velo autonomus: node-comm-package

The NodeJS implementation of the internal module communication system of velo autonomus

Install

npm install velo-comm-package

Basics

The system is modular and decentralized. All the modules organize themselves using UDP-Multicasts. Direct communication is with TCP-Sockets (or Shared Memory (SHM), not implemented yet).

Every module uses the comm-package for the specific programming language. There you first create a new VeloModule object, which represents the module you're building. Here you set all the important information such as Module-ID, version and so on (more at Reference -> VeloModule -> constructor).

Using this VeloModule instance, you can create direct Connections to other modules over TCP (or SHM). Important note: To be able to handle incoming connections, you have to start a tcp server yourself.

Examples

Create a simple module:

const velo = require('velo-comm-package');

var testModule = new velo.VeloModule({
    id: 'TEST',
    name: 'Test module',
    allowsTCP: true,
    allowsSHM: false
});

Set the status:

testModule.setStatus(0); //OFFLINE
testModule.setStatus(1); //ONLINE
testModule.setStatus(2); //ERROR

Build a direct connection:

var testConnection = testModule.connectToModule('ANOTHER-MODULE');

testConnection.events.on('connect', () => {
    console.log('Connected to ANOTHER-MODULE');
});

testConnection.events.on('message', (msg) => {
    console.log('Message from ANOTHER-MODULE:', msg);
});

testConnection.events.on('error', (err) => {
    console.error(err);
})

testConnection.events.on('close', () => {
    console.log('Connection to ANOTHER-MODULE closed');
});

Create a TCP-Socket-Server:

var net = require('net');

var connectedSockets = []; //To send data to sockets from other places in the code

var server = net.createServer((socket) => {
    connectedSockets.push(socket);

    //Probably terrible error-handling here
    socket.on('data', (data) => {
        data = data.toString();
        console.log(data, data.length);
    });

    socket.on('end', () => {
        connectedSockets.splice(connectedSockets.indexOf(socket), 1);
    });

    socket.on('error', () => {
        connectedSockets.splice(connectedSockets.indexOf(socket), 1);
    });
});

server.listen(() => {
  console.log(`TCP-Server listening on port: ${server.address().port}`));
  testModule.setStatus(1);
  testModule.tcpPort = server.address().port; //IMPORTANT! Needed for other modules to connect to yours
});

Reference

VeloModule

constructor(info?: ModuleInfo)

info (optional): The information about the module:

• id: string; The modules ID
• allowsSHM: boolean (default: false); Does the module accept incoming SHM-Connections?
• allowsTCP: boolean (default: true); Does the module accept incoming TCP-Connections?
• cluster: string; The modules cluster/machine name
• name: string; A well thats well readable
• version: string (default: '1.0'); The modules version

setStatus(status: number): void

Sets the status of the module.

status: The status you want to set as a number

| number | status | | -----: | ------ | | 0 | Offline | | 1 | Online | | 2 | Error |

connectToModule(id: string): DirectConnection

Builds a connection to a specified module and returns a DirectoConnection object. The kind of connection (TCP or SHM) is automatically chosen and it will chose SHM if possible, since it's faster.

id: The id of the module you want to connect to

DirectConnection

disconnect(): void

Ends the connection

send(message: any): void

Sends a message of any type.

on(event: string, eventHandler: Function)

Subscribes to an event like it's done with an event handler. You can also access the event handler directly using the event property.

Supported events are:

• connect: Emitted, when the connection is built up
• message: Emitted, when a new message is received; message is passed as string
• close: Emitted, when the connection is closed
• error: Emitted, when an error occurs; error is passed

Known issues

UDP Packets sent by Raspberry Pi aren't receiced on Windows

If the Raspberry Pi and the windows machine are on the same network, and Raspi receives packets from the windows machine but not the other way around, it's typically caused by the windows firewall. Deactivating the firewall should solve the problem.