module ActionDispatch::Http::Cache::Response

Constants

DATE
DEFAULT_CACHE_CONTROL
LAST_MODIFIED
MUST_REVALIDATE
NO_CACHE
NO_STORE
PRIVATE
PUBLIC
SPECIAL_KEYS

Attributes

cache_control[R]

Public Instance Methods

date() click to toggle source
# File lib/action_dispatch/http/cache.rb, line 68
def date
  if date_header = get_header(DATE)
    Time.httpdate(date_header)
  end
end
date=(utc_time) click to toggle source
# File lib/action_dispatch/http/cache.rb, line 78
def date=(utc_time)
  set_header DATE, utc_time.httpdate
end
date?() click to toggle source
# File lib/action_dispatch/http/cache.rb, line 74
def date?
  has_header? DATE
end
etag=(weak_validators) click to toggle source

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
etag?() click to toggle source
# File lib/action_dispatch/http/cache.rb, line 113
def etag?; etag; end
last_modified() click to toggle source
# File lib/action_dispatch/http/cache.rb, line 54
def last_modified
  if last = get_header(LAST_MODIFIED)
    Time.httpdate(last)
  end
end
last_modified=(utc_time) click to toggle source
# File lib/action_dispatch/http/cache.rb, line 64
def last_modified=(utc_time)
  set_header LAST_MODIFIED, utc_time.httpdate
end
last_modified?() click to toggle source
# File lib/action_dispatch/http/cache.rb, line 60
def last_modified?
  has_header? LAST_MODIFIED
end
strong_etag=(strong_validators) click to toggle source
# File lib/action_dispatch/http/cache.rb, line 109
def strong_etag=(strong_validators)
  set_header "ETag", generate_strong_etag(strong_validators)
end
strong_etag?() click to toggle source

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
weak_etag=(weak_validators) click to toggle source
# File lib/action_dispatch/http/cache.rb, line 105
def weak_etag=(weak_validators)
  set_header "ETag", generate_weak_etag(weak_validators)
end
weak_etag?() click to toggle source

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

cache_control_headers() click to toggle source
# 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
cache_control_segments() click to toggle source
# 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
generate_strong_etag(validators) click to toggle source
# File lib/action_dispatch/http/cache.rb, line 134
def generate_strong_etag(validators)
  %("#{ActiveSupport::Digest.hexdigest(ActiveSupport::Cache.expand_cache_key(validators))}")
end
generate_weak_etag(validators) click to toggle source
# File lib/action_dispatch/http/cache.rb, line 130
def generate_weak_etag(validators)
  "W/#{generate_strong_etag(validators)}"
end
handle_conditional_get!() click to toggle source
# 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
merge_and_normalize_cache_control!(cache_control) click to toggle source
# 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 extras = control.delete(:extras)
    cache_control[:extras] ||= []
    cache_control[:extras] += extras
    cache_control[:extras].uniq!
  end

  control.merge! cache_control

  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
prepare_cache_control!() click to toggle source
# File lib/action_dispatch/http/cache.rb, line 164
def prepare_cache_control!
  @cache_control = cache_control_headers
end