chore: add backwards compat for Port.command impl

lib/statix/conn.ex

@@ -7,6 +7,9 @@ defmodule Statix.Conn do
 
   require Logger
 
+  otp_release = :erlang.system_info(:otp_release)
+  @otp_gte_26 otp_release >= ~c"26"
+
   def new(host, port, prefix) when is_binary(host) do
     new(String.to_charlist(host), port, prefix)
   end
@@ -50,10 +53,30 @@ defmodule Statix.Conn do
   defp transmit(packet, %__MODULE__{address: address, port: port, sock: sock_name}) do
     sock = Process.whereis(sock_name)
 
-    if sock do
-      :gen_udp.send(sock, address, port, packet)
+    # The check below was implemented for backwards compatibility to avoid a performance issue on
+    # OTP on versiones older than 26. If the OTP version is 26 or above, we use gen_udp.send/4. If
+    # the version is older than that, we use the existing performance issue workaround.
+    if @otp_gte_26 do
+      if sock do
+        :gen_udp.send(sock, address, port, packet)
+      else
+        {:error, :port_closed}
+      end
     else
-      {:error, :port_closed}
+      # This branch will only be executed on older version of OTP and will be eventually removed.
+      packet_with_header = Packet.add_header(packet, address, port)
+
+      try do
+        Port.command(sock, packet_with_header)
+      rescue
+        ArgumentError ->
+          {:error, :port_closed}
+      else
+        true ->
+          receive do
+            {:inet_reply, _port, status} -> status
+          end
+      end
     end
   end
 end

lib/statix/packet.ex

@@ -1,6 +1,38 @@
 defmodule Statix.Packet do
   @moduledoc false
 
+  import Bitwise
+
+  @doc """
+  Adds header to a built packet.
+  This is implemented to keep backwards compatibility with older OTP versions
+  (< 26). Will be eventually removed.
+  """
+  def add_header(built_packet, {n1, n2, n3, n4}, port) do
+    true = Code.ensure_loaded?(:gen_udp)
+
+    anc_data_part =
+      if function_exported?(:gen_udp, :send, 5) do
+        [0, 0, 0, 0]
+      else
+        []
+      end
+
+    header =
+      [
+        _addr_family = 1,
+        band(bsr(port, 8), 0xFF),
+        band(port, 0xFF),
+        band(n1, 0xFF),
+        band(n2, 0xFF),
+        band(n3, 0xFF),
+        band(n4, 0xFF)
+      ] ++ anc_data_part
+
+    header_as_bytes = Enum.into(header, <<>>, fn byte -> <<byte>> end)
+    [header_as_bytes | built_packet]
+  end
+
   def build(prefix, name, key, val, options) do
     [prefix, key, ?:, val, ?|, metric_type(name)]
     |> set_option(:sample_rate, options[:sample_rate])