This module offers message sending and receiving of messages using ideas based on Kademlia. Contrary to Kademlia, the DHT_Router does not set up a connection to the closest destination of the message. Instead it sets up a list of buckets as in the Kademlia paper to have a restricted set of nodes with which it talks. Messages are then actually forwarded through these nodes until they reach destination. The advantage is that it doesn't need to set up new connections for every destination. The disadvantage is that the attack surface with regard to dropping messages is much bigger.
The DHT Router offers these three types of messages:
MessageClosestwhich correspond the most to the original Kademlia messages. It sends a message as close as possible to the destination.MessageDirectis used for replies in the system - it tries to match a node directly, but can fail silently if the destination is not reachable.MessageBroadcastsends the message to all currently connected nodes.
As long as all nodes get a full list of all other nodes, the system performs very nice:
as well MessageClosest and MessageDirect reach the defined targets.
Using the tests, it is shown that even with very short bucket lengths of 1 every message
reaches its target.
However, if some of the nodes only have a partial view of the network, this completely breaks. In this case, not all of the messages get to the closest or the target node. But for replies even in this scenario it should still hold: unless the network changed a lot between the request and the reply, the reply should be able to find the source node.
The implementation in kademlia.rs is split in two structures:
Kademliato manage adding/removing nodes and finding the relevant bucketsKBucketto implement one bucket of nodes, including calculation of the distance and handling the life-cycle of the nodes