Include related address and port in marshaled candidate

lib/ex_ice/candidate.ex

@@ -44,7 +44,19 @@ defmodule ExICE.Candidate do
  transport = transport_to_string(transport)
  address = address_to_string(address)
 
- "#{foundation} #{component_id} #{transport} #{priority} #{address} #{port} typ #{type}"
+ # This is based on RFC 8839 sec. 5.1.
+ # Reflexive candidates MUST contain rel-addr and rel-port.
+ # However, for security reasons, we always use "0.0.0.0"
+ # (or "::" for ipv6) as rel-addr and "9" as rel-port.
+ related_addr =
+ cond do
+ type == :host -> ""
+ ExICE.Priv.Utils.family(address) == :ipv4 -> "raddr 0.0.0.0 rport 9"
+ ExICE.Priv.Utils.family(address) == :ipv6 -> "raddr :: rport 9"
+ end
+
+ "#{foundation} #{component_id} #{transport} #{priority} #{address} #{port} typ #{type} #{related_addr}"
+ |> String.trim()
  end
 
  @spec unmarshal(String.t()) :: {:ok, t()} | {:error, term()}
@@ -100,6 +112,7 @@ defmodule ExICE.Candidate do
 
  defp address_to_string(address) when is_binary(address), do: address
  defp address_to_string(address), do: :inet.ntoa(address)
+
  defp transport_to_string(:udp), do: "UDP"
 
  defp parse_transport("udp"), do: {:ok, :udp}