soil_network/gossip/

mod.rs

// This file is part of Soil.

// Copyright (C) Soil contributors.
// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

//! Polite gossiping.
//!
//! This crate provides gossiping capabilities on top of a network.
//!
//! Gossip messages are separated by two categories: "topics" and consensus engine ID.
//! The consensus engine ID is sent over the wire with the message, while the topic is not,
//! with the expectation that the topic can be derived implicitly from the content of the
//! message, assuming it is valid.
//!
//! Topics are a single 32-byte tag associated with a message, used to group those messages
//! in an opaque way. Consensus code can invoke [`ValidatorContext::broadcast_topic`] to
//! attempt to send all messages under a single topic to all peers who don't have them yet, and
//! [`ValidatorContext::send_topic`] to send all messages under a single topic to a specific peer.
//!
//! # Usage
//!
//! - Implement the [`Network`] trait, representing the low-level networking primitives. It is
//!   already implemented on `soil_network::NetworkService`.
//! - Implement the [`Validator`] trait. See the section below.
//! - Decide on a protocol name. Each gossiping protocol should have a different one.
//! - Build a [`GossipEngine`] using these three elements.
//! - Use the methods of the [`GossipEngine`] in order to send out messages and receive incoming
//!   messages.
//!
//! The [`GossipEngine`] will automatically use [`Network::add_set_reserved`] and
//! [`NetworkPeers::remove_peers_from_reserved_set`] to maintain a set of peers equal to the set of
//! peers the node is syncing from. See the documentation of `soil-network` for more explanations
//! about the concepts of peer sets.
//!
//! # What is a validator?
//!
//! The primary role of a [`Validator`] is to process incoming messages from peers, and decide
//! whether to discard them or process them. It also decides whether to re-broadcast the message.
//!
//! The secondary role of the [`Validator`] is to check if a message is allowed to be sent to a
//! given peer. All messages, before being sent, will be checked against this filter.
//! This enables the validator to use information it's aware of about connected peers to decide
//! whether to send messages to them at any given moment in time - In particular, to wait until
//! peers can accept and process the message before sending it.
//!
//! Lastly, the fact that gossip validators can decide not to rebroadcast messages
//! opens the door for neighbor status packets to be baked into the gossip protocol.
//! These status packets will typically contain light pieces of information
//! used to inform peers of a current view of protocol state.

pub use self::{
	bridge::GossipEngine,
	state_machine::TopicNotification,
	validator::{DiscardAll, MessageIntent, ValidationResult, Validator, ValidatorContext},
};

use soil_network::sync::SyncEventStream;
use soil_network::types::{
	multiaddr::{Multiaddr, Protocol},
	PeerId,
};
use soil_network::{types::ProtocolName, NetworkBlock, NetworkEventStream, NetworkPeers};
use std::iter;
use subsoil::runtime::traits::{Block as BlockT, NumberFor};

mod bridge;
mod state_machine;
mod validator;

/// Abstraction over a network.
pub trait Network<B: BlockT>: NetworkPeers + NetworkEventStream {
	fn add_set_reserved(&self, who: PeerId, protocol: ProtocolName) {
		let addr = Multiaddr::empty().with(Protocol::P2p(*who.as_ref()));
		let result = self.add_peers_to_reserved_set(protocol, iter::once(addr).collect());
		if let Err(err) = result {
			log::error!(target: "gossip", "add_set_reserved failed: {}", err);
		}
	}
	fn remove_set_reserved(&self, who: PeerId, protocol: ProtocolName) {
		let result = self.remove_peers_from_reserved_set(protocol, iter::once(who).collect());
		if let Err(err) = result {
			log::error!(target: "gossip", "remove_set_reserved failed: {}", err);
		}
	}
}

impl<T, B: BlockT> Network<B> for T where T: NetworkPeers + NetworkEventStream {}

/// Abstraction over the syncing subsystem.
pub trait Syncing<B: BlockT>: SyncEventStream + NetworkBlock<B::Hash, NumberFor<B>> {}

impl<T, B: BlockT> Syncing<B> for T where T: SyncEventStream + NetworkBlock<B::Hash, NumberFor<B>> {}