A script that takes a heap snapshot from a nodejs process in debug mode

take-memory-snapshot.ts

const { exec, spawn } = require("child_process");
const fs = require("fs");
const { promisify } = require("util");
import { WebSocket } from "ws";

async function getWebSocketDebuggerUrl() {
  const res = await fetch("http://localhost:9229/json");
  const data = await res.json();
  return data[0].webSocketDebuggerUrl;
}

async function takeHeapSnapshot() {
  let ws: WebSocket;
  try {
    process.on("uncaughtException", (err) => {
      console.error(err);
      process.exit(1);
    });

    // Create temp file
    const fileName = "profile-" + Date.now() + ".heapsnapshot";

    console.log("File: ", fileName);

    // Get the WebSocket URL
    const webSocketDebuggerUrl = await getWebSocketDebuggerUrl();

    console.log("WebSocket URL:", webSocketDebuggerUrl);

    await new Promise<void>((resolve) => {
      // use WebSocket to connect to the target process
      ws = new WebSocket(webSocketDebuggerUrl);

      let startedReceiving = false;

      // listen for addChunk events
      ws.on("message", (data) => {
        const message = JSON.parse(data.toString());
        if (message.method === "HeapProfiler.addHeapSnapshotChunk") {
          if (!startedReceiving) {
            startedReceiving = true;
            console.log("Receiving HeapSnapshot...");
          }
          fs.appendFileSync(fileName, message.params.chunk);
        } else if (message.id === 2) {
          resolve();
        }
      });

      ws.on("error", console.error);

      ws.on("open", function open() {
        console.log("connected");

        // Enable the HeapProfiler
        console.log("Enabling HeapProfiler...");
        ws.send(
          JSON.stringify({
            id: 1,
            method: "HeapProfiler.enable",
          })
        );

        // Take the HeapSnapshot
        console.log("Taking HeapSnapshot...");
        ws.send(
          JSON.stringify({
            id: 2,
            method: "HeapProfiler.takeHeapSnapshot",
          })
        );
      });
    });
    console.log("Heap Snapshot captured!");
  } catch (err) {
    console.error("An error occurred:", err);
  } finally {
    if (ws) {
      ws.close();
    }
  }
}

takeHeapSnapshot();