# Get the list of keys stored under the collection `key`.
	fun list_collection(key: String): JsonArray do
		var res = new JsonArray
		var coll = ("{store_dir}/{key}".simplify_path).to_path
		if not coll.exists or not coll.stat.is_dir then return res
		for file in coll.files do
			if file.to_s.has_suffix(".json") then
				res.add(file.to_s.basename(".json"))
			end
		end
		return res
	end