Rack::Backstage - maintenance page middleware

If specified file exists, serve that one. Convenient for
maintenance pages.

README.rdoc

@@ -38,6 +38,8 @@ interface:
   to Disk or a user provider Ruby object. Similar to Rails' page caching.
 * Rack::RelativeRedirect - Transforms relative paths in redirects to
   absolute URLs.
+* Rack::Backstage - Returns content of specified file if it exists, which makes
+  it convenient for putting up maintenance pages.
 
 === Use
 

lib/rack/contrib/backstage.rb

@@ -0,0 +1,20 @@
+module Rack
+  class Backstage
+    File = ::File
+
+    def initialize(app, path)
+      @app = app
+      @file = File.expand_path(path)
+    end
+
+    def call(env)
+      if File.exists?(@file)
+        content = File.read(@file)
+        length = "".respond_to?(:bytesize) ? content.bytesize.to_s : content.size.to_s
+        [503, {'Content-Type' => 'text/html', 'Content-Length' => length}, content]
+      else
+        @app.call(env)
+      end
+    end
+  end
+end

test/Maintenance.html

@@ -0,0 +1 @@
+Under maintenance.

test/spec_rack_backstage.rb

@@ -0,0 +1,25 @@
+require 'test/spec'
+require 'rack/mock'
+require 'rack/contrib/backstage'
+
+context "Rack::Backstage" do
+  specify "shows maintenances page if present" do
+    app = Rack::Builder.new do
+      use Rack::Backstage, 'test/Maintenance.html'
+      run lambda { |env| [200, {'Content-Type' => 'text/plain'}, "Hello, World!"] }
+    end
+    response = Rack::MockRequest.new(app).get('/')
+    response.body.should.equal('Under maintenance.')
+    response.status.should.equal(503)
+  end
+
+  specify "passes on request if page is not present" do
+    app = Rack::Builder.new do
+      use Rack::Backstage, 'test/Nonsense.html'
+      run lambda { |env| [200, {'Content-Type' => 'text/plain'}, "Hello, World!"] }
+    end
+    response = Rack::MockRequest.new(app).get('/')
+    response.body.should.equal('Hello, World!')
+    response.status.should.equal(200)
+  end
+end