chriskottom · October 29, 2009 08:38 · Oct 29, 2009
diff --git a/Rack::DomainSprinkler b/Rack::DomainSprinkler
@@ -0,0 +1,91 @@
+require 'nokogiri'
+require 'pstore'
+
+
+#
+#  Rack::DomainSprinkler
+#
+#  Modifies outgoing HTML markup so that common static assets like script source
+#  files, images, and stylesheets will be served from one of a number of domains
+#  rather than just a single one in order to improve parallelization of resource
+#  downloads during page loads.
+#
+module Rack
+  class DomainSprinkler
+
+    #
+    #  Options:
+    #    A list of domains across which to spread requests
+    #    The name of the file to be used for caching URL/path mappings
+    #
+    def initialize(app, domains=[], cache_loc="tmp/sprinklins.pstore")
+      @app = app
+      @@domains = domains
+      @@url_cache = PStore.new(cache_loc)
+    end
+
+
+    def call(env)
+      dup._call(env)
+    end
+
+
+    #
+    #  Currently only looks for <link>, <script>, and <img> tags.
+    #  Should be refactored to provide more generic mapping.
+    #
+    def _call(env)
+      status, headers, response = @app.call(env)
+      if headers["Content-Type"] =~ /^text\/html/
+        document = Nokogiri::HTML(response.body)
+
+        sprinkle(env, document, 'link', 'href')
+        sprinkle(env, document, 'script', 'src')
+        sprinkle(env, document, 'img', 'src')
+
+        response.body = document.to_html
+      end
+
+      [status, headers, response]
+    end
+
+
+    def sprinkle(env, document, selector, property)
+      document.search(selector).each do |node|
+        url = node[property]
+        if !url.empty? and url !~ /^\#/ and url !~ /^http\:\/\//
+          node[property] = domainify(url, env)
+        end
+      end
+    end
+
+
+    def domainify(path, env)
+      if path !~ /\//
+        path = absolutify(path)
+      end
+
+      full_url = nil
+      @@url_cache.transaction do
+        unless @@url_cache[path]
+          domain = @@domains.shift and @@domains.push(domain)
+          @@url_cache[path] = "http://#{ domain }#{ path }"
+        end
+        full_url = @@url_cache[path]
+      end
+
+      full_url
+    end
+
+
+    def absolutify(path, env)
+      path_prefix = env['REQUEST_PATH']
+      unless path_prefix =~ /\/$/
+        path_prefix.sub!(/\/[^\/]+$/, '')
+      end
+
+      "#{ tmp_path }/#{ path }"
+    end
+
+  end
+end