Implementing a DHT in Go, part 2

In the previous post, we started a straightforward implementation of a Kademlia Distributed Hash Table in Go. Today, we'll add in the real meat - interaction between peers to find nodes.

First, though, a correction to the previous post. There were a couple of errors in it, the most notable of which is that the routing table's FindClosest method failed to order the returned results correctly. The original implementation ordered results by their absolute node ID, but the correct ordering is by their ID xor the target ID. To my shame, my rudimentary unit tests did not catch thils. This is now fixed in the original article with the introduction of a 'ContactRecord' struct.

Let's start by defining a Kademlia struct to hold information about a Kademlia network:

type Kademlia struct {
  routes *RoutingTable;
  NetworkId string;

func NewKademlia(self *Contact, networkId string) (ret *Kademlia) {
  ret = new(Kademlia);
  ret.routes = NewRoutingTable(self);
  ret.NetworkId = networkId;

Note the presence of the 'NetworkId' field in the above code. This is an arbitrary string that should be unique for each deployment of our Kademlia implementation, to prevent different instances of the network merging together.

Go supports RPC calls using its built in ...

Implementing a DHT in Go, part 1

In order to further explore the capabilities and limitations of Go, I thought it would be interesting to try implementing something that was practical, non-trivial, and of interest on its own. With that in mind, we're going to spend the next few posts creating an implementation of the Kademlia DHT in Go.

A DHT, or Distributed Hash Table is a peer-to-peer networking primitive that, in its most basic formulation, permits storage and lookup of key, value pairs - that is, it's a hash table that's distributed across many nodes. The name is not entirely accurate for some newer DHTs, as some formulations permit many other operations besides those focused around data storage and retrieval.

Kademlia is a good example of a basic DHT, because unlike some competing algorithms, it's extremely simple. There are no explicit routing update messages, and the internal state it maintains is fairly straightforward and easy to understand. Lookups are also accomplished in an obvious - yet very efficient - manner. In return for this simplicity, Kademlia sacrifices a few of the features of competitors like Pastry and Chord - it's not as practical to implement other primitives such as pubsub over it.

The reference we ...