Docker image rcjsuen/docker-langserver exits abruptly 3 seconds after starting

[Nexion]

Expected behavior:
Emacs LSP client package lsp-mode runs docker-langserver executable with --stdio argument. It works well with docker-language-server installed on the same host, but there's an issue if you instead try to use the official docker image.

Wrapper script to execute the server in a container:

#!/bin/bash

exec podman run -i --rm --network=none rcjsuen/docker-langserver:latest "$@"

What's wrong:
On opening a file of Dockerfile format in Emacs the container successfully starts, LSP client and server begin message exchange, but 3 seconds later the container shuts down with exit code 1 without any visible reason.

Why:
Running the container with exit trace shows that the issue happens in vscode-languageserver dependency code.

podman run -i --rm --entrypoint='["sh", "-c", "node --trace-exit lib/server.js --stdio"]' rcjsuen/docker-langserver:latest "$@" 2>/tmp/stderr.log

stderr.log:

(node:1) WARNING: Exited the environment with code 1
    at exit (node:internal/process/per_thread:187:13)
    at /docker-langserver/node_modules/vscode-languageserver/lib/node/main.js:101:29
    at listOnTimeout (node:internal/timers:573:17)
    at processTimers (node:internal/timers:514:7)

Corresponding code in node_modules/vscode-languageserver/lib/node/main.js:

const watchDog = {
    initialize: (params) => {
        const processId = params.processId;
        if (Is.number(processId) && exitTimer === undefined) {
            // We received a parent process id. Set up a timer to periodically check
            // if the parent is still alive.
            setInterval(() => {
                try {
                    process.kill(processId, 0);
                }
                catch (ex) {
                    // Parent process doesn't exist anymore. Exit the server.
                    process.exit(_shutdownReceived ? 0 : 1);
                }
            }, 3000);
        }
    },
    get shutdownReceived() {
        return _shutdownReceived;
    },
    set shutdownReceived(value) {
        _shutdownReceived = value;
    },
    exit: (code) => {
        endProtocolConnection();
        process.exit(code);
    }
};

So as it turns out, an LSP client sends its PID as processId within its first initialization request message to server, and the server code checks if that PID is still alive with a 3000ms interval, but obviously can't find that PID within a container namespace. Guess this check has to be turned off in the docker image.

[rcjsuen]

@Nexion Very interesting. Thank you for the bug report. I wonder if this is worth mentioning in the microsoft/vscode-languageserver-node repository for visibility?

[Nexion]

@rcjsuen The only other LSP server written in typescript that I'm also using is bash-language-server and I had the same issue trying to run the latest release in a container. They don't publish their own official image though.

Now that you asked about that library, I suddenly noticed this code and gotta say that running the server in a container with --clientProcessId 1 does the magic, the watchdog ignores the PID provided by the client during session initialization.

Guess that solves the issue — but I know very little about the subject, so if you don't consider it a reliable workaround then maybe it's worth mentioning.