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Discovery v5

Introduction

This eth/p2p/discoveryv5 directory holds a Nim implementation of the discovery v5 protocol specified here.

This specification is still in DRAFT and thus subject to change. In fact, it is likely that the current packet format will change, see https://github.com/ethereum/devp2p/issues/152.

This implementation does not support "Topic Advertisement" yet.

The implementation relies on other modules in the eth package, namely: keys, rlp, async_utils and trie/db. The latter is likely to change, see https://github.com/status-im/nim-eth/issues/242

How to use

let
  rng = keys.newRng
  privKey = PrivateKey.random(rng[])
  (ip, tcpPort, udpPort) = setupNat(config) # Or fill in external IP/ports manually
  ddb = DiscoveryDB.init(newMemoryDB())
  d = newProtocol(privKey, ddb, ip, tcpPort, udpPort, rng = rng)

d.open() # Start listening

This will initialize the Protocol and start listening. However, as no bootstrap nodes were passed in the newProtocol call, the created ENR will need to be advertised somehow ("out of band"), so that the node can become known to other nodes in the network.

To initialize with a bootnode or a set of bootnodes, the ENRs need to be passed as parameter in newProtocol.

d = newProtocol(privKey, ddb, ip, tcpPort, udpPort,
      bootstrapRecords = bootnodes)
d.open() # Start listening and add bootstrap nodes to the routing table.

Now there are two ways to run the protocol.

One can call d.start() and two loops will be started:

Random lookup loop
Revalidation loop

The first loop will at specific interval do a lookup with a random NodeId. This lookup will add discovered nodes to the routing table. The second loop will at random ranged interval send a ping to the least recently seen node in a random bucket. This is to keep the routing table cleared of unreachable/dead nodes.

Or, one can decide to do this manually within its application by using the available calls:

lookupRandom and lookup for discovering more peers.
revalidateNode or directly ping for revalidating nodes.

In the future, the random lookup loop might be altered to only run in case no lookup was done in the last x minutes. This way d.start() could still be run while maintaining control over the lookups.

Of course, in either scenario, lookups can still be done for actually finding a specific node. There is a resolve call that can help with this, it will first look in the local routing table and if it finds the node it will try to contact the node directly to check if the ENR is up to date. If any of this fail a lookup will be done.

Test suite

To run the test suite specifically for discovery v5 related (discovery v5 + its nim-eth dependencies) tests, one can run following command:

# Install required modules
nimble install
# Run only discovery v5 related test suite
nimble tests_discv5

dcli

This is a small command line application that allows you to run a discovery node. It also has the options to do a ping or findNode request to a specific node, by providing its ENR.

Example usage

# Build dcli
nim c -d:chronicles_log_level:trace -d:release eth/p2p/discoveryv5/dcli
# See all options
./eth/p2p/discoveryv5/dcli --help
# Ping another node
./eth/p2p/discoveryv5/dcli ping enr:<base64 encoding of ENR>
# Run discovery node
./eth/p2p/discoveryv5/dcli --log-level:debug --bootnode:enr:<base64 encoding of ENR>

Metrics

Metrics are available for routing_table_nodes, which holds the amount of nodes in the routing table.

To compile in an HTTP endpoint for accessing the metrics add the insecure compile time flag:

# Build dcli with metrics
nim c -d:insecure -d:chronicles_log_level:trace -d:release eth/p2p/discoveryv5/dcli
# Run dcli with metrics
./eth/p2p/discoveryv5/dcli --metrics --bootnode:enr:<base64 encoding of ENR>

You can now see the metrics at http://localhost:8008/metrics. Or use e.g. Prometheus to grab the data.

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