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    0.0.8 • Public • Published

    Foxglove Studio WebSocket protocol

    This package provides server and client implementations of the Foxglove Studio WebSocket protocol, enabling Foxglove Studio to ingest arbitrary “live” streamed data.

    The protocol is encoding-agnostic, i.e. it can support Protobuf messages, JSON messages, etc. (as long as the desired encoding is supported by both client and server).


    $ npm install @foxglove/ws-protocol

    This package does not require a specific WebSocket server or client implementation, so you will need to install your own. For Node.js, you can use the ws package:

    $ npm install ws

    Example servers

    System monitor

    A system monitor script is provided as an illustrative example of a WebSocket server. To try it out:

    1. Run npx @foxglove/ws-protocol-examples@latest sysmon.
    2. In a browser, open up https://studio.foxglove.dev and initiate a Foxglove WebSocket connection to ws://localhost:8765/.

    Foxglove Studio displaying memory and CPU usage from the system monitor example

    Generic server template

    The following script provides a simple example server which publishes messages on a single topic called example_msg, using JSON to encode message data and JSON Schema to describe the message layout. This is meant to be a simple example from which you can begin to build a custom server.

    To get started with the example server:

    1. Copy the script below into a file named server.js.
    2. Run node server.js.
    3. In a browser, open up https://studio.foxglove.dev and initiate a Foxglove WebSocket connection to ws://localhost:8765/.

    Foxglove Studio displaying data from the example server

    const { FoxgloveServer } = require("@foxglove/ws-protocol");
    const { WebSocketServer } = require("ws");
    function delay(durationSec) {
      return new Promise((resolve) => setTimeout(resolve, durationSec * 1000));
    async function main() {
      const server = new FoxgloveServer({ name: "example-server" });
      const ws = new WebSocketServer({
        port: 8765,
        handleProtocols: (protocols) => server.handleProtocols(protocols),
      ws.on("listening", () => {
        console.log("server listening on %s", ws.address());
      ws.on("connection", (conn, req) => {
        const name = `${req.socket.remoteAddress}:${req.socket.remotePort}`;
        console.log("connection from %s via %s", name, req.url);
        server.handleConnection(conn, name);
      server.on("subscribe", (chanId) => {
        console.log("first client subscribed to %d", chanId);
      server.on("unsubscribe", (chanId) => {
        console.log("last client unsubscribed from %d", chanId);
      server.on("error", (err) => {
        console.error("server error: %o", err);
      const ch1 = server.addChannel({
        topic: "example_msg",
        encoding: "json",
        schemaName: "ExampleMsg",
        schema: JSON.stringify({
          type: "object",
          properties: {
            msg: { type: "string" },
            count: { type: "number" },
      const textEncoder = new TextEncoder();
      let i = 0;
      while (true) {
        await delay(0.2);
          BigInt(Date.now()) * 1_000_000n,
          textEncoder.encode(JSON.stringify({ msg: "Hello!", count: ++i })),

    Example client

    The following script provides a simple example client which subscribes to messages on all channels that use the json encoding. To get started with the example client:

    1. Copy the script below into a file named client.js.
    2. Run the example server above or any other Foxglove WebSocket server.
    3. In a separate terminal, run node client.js.
    $ node client.js
      subscriptionId: 0,
      timestamp: 1638999307183000000n,
      data: { msg: 'Hello!', count: 2849 }
      subscriptionId: 0,
      timestamp: 1638999307384000000n,
      data: { msg: 'Hello!', count: 2850 }
    const { FoxgloveClient } = require("@foxglove/ws-protocol");
    const { WebSocket } = require("ws");
    async function main() {
      const client = new FoxgloveClient({
        ws: new WebSocket(`ws://localhost:8765`, [FoxgloveClient.SUPPORTED_SUBPROTOCOL]),
      const deserializers = new Map();
      client.on("advertise", (channels) => {
        for (const channel of channels) {
          if (channel.encoding !== "json") {
            console.warn(`Unsupported encoding ${channel.encoding}`);
          const subId = client.subscribe(channel.id);
          const textDecoder = new TextDecoder();
          deserializers.set(subId, (data) => JSON.parse(textDecoder.decode(data)));
      client.on("message", ({ subscriptionId, timestamp, data }) => {
          data: deserializers.get(subscriptionId)(data),


    Note: This package lives inside a monorepo which uses yarn workspaces, so most commands (other than yarn install) should be prefixed with yarn workspace @foxglove/ws-protocol ....

    • Run yarn install to install development dependencies.
    • Run yarn workspace @foxglove/ws-protocol version --patch (or --minor or --major) to increment the version number and create the appropriate git tag.


    npm i @foxglove/ws-protocol

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    • foxglovebot
    • amacneil