`nix copy` and `nix-copy-closure` works inconsistently on nixbuild.net

[rickynils]

The following works:

• nix-copy-closure --to eu.nixbuild.net
• nix copy --to ssh-ng://eu.nixbuild.net
• nix copy --from ssh-ng://eu.nixbuild.net

The following does not work:

• nix-copy-closure --from eu.nixbuild.net
• nix copy --from ssh://eu.nixbuild.net

So, you can copy both to and from nixbuild.net but you have to select the right combination of commands and protocols. We should fix this so all combinations work.

[rickynils]

Most of the closure copying scenarios have now been fixed, but this is still not working: nix copy --from ssh://eu.nixbuild.net. This issue will be kept open until that use case has been fixed.

[treyfortmuller]

Let me know if this is a user error on my end or not. I built an SD card image for my aarch64-linux target via nixbuild.net successfully, with a --store arg pointing to the remote store, so the built closure wasn't copied to my local machine. I set out to do that manually:

nix copy --from ssh-ng://eu.nixbuild.net /nix/store/w16h6jfvg47nqgxp50qzk42dgmrz5azi-nixos-image-sd-card-25.11.20260107.d351d06-aarch64-linux.img.zst -vvvv

and that command hung indefinitely, the last few lines of the verbose logs were:

debug1: Sending command: nix-daemon --stdio
debug1: pledge: fork
debug1: set_sock_tos: invalid TOS 2147483647
don't know how to build these paths:
  /nix/store/w16h6jfvg47nqgxp50qzk42dgmrz5azi-nixos-image-sd-card-25.11.20260107.d351d06-aarch64-linux.img.zst

<hanging, without verbose logs enabled this looks like it could be working>

Trying

nix-copy-closure --from eu.nixbuild.net /nix/store/w16h6jfvg47nqgxp50qzk42dgmrz5azi-nixos-image-sd-card-25.11.20260107.d351d06-aarch64-linux.img.zst -vvv

worked without issue.

I know this is a fraught part of the nix CLI and may not be a nixbuild.net issue specifically, just calling out my observations.