support redis as well as memcache for a rails cache store

closes #4498

Change-Id: Icf29882d8c0d351574496ba0494c1d8c518a3e7f
Reviewed-on: https://gerrit.instructure.com/4580
Tested-by: Hudson <hudson@instructure.com>
Reviewed-by: Zach Wily <zach@instructure.com>

Gemfile

@@ -75,7 +75,7 @@ group :development do
 end
 
 group :redis do
-  gem 'redis-store', '1.0.0.beta4'
+  gem 'redis-store', '1.0.0.rc1'
 end
 
 # The closure-compiler gem has an undocumented

config/cache_store.yml.example

@@ -0,0 +1,13 @@
+# if this file doesn't exist, memcache will be used if there are any
+# servers configured in config/memcache.yml
+development:
+  cache_store: mem_cache_store
+  # if no servers are specified, we'll look in config/memcache.yml
+  # servers:
+  # - localhost
+  #
+  # cache_store: redis_store
+  # # if no servers are specified, we'll look in config/redis.yml
+  # servers:
+  # - localhost
+  # database: 0

config/environment.rb

@@ -35,13 +35,6 @@ Rails::Initializer.run do |config|
   # Run "rake -D time" for a list of tasks for finding time zone names. Comment line to use default local time.
   config.time_zone = 'UTC'
 
-  memcache_servers = File.exists?(Rails.root+"config/memcache.yml") ? (YAML.load_file(Rails.root+"config/memcache.yml")[RAILS_ENV] || []) : []
-  if memcache_servers.empty?
-    config.cache_store = :nil_store
-  else
-    config.cache_store = :mem_cache_store, *memcache_servers
-  end
-
   log_config = File.exists?(Rails.root+"config/logging.yml") && YAML.load_file(Rails.root+"config/logging.yml")[RAILS_ENV]
   if log_config && log_config["logger"] == "syslog"
     require 'syslog_wrapper'

config/environments/development.rb

@@ -30,5 +30,11 @@ end
 # eval <env>-local.rb if it exists
 Dir[File.dirname(__FILE__) + "/" + File.basename(__FILE__, ".rb") + "-*.rb"].each { |localfile| eval(File.new(localfile).read) }
 
+# initialize cache store
+# this needs to happen in each environment config file, rather than a
+# config/initializer/* file, to allow Rails' full initialization of the cache
+# to take place, including middleware inserts and such.
+config.cache_store = Canvas.cache_store_config
+
 # allow debugging only in development environment by default
 require "ruby-debug"

config/environments/production.rb

@@ -17,3 +17,9 @@ config.action_view.cache_template_loading            = true
 
 # eval <env>-local.rb if it exists
 Dir[File.dirname(__FILE__) + "/" + File.basename(__FILE__, ".rb") + "-*.rb"].each { |localfile| eval(File.new(localfile).read) }
+
+# initialize cache store
+# this needs to happen in each environment config file, rather than a
+# config/initializer/* file, to allow Rails' full initialization of the cache
+# to take place, including middleware inserts and such.
+config.cache_store = Canvas.cache_store_config

config/environments/test.rb

@@ -32,3 +32,5 @@ Canvas.dynamic_finder_type_cast_error = :raise
 
 # eval <env>-local.rb if it exists
 Dir[File.dirname(__FILE__) + "/" + File.basename(__FILE__, ".rb") + "-*.rb"].each { |localfile| eval(File.new(localfile).read) }
+
+config.cache_store = :nil_store

config/memcache.yml.example

@@ -1,5 +1,4 @@
-# if an environment has no servers defined, we'll use NilStore instead, which
-# effectively disables caching
+# see also config/cache_store.yml.example
 production:
 
 development:

lib/canvas.rb

@@ -47,6 +47,32 @@ module Canvas
     @redis_enabled ||= Setting.from_config('redis').present?
   end
 
+  def self.cache_store_config
+    cache_store_config = {
+      'cache_store' => 'mem_cache_store',
+    }.merge(Setting.from_config('cache_store') || {})
+    config = nil
+    case cache_store_config.delete('cache_store')
+    when 'mem_cache_store'
+      cache_store_config['namespace'] ||= cache_store_config['key']
+      servers = cache_store_config['servers'] || (Setting.from_config('memcache'))
+      if servers
+        config = :mem_cache_store, servers, cache_store_config
+      end
+    when 'redis_store'
+      Bundler.require 'redis'
+      Canvas::Redis.patch
+      # merge in redis.yml, but give precedence to cache_store.yml
+      cache_store_config = (Setting.from_config('redis') || {}).merge(cache_store_config)
+      cache_store_config['key_prefix'] ||= cache_store_config['key']
+      config = :redis_store, cache_store_config
+    end
+    unless config
+      config = :nil_store
+    end
+    config
+  end
+
   # `sample` reports KB, not B
   if File.directory?("/proc")
     # linux w/ proc fs

lib/canvas/redis.rb

@@ -0,0 +1,43 @@
+module Canvas::Redis
+  # while we wait for this pull request
+  # https://github.com/jodosha/redis-store/pull/83
+  def self.patch
+
+    ::ActiveSupport::Cache::RedisStore.class_eval do
+      def write_with_econnrefused(key, value, options = nil)
+        write_without_econnrefused(key, value, options)
+      rescue Errno::ECONNREFUSED => e
+        false
+      end
+      alias_method_chain :write, :econnrefused
+
+      def read_with_econnrefused(key, options = nil)
+        read_without_econnrefused(key, options)
+      rescue Errno::ECONNREFUSED => e
+        nil
+      end
+      alias_method_chain :read, :econnrefused
+
+      def delete_with_econnrefused(key, options = nil)
+        delete_without_econnrefused(key, options)
+      rescue Errno::ECONNREFUSED => e
+        false
+      end
+      alias_method_chain :delete, :econnrefused
+
+      def exist_with_econnrefused?(key, options = nil)
+        exist_without_econnrefused?(key, options = nil)
+      rescue Errno::ECONNREFUSED => e
+        false
+      end
+      alias_method_chain :exist?, :econnrefused
+
+      def delete_matched_with_econnrefused(matcher, options = nil)
+        delete_matched_without_econnrefused(matcher, options)
+      rescue Errno::ECONNREFUSED => e
+        false
+      end
+      alias_method_chain :delete_matched, :econnrefused
+    end
+  end
+end