ATS should ignore the Expires header when there is a Cache-Control with max-age or s-maxage

[bryancall]

https://tools.ietf.org/html/rfc7234#section-5.3

If a response includes a Cache-Control field with the max-age
directive (Section 5.2.2.8), a recipient MUST ignore the Expires
field. Likewise, if a response includes the s-maxage directive
(Section 5.2.2.9), a shared cache recipient MUST ignore the Expires
field. In both these cases, the value in Expires is only intended
for recipients that have not yet implemented the Cache-Control field.

08:38:02 bart:/var/www/html$ curl -D - http://127.0.0.1:81/expires.php
HTTP/1.1 200 OK
Date: Tue, 25 Aug 2020 15:38:07 GMT
Server: Apache/2.4.43 (Fedora)
X-Powered-By: PHP/7.4.9
Cache-Control: 1536000, public
Expires: Thu, 30 Jul 2020 15:18:11 GMT
Transfer-Encoding: chunked
Content-Type: text/html; charset=UTF-8

xxx
08:38:07 bart:/var/www/html$ curl -D - http://127.0.0.1:8080/expires.php
HTTP/1.1 200 OK
Date: Tue, 25 Aug 2020 15:38:09 GMT
Server: ATS/10.0.0
X-Powered-By: PHP/7.4.9
Cache-Control: 1536000, public
Expires: Thu, 30 Jul 2020 15:18:11 GMT
Content-Type: text/html; charset=UTF-8
Age: 0
Transfer-Encoding: chunked
Connection: keep-alive
Via: http/1.1 traffic_server (ApacheTrafficServer/10.0.0 [uScSsSfUpSeN:t cCSp sS])

xxx
08:38:09 bart:/var/www/html$ traffic_via 'uScSsSfUpSeN:t cCSp sS'
Via header is [uScSsSfUpSeN:t cCSp sS], Length is 22
Via Header Details:
Request headers received from client                   :simple request (not conditional)
Result of Traffic Server cache lookup for URL          :in cache, stale (a cache "MISS")
Response information received from origin server       :connection opened successfully
Result of document write-to-cache:                     :updated old cache copy
Proxy operation result                                 :served or connection opened successfully
Error codes (if any)                                   :no error
Tunnel info                                            :no tunneling
Cache Type                                             :cache
Cache Lookup Result                                    :cache hit, but expired
Parent proxy connection status                         :no parent proxy or unknown
Origin server connection status                        :connection opened successfully
08:38:37 bart:/var/www/html$ curl -D - http://127.0.0.1:8080/expires.php
HTTP/1.1 200 OK
Date: Tue, 25 Aug 2020 15:38:42 GMT
Server: ATS/10.0.0
X-Powered-By: PHP/7.4.9
Cache-Control: 1536000, public
Expires: Thu, 30 Jul 2020 15:18:11 GMT
Content-Type: text/html; charset=UTF-8
Age: 0
Transfer-Encoding: chunked
Connection: keep-alive
Via: http/1.1 traffic_server (ApacheTrafficServer/10.0.0 [uScSsSfUpSeN:t cCSp sS])

xxx
08:38:42 bart:/var/www/html$ traffic_via 'uScSsSfUpSeN:t cCSp sS'
Via header is [uScSsSfUpSeN:t cCSp sS], Length is 22
Via Header Details:
Request headers received from client                   :simple request (not conditional)
Result of Traffic Server cache lookup for URL          :in cache, stale (a cache "MISS")
Response information received from origin server       :connection opened successfully
Result of document write-to-cache:                     :updated old cache copy
Proxy operation result                                 :served or connection opened successfully
Error codes (if any)                                   :no error
Tunnel info                                            :no tunneling
Cache Type                                             :cache
Cache Lookup Result                                    :cache hit, but expired
Parent proxy connection status                         :no parent proxy or unknown
Origin server connection status                        :connection opened successfully

[bryancall]

An added <sarcasm>benefit</sarcasm> it is going to origin and fetching the entire object instead of doing an IMS request:

GET /expires.php HTTP/1.1
Host: 192.168.1.10:81
User-Agent: curl/7.69.1
Accept: */*
Client-ip: 127.0.0.1
X-Forwarded-For: 127.0.0.1
Via: http/1.1 traffic_server[d95dd056-eff1-4b35-9e88-500e5d02de2d] (ApacheTrafficServer/10.0.0)

[bryancall]

I messed up on the copy and paste for the origin response and left out the max-age= in the cache control header. ATS does the correct thing and ignores the Expires header in the presence of s-maxage and max-age.

09:54:14 bart:/var/www/html$ curl -D - http://127.0.0.1:8080/expires.php
HTTP/1.1 200 OK
Date: Tue, 25 Aug 2020 16:49:44 GMT
Server: ATS/10.0.0
X-Powered-By: PHP/7.4.9
Cache-Control: max-age=31536000, public
Expires: Thu, 30 Jul 2020 15:18:11 GMT
Content-Type: text/html; charset=UTF-8
Age: 272
Content-Length: 4
Connection: keep-alive
Via: http/1.1 traffic_server (ApacheTrafficServer/10.0.0 [uScRs f p eN:t cCHp s ])

xxx
09:54:16 bart:/var/www/html$ traffic_via 'uScRs f p eN:t cCHp s '
Via header is [uScRs f p eN:t cCHp s ], Length is 22
Via Header Details:
Request headers received from client                   :simple request (not conditional)
Result of Traffic Server cache lookup for URL          :in cache, fresh Ram hit (a cache "HIT")
Response information received from origin server       :no server connection needed
Result of document write-to-cache:                     :no cache write performed
Proxy operation result                                 :unknown
Error codes (if any)                                   :no error
Tunnel info                                            :no tunneling
Cache Type                                             :cache
Cache Lookup Result                                    :cache hit
Parent proxy connection status                         :no parent proxy or unknown
Origin server connection status                        :no server connection needed