Gossipsub is a P2P pubsub (publish/subscription) routing layer designed to extend upon floodsub and meshsub routing protocols.

Overview

Note: The gossipsub protocol specifications (https://github.com/libp2p/specs/tree/master/pubsub/gossipsub) provide an outline for the routing protocol. They should be consulted for further detail.

Gossipsub is a blend of meshsub for data and randomsub for mesh metadata. It provides bounded degree and amplification factor with the meshsub construction and augments it using gossip propagation of metadata with the randomsub technique.

The router maintains an overlay mesh network of peers on which to efficiently send messages and metadata. Peers use control messages to broadcast and request known messages and subscribe/unsubscribe from topics in the mesh network.

Important Discrepancies

This section outlines the current implementation's potential discrepancies from that of other implementations, due to undefined elements in the current specification.

• Topics - In gossipsub, topics configurable by the hash_topics configuration parameter. Topics are of type TopicHash. The current go implementation uses raw utf-8 strings, and this is default configuration in rust-libp2p. Topics can be hashed (SHA256 hashed then base64 encoded) by setting the hash_topics configuration parameter to true.

• Sequence Numbers - A message on the gossipsub network is identified by the source mwc_libp2p_core::PeerId and a nonce (sequence number) of the message. The sequence numbers in this implementation are sent as raw bytes across the wire. They are 64-bit big-endian unsigned integers. They are chosen at random in this implementation of gossipsub, but are sequential in the current go implementation.

Using Gossipsub

GossipsubConfig

The GossipsubConfig struct specifies various network performance/tuning configuration parameters. Specifically it specifies:

This struct implements the Default trait and can be initialised via [GossipsubConfig::default()].

Gossipsub

The Gossipsub struct implements the mwc_libp2p_swarm::NetworkBehaviour trait allowing it to act as the routing behaviour in a mwc_libp2p_swarm::Swarm. This struct requires an instance of mwc_libp2p_core::PeerId and GossipsubConfig.

Example

An example of initialising a gossipsub compatible swarm:

use mwc_libp2p_gossipsub::GossipsubEvent;
use mwc_libp2p_core::{identity::Keypair,transport::{Transport, MemoryTransport}, Multiaddr};
use mwc_libp2p_gossipsub::MessageAuthenticity;
let local_key = Keypair::generate_ed25519();
let local_peer_id = mwc_libp2p_core::PeerId::from_public_key(local_key.public());

// Set up an encrypted TCP Transport over the Mplex
// This is test transport (memory).
let noise_keys = mwc_libp2p_noise::Keypair::<mwc_libp2p_noise::X25519Spec>::new().into_authentic(&local_key).unwrap();
let transport = MemoryTransport::default()
           .upgrade(mwc_libp2p_core::upgrade::Version::V1)
           .authenticate(mwc_libp2p_noise::NoiseConfig::xx(noise_keys).into_authenticated())
           .multiplex(mwc_libp2p_mplex::MplexConfig::new())
           .boxed();

// Create a Gossipsub topic
let topic = mwc_libp2p_gossipsub::IdentTopic::new("example");

// Set the message authenticity - How we expect to publish messages
// Here we expect the publisher to sign the message with their key.
let message_authenticity = MessageAuthenticity::Signed(local_key);

// Create a Swarm to manage peers and events
let mut swarm = {
    // set default parameters for gossipsub
    let gossipsub_config = mwc_libp2p_gossipsub::GossipsubConfig::default();
    // build a gossipsub network behaviour
    let mut gossipsub: mwc_libp2p_gossipsub::Gossipsub =
        mwc_libp2p_gossipsub::Gossipsub::new(message_authenticity, gossipsub_config).unwrap();
    // subscribe to the topic
    gossipsub.subscribe(&topic);
    // create the swarm
    mwc_libp2p_swarm::Swarm::new(
        transport,
        gossipsub,
        local_peer_id,
    )
};

// Listen on a memory transport.
let memory: Multiaddr = mwc_libp2p_core::multiaddr::Protocol::Memory(10).into();
let addr = mwc_libp2p_swarm::Swarm::listen_on(&mut swarm, memory).unwrap();
println!("Listening on {:?}", addr);