Added support of unchanged requests

lib/her/middleware.rb

@@ -2,6 +2,7 @@
 require "her/middleware/first_level_parse_json"
 require "her/middleware/second_level_parse_json"
 require "her/middleware/accept_json"
+require "her/middleware/cache_unmodified"
 
 module Her
   module Middleware

lib/her/middleware/cache_unmodified.rb

@@ -0,0 +1,74 @@
+# Easy way to begin support 304 status, so on ther side if data was not changed
+# You will load it from local cache. Of course, other side must support
+# Of course, other side must support 304 status also.
+# Here is Rails controller example with this support:
+#
+# class Post < ApplicationController
+#   before_action :check_changes
+#
+#   private
+#
+#   def check_changes
+#     return unless request.headers['HTTP_IF_MODIFIED_SINCE']
+#     return if request.headers['HTTP_IF_MODIFIED_SINCE'].to_datetime > resource.updated_at
+#     render body: nil, status: 304
+#   end
+# end
+class Her::Middleware::CacheUnmodified < Faraday::Middleware
+  SAVE_METHODS = [:get, :head].freeze
+
+  attr_reader :cache, :options
+  attr_accessor :url
+
+  # apply with optinos:
+  # cache                 # default value is Rails.cache if Rails is used
+  # cache_key_prefix      # defauilt is nil
+
+  def initialize(app, options={})
+    @app = app
+    @cache = options[:cache] 
+    @cache ||= Rails.cache if defined?(Rails)
+    @options = options
+  end
+
+  def call(env)
+    return @app.call(env) unless SAVE_METHODS.include?(env[:method])
+    self.url = env.url.to_s
+    env[:request_headers]["If-Modified-Since"] ||= cached_time if cached_time
+
+    @app.call(env).on_complete do
+      if env[:status] == 304
+        if cached_body
+          env[:body] = cached_body
+          # with out this hack Her crushes
+          env[:status] = 200
+        end
+      elsif env[:status] == 200
+        cache.write cache_key_body, env[:body], expires_in: cache_key_ttl
+        cache.write cache_key_time, Time.zone.now.httpdate, expires_in: cache_key_ttl
+      end
+    end
+  end
+
+  private
+
+  def cache_key_time
+    [options[:cache_key_prefix], "time", url].compact.join("/")
+  end
+
+  def cache_key_body
+    [options[:cache_key_prefix], "body", url].compact.join("/")
+  end
+
+  def cached_time
+    cache.read(cache_key_time)
+  end
+
+  def cached_body
+    cache.read(cache_key_body)
+  end
+
+  def cache_key_ttl
+    1.week.freeze
+  end
+end