AddHandlerFunc will add a handler-function to a P2PHandler instance: The passed in handlerFunc function takes a specific message of type M complying to the P2PMessage interface, processes it and returns a slice of resulting P2PMessages.

AddValidator will add a validator-function to a P2PHandler instance: The passed in ValidatorFunc function takes a specific message of type M complying to the P2PMessage interface, processes it and returns wether it is valid or not (bool value).

MustMultiaddr converts the given string to a multiaddr.Multiaddr.

Message envelopes the serialized protobuf bytes with additional topic and sender info.