From 7ba372e5246c18ebe05c5935b9f6390d0171c7ec Mon Sep 17 00:00:00 2001
From: Geoff Buesing <gbuesing@gmail.com>
Date: Sun, 17 Jan 2010 09:59:50 -0600
Subject: [PATCH] Rack::Branch - Conditionally re-route the Rack pipeline to an alternate endpoint

---
 README.rdoc                |    1 +
 lib/rack/contrib.rb        |    1 +
 lib/rack/contrib/branch.rb |   47 ++++++++++++++++++++++++++
 test/spec_rack_branch.rb   |   79 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 128 insertions(+), 0 deletions(-)
 create mode 100644 lib/rack/contrib/branch.rb
 create mode 100644 test/spec_rack_branch.rb

diff --git a/README.rdoc b/README.rdoc
index ca015ae..a913826 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -46,6 +46,7 @@ interface:
 * Rack::HostMeta - Configures /host-meta using a block
 * Rack::Cookies - Adds simple cookie jar hash to env
 * Rack::Access - Limit access based on IP address
+* Rack::Branch - Conditionally re-route the Rack pipeline to an alternate endpoint
 
 === Use
 
diff --git a/lib/rack/contrib.rb b/lib/rack/contrib.rb
index 8905437..83a225e 100644
--- a/lib/rack/contrib.rb
+++ b/lib/rack/contrib.rb
@@ -10,6 +10,7 @@ module Rack
   autoload :AcceptFormat,               "rack/contrib/accept_format"
   autoload :Access,                     "rack/contrib/access"
   autoload :BounceFavicon,              "rack/contrib/bounce_favicon"
+  autoload :Branch,                     "rack/contrib/branch"
   autoload :Cookies,                    "rack/contrib/cookies"
   autoload :CSSHTTPRequest,             "rack/contrib/csshttprequest"
   autoload :Deflect,                    "rack/contrib/deflect"
diff --git a/lib/rack/contrib/branch.rb b/lib/rack/contrib/branch.rb
new file mode 100644
index 0000000..a9edb00
--- /dev/null
+++ b/lib/rack/contrib/branch.rb
@@ -0,0 +1,47 @@
+module Rack
+  # Rack::Branch lets you conditionally re-route the Rack stack at runtime to
+  # an alternate endpoint.
+  #
+  # You initialize this middleware with a block, which should either 1. return a
+  # valid rack endpoint, when want to branch away from the current Rack pipeline,
+  # or 2. nil/false, when you want to continue on. The block is passed the current
+  # Rack env hash.
+  #
+  # config.ru usage example:
+  #
+  #   use Rack::Branch do |env|
+  #     ApiApp if env["PATH_INFO"] =~ /\.xml$/
+  #   end
+  #  
+  #   run MyEndpointApp
+  #
+  #
+  # X-Cascade Support:
+  #
+  # If the app returned from the block responds with an X-Cascade: pass header,
+  # control will be passed back to the main rack pipeline.
+  #
+  # In this contrived example, MyEndpointApp will always be called:
+  #
+  #   use Rack::Branch do |env|
+  #     Proc.new { [404, {'X-Cascade' => 'pass'}, []] }
+  #   end
+  #
+  #   run MyEndpointApp
+  class Branch
+    def initialize(app, &block)
+      @app = app
+      @block = block
+    end
+
+    def call(env)
+      if branch_app = @block.call(env)
+        response = branch_app.call(env)
+        cascade = response[1]['X-Cascade']
+        cascade == 'pass' ? @app.call(env) : response
+      else
+        @app.call(env)
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/test/spec_rack_branch.rb b/test/spec_rack_branch.rb
new file mode 100644
index 0000000..3c63de5
--- /dev/null
+++ b/test/spec_rack_branch.rb
@@ -0,0 +1,79 @@
+require 'test/spec'
+require 'rack/builder'
+require 'rack/mock'
+require 'rack/contrib/branch'
+
+context "Rack::Branch" do
+  
+  context "Unit Tests" do
+    setup do
+      @main_app = Proc.new { [200, {}, ["Main app"]] }
+      @blog_app = Proc.new { [200, {}, ["Blog app"]] }
+      @cascade_app = Proc.new { [404, {'X-Cascade' => 'pass'}, []] }
+    end
+    
+    specify "calls app returned from block" do
+      middleware = Rack::Branch.new(@main_app) { @blog_app }
+      response = middleware.call({})
+      response.last.should == ['Blog app']
+    end
+
+    specify "calls app passed in to initialize when block returns false" do
+      middleware = Rack::Branch.new(@main_app) { false }
+      response = middleware.call({})
+      response.last.should == ['Main app']
+    end
+
+    specify "calls app passed in to initialize when block returns nil" do
+      middleware = Rack::Branch.new(@main_app) { nil }
+      response = middleware.call({})
+      response.last.should == ['Main app']
+    end
+
+    specify "calls app passed in to initialize when app returned from block returns X-Cascade: pass header" do
+      middleware = Rack::Branch.new(@main_app) { @cascade_app }
+      response = middleware.call({})
+      response.last.should == ['Main app']
+    end
+  end
+
+  context "Integration Tests" do
+    setup do
+      main_app =    Proc.new { Rack::Response.new {|r| r.body = "Main app"}.finish }
+      blog_app =    Proc.new { Rack::Response.new {|r| r.body = "Blog app"}.finish }
+      cascade_app = Proc.new { Rack::Response.new {|r| r.status = 404; r['X-Cascade'] = 'pass'}.finish }
+      
+      outer_app = Rack::Builder.app do
+        use Rack::Lint
+
+        use Rack::Branch do |env|
+          blog_app if env["PATH_INFO"] == '/blog'
+        end
+
+        use Rack::Branch do |env|
+          cascade_app if env["PATH_INFO"] == '/cascade'
+        end
+
+        run main_app
+      end
+      
+      @mock_request = Rack::MockRequest.new(outer_app)
+    end
+
+    specify "returns blog response when path is /blog" do
+      response = @mock_request.get('/blog')
+      response.body.should.equal('Blog app')
+    end
+  
+    specify "returns main app response when path is /cascade" do
+      response = @mock_request.get('/cascade')
+      response.body.should.equal('Main app')
+    end
+    
+    specify "returns main app response when path is /foo" do
+      response = @mock_request.get('/foo')
+      response.body.should.equal('Main app')
+    end
+  end
+
+end
-- 
1.6.1