{
  "remoteRoots": [
    {
      "remoteRoot": "/path/to/app",
      "localfs": true
    }, {
      "remoteRoot": "/path/to/gems",
      "localfs": false
    }
  ]
}

I believe the localfs* is an internal(ish) vscode configuration, so I think that option applying to different directories might be a pipe dream. But at the very least maybe multiple remote mappings could be supported? If my internal ruby gem files opened in edit mode - that wouldn't be the worst thing.

---

*correction, localfs is passed on to the ruby debugger

[firien]

https://github.com/firien/vscode-rdbg/tree/multi-remote-root

well I just did it, branch above will map multiple directories. The ruby gems files load as editable - but 🤷‍♂️.

{
  "type": "rdbg",
  "name": "Attach with rdbg",
  "request": "attach",
  "debugPort": "12345",
  "localfs": true,
  "sourceMappings": [
    {
      "remoteRoot": "/rails_app" //this is dockerized rails app
      // with localRoot missing - it defaults to workspaceFolder
    },
    {
      "remoteRoot": "/usr/local/bundle", //ruby gems in docker
      "localRoot": "/home/user/.local/share/docker/volumes/app_gems/_data" //local mapping of ruby gem docker volume
    },
  ]
}