P2P

Every rollup node (both full and light) runs a P2P client using go-libp2p P2P networking stack for gossiping transactions in the rollup's P2P network. The same P2P client is also used by the header and block sync services for gossiping headers and blocks.

Following parameters are required for creating a new instance of a P2P client:

• P2PConfig (described below)
• go-libp2p private key used to create a libp2p connection and join the p2p network.
• chainID: rollup identifier used as namespace within the p2p network for peer discovery. The namespace acts as a sub network in the p2p network, where peer connections are limited to the same namespace.
• datastore: an instance of go-datastore used for creating a connection gator and stores blocked and allowed peers.
• logger

// P2PConfig stores configuration related to peer-to-peer networking.
type P2PConfig struct {
	ListenAddress string // Address to listen for incoming connections
	Seeds         string // Comma separated list of seed nodes to connect to
	BlockedPeers  string // Comma separated list of nodes to ignore
	AllowedPeers  string // Comma separated list of nodes to whitelist
}

A P2P client also instantiates a connection gator to block and allow peers specified in the P2PConfig.

It also sets up a gossiper using the gossip topic <chainID>+<txTopicSuffix> (txTopicSuffix is defined in p2p/client.go), a Distributed Hash Table (DHT) using the Seeds defined in the P2PConfig and peer discovery using go-libp2p's discovery.RoutingDiscovery.

A P2P client provides an interface SetTxValidator(p2p.GossipValidator) for specifying a gossip validator which can define how to handle the incoming GossipMessage in the P2P network. The GossipMessage represents message gossiped via P2P network (e.g. transaction, Block etc).

// GossipValidator is a callback function type.
type GossipValidator func(*GossipMessage) bool

The full nodes define a transaction validator (shown below) as gossip validator for processing the gossiped transactions to add to the mempool, whereas light nodes simply pass a dummy validator as light nodes do not process gossiped transactions.

// newTxValidator creates a pubsub validator that uses the node's mempool to check the
// transaction. If the transaction is valid, then it is added to the mempool
func (n *FullNode) newTxValidator() p2p.GossipValidator {

// Dummy validator that always returns a callback function with boolean `false`
func (ln *LightNode) falseValidator() p2p.GossipValidator {

References

[1] client.go

[2] go-datastore

[3] go-libp2p

[4] conngater