1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
|
module ActionDispatch
module Http
module Cache
module Request
HTTP_IF_MODIFIED_SINCE = "HTTP_IF_MODIFIED_SINCE".freeze
HTTP_IF_NONE_MATCH = "HTTP_IF_NONE_MATCH".freeze
def if_modified_since
if since = get_header(HTTP_IF_MODIFIED_SINCE)
Time.rfc2822(since) rescue nil
end
end
def if_none_match
get_header HTTP_IF_NONE_MATCH
end
def if_none_match_etags
if_none_match ? if_none_match.split(/\s*,\s*/) : []
end
def not_modified?(modified_at)
if_modified_since && modified_at && if_modified_since >= modified_at
end
def etag_matches?(etag)
if etag
validators = if_none_match_etags
validators.include?(etag) || validators.include?("*")
end
end
# Check response freshness (Last-Modified and ETag) against request
# If-Modified-Since and If-None-Match conditions. If both headers are
# supplied, both must match, or the request is not considered fresh.
def fresh?(response)
last_modified = if_modified_since
etag = if_none_match
return false unless last_modified || etag
success = true
success &&= not_modified?(response.last_modified) if last_modified
success &&= etag_matches?(response.etag) if etag
success
end
end
module Response
attr_reader :cache_control
def last_modified
if last = get_header(LAST_MODIFIED)
Time.httpdate(last)
end
end
def last_modified?
has_header? LAST_MODIFIED
end
def last_modified=(utc_time)
set_header LAST_MODIFIED, utc_time.httpdate
end
def date
if date_header = get_header(DATE)
Time.httpdate(date_header)
end
end
def date?
has_header? DATE
end
def date=(utc_time)
set_header DATE, utc_time.httpdate
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.
def etag=(weak_validators)
self.weak_etag = weak_validators
end
def weak_etag=(weak_validators)
set_header "ETag", generate_weak_etag(weak_validators)
end
def strong_etag=(strong_validators)
set_header "ETag", generate_strong_etag(strong_validators)
end
def etag?; etag; end
# True if an ETag is set and it's a weak validator (preceded with W/)
def weak_etag?
etag? && etag.starts_with?('W/"')
end
# True if an ETag is set and it isn't a weak validator (not preceded with W/)
def strong_etag?
etag? && !weak_etag?
end
private
DATE = "Date".freeze
LAST_MODIFIED = "Last-Modified".freeze
SPECIAL_KEYS = Set.new(%w[extras no-cache max-age public private must-revalidate])
def generate_weak_etag(validators)
"W/#{generate_strong_etag(validators)}"
end
def generate_strong_etag(validators)
%("#{Digest::MD5.hexdigest(ActiveSupport::Cache.expand_cache_key(validators))}")
end
def cache_control_segments
if cache_control = _cache_control
cache_control.delete(" ").split(",")
else
[]
end
end
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
def prepare_cache_control!
@cache_control = cache_control_headers
end
def handle_conditional_get!
if etag? || last_modified? || !@cache_control.empty?
set_conditional_cache_control!(@cache_control)
end
end
DEFAULT_CACHE_CONTROL = "max-age=0, private, must-revalidate".freeze
NO_CACHE = "no-cache".freeze
PUBLIC = "public".freeze
PRIVATE = "private".freeze
MUST_REVALIDATE = "must-revalidate".freeze
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
end
end
end
end
|
