Crate discv5

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An implementation of Discovery V5.

§Overview

Discovery v5 is a protocol designed for encrypted peer discovery and topic advertisement. Each peer/node on the network is identified via it’s ENR (Ethereum Name Record), which is essentially a signed key-value store containing the node’s public key and optionally IP address and port.

Discv5 employs a kademlia-like routing table to store and manage discovered peers. The protocol allows for external IP discovery in NAT environments through regular PING/PONG’s with discovered nodes. Nodes return the external IP address that they have received and a simple majority is chosen as our external IP address. If an external IP address is updated, this is produced as an event.

For a simple CLI discovery service see discv5-cli

This protocol is split into four main layers:

  • socket: Responsible for opening the underlying UDP socket. It creates individual tasks for sending/encoding and receiving/decoding packets from the UDP socket.
  • handler: The protocol’s communication is encrypted with AES_GCM. All node communication undergoes a handshake, which results in a Session. These are established when needed and get dropped after a timeout. The creation and maintenance of sessions between nodes and the encryption/decryption of packets from the socket is realised by the handler::Handler struct runnning in its own task.
  • service: Contains the protocol-level logic. The service::Service manages the routing table of known ENR’s, and performs parallel queries for peer discovery. It also runs in it’s own task.
  • Discv5: The application level. Manages the user-facing API. It starts/stops the underlying tasks, allows initiating queries and obtain metrics about the underlying server.

§Event Stream

The Discv5 struct provides access to an event-stream which allows the user to listen to Event that get generated from the underlying server. The stream can be obtained from the Discv5::event_stream function.

§Runtimes

Discv5 requires a tokio runtime with timing and io enabled. An explicit runtime can be given via the configuration. See the ConfigBuilder for further details. Such a runtime must implement the Executor trait.

If an explicit runtime is not provided via the configuration parameters, it is assumed that a tokio runtime is present when creating the Discv5 struct. The struct will use the existing runtime for spawning the underlying server tasks. If a runtime is not present, the creation of the Discv5 struct will panic.

§Usage

A simple example of creating this service is as follows:

   use discv5::{enr, enr::{CombinedKey, Enr, NodeId}, TokioExecutor, Discv5, ConfigBuilder};
   use discv5::socket::ListenConfig;
   use std::net::{Ipv4Addr, SocketAddr};

   // construct a local ENR
   let enr_key = CombinedKey::generate_secp256k1();
   let enr = enr::Enr::empty(&enr_key).unwrap();

   // build the tokio executor
   let mut runtime = tokio::runtime::Builder::new_multi_thread()
       .thread_name("Discv5-example")
       .enable_all()
       .build()
       .unwrap();

   // configuration for the sockets to listen on
   let listen_config = ListenConfig::Ipv4 {
       ip: Ipv4Addr::UNSPECIFIED,
       port: 9000,
   };

   // default configuration
   let config = ConfigBuilder::new(listen_config).build();

   // construct the discv5 server
   let mut discv5: Discv5 = Discv5::new(enr, enr_key, config).unwrap();

   // In order to bootstrap the routing table an external ENR should be added
   // This can be done via add_enr. I.e.:
   // discv5.add_enr(<ENR>)

   // start the discv5 server
   runtime.block_on(discv5.start());

   // run a find_node query
   runtime.block_on(async {
      let found_nodes = discv5.find_node(NodeId::random()).await.unwrap();
      println!("Found nodes: {:?}", found_nodes);
   });

Re-exports§

Modules§

  • handler
    Session and packet handling for the Discv5 Discovery service.
  • kbucket
    Implementation of a Kademlia routing table as used by a single peer participating in a Kademlia DHT.
  • metrics
  • packet
    This module defines the raw UDP message packets for Discovery v5.1.
  • permit_ban
  • rpc
  • service
    The Discovery v5 protocol. See lib.rs for further details.
  • socket

Structs§

  • Config
    Configuration parameters that define the performance of the discovery network.
  • ConfigBuilder
  • Discv5
    The main Discv5 Service struct. This provides the user-level API for performing queries and interacting with the underlying service.
  • TokioExecutor

Enums§

  • Error
    A general error that is used throughout the Discv5 library.
  • Event
    Events that can be produced by the Discv5 event stream.
  • IpMode
    Sets the socket type to be established and also determines the type of ENRs that we will store in our routing table. We store ENR’s that have a get_contractable_addr() based on the IpMode set.
  • QueryError
  • RequestError
  • ResponseError

Traits§

Type Aliases§