net-simulator v0.2.1

net-simulator

simulate terrible internet connections

The public internet is a rough operating environment. There are varying levels of latency, jitter, packet loss, and packet duplication.

When building network protocols, it's important to test implementations against real-world operating conditions.

net-simulator provides a way to simulate network conditions in a configurable way.

usage

Here is an example of setting up 1 client and 1 server, sending data between them over a simulated internet connection.

You can run this example with npm run example.

const delay = require('delay')
const sim   = require('net-simulator')


function update_peer(peer, time) {
  const CLIENT_MAX_RECEIVE_PACKETS = 64
  const num_packets_received = sim.network_simulator_receive_packets(peer.network_simulator,
                                                                      peer.address,
                                                                      CLIENT_MAX_RECEIVE_PACKETS,
                                                                      peer.receive_packet_data,
                                                                      peer.receive_packet_bytes,
                                                                      peer.receive_from)

  if(num_packets_received)
    console.log(peer.name, 'received', num_packets_received, 'packets')

  for (let i = 0; i < num_packets_received; i++) {
    console.log('packet data:', peer.receive_packet_data[i])
    console.log('packet bytes:', peer.receive_packet_bytes[i])

    // do something with the data...

    // destroy the received packet
    peer.receive_packet_data[i] = null
  }
}


async function main() {
  let time = 0 // time elapsed in seconds

  const network_simulator = sim.network_simulator_create()
  network_simulator.latency_milliseconds = 250
  network_simulator.jitter_milliseconds = 250
  network_simulator.packet_loss_percent = 5
  network_simulator.duplicate_packet_percent = 10

  const clientAddress = sim.network_simulator_create_address('ADDRESS_IPV4', '127.0.0.1', 5001)
  const serverAddress = sim.network_simulator_create_address('ADDRESS_IPV4', '127.0.0.1', 5002)

  const client = {
    name: 'client',
    network_simulator,
    address: clientAddress,
    receive_from: serverAddress,
    receive_packet_data: [],
    receive_packet_bytes: []
  }

  const server = {
    name: 'server',
    network_simulator,
    address: serverAddress,
    receive_from: clientAddress,
    receive_packet_data: [],
    receive_packet_bytes: []
  }

  while(true) {
    // send message from client to server
    const packet_data = new Uint8Array(20)
    sim.network_simulator_send_packet(network_simulator, clientAddress, serverAddress, packet_data, packet_data.byteLength)

    // send message from server to client
    const pd2 = new Uint8Array(15)
    sim.network_simulator_send_packet(network_simulator, serverAddress, clientAddress, pd2, pd2.byteLength)

    update_peer(client, time)
    update_peer(server, time)

    sim.network_simulator_update(network_simulator, time)

    // for every 3 seconds in real time, advance the network clock by 0.1 seconds
    await delay(3000)
    time += 0.1
  }
}


main()

inspiration & credit

This module is essentially a port of the network simulation logic found in https://github.com/networkprotocol/netcode.io