WebSocket connection closes after calling child process

Question

Here's the setup: I create simple WebSocket Server using the ws library. I then attach a listener for when the client sends me the URL of a PDF to transform. I download it locally then I call another command to transform it:

const download = require("download");
wss.on("connection", ws => {
  ws.onmessage = async msg => {
    await download(msg.data, destination, {
      filename: fileName
    });

    transformPDF(ws, msg.data);
  };

  // ...
});

After that, the transformPDF function calls the spawn command to execute a command line binary. I parse the percentage done from the stdout and then try to emit it to the client. But even before this, the connection has been closed and I'm not sure why:

const { spawn } = require("child_process");
const transformPDF = (ws, url) => {
  // ...
  const child = spawn("k2pdfopt", settings);

  child.stdout.on("data", data => {
    // ...
    ws.send(percentageDone); // <--- connection is broken before this is called
  });
};

I have tried to make the transformPDF function a promise and then awaiting it. I have also tried adding an optional detached option to the spawn process. I'm not really sure why it's closing since I've also successfully replaced the command k2pdfopt with something like a lengthy find, and that worked just fine (although it did batch all of the data in the stdout before calling ws.send).

Any help or insight on why it's closing is much appreciated.

Answer 1

Turns out that when I was creating a child process, it was resetting the Visual Studio Code live-server extension that I had running the index.html. That explains why I was also getting a status code of 1001, which I found out most likely means the client refreshed.

I fixed the issue by simply installing the node package live-server and running my index.html from a different terminal.