Expose md5/hash for emoji CDN in HEAD/GET

[muddyfish]

On cdn.discordapp.com/emojis/..., it would help if Discord could expose a hash for emojis. This hash could be exposed through the response headers (x-hash-md5 for instance).

Bots which need to perform analysis on the image content would find this useful, as they could simply HEAD the object and detect if it had already been processed, saving bandwidth and CPU processing. If it had not already been processed, then it can do another request to download the image content.

Currently this is available through unsupported means, but this feature request is for making the hash available through the CDN endpoint.

[devsnek]

Our cdn uses the standard etag header: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag

[muddyfish]

In an example call, I don't see any etag:

curl --head https://cdn.discordapp.com/emojis/674758248506851379.png

HTTP/2 200
date: Tue, 14 Dec 2021 17:38:21 GMT
content-type: image/png
content-length: 17817
expires: Thu, 13 Jan 2022 17:38:21 GMT
last-modified: Wed, 05 Feb 2020 23:28:22 GMT
cache-control: public, max-age=2592000
x-envoy-upstream-service-time: 1
access-control-allow-origin: *
cf-cache-status: MISS
accept-ranges: bytes
expect-ct: max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
x-robots-tag: noindex, nofollow, noarchive, nocache, noimageindex, noodp
report-to: {"endpoints":[{"url":"https:\/\/a.nel.cloudflare.com\/report\/v3?s=dcOX7bKwgzIyyY00UkYGJUuaIQz%2BqGrwXFQNnmcMIin64juJjEa3JUzc5XeHfP%2BzyPu9%2FGOlXpmat1zRPGKvMS9VFByV5DdAhGBp1m4SjI1J6W0D2zp9KtS%2Bpep08IaH8xYrZg%3D%3D"}],"group":"cf-nel","max_age":604800}
nel: {"success_fraction":0,"report_to":"cf-nel","max_age":604800}
server: cloudflare
cf-ray: 6bd93490a8418883-LHR
alt-svc: h3=":443"; ma=86400, h3-29=":443"; ma=86400, h3-28=":443"; ma=86400, h3-27=":443"; ma=86400

So therefore this does not answer my query