HTTP ETag

[johnjohndoe]

Context

The provided schedule.xml is fetched by the FOSDEM Schedule app for Android to render the conference program in the mobile app.
To avoid unneeded downloads of the schedule when unchanged the app reads the HTTP ETag of the response and adds it to each subsequent request. If the schedule has not changed a server supporting HTTP ETag would respond with an HTTP 304 NOT MODIFIED status code and an empty response payload.
Also, schedule update announcements are presented to the user of the app. These should not be shown when the schedule has not changed.

Current state

The server seems not to support HTTP ETag for the given URL:

$ curl -I -H "If-None-Match: " https://fosdem.org/2024/schedule/xml /dev/null 2>&1
HTTP/2 200 
server: nginx
date: Fri, 12 Jan 2024 09:09:07 GMT
content-type: text/xml; charset=utf-8
content-length: 1579543
last-modified: Fri, 12 Jan 2024 06:48:51 GMT
vary: Accept-Encoding
expires: Fri, 12 Jan 2024 09:14:07 GMT
cache-control: max-age=300
strict-transport-security: max-age=31536000; includeSubDomains; preload
x-frame-options: SAMEORIGIN
x-content-type-options: nosniff
x-xss-protection: 1; mode=block
content-security-policy: default-src 'self'; script-src 'self' 'unsafe-inline'; media-src 'self' http: https:; img-src 'self' data: *.fosdem.org; object-src 'self'; style-src 'self' 'unsafe-inline'; 
accept-ranges: bytes

Request

Can you please add support for HTTP ETag to the webserver before/during/after the conference? I am mentioning all time frames because some conferences tend to archive their schedule as a static resource which then no longer supports HTTP ETag.

[johnjohndoe]

@cbeyls, @Wilm0r fyi

[cbeyls]

For the record, you should be able to use HTTP If-Modified-Since with the date returned by the last-modified header to achieve the same effect as ETag: skip downloading the content if it hasn't changed.

[johnjohndoe]

@cbeyls Thank you for the heads up! 👍 I wasn't aware that the app does not make use of this header. I have now implemented it.
Still, I would be interested to know if supporting ETags is considered best practice or not.

[johanvdw]

@gerryd - you added etag off previously (April 2019).

+    custom_config: |
+      etag off; # Disable file-based ETags, we use Expires in a much more efficient way
+      #
+      expires 300s; # By default, set an expires on 5 minutes

Any reason I'm not aware of not to enable it again?

[gerryd]

Good question. I'm not entirely sure, but I think I remember there were issues with the CSS sprites and caching.