class Rack::LazyConditionalGet
This middleware is like Rack::ConditionalGet except that it does not have to go down the rack stack and build the resource to check the modification date or the ETag.
Instead it makes the assumption that only non-reading requests can potentially change the content, meaning any request which is not GET or HEAD. Each time you make one of these request, the date is cached and any resource is considered identical until the next non-reading request.
Basically you use it this way:
“` ruby use Rack::LazyConditionalGet
“`
Although if you have multiple instances, it is better to use something like memcached. An argument can be passed to give the cache object. By default it is just a Hash. But it can take other objects, including objects which respond to `:get` and `:set`. Here is how you would use it with Dalli.
“` Ruby dalli_client = Dalli::Client.new use Rack::LazyConditionalGet
, dalli_client “`
By default, the middleware only delegates to Rack::ConditionalGet to avoid any unwanted behaviour. You have to set a header to any resource which you want to be cached. And it will be cached until the next “potential update” of your site, that is whenever the next POST/PUT/PATCH/DELETE request is received.
The header is `Rack-Lazy-Conditional-Get`. You have to set it to 'yes' if you want the middleware to set `Last-Modified` for you.
Bear in mind that if you set `Last-Modified` as well, the middleware will not change it.
Regarding the POST/PUT/PATCH/DELETE… requests, they will always reset your global modification date. But if you have one of these request and you know for sure that it does not modify the cached content, you can set the `Rack-Lazy-Conditional-Get` on response to `skip`. This will not update the global modification date.
NOTE: This will not work properly in a multi-threaded environment with default cache object. A provided cache object should ensure thread-safety of the `get`/`set`/`[]`/`=` methods.
Constants
- KEY
- READ_METHODS
Public Class Methods
# File lib/rack/contrib/lazy_conditional_get.rb 58 def self.new(*) 59 # This code automatically uses `Rack::ConditionalGet` before 60 # our middleware. It is equivalent to: 61 # 62 # ``` ruby 63 # use Rack::ConditionalGet 64 # use Rack::LazyConditionalGet 65 # ``` 66 ::Rack::ConditionalGet.new(super) 67 end
# File lib/rack/contrib/lazy_conditional_get.rb 69 def initialize app, cache={} 70 @app = app 71 @cache = cache 72 update_cache 73 end
Public Instance Methods
# File lib/rack/contrib/lazy_conditional_get.rb 75 def call env 76 if reading? env and fresh? env 77 return [304, {'Last-Modified' => env['HTTP_IF_MODIFIED_SINCE']}, []] 78 end 79 80 status, headers, body = @app.call env 81 headers = Utils::HeaderHash.new(headers) 82 83 update_cache unless (reading?(env) or skipping?(headers)) 84 headers['Last-Modified'] = cached_value if stampable? headers 85 [status, headers, body] 86 end
Private Instance Methods
# File lib/rack/contrib/lazy_conditional_get.rb 115 def cached_value 116 @cache.respond_to?(:get) ? @cache.get(KEY) : @cache[KEY] 117 end
# File lib/rack/contrib/lazy_conditional_get.rb 90 def fresh? env 91 env['HTTP_IF_MODIFIED_SINCE'] == cached_value 92 end
# File lib/rack/contrib/lazy_conditional_get.rb 94 def reading? env 95 READ_METHODS.include?(env['REQUEST_METHOD']) 96 end
# File lib/rack/contrib/lazy_conditional_get.rb 98 def skipping? headers 99 headers['Rack-Lazy-Conditional-Get'] == 'skip' 100 end
# File lib/rack/contrib/lazy_conditional_get.rb 102 def stampable? headers 103 !headers.has_key?('Last-Modified') and headers['Rack-Lazy-Conditional-Get'] == 'yes' 104 end
# File lib/rack/contrib/lazy_conditional_get.rb 106 def update_cache 107 stamp = Time.now.httpdate 108 if @cache.respond_to?(:set) 109 @cache.set(KEY,stamp) 110 else 111 @cache[KEY] = stamp 112 end 113 end