osc

A JavaScript Open Sound Control (OSC) library that works in Node.js and the browser.

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osc.js

osc.js is a library for reading and writing Open Sound Control messages in JavaScript. It works in both Node.js and in a web browser.

Why osc.js?

There are several other OSC libraries available for JavaScript. However, most depend on Node.js-specific APIs. This means that they can't be run in a browser or on web-only platforms such as Chrome OS. osc.js uses only cross-platform APIs (TypedArrays and DataView), ensuring that it can run in any modern JavaScript environment.

osc.js is fast, comprehensive, fully spec-compliant, tested, modular, and provides a wide variety of optional transports for sending and receiving OSC data.

What Does it Do?

osc.js reads and writes OSC-formatted binary data into plain JavaScript objects. It provides adaptors for Node.js Buffer objects as well as standard ArrayBuffers.

The core of osc.js is transport agnostic. You can receive OSC data in whatever manner works best for your application: serial port APIs such as node-serialport or chrome.serial, socket APIs such as Node.js dgram or WebRTC data channels, WebSockets or binary XHR messages should all work. Connect osc.js up to your source of incoming/outgoing data, and you're all set. This approach is consistent with the design of Open Sound Control as a content format that is independent from its means of transport.

In addition to the low-level encoder/decoder functions, osc.js also provides a comprehensive set of transport objects, called Ports, for use in standard browsers, Chrome Apps, and Node.js applications. These include:

Transport Supported Platforms
UDP Node.js, Chrome Apps
Serial port Node.js, Chrome Apps
Web Sockets Browsers, Node.js, Chrome Apps
TCP Node.js

For stream-based protocols such as serial and TCP, osc.js will take care of SLIP framing for you.

Status

osc.js supports all OSC 1.0 and 1.1 required types. It supports all OSC 1.1 optional types except Int64s ("h"), since JavaScript numbers are represented as IEEE 754 Doubles and thus don't have sufficient precision to represent all 64 bits. Int64 support using Google's long library is planned in the future.

How it Works

osc.js consists of two distinct layers:

  1. The transports, which provide a simple EventEmitter-style API for sending an receiving OSC packets using a variety of transports such as UDP and Web Sockets.
  2. The underlying stateless API that provides functions for reading and writing OSC packets.

Examples

Web Sockets in the Browser

Including osc.js in your HTML page:

<!DOCTYPE html>
<html>
    <head>
        <title>osc.js Web Sockets</title>
        <meta charset="UTF-8" />
        <script src="bower_components/osc.js/dist/osc-browser.min.js"></script>
    </head>
    <body></body>
</html>

Creating an OSC Web Socket Port object:

var oscPort = new osc.WebSocketPort({
    url: "ws://localhost:8081" // URL to your Web Socket server.
});

Listening for incoming OSC messages:

oscPort.on("message", function (oscMsg) {
    console.log("An OSC message just arrived!", oscMsg);
});

Sending OSC messages:

oscPort.send({
    address: "/carrier/frequency",
    args: 440
});

Sending OSC bundles:

oscPort.send({
    timeTag: osc.timeTag(60), // Schedules this bundle 60 seconds from now.
    packets: [
        {
            address: "/carrier/frequency",
            args: 440
        },
        {
            address: "/carrier/amplitude"
            args: 0.5
        }
    ]
});

Web Sockets in Node.js

var osc = require("osc"),
    http = require("http"),
    WebSocket = require("ws");

// Create an Express server app
// and serve up a directory of static files.
var app = require("express").express(),
    server = app.listen(8081);
app.use("/", express.static(__dirname + "/static"));

// Listen for Web Socket requests.
var wss = new WebSocket.Server({
    server: server
});

// Listen for Web Socket connections.
wss.on("connection", function (socket) {
    var socketPort = new osc.WebSocketPort({
        socket: socket
    });

    socketPort.on("message", function (oscMsg) {
        console.log("An OSC Message was received!", oscMsg);
    });
});

UDP in Node.js

// Create an osc.js UDP Port listening on port 57121.
var udpPort = new osc.UDPPort({
    localAddress: "0.0.0.0",
    localPort: 57121
});

// Listen for incoming OSC bundles.
udpPort.on("bundle", function (oscBundle) {
    console.log("An OSC bundle just arrived!", oscBundle);
});

// Open the socket.
udpPort.open();

// Send an OSC message to, say, SuperCollider
udpPort.send({
    address: "/s_new",
    args: ["default", 100]
}, 127.0.0.1, 57110);

Serial in a Chrome App

Including osc.js in your Chrome App page

<script src="../bower_components/osc.js/dist/osc-chromeapp.min.js"></script>

Defining the appropriate permissions in manifest.json

{
    "name": "OSC.js Chrome App Demo",
    "version": "1",
    "manifest_version": 2,
    "permissions": [
        "serial"
    ],
    "app": {
        "background": {
            "scripts": ["js/launch.js"],
            "transient": true
        }
    }
}

Connecting to the serial port and listening for OSC messages

// Instantiate a new OSC Serial Port.
var serialPort = new osc.SerialPort({
    devicePath: "/dev/cu.usbmodem22131"
});

// Listen for the message event and map the OSC message to the synth.
serialPort.on("message", function (oscMsg) {
    console.log("An OSC message was received!", oscMsg);
});

// Open the port.
serialPort.open();

More code examples showing how osc.js can be used in browser-based, Node.js, and Chrome App applications can be found in the osc.js examples repository.

The osc.js Low-Level API

There are two primary functions in osc.js used to read and write OSC data:

  • osc.readPacket(), which takes a DataView-friendly data buffer (i.e. an ArrayBuffer, TypedArray, DataView, or Node.js Buffer) and returns a tree of JavaScript objects representing the messages and bundles that were read
  • osc.writePacket(), which takes a message or bundle object and packs it up into a Uint8Array or Buffer object

Both functions take an optional withMetadata parameter, which specifies if the OSC type metadata should be included. By default, type metadata isn't included when reading packets, and is inferred automatically when writing packets.If you need greater precision in regards to the arguments in an OSC message, set the withMetadata argument to true.

OSC Bundle and Message Objects

osc.js represents bundles and messages as (mostly) JSON-compatible objects. Here's how they are structured:

Messages

OSC Message objects consist of two properties, address, which contains the URL-style address path and args which is an array of either raw argument values or type-annotated Argument objects (depending on the value of withMetadata when reading the message).

{
    address: "/an/osc/address",
    args: [
        {} // Raw or type-annotated OSC arguments
    ]
}

Bundles

OSC bundle objects consist of a time tag and an array of packets. Packets can be a mix of OSC bundle objects and message objects.

{
    timeTag: {
        // OSC Time Tag object
    },
    packets: [
        {} // Nested OSC bundle and message objects>
    ]
}

Argument Objects with Type Metadata

Type-annotated argument objects contain two properties: type, which contains the OSC type tag character (e.g. "i", "f", "t", etc.) and the raw value.

{
    type: "f", // OSC type tag string
    value: 444.4
}

Time Tags

Time tag objects contain two different representations: the raw NTP time and the equivalent (though less precise) native JavaScript timestamp. NTP times consist of a pair of values in an array. The first value represents the number of seconds since January 1, 1900. The second value is a Uint32 value (i.e. between 0 and 4294967296) that represents fractions of a second.

JavaScript timestamps are represented as milliseconds since January 1, 1970, which is the same unit as is returned by calls to Date.now().

{
    raw: [
        3608146800, // seconds since January 1, 1900.
        2147483648  // fractions of a second
    ],
    native: Number // Milliseconds since January 1, 1970
}

Colours

Colours are automatically normalized to CSS 3 rgba values (i.e. the alpha channel is represented as a float from 0.0 to 1.0).

{
    r: 255,
    g: 255,
    b: 255,
    a: 1.0
}

Mapping OSC to JSON

Here are a few examples showing how OSC packets are mapped to JSON objects by osc.js.

Message Objects
"/carrier/freq" ",f" 440.4
{
  address: "/carrier/freq",
  args: [440.4]
}
"/float/andArray" ",f[ii]" 440.4 42 47
{
  address: "/carrier/freq",
  args: [
    440.4, [42, 47]
  ]
}
"/aTimeTag" ",t" 3608146800 2147483648
{
  address: "/scheduleAt",
  args: [
    {
      raw: [3608146800, 2147483648],
      jsTime: 1399158000500
    }
  ]
}
"/blob" ",b" 0x63 0x61 0x74 0x21

{
  address: "/blob",
  args: [
    Uint8Aray([0x63, 0x61, 0x74, 0x21])
  ]
}
    
"/colour" ",r" "255 255 255 255"
{
  address: "/colour",
  args: [{
      r: 255,
      g: 255,
      b: 255,
      a: 1.0
    }
  ]
}
"/midiMessage" ",m" 0x00 0x90 0x45 0x65
{
  address: "/midiMessage",
  args: [
    // Port ID, Status, Data 1, Data 2
    Uint8Array([0, 144, 69, 101])
  ]
}

License

osc.js is written by Colin Clark and distributed under the MIT and GPL 3 licenses.

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