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Ping Tutorial - Getting started with rust-libp2p
This tutorial aims to give newcomers a hands-on overview of how to use the Rust libp2p implementation. People new to Rust likely want to get started on Rust itself, before diving into all the networking fun. This library makes heavy use of asynchronous Rust. In case you are not familiar with this concept, the Rust async-book should prove useful. People new to libp2p might prefer to get a general overview at libp2p.io first, although libp2p knowledge is not required for this tutorial.
We are going to build a small ping
clone, sending a ping to a peer,
expecting a pong as a response.
Scaffolding
Let’s start off by
-
Updating to the latest Rust toolchain, e.g.:
rustup update
-
Creating a new crate:
cargo init rust-libp2p-tutorial
-
Adding
libp2p
as well asfutures
as dependencies in theCargo.toml
file. Current crate versions may be found at crates.io. We will also includeasync-std
with the “attributes” feature to allow for anasync main
. At the time of writing we have:[package] name = "rust-libp2p-tutorial" version = "0.1.0" edition = "2021" [dependencies] libp2p = "0.43.0" futures = "0.3.21" async-std = { version = "1.10.0", features = ["attributes"] }
Network identity
With all the scaffolding in place, we can dive into the libp2p specifics.
First we need to create a network identity for our local node in async fn main()
, annotated with an attribute to allow main
to be async
.
Identities in libp2p are handled via a public/private key pair.
Nodes identify each other via their PeerId
which is
derived from their public key. Now, replace the contents of main.rs by:
use libp2p::{identity, PeerId};
use std::error::Error;
#[async_std::main]
async fn main() -> Result<(), Box<dyn Error>> {
let local_key = identity::Keypair::generate_ed25519();
let local_peer_id = PeerId::from(local_key.public());
println!("Local peer id: {:?}", local_peer_id);
Ok(())
}
Go ahead and build and run the above code with: cargo run
. A unique
PeerId
should be displayed.
Transport
Next up we need to construct a transport. A transport in libp2p provides
connection-oriented communication channels (e.g. TCP) as well as upgrades
on top of those like authentication and encryption protocols. Technically,
a libp2p transport is anything that implements the Transport
trait.
Instead of constructing a transport ourselves for this tutorial, we use the
convenience function development_transport
that creates a TCP transport with noise
for authenticated
encryption.
Furthermore, development_transport
builds a multiplexed transport,
whereby multiple logical substreams can coexist on the same underlying (TCP)
connection. For further details on substream multiplexing, take a look at
crate::core::muxing
and yamux
.
use libp2p::{identity, PeerId};
use std::error::Error;
#[async_std::main]
async fn main() -> Result<(), Box<dyn Error>> {
let local_key = identity::Keypair::generate_ed25519();
let local_peer_id = PeerId::from(local_key.public());
println!("Local peer id: {:?}", local_peer_id);
let transport = libp2p::development_transport(local_key).await?;
Ok(())
}
Network behaviour
Now it is time to look at another core trait of rust-libp2p: the
NetworkBehaviour
. While the previously introduced trait Transport
defines how to send bytes on the network, a NetworkBehaviour
defines
what bytes to send on the network.
To make this more concrete, let’s take a look at a simple implementation of
the NetworkBehaviour
trait: the ping::Behaviour
.
As you might have guessed, similar to the good old ping
network tool,
libp2p ping::Behaviour
sends a ping to a peer and expects
to receive a pong in turn. The ping::Behaviour
does not care how
the ping and pong messages are sent on the network, whether they are sent via
TCP, whether they are encrypted via noise or just in
plaintext. It only cares about what messages are sent
on the network.
The two traits Transport
and NetworkBehaviour
allow us to cleanly
separate how to send bytes from what bytes to send.
With the above in mind, let’s extend our example, creating a ping::Behaviour
at the end:
use libp2p::{identity, PeerId, ping};
use std::error::Error;
#[async_std::main]
async fn main() -> Result<(), Box<dyn Error>> {
let local_key = identity::Keypair::generate_ed25519();
let local_peer_id = PeerId::from(local_key.public());
println!("Local peer id: {:?}", local_peer_id);
let transport = libp2p::development_transport(local_key).await?;
// Create a ping network behaviour.
//
// For illustrative purposes, the ping protocol is configured to
// keep the connection alive, so a continuous sequence of pings
// can be observed.
let behaviour = ping::Behaviour::new(ping::Config::new().with_keep_alive(true));
Ok(())
}
Swarm
Now that we have a Transport
and a NetworkBehaviour
, we need
something that connects the two, allowing both to make progress. This job is
carried out by a Swarm
. Put simply, a Swarm
drives both a
Transport
and a NetworkBehaviour
forward, passing commands from the
NetworkBehaviour
to the Transport
as well as events from the
Transport
to the NetworkBehaviour
.
use libp2p::{identity, PeerId, ping};
use libp2p::swarm::Swarm;
use std::error::Error;
#[async_std::main]
async fn main() -> Result<(), Box<dyn Error>> {
let local_key = identity::Keypair::generate_ed25519();
let local_peer_id = PeerId::from(local_key.public());
println!("Local peer id: {:?}", local_peer_id);
let transport = libp2p::development_transport(local_key).await?;
// Create a ping network behaviour.
//
// For illustrative purposes, the ping protocol is configured to
// keep the connection alive, so a continuous sequence of pings
// can be observed.
let behaviour = ping::Behaviour::new(ping::Config::new().with_keep_alive(true));
let mut swarm = Swarm::new(transport, behaviour, local_peer_id);
Ok(())
}
Multiaddr
With the Swarm
in place, we are all set to listen for incoming
connections. We only need to pass an address to the Swarm
, just like for
std::net::TcpListener::bind
. But instead of passing an IP address, we
pass a Multiaddr
which is yet another core concept of libp2p worth
taking a look at.
A Multiaddr
is a self-describing network address and protocol stack that
is used to establish connections to peers. A good introduction to
Multiaddr
can be found at
docs.libp2p.io/concepts/addressing
and its specification repository
github.com/multiformats/multiaddr.
Let’s make our local node listen on a new socket.
This socket is listening on multiple network interfaces at the same time. For
each network interface, a new listening address is created. These may change
over time as interfaces become available or unavailable.
For example, in case of our TCP transport it may (among others) listen on the
loopback interface (localhost) /ip4/127.0.0.1/tcp/24915
as well as the local
network /ip4/192.168.178.25/tcp/24915
.
In addition, if provided on the CLI, let’s instruct our local node to dial a remote peer.
use libp2p::{identity, Multiaddr, PeerId, ping};
use libp2p::swarm::{Swarm, dial_opts::DialOpts};
use std::error::Error;
#[async_std::main]
async fn main() -> Result<(), Box<dyn Error>> {
let local_key = identity::Keypair::generate_ed25519();
let local_peer_id = PeerId::from(local_key.public());
println!("Local peer id: {:?}", local_peer_id);
let transport = libp2p::development_transport(local_key).await?;
// Create a ping network behaviour.
//
// For illustrative purposes, the ping protocol is configured to
// keep the connection alive, so a continuous sequence of pings
// can be observed.
let behaviour = ping::Behaviour::new(ping::Config::new().with_keep_alive(true));
let mut swarm = Swarm::new(transport, behaviour, local_peer_id);
// Tell the swarm to listen on all interfaces and a random, OS-assigned
// port.
swarm.listen_on("/ip4/0.0.0.0/tcp/0".parse()?)?;
// Dial the peer identified by the multi-address given as the second
// command-line argument, if any.
if let Some(addr) = std::env::args().nth(1) {
let remote: Multiaddr = addr.parse()?;
swarm.dial(remote)?;
println!("Dialed {}", addr)
}
Ok(())
}
Continuously polling the Swarm
We have everything in place now. The last step is to drive the Swarm
in
a loop, allowing it to listen for incoming connections and establish an
outgoing connection in case we specify an address on the CLI.
use futures::prelude::*;
use libp2p::swarm::{Swarm, SwarmEvent, dial_opts::DialOpts};
use libp2p::{identity, Multiaddr, PeerId, ping};
use std::error::Error;
#[async_std::main]
async fn main() -> Result<(), Box<dyn Error>> {
let local_key = identity::Keypair::generate_ed25519();
let local_peer_id = PeerId::from(local_key.public());
println!("Local peer id: {:?}", local_peer_id);
let transport = libp2p::development_transport(local_key).await?;
// Create a ping network behaviour.
//
// For illustrative purposes, the ping protocol is configured to
// keep the connection alive, so a continuous sequence of pings
// can be observed.
let behaviour = ping::Behaviour::new(ping::Config::new().with_keep_alive(true));
let mut swarm = Swarm::new(transport, behaviour, local_peer_id);
// Tell the swarm to listen on all interfaces and a random, OS-assigned
// port.
swarm.listen_on("/ip4/0.0.0.0/tcp/0".parse()?)?;
// Dial the peer identified by the multi-address given as the second
// command-line argument, if any.
if let Some(addr) = std::env::args().nth(1) {
let remote: Multiaddr = addr.parse()?;
swarm.dial(remote)?;
println!("Dialed {}", addr)
}
loop {
match swarm.select_next_some().await {
SwarmEvent::NewListenAddr { address, .. } => println!("Listening on {:?}", address),
SwarmEvent::Behaviour(event) => println!("{:?}", event),
_ => {}
}
}
}
Running two nodes
For convenience the example created above is also implemented in full in
examples/ping.rs
. Thus, you can either run the commands below from your
own project created during the tutorial, or from the root of the rust-libp2p
repository. Note that in the former case you need to ignore the --example ping
argument.
You need two terminals. In the first terminal window run:
cargo run --example ping
It will print the PeerId and the new listening addresses, e.g.
Local peer id: PeerId("12D3KooWT1As4mwh3KYBnNTw9bSrRbYQGJTm9SSte82JSumqgCQG")
Listening on "/ip4/127.0.0.1/tcp/24915"
Listening on "/ip4/192.168.178.25/tcp/24915"
Listening on "/ip4/172.17.0.1/tcp/24915"
Listening on "/ip6/::1/tcp/24915"
In the second terminal window, start a new instance of the example with:
cargo run --example ping -- /ip4/127.0.0.1/tcp/24915
Note: The Multiaddr
at the end being one of the Multiaddr
printed
earlier in terminal window one.
Both peers have to be in the same network with which the address is associated.
In our case any printed addresses can be used, as both peers run on the same
device.
The two nodes will establish a connection and send each other ping and pong messages every 15 seconds.