Implementation of the Gossipsub protocol.

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 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. When messages are signed, they are monotonically increasing integers starting from a random value and wrapping around u64::MAX. When messages are unsigned, they are chosen at random. NOTE: These numbers are sequential in the current go implementation.

Peer Discovery

Gossipsub does not provide peer discovery by itself. Peer discovery is the process by which peers in a p2p network exchange information about each other among other reasons to become resistant against the failure or replacement of the boot nodes of the network.

Peer discovery can e.g. be implemented with the help of the Kademlia protocol in combination with the Identify protocol. See the Kademlia implementation documentation for more information.

Using Gossipsub

Gossipsub Config

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

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

Behaviour

The Behaviour struct implements the libp2p_swarm::NetworkBehaviour trait allowing it to act as the routing behaviour in a libp2p_swarm::Swarm. This struct requires an instance of PeerId and Config.

Example

For an example on how to use gossipsub, see the chat-example.