Udp-json NPM | npm.io

udp-json

Lightweight JSON UDP socket API written in JavaScript for NodeJS. It provides a simple protocol on top of UDP to send/receive JSON objects. It does not handle UDP unreliability.

Protocol

A UDP datagram consists of a datagram header and a data section. In the data section of each UDP datagram, udp-json adds another header and a new data section. The header consists of 3 fields, each of which is 4 bytes (32 bits):

+----------+----------------------+------------------------+
| ID (4 B) | Datagram count (4 B) | Current datagram (4 B) |
+----------+----------------------+------------------------+
|                                                          |
|                     Partial Data                         |
|                                                          |
+----------+----------------------+------------------------+

ID

This field identifies to which data refers this partial data.

Datagram count

This field specifies the number of UDP datagrams needed to complete the data.

Current datagram

This field identifies this UDP datagram location inside all the UDP datagrams to complete the data in the correct order.

Partial Data

Fragment of JSON stringified data encoded in utf-8.

Example

Example of sending the object { attribute: "dummy" } split in two datagrams.

+----------+----------------------+------------------------+
| ID = 333 | Datagram count = 2   | Current datagram = 0   |
+----------+----------------------+------------------------+
|                                                          |
|                         {attr                            |
|                                                          |
+----------+----------------------+------------------------+

+----------+----------------------+------------------------+
| ID = 333 | Datagram count = 2   | Current datagram = 1   |
+----------+----------------------+------------------------+
|                                                          |
|                    ibute: "dummy"}                       |
|                                                          |
+----------+----------------------+------------------------+

Usage

See examples folder for more info.

const JSONSocket = require('udp-json');

// Listener socket
const socket = dgram.createSocket('udp4');
socket.bind(56554, '127.0.0.1');
const jsonSocket = new JSONSocket(socket)
jsonSocket.on('message-complete', (msg, rinfo) => {
    console.log('Message received', rinfo, msg);
})

// Sender socket
const socket2 = dgram.createSocket('udp4');
const jsonSocket2 = new JSONSocket(socket2, {maxPayload: 496, timeout: 1000});
jsonSocket2.send({ dummy: 'Dummy Text' }, 56554, '127.0.0.1', (e) => {
    if (e) {
        console.log('error', e);
        return;
    }
    console.log('Message sent');
});

API

Here are listed all methods implemented in udp-json.

JSONSocket

Methods:
- JSONSocket(Socket[, options])
- send(obj, port[, address][, callback])
Events:

`JSONSocket()`

JSONSocket(Socket[, options]). Creates a JSON socket using the given options.

`JSONSocket: options`

Available options for creating a socket. It must be an object with the following properties:

Property	Type	Description
`maxPayload`	`<number>`	Max payload size (in bytes). If the resulting byte array exceeds this size, it will be splitted in chunks sent in different datagrams. Default: `496`.
`timeout`	`<number>`	Max time (in ms) between receiving a new datagram and the last datagram received. Default: `1000`.

`send()`

send(obj, port[, address][, callback]). Broadcasts an object on the socket. The destination port must be specified. An optional callback function may be specified to as a way of reporting errors or for determining when all datagrams have been sent.

`'message-complete'`

The 'message-complete' event is emitted when a new object is available on a socket. The event handler function is passed two arguments: obj and rinfo.

`'message-error'`

The 'message-error' event is emitted whenever any error occurs. The event handler function is passed a single Error object.

`'message-timeout'`

The 'message-timeout' event is emitted if a partial message times out from not receiving a new datagram. The event handler function is passed a single Error object.