rosbags – zero-dependency ROS1 bag writer for Node & the browser

This directory contains a minimal implementation of a ROS1 (format v2.0) bag writer in pure JavaScript with zero runtime dependencies – not even buffer (we prebundle a polyfill for browser), ieee754 or friends. The only modules it relies on are provided by Node.js itself (fs, path, …), which means it also works unchanged in the browser after bundling.

The code is a direct, line-for-line port of the rosbags reference implementation written in Python. All record layouts, headers and constants are identical, so a bag produced here can be opened with any existing ROS tooling.

Quick start

```bash

Run the small unit-test suite (writes & reads a few bags)

node js/tests/run.mjs ```

Install via npm

bash npm install rosbags

Usage in Node (ESM)

```js import { Writer } from 'rosbags';

const bag = new Writer('example.bag'); bag.open(); const conn = bag.addConnection('/foo', 'std_msgs/msg/Int8'); bag.write(conn, 1, Buffer.from([0x01])); bag.close(); ```

Usage in Node (CommonJS)

js const { Writer } = require('rosbags'); // ...identical to above

Usage in the Browser via CDN

Add a single script tag that exposes rosbagsWriter globally:

html <script src="https://unpkg.com/rosbags/dist/rosbags.browser.js"></script> <script> // The bundle already contains a Buffer poly-fill, no extra scripts needed. const { Writer } = rosbagsWriter; const w = new Writer(); w.open(); const c = w.addConnection('/foo', 'std_msgs/msg/Int8'); w.write(c, 123n, new Uint8Array([0x42])); w.close(); const blob = new Blob([w.getUint8Array()], { type: 'application/octet-stream' }); // download or upload blob here </script>

Write a bag on disk (from source checkout)

```js // After installing from npm: import { Writer } from 'rosbags'; // Node ESM variant

const bag = new Writer('example.bag'); // pass a path ⇒ write to disk bag.open();

// Register a topic/connection first const conn = bag.addConnection('/foo', 'std_msgs/msg/Int8');

// Then stream messages (timestamp in nanoseconds) bag.write(conn, 1, Buffer.from([0x01])); bag.write(conn, 2, Buffer.from([0x02]));

bag.close(); ```

Create a bag entirely in memory (browser-friendly)

```js import { Writer } from 'rosbags';

const writer = new Writer(); // no path ⇒ keep data in memory writer.open(); const conn = writer.addConnection('/bar', 'std_msgs/msg/Int8'); writer.write(conn, 42, new Uint8Array([0xff])); writer.close();

const raw = writer.getUint8Array(); // Uint8Array containing the .bag file // …upload, download or feed into a WebWorker here… ```

Read the resulting bag with the official npm package

```js const rosbag = require('rosbag');

(async () => { const bag = await rosbag.open('example.bag'); await bag.readMessages({ noParse: true }, (msg) => { console.log(msg.topic, msg.data); }); })(); ```

Testing

Two kinds of tests live in js/tests/:

• test_writer1.js – verifies the writer against a set of hand-rolled assertions (header sizes, chunk flags, …).
• test_writer_rosbag_read.js – round-trip check that writes with this writer and reads back using the upstream rosbag npm dependency.

The tests load dist/rosbags.js (CommonJS stub) so they exercise the same API surface without requiring a build step. When you run npm run build, the real bundles dist/rosbags.node.mjs (ESM) and dist/rosbags.browser.js overwrite / complement the stub.

Run the suite via:

```bash node js/tests/run.mjs

Publishing to npm

The package.json includes convenience scripts:

• npm run build – Generates two self-contained bundles using esbuild:
  • dist/rosbags.node.mjs (ESM for Node)
  • dist/rosbags.browser.js (IIFE for browsers)
• npm publish – Publish the package. A prepublishOnly hook ensures the bundle is rebuilt and the tests are green before the actual upload.

Everything required at runtime is embedded in the generated bundle, so the published module stays dependency-free. ```

License

This JavaScript port is released under the MIT license (see LICENSE).