Use a controller to hold request values

So that we don't need to hold env after the request.
This makes it much harder to test, especially Rails session is
acting weirdly, so we need `dig('flash', 'flashes', 'alert')`
to dig the actual flash value.

lib/gitlab/middleware/read_only.rb

@@ -5,15 +5,13 @@ module Gitlab
       APPLICATION_JSON = 'application/json'.freeze
       API_VERSIONS = (3..4)
 
-      def initialize(app)
+      class Controller
+        def initialize(app, env)
           @app = app
-        @whitelisted = internal_routes
-      end
-
-      def call(env)
           @env = env
-        @route_hash = nil
+        end
 
+        def call
           if disallowed_request? && Gitlab::Database.read_only?
             Rails.logger.debug('GitLab ReadOnly: preventing possible non read-only operation')
             error_message = 'You cannot do writing operations on a read-only GitLab instance'
@@ -28,17 +26,14 @@ module Gitlab
             end
           end
 
-        @app.call(env).tap { @env = nil }
+          @app.call(@env)
         end
 
         private
 
-      def internal_routes
-        API_VERSIONS.flat_map { |version| "api/v#{version}/internal" }
-      end
-
         def disallowed_request?
-        DISALLOWED_METHODS.include?(@env['REQUEST_METHOD']) && !whitelisted_routes
+          DISALLOWED_METHODS.include?(@env['REQUEST_METHOD']) &&
+            !whitelisted_routes
         end
 
         def json_request?
@@ -66,7 +61,7 @@ module Gitlab
         end
 
         def whitelisted_routes
-        grack_route || @whitelisted.any? { |path| request.path.include?(path) } || lfs_route || sidekiq_route
+          grack_route || ReadOnly.internal_routes.any? { |path| request.path.include?(path) } || lfs_route || sidekiq_route
         end
 
         def sidekiq_route
@@ -87,5 +82,19 @@ module Gitlab
           route_hash[:controller] == 'projects/lfs_api' && route_hash[:action] == 'batch'
         end
       end
+
+      def self.internal_routes
+        @internal_routes ||=
+          API_VERSIONS.map { |version| "api/v#{version}/internal" }
+      end
+
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        Controller.new(@app, env).call
+      end
+    end
   end
 end

spec/lib/gitlab/middleware/read_only_spec.rb

@@ -11,8 +11,10 @@ describe Gitlab::Middleware::ReadOnly do
 
   RSpec::Matchers.define :disallow_request do
     match do |middleware|
-      flash = middleware.send(:rack_flash)
-      flash['alert'] && flash['alert'].include?('You cannot do writing operations')
+      alert = middleware.env['rack.session'].to_hash
+        .dig('flash', 'flashes', 'alert')
+
+      alert&.include?('You cannot do writing operations')
     end
   end
 
@@ -34,7 +36,22 @@ describe Gitlab::Middleware::ReadOnly do
     rack.to_app
   end
 
-  subject { described_class.new(fake_app) }
+  let(:observe_env) do
+    Module.new do
+      attr_reader :env
+
+      def call(env)
+        @env = env
+        super
+      end
+    end
+  end
+
+  subject do
+    app = described_class.new(fake_app)
+    app.extend(observe_env)
+    app
+  end
 
   let(:request) { Rack::MockRequest.new(rack_stack) }