api: don't download files as root when Homebrew's not owned by root.

[MikeMcQuaid]

This was mentioned in a random comment. While we're here, make some helper functions to query this a bit more nicely elsewhere when we do it.

[BrewTestBot]

Review period skipped due to critical label.

[laggardkernel]

This fix may break the use of sudo brew servcies. Are you decided to drop sudo brew completely? I just wanna start a services using a privileged port, port 53.

❯ sudo brew services restart adguardhome
Password:
Error: Need to download https://formulae.brew.sh/api/formula.jws.json but cannot as root! Run `brew update` without `sudo` first then try again.

[Bo98]

No, this message only appears if the file doesn't exist in the cache (or is empty). The cache never expires.

You can't use sudo for the first time the file is created as it will prevent it being updated when you later don't use sudo. But after the first run the file should stay around permanently.

[laggardkernel]

I just find out the cause. HOMEBREW_CACHE is not respected when using sudo. After I made a copy of formula.jws.json to the default location ~/Library/Caches/Homebrew/api/, the error above disappeared.

[carlocab]

sudo will clear most environment variables when running. You'll need to adjust your sudo invocation or configuration if you need HOMEBREW_CACHE to be preserved when running sudo.

[michael1900]

I just find out the cause. HOMEBREW_CACHE is not respected when using sudo. After I made a copy of formula.jws.json to the default location ~/Library/Caches/Homebrew/api/, the error above disappeared.

How to make this copy? Please help me to fix this, i need it to restart dnscrypt.

[laggardkernel]

@michael1900 I don't think we encountered the same problem. The current implementation is to download the services api related jws using brew update without sudo. sudo brew services depends on this very jws file.

In my case, I set HOMEBREW_CACHE to a custom location ~/.cache/homebrew. Since HOMEBREW_CACHE environment variable is not inherited bysudo, it fails to find this jws file.