distributed memoizer added to ensure absolute duplicate posts don't get through

in case of an absolute dupe just return the memoized post

This works around issues with wordpress being crazy

app/controllers/posts_controller.rb

@@ -1,5 +1,6 @@
 require_dependency 'post_creator'
 require_dependency 'post_destroyer'
+require_dependency 'distributed_memoizer'
 
 class PostsController < ApplicationController
 
@@ -25,21 +26,36 @@ class PostsController < ApplicationController
   end
 
   def create
-    post_creator = PostCreator.new(current_user, create_params)
-    post = post_creator.create
-    if post_creator.errors.present?
+    params = create_params
 
-      # If the post was spam, flag all the user's posts as spam
-      current_user.flag_linked_posts_as_spam if post_creator.spam?
+    key = params_key(params)
 
-      render_json_error(post_creator)
-    else
-      post_serializer = PostSerializer.new(post, scope: guardian, root: false)
-      post_serializer.topic_slug = post.topic.slug if post.topic.present?
-      post_serializer.draft_sequence = DraftSequence.current(current_user, post.topic.draft_key)
-      render_json_dump(post_serializer)
+    result = DistributedMemoizer.memoize(key, 120) do
+      post_creator = PostCreator.new(current_user, params)
+      post = post_creator.create
+      if post_creator.errors.present?
+
+        # If the post was spam, flag all the user's posts as spam
+        current_user.flag_linked_posts_as_spam if post_creator.spam?
+
+        "e" << MultiJson.dump(errors: post_creator.errors.full_messages)
+      else
+        post_serializer = PostSerializer.new(post, scope: guardian, root: false)
+        post_serializer.topic_slug = post.topic.slug if post.topic.present?
+        post_serializer.draft_sequence = DraftSequence.current(current_user, post.topic.draft_key)
+        "s" << MultiJson.dump(post_serializer)
+      end
     end
 
+
+    payload = result[1..-1]
+    if result[0] == "e"
+      # don't memoize errors
+      $redis.del(DistributedMemoizer.redis_key(key))
+      render json: payload, status: 422
+    else
+      render json: payload
+    end
   end
 
   def update
@@ -193,6 +209,15 @@ class PostsController < ApplicationController
 
   private
 
+    def params_key(params)
+      "post##" << Digest::SHA1.hexdigest(params
+        .to_a
+        .concat([["user", current_user.id]])
+        .sort{|x,y| x[0] <=> y[0]}.join do |x,y|
+          "#{x}:#{y}"
+        end)
+    end
+
     def create_params
       permitted = [
         :raw,