Return proper TURN address when requesting credentials from AuthProvider

lib/ex_turn/auth_provider.ex

@@ -23,6 +23,8 @@ defmodule ExTURN.AuthProvider do
       ip_addr = Application.fetch_env!(:ex_turn, :listen_ip)
       port = Application.fetch_env!(:ex_turn, :listen_port)
 
+      ip_addr = if(ip_addr == {0, 0, 0, 0}, do: get_public_ip_addr(), else: ip_addr)
+
       response =
         Jason.encode!(%{
           "username" => username,
@@ -51,4 +53,15 @@ defmodule ExTURN.AuthProvider do
   match _ do
     send_resp(conn, 400, "invalid request")
   end
+
+  defp get_public_ip_addr() do
+    with {:ok, opts} <- :inet.getifaddrs(),
+         addrs <- Enum.flat_map(opts, fn {_if, opt} -> Keyword.get_values(opt, :addr) end),
+         addr <- Enum.find(addrs, &match?({a, _, _, _} when a != 127, &1)),
+         false <- is_nil(addr) do
+      addr
+    else
+      _other -> "AuthProvider listens on 0.0.0.0, but failed to find public IP interface"
+    end
+  end
 end

lib/ex_turn/listener.ex

@@ -40,10 +40,6 @@ defmodule ExTURN.Listener do
         ]
       )
 
-    # in case 0.0.0.0 was used, AuthProvider requires actuall interface address
-    {:ok, {server_ip, _port}} = :inet.sockname(socket)
-    Application.put_env(:ex_turn, :listen_ip, server_ip)
-
     spawn(ExTURN.Monitor, :start, [self(), socket])
 
     recv_loop(socket, %{