Add ability to use multiple instances of middleware

lib/rack/attack.rb

@@ -96,9 +96,16 @@ def reset!
 
     attr_reader :configuration
 
-    def initialize(app)
+    def initialize(app, &block)
       @app = app
-      @configuration = self.class.configuration
+      @configuration =
+        if block_given?
+          configuration = Configuration.new
+          configuration.instance_exec(&block)
+          configuration
+        else
+          self.class.configuration
+        end
     end
 
     def call(env)

spec/acceptance/middleware_spec.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require_relative "../spec_helper"
+
+describe "Middleware" do
+  it "is used in Rails by default" do
+    skip unless defined?(Rails)
+
+    app = Class.new(Rails::Application) do
+      config.eager_load = false
+      config.logger = Logger.new(nil) # avoid creating the log/ directory automatically
+      config.cache_store = :null_store # avoid creating tmp/ directory for cache
+    end
+
+    app.initialize!
+    assert app.middleware.include?(Rack::Attack)
+  end
+
+  def app
+    Rack::Builder.new do
+      use Rack::Attack do
+        blocklist_ip("1.2.3.4")
+      end
+
+      run lambda { |_env| [200, {}, ['Hello World']] }
+    end.to_app
+  end
+
+  it "can be configured via a block" do
+    get "/", {}, "REMOTE_ADDR" => "1.2.3.4"
+    assert_equal 403, last_response.status
+
+    get "/", {}, "REMOTE_ADDR" => "4.3.2.1"
+    assert_equal 200, last_response.status
+  end
+end