delegate post url generation to config

app/models/post.rb

@@ -145,7 +145,7 @@ class Post < ApplicationRecord
     end
 
     def file_url
-      "#{Danbooru.config.image_server_host(self)}/data/#{seo_tag_string}#{file_path_prefix}#{md5}.#{file_ext}"
+      Danbooru.config.build_file_url(self)
     end
 
     # this is for the 640x320 version
@@ -154,7 +154,7 @@ class Post < ApplicationRecord
 
     def large_file_url
       if has_large?
-        "#{Danbooru.config.image_server_host(self)}/data/sample/#{seo_tag_string}#{file_path_prefix}#{Danbooru.config.large_image_prefix}#{md5}.#{large_file_ext}"
+        Danbooru.config.build_large_file_url(self)
       else
         file_url
       end

config/danbooru_default_config.rb

@@ -217,8 +217,12 @@ module Danbooru
       "albert"
     end
 
-    def image_server_host(post)
-      ""
+    def build_file_url(post)
+      "/data/#{post.file_path_prefix}/#{post.md5}.#{post.file_ext}"
+    end
+
+    def build_large_file_url(post)
+      "/data/#{post.file_path_prefix}#{Danbooru.config.large_image_prefix}/#{post.md5}.#{post.large_file_ext}"
     end
 
 #TAG CONFIGURATION