implement basic dead letter exchange behaviour

lib/bunny_mock/channel.rb

@@ -282,7 +282,7 @@ def ack(delivery_tag, multiple = false)
           ack(key, false) if key <= delivery_tag
         end
       elsif @acknowledged_state[:pending].key?(delivery_tag)
-        update_acknowledgement_state(delivery_tag, :acked)
+        handle_acknowledgement(delivery_tag, :acked)
       end
       nil
     end
@@ -304,8 +304,7 @@ def nack(delivery_tag, multiple = false, requeue = false)
           nack(key, false, requeue) if key <= delivery_tag
         end
       elsif @acknowledged_state[:pending].key?(delivery_tag)
-        delivery, header, body = update_acknowledgement_state(delivery_tag, :nacked)
-        delivery.queue.publish(body, header.to_hash) if requeue
+        handle_acknowledgement(delivery_tag, :nacked, requeue)
       end
       nil
     end
@@ -322,8 +321,7 @@ def nack(delivery_tag, multiple = false, requeue = false)
     #
     def reject(delivery_tag, requeue = false)
       if @acknowledged_state[:pending].key?(delivery_tag)
-        delivery, header, body = update_acknowledgement_state(delivery_tag, :rejected)
-        delivery.queue.publish(body, header.to_hash) if requeue
+        handle_acknowledgement(delivery_tag, :rejected, requeue)
       end
       nil
     end
@@ -399,6 +397,27 @@ def xchg_find_or_create(name, opts = {})
       @connection.find_exchange(name) || Exchange.declare(self, name, opts)
     end
 
+    # @private
+    def handle_acknowledgement(delivery_tag, new_state, requeue = false)
+      delivery, header, body = update_acknowledgement_state(delivery_tag, new_state)
+      return unless %i(nacked rejected).include?(new_state)
+
+      options = header.to_hash
+      return delivery.queue.publish(body, options) if requeue
+
+      dlx, routing_key = dead_letter_arguments(delivery.queue)
+      return unless dlx
+      options[:routing_key] = routing_key if routing_key
+      exchange(dlx).publish(body, options)
+    end
+
+    # @private
+    def dead_letter_arguments(queue)
+      arguments = queue.opts[:arguments]
+      return [nil, nil] unless arguments
+      [arguments['x-dead-letter-exchange'], arguments['x-dead-letter-routing-key']]
+    end
+
     # @private
     def update_acknowledgement_state(delivery_tag, new_state)
       @acknowledged_state[new_state][delivery_tag] = @acknowledged_state[:pending].delete(delivery_tag)

spec/integration/message_acknowledgement_spec.rb

@@ -110,5 +110,57 @@
         expect(@channel.acknowledged_state[:pending]).to include(new_delivery_tag)
       end
     end
+
+    context 'when having a dead letter exchange defined' do
+      let(:dlx) { @channel.fanout('test.dlx') }
+      let(:dlq) { @channel.temporary_queue.bind(dlx) }
+      before do
+        dlq
+        queue.opts.merge!(arguments: { 'x-dead-letter-exchange' => dlx.name })
+      end
+
+      it 'should send nacked message to dead letter exchange if specified' do
+        queue.publish 'Message to nack'
+        @channel.nack delivery_tags['Message to nack']
+
+        expect(dlq.message_count).to be 1
+        expect(dlq.pop.last).to eq 'Message to nack'
+      end
+
+      it 'should not send nacked message to dead letter exchange if it is requeued' do
+        queue.publish 'Message to nack'
+        @channel.nack delivery_tags['Message to nack'], false, true
+
+        expect(dlq.message_count).to be 0
+      end
+
+      it 'should send rejected message to dead letter exchange if specified' do
+        queue.publish 'Message to reject'
+        @channel.reject delivery_tags['Message to reject']
+
+        expect(dlq.message_count).to be 1
+        expect(dlq.pop.last).to eq 'Message to reject'
+      end
+
+      it 'should not send rejected message to dead letter exchange if it is requeued' do
+        queue.publish 'Message to reject'
+        @channel.nack delivery_tags['Message to reject'], false, true
+
+        expect(dlq.message_count).to be 0
+      end
+
+      it 'should be possible to overwrite the dead letter routing key' do
+        queue.opts.merge!(arguments: { 'x-dead-letter-exchange' => dlx.name, 'x-dead-letter-routing-key' => 'dl_key' })
+        queue.publish 'Message to reject'
+        @channel.reject delivery_tags['Message to reject']
+
+        expect(dlq.message_count).to be 1
+        delivery_info, headers, payload = dlq.pop
+        expect(payload).to eq 'Message to reject'
+        expect(headers[:routing_key]).to eq 'dl_key'
+        expect(delivery_info[:routing_key]).to eq 'dl_key'
+      end
+
+    end
   end
 end