Crate sc_network_gossip
source ·Expand description
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
Networktrait, representing the low-level networking primitives. It is already implemented onsc_network::NetworkService. - Implement the
Validatortrait. See the section below. - Decide on a protocol name. Each gossiping protocol should have a different one.
- Build a
GossipEngineusing these three elements. - Use the methods of the
GossipEnginein 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 sc-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.
Structs
Network trait and provides gossiping capabilities on
top of it.