--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/util/hashring.lua	Mon May 13 10:03:46 2019 +0100
@@ -0,0 +1,88 @@
+local function generate_ring(nodes, num_replicas, hash)
+	local new_ring = {};
+        for _, node_name in ipairs(nodes) do
+                for replica = 1, num_replicas do
+                        local replica_hash = hash(node_name..":"..replica);
+                        new_ring[replica_hash] = node_name;
+                        table.insert(new_ring, replica_hash);
+                end
+        end
+        table.sort(new_ring);
+	return new_ring;
+end
+
+local hashring_methods = {};
+local hashring_mt = {
+	__index = function (self, k)
+		-- Automatically build self.ring if it's missing
+		if k == "ring" then
+			local ring = generate_ring(self.nodes, self.num_replicas, self.hash);
+			rawset(self, "ring", ring);
+			return ring;
+		end
+		return rawget(hashring_methods, k);
+	end
+};
+
+local function new(num_replicas, hash_function)
+	return setmetatable({ nodes = {}, num_replicas = num_replicas, hash = hash_function }, hashring_mt);
+end;
+
+function hashring_methods:add_node(name)
+	self.ring = nil;
+	self.nodes[name] = true;
+	table.insert(self.nodes, name);
+	return true;
+end
+
+function hashring_methods:add_nodes(nodes)
+	self.ring = nil;
+	for _, node_name in ipairs(nodes) do
+		if not self.nodes[node_name] then
+			self.nodes[node_name] = true;
+			table.insert(self.nodes, node_name);
+		end
+	end
+	return true;
+end
+
+function hashring_methods:remove_node(node_name)
+	self.ring = nil;
+	if self.nodes[node_name] then
+		for i, stored_node_name in ipairs(self.nodes) do
+			if node_name == stored_node_name then
+				self.nodes[node_name] = nil;
+				table.remove(self.nodes, i);
+				return true;
+			end
+		end
+	end
+	return false;
+end
+
+function hashring_methods:remove_nodes(nodes)
+	self.ring = nil;
+	for _, node_name in ipairs(nodes) do
+		self:remove_node(node_name);
+	end
+end
+
+function hashring_methods:clone()
+	local clone_hashring = new(self.num_replicas, self.hash);
+	clone_hashring:add_nodes(self.nodes);
+	return clone_hashring;
+end
+
+function hashring_methods:get_node(key)
+	local key_hash = self.hash(key);
+	for _, replica_hash in ipairs(self.ring) do
+		if key_hash < replica_hash then
+			return self.ring[replica_hash];
+		end
+	end
+	return self.ring[self.ring[1]];
+end
+
+return {
+	new = new;
+}