module ActionDispatch::Http::Cache::Response
Constants
- DATE
- DEFAULT_CACHE_CONTROL
- LAST_MODIFIED
- MUST_REVALIDATE
- NO_CACHE
- NO_STORE
- PRIVATE
- PUBLIC
- SPECIAL_KEYS
Attributes
Public Instance Methods
# File lib/action_dispatch/http/cache.rb, line 68 def date if date_header = get_header(DATE) Time.httpdate(date_header) end end
# File lib/action_dispatch/http/cache.rb, line 78 def date=(utc_time) set_header DATE, utc_time.httpdate end
# File lib/action_dispatch/http/cache.rb, line 74 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 101 def etag=(weak_validators) self.weak_etag = weak_validators end
# File lib/action_dispatch/http/cache.rb, line 113 def etag?; etag; end
# File lib/action_dispatch/http/cache.rb, line 54 def last_modified if last = get_header(LAST_MODIFIED) Time.httpdate(last) end end
# File lib/action_dispatch/http/cache.rb, line 64 def last_modified=(utc_time) set_header LAST_MODIFIED, utc_time.httpdate end
# File lib/action_dispatch/http/cache.rb, line 60 def last_modified? has_header? LAST_MODIFIED end
# File lib/action_dispatch/http/cache.rb, line 109 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 121 def strong_etag? etag? && !weak_etag? end
# File lib/action_dispatch/http/cache.rb, line 105 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 116 def weak_etag? etag? && etag.start_with?('W/"') end
Private Instance Methods
# File lib/action_dispatch/http/cache.rb, line 146 def cache_control_headers cache_control = {} cache_control_segments.each do |segment| directive, argument = segment.split("=", 2) if SPECIAL_KEYS.include? directive directive.tr!("-", "_") cache_control[directive.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 138 def cache_control_segments if cache_control = _cache_control cache_control.delete(" ").split(",") else [] end end
# File lib/action_dispatch/http/cache.rb, line 134 def generate_strong_etag(validators) %("#{ActiveSupport::Digest.hexdigest(ActiveSupport::Cache.expand_cache_key(validators))}") end
# File lib/action_dispatch/http/cache.rb, line 130 def generate_weak_etag(validators) "W/#{generate_strong_etag(validators)}" end
# File lib/action_dispatch/http/cache.rb, line 175 def handle_conditional_get! # Normally default cache control setting is handled by ETag # middleware. But, if an etag is already set, the middleware # defaults to `no-cache` unless a default `Cache-Control` value is # previously set. So, set a default one here. if (etag? || last_modified?) && !self._cache_control self._cache_control = DEFAULT_CACHE_CONTROL end end
# File lib/action_dispatch/http/cache.rb, line 185 def merge_and_normalize_cache_control!(cache_control) control = cache_control_headers return if control.empty? && cache_control.empty? # Let middleware handle default behavior if cache_control.any? # Any caching directive coming from a controller overrides # no-cache/no-store in the default Cache-Control header. control.delete(:no_cache) control.delete(:no_store) if extras = control.delete(:extras) cache_control[:extras] ||= [] cache_control[:extras] += extras cache_control[:extras].uniq! end control.merge! cache_control end options = [] if control[:no_store] options << PRIVATE if control[:private] options << NO_STORE elsif control[:no_cache] options << PUBLIC if control[:public] options << NO_CACHE options.concat(control[:extras]) if control[:extras] else extras = control[:extras] max_age = control[:max_age] stale_while_revalidate = control[:stale_while_revalidate] stale_if_error = control[:stale_if_error] options << "max-age=#{max_age.to_i}" if max_age options << (control[:public] ? PUBLIC : PRIVATE) options << MUST_REVALIDATE if control[:must_revalidate] options << "stale-while-revalidate=#{stale_while_revalidate.to_i}" if stale_while_revalidate options << "stale-if-error=#{stale_if_error.to_i}" if stale_if_error options.concat(extras) if extras end self._cache_control = options.join(", ") end
# File lib/action_dispatch/http/cache.rb, line 164 def prepare_cache_control! @cache_control = cache_control_headers end