Tracer

A UI tool for capturing the LSP requests and responses that are exchanged between the client and the server.

It doesn't matter what the target LSP is implemented with, as we only intercept JSONRPC payloads sent to stdin and stdout.

Currently, primary method of distribution is via Coursier.

To integrate with an LSP of your choosing, you need to have access to the CLI command that launches it.

The principle remains the same regardless of the editor:

cs launch tech.neander:langoustine-tracer_3:latest.release -- <lsp command>

where <lsp command> is passed as a list of arguments, not as a string.

Once the tracer is launched, it'll bind itself to a random port (see below if you'd like to make it non-random) and send a message to the LSP client with the port bound. You can then reach the UI by going to localhost:<port bound> in your browser.

Packaging with coursier

You can make your life considerably easier by using the bootstrap command that Coursier provides:

cs bootstrap tech.neander:langoustine-tracer_3:latest.release -f -o langoustine-tracer

# now you can use ./langoustine-tracer,
# put it somewhere on your PATH so that it's globally avalable
# and use it like this:
langoustine-tracer my-awesome lsp --stdin true

Alternatively, if your system was setup with coursier (i.e. the path where it puts installed applications is in your system's PATH), then life is even easier, hedonistic even:

cs install tech.neander:langoustine-tracer_3:latest.release

From this point in the document we assume that you somehow installed this app in a global location

For example, if your command to launch the LSP is my-awesome lsp --stdin true, then to trace it you need to use the following command:

langoustine-tracer my-awesome lsp --stdin true

Tips

Changing port

By default, it will start the server at random port, but you can change that using the --port argument:

langoustine-tracer --port 9911 my-awesome lsp --stdin true

Changing host

By default, tracer will bind to localhost. On some systems this may cause issues, for example under WSL on Windows.

In this scenario you might want to change the host to 0.0.0.0 with the --host parameter:

langoustine-tracer --host 0.0.0.0 my-awesome lsp --stdin true

Local development

If you are working on the tracer itself, you can globally alias langoustine-tracer to a local installation:

alias langoustine-tracer=<path-to-langoustine>/modules/tracer/backend/target/jvm-3/universal/stage/bin/langoustine-tracer

That launcher is created by running sbt tracer/stage

If your focus is on the frontend, you can speed up your development cycle considerably by doing the following:

1. Start your traced LSP somehow (doesn't matter if it's a coursier-installed one or your local)
2. Take note of the port number
3. cd modules/tracer/frontend
4. LANGOUSTINE_PORT=<port> npm run dev
5. In a separate terminal, run sbt ~tracerFrontendJS/fastLinkJS

Now you can edit just the frontend code and Vite will automatically refresh the page - no need to restart the LSP to pick up changes.