Add get_current_tip query

lib/xander/messages.ex

@@ -14,6 +14,7 @@ defmodule Xander.Messages do
   @get_current_block_height [2]
   @get_current_era [0, [2, [1]]]
   @get_epoch_number [0, [0, [6, [1]]]]
+  @get_current_tip [3]
 
   # See the CDDL for details on mapping of messages to numbers.
   # https://github.com/IntersectMBO/ouroboros-network/blob/main/ouroboros-network-protocols/cddl/specs/local-state-query.cddl
@@ -111,6 +112,27 @@ defmodule Xander.Messages do
     header(@mini_protocols.local_state_query, bitstring_payload) <> bitstring_payload
   end
 
+  @doc """
+  Builds a static query to get the current tip of the chain
+
+  Payload CBOR: [3]
+  Payload Bitstring: <<129, 3>>
+
+  ## Examples
+
+    iex> <<_timestamp::32, msg::binary>> = Xander.Messages.get_current_tip()
+    iex> msg
+    <<0, 7, 0, 4, 130, 3, 129, 3>>
+
+  """
+  @spec get_current_tip() :: binary()
+  def get_current_tip do
+    payload = build_query(@get_current_tip)
+    bitstring_payload = CBOR.encode(payload)
+
+    header(@mini_protocols.local_state_query, bitstring_payload) <> bitstring_payload
+  end
+
   defp build_query(query), do: [@message_query, query]
 
   # middle 16 bits are: 1 bit == 0 for initiator and 15 bits for the mini protocol ID

lib/xander/query.ex

@@ -135,6 +135,7 @@ defmodule Xander.Query do
         :get_current_era -> Messages.get_current_era()
         :get_current_block_height -> Messages.get_current_block_height()
         :get_epoch_number -> Messages.get_epoch_number()
+        :get_current_tip -> Messages.get_current_tip()
       end
 
     :ok = client.send(socket, message)

lib/xander/query/response.ex

@@ -13,6 +13,12 @@ defmodule Xander.Query.Response do
     end
   end
 
+  # This clause parses the response from the get_current_tip query
+  defp parse_cbor([@message_response, [slot_number, %CBOR.Tag{tag: :bytes, value: response}]]) do
+    block_hash = Base.encode16(response, case: :lower)
+    {:ok, {slot_number, block_hash}}
+  end
+
   # For get_current_block_height
   defp parse_cbor([@message_response, [@slot_timeline, response]]) do
     {:ok, response}

run.exs

@@ -20,7 +20,8 @@ config = Config.default_config!(socket_path)
 queries = [
   :get_epoch_number,
   :get_current_era,
-  :get_current_block_height
+  :get_current_block_height,
+  :get_current_tip
 ]
 
 case Query.start_link(config) do

run_with_demeter.exs

@@ -23,7 +23,8 @@ config = Config.demeter_config!(demeter_url, network: network)
 queries = [
   :get_epoch_number,
   :get_current_era,
-  :get_current_block_height
+  :get_current_block_height,
+  :get_current_tip
 ]
 
 case Query.start_link(config) do