fileserver: Read Etags from precomputed files

[armadi1809]

Initial pass at closing #5734

[mholt]

Thanks for the great enhancement! This looks pretty good but I just have a few comments.

[armadi1809]

Thanks for taking a look at this Matt. All the feedback discussions should now be resolved.

[mholt]

Awesome, thanks for working on this!

[hanikesn]

Nice! I wish there were docs for this. I stumbled upon this while looking in the source code to check why my custom etag headers weren't used to serve 304s.

[hanikesn]

This only seems to work for precompressed files though, any particular reason for that? I'd be quite useful for this to work on any files. Sorry for the noise I misread the code and had another issue.

[mholt]

Docs are being updated with the new features shortly :)

[hanikesn]

Docs are being updated with the new features shortly :)

Thanks, right now this is quite easy to misuse. I.e. the etag files must not have newlines and must include quotes "". Otherwise http.serveContent won't send 304s for requests including If-None-Match requests.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-None-Match is specific for that as well.

Here's a short cmd to generate them in the correct format:

find . -type f -not -name "*.sha256" -exec sh -c 'sha256sum "$0" | cut -d " " -f 1 | tr -d "\n" | xargs -0 printf "\"%s\"" > "$0.sha256"' '{}' \;

I'm wondering whether this should create a warning in the logs or Caddy can just do the "right thing" and trim and quote the value.

[mholt]

If the etag is weak, though, the quotes won't be around the whole thing.

We could probably trim newlines if that's a common occurrence, but it's not something I've encountered in my (limited) experience.

[hanikesn]

We could probably trim newlines if that's a common occurrence, but it's not something I've encountered in my (limited) experience.

As long as it ends up in the docs I'm happy 🙂 It's easy to waste time with this digging into the source code of http.serveContent(), but also pre-computing etags is already a quite advanced use case. With reproducible builds on the advance though it'll become more common.

[mholt]

I'd welcome a PR at least for the newline patch!