Allow to skip the dlk check

lib/amqp/helper.ex

@@ -3,8 +3,12 @@ defmodule Amqpx.Helper do
   Helper functions
   """
 
+  require Logger
+
   alias Amqpx.{Exchange, Queue}
 
+  @skip_dlk_check Application.compile_env(:amqpx, :skip_dlk_check, false)
+
   def manager_supervisor_configuration(config) do
     {Amqpx.Gen.ConnectionManager, %{connection_params: encrypt_password(config)}}
   end
@@ -92,7 +96,17 @@ defmodule Amqpx.Helper do
   end
 
   def setup_dead_lettering(_channel, %{queue: dlq, exchange: "", routing_key: bad_dlq}) do
-    raise "If x-dead-letter-exchange is an empty string, x-dead-letter-routing-key should be '#{dlq}' instead of '#{bad_dlq}'"
+    case @skip_dlk_check do
+      false ->
+        raise "If x-dead-letter-exchange is an empty string, x-dead-letter-routing-key should be '#{dlq}' instead of '#{bad_dlq}'"
+
+      true ->
+        Logger.warn(
+          "If x-dead-letter-exchange is an empty string, x-dead-letter-routing-key should be '#{dlq}' instead of '#{bad_dlq}'"
+        )
+
+        :ok
+    end
   end
 
   def setup_dead_lettering(channel, %{queue: dlq, exchange: exchange, routing_key: routing_key}) do

test/helper_test.exs

@@ -120,6 +120,32 @@ defmodule HelperTest do
                  end
   end
 
+  test "bad configuration with empty dead letter exchange and routing key is not a blocking error if the check is disabled",
+       meta do
+    queue_name = rand_name()
+    routing_key_name = rand_name()
+    exchange_name = rand_name()
+
+    Application.put_env(:amqpx, :skip_dlk_check, true)
+
+    :ok =
+      Helper.declare(meta[:chan], %{
+        exchanges: [
+          %{name: exchange_name, opts: [durable: true], routing_keys: [routing_key_name], type: :topic}
+        ],
+        opts: [
+          durable: true,
+          arguments: [
+            {"x-dead-letter-exchange", :longstr, ""},
+            {"x-dead-letter-routing-key", :longstr, ""}
+          ]
+        ],
+        queue: queue_name
+      })
+
+    Application.put_env(:amqpx, :skip_dlk_check, false)
+  end
+
   defp rand_name do
     :crypto.strong_rand_bytes(8) |> Base.encode64()
   end