Implementation of the [Gossipsub](https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/README.md) 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
() 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`](libp2p_identity::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](https://docs.libp2p.io/reference/glossary/#boot-node) of the network.
Peer
discovery can e.g. be implemented with the help of the [Kademlia](https://github.com/libp2p/specs/blob/master/kad-dht/README.md) protocol
in combination with the [Identify](https://github.com/libp2p/specs/tree/master/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:
[`Config`]: struct.Config.html
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`](libp2p_identity::PeerId) and [`Config`].
[`Behaviour`]: struct.Behaviour.html
## Example
For an example on how to use gossipsub, see the [chat-example](https://github.com/libp2p/rust-libp2p/tree/master/examples/chat).