netsim - A Rust library for network simulation and testing (currently linux-only).

netsim is a crate for simulating networks for the sake of testing network-oriented Rust code. You can use it to run Rust functions in network-isolated containers, and assemble virtual networks for these functions to communicate over.

Spawning threads into isolated network namespaces

Network namespaces are a linux feature which can provide a thread or process with its own view of the system's network interfaces and routing table. This crate's spawn module provides functions for spawning threads into their own network namespaces. The most primitive of these functions is new_namespace, which is demonstrated below. In this example we list the visible network interfaces using the get_if_addrs crate.

extern crate tokio_core;
extern crate netsim;
extern crate get_if_addrs;
use tokio_core::reactor::Core;
use netsim::spawn;

// First, check that there is more than one network interface. This will generally be true
// since there will at least be the loopback interface.
let interfaces = get_if_addrs::get_if_addrs().unwrap();
assert!(interfaces.len() > 0);

// Now check how many network interfaces we can see inside a fresh network namespace. There
// should be zero.
let spawn_complete = spawn::new_namespace(|| {
    get_if_addrs::get_if_addrs().unwrap()
});
let interfaces = Core::new().unwrap().run(spawn_complete).unwrap();
assert!(interfaces.is_empty());

This demonstrates how to launch a thread - perhaps running an automated test - into a clean environment. However an environment with no network interfaces is pretty useless...

Creating virtual interfaces

We can create virtual IP and Ethernet interfaces using the types in the iface module. For example, Ipv4Iface lets you create a new IP (TUN) interface and implements futures::{Stream, Sink} so that you can read/write raw packets to it.

extern crate netsim;
extern crate tokio_core;
extern crate futures;

use std::net::Ipv4Addr;
use tokio_core::reactor::Core;
use futures::{Future, Stream};
use netsim::iface::Ipv4IfaceBuilder;

let mut core = Core::new().unwrap();
let handle = core.handle();

// Create a network interface named "netsim"
let iface = {
    Ipv4IfaceBuilder::new()
    .name("netsim")
    .address(Ipv4Addr::new(192, 168, 0, 23))
    .netmask(Ipv4Addr::new(255, 255, 255, 0))
    .build(&handle)
    .unwrap()
};

// Read the first `Ipv4Packet` sent from the interface.
let packet = core.run({
    iface
    .into_future()
    .map_err(|(e, _)| e)
    .map(|(packet_opt, _)| packet_opt.unwrap())
}).unwrap();

However for simply testing network code, you don't need to create interfaces manually like this.

Sandboxing network code

Rather than performing the above two steps individually you can use the functions in the spawn module to set up various network environments for you. For example, spawn::on_subnet_v4 will spawn a thread with a single network interface configured to use the given subnet. It returns a JoinHandle to join the thread with and an Ipv4Plug to read/write packets to the thread's network interface.

extern crate netsim;
extern crate tokio_core;
extern crate futures;

use std::net::UdpSocket;
use tokio_core::reactor::Core;
use futures::{Future, Stream};
use netsim::{spawn, SubnetV4};
use netsim::wire::Ipv4Payload;

let mut core = Core::new().unwrap();
let handle = core.handle();

let subnet = SubnetV4::local_10();
let (spawn_complete, plug) = spawn::on_subnet_v4(&handle, subnet, |ip_addr| {
    let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
    socket.send_to(b"hello world", "10.1.2.3:4567").unwrap();
});

core.run({
    plug.rx
    .into_future()
    .map(|(packet_opt, _)| {
        let packet = packet_opt.unwrap();
        match packet.payload() {
            Ipv4Payload::Udp(udp) => {
                assert_eq!(&udp.payload()[..], &b"hello world"[..]);
            },
            _ => panic!(),
        }
    })
}).unwrap()

Simulating networks of communicating nodes

To simulate a bunch of IPv4-connected nodes you can use the functions in the node module along with the spawn::network_v4 function to describe and launch a simluated network test.

extern crate tokio_core;
extern crate future_utils;
extern crate netsim;

use std::net::UdpSocket;
use tokio_core::reactor::Core;
use netsim::{spawn, node, SubnetV4};

let mut core = Core::new().unwrap();
let handle = core.handle();

let (tx, rx) = std::sync::mpsc::channel();
let node_a = node::endpoint_v4(move |ip_addr| {
    let socket = UdpSocket::bind(("0.0.0.0", 1234)).unwrap();
    tx.send(ip_addr).unwrap();
    let mut buffer = [0; 1024];
    let (n, addr) = socket.recv_from(&mut buffer).unwrap();
    buffer[..n].to_owned()
});

let node_b = node::endpoint_v4(move |_ip_addr| {
    let ip = rx.recv().unwrap();
    let socket = UdpSocket::bind("0.0.0.0:0").unwrap();
    socket.send_to(b"hello world", (ip, 1234)).unwrap();
});

let router_node = node::router_v4((node_a, node_b));
let (spawn_complete, _plug) = spawn::network_v4(&handle, SubnetV4::global(), router_node);
let (received, ()) = core.run(spawn_complete).unwrap();
assert_eq!(&received[..], b"hello world");

Note that we need to make sure to drive the Core while blocking on the JoinHandle in a separate thread. A future version of this library may clean this situation up.

All the rest

It's possible to set up more complicated (non-hierarchal) network topologies, ethernet networks, namespaces with multiple interfaces etc. by directly using the primitives in this library. Have an explore of the API, and if anything needs clarification or could be designed better then drop a message on the bug tracker :)