Rack handler should use provided default host

lib/puma/dsl.rb

@@ -57,6 +57,14 @@ def _offer_plugins
       @plugins.clear
     end
 
+    def set_default_host(host)
+      @options[:default_host] = host
+    end
+
+    def default_host
+      @options[:default_host] || Configuration::DefaultTCPHost
+    end
+
     def inject(&blk)
       instance_eval(&blk)
     end
@@ -140,7 +148,7 @@ def clear_binds!
     # Define the TCP port to bind to. Use +bind+ for more advanced options.
     #
     def port(port, host=nil)
-      host ||= Configuration::DefaultTCPHost
+      host ||= default_host
       bind "tcp://#{host}:#{port}"
     end
 

lib/rack/handler/puma.rb

@@ -49,6 +49,9 @@ def self.config(app, options = {})
             self.set_host_port_to_config(host, port, user_config)
           end
 
+          if default_options[:Host]
+            file_config.set_default_host(default_options[:Host])
+          end
           self.set_host_port_to_config(default_options[:Host], default_options[:Port], default_config)
 
           user_config.app app

test/test_rack_handler.rb

@@ -123,6 +123,44 @@ def test_config_file_wins_over_port
       end
     end
   end
+
+  def test_default_host_when_using_config_file
+    user_port = 5001
+    file_port = 6001
+
+    Dir.mktmpdir do |d|
+      Dir.chdir(d) do
+        FileUtils.mkdir("config")
+        File.open("config/puma.rb", "w") { |f| f << "port #{file_port}" }
+
+        @options[:Host] = "localhost"
+        @options[:Port] = user_port
+        conf = Rack::Handler::Puma.config(->{}, @options)
+        conf.load
+
+        assert_equal ["tcp://localhost:#{file_port}"], conf.options[:binds]
+      end
+    end
+  end
+
+  def test_default_host_when_using_config_file_with_explicit_host
+    user_port = 5001
+    file_port = 6001
+
+    Dir.mktmpdir do |d|
+      Dir.chdir(d) do
+        FileUtils.mkdir("config")
+        File.open("config/puma.rb", "w") { |f| f << "port #{file_port}, '1.2.3.4'" }
+
+        @options[:Host] = "localhost"
+        @options[:Port] = user_port
+        conf = Rack::Handler::Puma.config(->{}, @options)
+        conf.load
+
+        assert_equal ["tcp://1.2.3.4:#{file_port}"], conf.options[:binds]
+      end
+    end
+  end
 end
 
 class TestUserSuppliedOptionsIsNotPresent < Minitest::Test