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0.4.0 • Public • Published

@foxglove/rosbag   npm version

@foxglove/rosbag is a node.js & browser compatible module for reading rosbag binary data files.


npm install @foxglove/rosbag


yarn add @foxglove/rosbag

Quick start

The most common way to interact with a rosbag is to read data records for a specific set of topics. The rosbag format encodes type information for topics, and rosbag reads this type information and parses the data records into JavaScript objects and arrays.

Here is an example of reading messages from a rosbag in node.js:

import { Bag } from "@foxglove/rosbag";
import { FileReader } from "@foxglove/rosbag/node";

async function logMessagesFromFooBar() {
  // open a new bag with a speific file reader
  const bag = new Bag(new FileReader("../path/to/ros.bag"));

  await bag.open();

  for await (const result of bag.messageIterator({ topics: ["/foo", "/bar"] })) {
    // topic is the topic the data record was in
    // in this case it will be either '/foo' or '/bar'

    // message is the parsed payload
    // this payload will likely differ based on the topic



Bag instance

class Bag {
  // the time of the earliest message in the bag
  startTime: Time,

  // the time of the last message in the bag
  endTime: Time,

  // a hash of connection records by their id
  connections: { [number]: Connection },

  // an array of ChunkInfos describing the chunks within the bag
  chunkInfos: Array<ChunkInfo>,


const options = {
  // decompression callbacks:
  // if your bag is compressed you can supply a callback to decompress it
  // based on the compression type. The callback should accept a buffer of compressed bytes
  // and return a buffer of uncompressed bytes.  For examples on how to decompress lz4 and bz2 compressed bags
  // please see the tests here: https://github.com/cruise-automation/rosbag.js/blob/545529344c8c2a0b3a3126646d065043c2d67d84/src/bag.test.js#L167-L192
  // The decompression callback is also passed the uncompressedByteLength which is stored in the bag.
  // This byte length can be used with some decompression libraries to increase decompression efficiency.
  decompress?: {
    bz2?: (buffer: Uint8Array, uncompressedByteLength: number) => Uint8Array,
    lz4?: (buffer: Uint8Array, uncompressedByteLength: number) => Uint8Array,

  // Toggle the message deserialization behavior. By default, messages are deserialized into javascript objects. You can override this behavior by setting this to `false`.
  parse?: boolean;

Consuming messages from the bag instance

bag.messageIterator method returns an Async Iterator for messages in the file. Each item is a MessageEvent.


const options {
  // an optional array of topics used to filter down
  // which data records will be read
  // the default is all records on all topics
  topics?: Array<string>,

  // an optional Time instance used to filter data records
  // to only those which start on or after the given start time
  // the default is undefined which will apply no filter
  start?: Time,


const messageEvent {
  // the topic from which the current record was read
  topic: string,

  // the receive time of the message
  timestamp: Time

  // the raw buffer data from the data record
  // a node.js buffer in node & an array buffer in the browser
  data: Uint8Array,

  // the parsed message contents as a JavaScript object
  // this can contain nested complex types
  // and arrays of complex & simple types
  // If parsing is disabled this field is set to `undefined`
  message?: { [string]: unknown },


class Connection {
  // the id of the connection
  conn: number,

  // the topic for the connection
  topic: string,

  // the md5 hash for the connection message definition
  md5sum: string,

  // the rosbag formatted message definition for records on this connection's topic
  messageDefinition: string,

Stay in touch

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  • foxglovebot
  • amacneil