module ActionDispatch::Http::Cache::Response
Constants
- DATE
- DEFAULT_CACHE_CONTROL
- LAST_MODIFIED
- MUST_REVALIDATE
- NO_CACHE
- PRIVATE
- PUBLIC
- SPECIAL_KEYS
Attributes
Public Instance Methods
# File lib/action_dispatch/http/cache.rb, line 66 def date if date_header = get_header(DATE) Time.httpdate(date_header) end end
# File lib/action_dispatch/http/cache.rb, line 76 def date=(utc_time) set_header DATE, utc_time.httpdate end
# File lib/action_dispatch/http/cache.rb, line 72 def date? has_header? DATE end
This method sets a weak ETag validator on the response so browsers and proxies may cache the response, keyed on the ETag. On subsequent requests, the If-None-Match header is set to the cached ETag. If it matches the current ETag, we can return a 304 Not Modified response with no body, letting the browser or proxy know that their cache is current. Big savings in request time and network bandwidth.
Weak ETags are considered to be semantically equivalent but not byte-for-byte identical. This is perfect for browser caching of HTML pages where we don't care about exact equality, just what the user is viewing.
Strong ETags are considered byte-for-byte identical. They allow a browser or proxy cache to support Range requests, useful for paging through a PDF file or scrubbing through a video. Some CDNs only support strong ETags and will ignore weak ETags entirely.
Weak ETags are what we almost always need, so they're the default. Check out `#strong_etag=` to provide a strong ETag validator.
# File lib/action_dispatch/http/cache.rb, line 99 def etag=(weak_validators) self.weak_etag = weak_validators end
# File lib/action_dispatch/http/cache.rb, line 111 def etag?; etag; end
# File lib/action_dispatch/http/cache.rb, line 52 def last_modified if last = get_header(LAST_MODIFIED) Time.httpdate(last) end end
# File lib/action_dispatch/http/cache.rb, line 62 def last_modified=(utc_time) set_header LAST_MODIFIED, utc_time.httpdate end
# File lib/action_dispatch/http/cache.rb, line 58 def last_modified? has_header? LAST_MODIFIED end
# File lib/action_dispatch/http/cache.rb, line 107 def strong_etag=(strong_validators) set_header "ETag", generate_strong_etag(strong_validators) end
True if an ETag is set and it isn't a weak validator (not preceded with W/)
# File lib/action_dispatch/http/cache.rb, line 119 def strong_etag? etag? && !weak_etag? end
# File lib/action_dispatch/http/cache.rb, line 103 def weak_etag=(weak_validators) set_header "ETag", generate_weak_etag(weak_validators) end
True if an ETag is set and it's a weak validator (preceded with W/)
# File lib/action_dispatch/http/cache.rb, line 114 def weak_etag? etag? && etag.starts_with?('W/"') end
Private Instance Methods
# File lib/action_dispatch/http/cache.rb, line 145 def cache_control_headers cache_control = {} cache_control_segments.each do |segment| directive, argument = segment.split("=", 2) if SPECIAL_KEYS.include? directive key = directive.tr("-", "_") cache_control[key.to_sym] = argument || true else cache_control[:extras] ||= [] cache_control[:extras] << segment end end cache_control end
# File lib/action_dispatch/http/cache.rb, line 137 def cache_control_segments if cache_control = _cache_control cache_control.delete(" ").split(",") else [] end end
# File lib/action_dispatch/http/cache.rb, line 133 def generate_strong_etag(validators) %("#{Digest::MD5.hexdigest(ActiveSupport::Cache.expand_cache_key(validators))}") end
# File lib/action_dispatch/http/cache.rb, line 129 def generate_weak_etag(validators) "W/#{generate_strong_etag(validators)}" end
# File lib/action_dispatch/http/cache.rb, line 167 def handle_conditional_get! if etag? || last_modified? || !@cache_control.empty? set_conditional_cache_control!(@cache_control) end end
# File lib/action_dispatch/http/cache.rb, line 163 def prepare_cache_control! @cache_control = cache_control_headers end
# File lib/action_dispatch/http/cache.rb, line 179 def set_conditional_cache_control!(cache_control) control = {} cc_headers = cache_control_headers if extras = cc_headers.delete(:extras) cache_control[:extras] ||= [] cache_control[:extras] += extras cache_control[:extras].uniq! end control.merge! cc_headers control.merge! cache_control if control.empty? self._cache_control = DEFAULT_CACHE_CONTROL elsif control[:no_cache] self._cache_control = NO_CACHE if control[:extras] self._cache_control = _cache_control + ", #{control[:extras].join(', ')}" end else extras = control[:extras] max_age = control[:max_age] options = [] options << "max-age=#{max_age.to_i}" if max_age options << (control[:public] ? PUBLIC : PRIVATE) options << MUST_REVALIDATE if control[:must_revalidate] options.concat(extras) if extras self._cache_control = options.join(", ") end end