Improve error handling and message wrt libcurl failures

[samuela]

I am consistently getting these errors from nix, but the download works fine via curl, Zen browser, or any other reasonable method of downloading files from the internet.

❯ sudo nixos-rebuild switch
Place your right index finger on the fingerprint reader
unpacking 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz' into the Git cache...
unpacking 'https://github.com/nix-community/home-manager/archive/44777152652bc9eacf8876976fa72cc77ca8b9d8.tar.gz' into the Git cache...
unpacking 'https://github.com/nix-community/stylix/archive/a7fb3944d1fb4daa073ba82e1a9d34b5f05adb9f.tar.gz' into the Git cache...
^Bbuilding the system configuration...
unpacking 'https://github.com/NixOS/nixpkgs/archive/b9cd0cd124fe67c744e77782bf4b684a43cb44f3.tar.gz' into the Git cache...
warning: error: unable to download 'https://github.com/NixOS/nixpkgs/archive/b9cd0cd124fe67c744e77782bf4b684a43cb44f3.tar.gz': Timeout was reached (28) Connection timed out after 15031 milliseconds; retrying in 274 ms

❯ curl https://github.com/NixOS/nixpkgs/archive/b9cd0cd124fe67c744e77782bf4b684a43cb44f3.tar.gz > /dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0   0     0   0     0     0     0  --:--:--  0:00:02 --:--:--     0

❯ echo $status
0

[samuela]

btw

❯ nix --version
nix (Nix) 2.31.2

[samuela]

Further weirdness: it appears to work with nixos-rebuild build but fail with nixos-rebuild switch:

nixos-config on  main [$!] took 32s
❯ ./rebuild.sh switch
building the system configuration...
evaluation warning: skainswo profile: stylix: firefox: `config.stylix.targets.firefox.profileNames` is not set. Declare profile names with 'config.stylix.targets.firefox.profileNames = [ "<PROFILE_NAME>" ];'.
error: creating symlink '/nix/var/nix/profiles/system-151-link.tmp-180204-1804289383' -> '/nix/store/mw7b467fdl5grxg4118gfx4c73r1w3mf-nixos-system-tropical-turnip-25.11.3357.d351d0653aeb': Permission denied
Command 'nix-env -p /nix/var/nix/profiles/system --set /nix/store/mw7b467fdl5grxg4118gfx4c73r1w3mf-nixos-system-tropical-turnip-25.11.3357.d351d0653aeb' returned non-zero exit status 1.

nixos-config on  main [$!] took 15s
❯ sudo ./rebuild.sh switch
Place your right index finger on the fingerprint reader
building the system configuration...
unpacking 'https://github.com/noctalia-dev/noctalia-shell/archive/2b55ae2c348fcad50089bc334c4a8155b2941d3b.tar.gz' into the Git cache...
warning: error: unable to download 'https://github.com/noctalia-dev/noctalia-shell/archive/2b55ae2c348fcad50089bc334c4a8155b2941d3b.tar.gz': Timeout was reached (28) Resolving timed out after 15000 milliseconds; retrying in 336 ms
warning: error: unable to download 'https://github.com/noctalia-dev/noctalia-shell/archive/2b55ae2c348fcad50089bc334c4a8155b2941d3b.tar.gz': Timeout was reached (28) Resolving timed out after 15001 milliseconds; retrying in 673 ms
^C

nixos-config on  main [$!] took 47s
❯ sudo ./rebuild.sh switch
building the system configuration...
unpacking 'https://github.com/noctalia-dev/noctalia-shell/archive/2b55ae2c348fcad50089bc334c4a8155b2941d3b.tar.gz' into the Git cache...
warning: error: unable to download 'https://github.com/noctalia-dev/noctalia-shell/archive/2b55ae2c348fcad50089bc334c4a8155b2941d3b.tar.gz': Timeout was reached (28) Resolving timed out after 15001 milliseconds; retrying in 318 ms
^C

nixos-config on  main [$!] took 20s
❯ ./rebuild.sh build
building the system configuration...
evaluation warning: skainswo profile: stylix: firefox: `config.stylix.targets.firefox.profileNames` is not set. Declare profile names with 'config.stylix.targets.firefox.profileNames = [ "<PROFILE_NAME>" ];'.
Done. The new configuration is /nix/store/mw7b467fdl5grxg4118gfx4c73r1w3mf-nixos-system-tropical-turnip-25.11.3357.d351d0653aeb

nixos-config on  main [$!] took 13s
❯ cat rebuild.sh
#!/usr/bin/env bash
set -euo pipefail
repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
nixos-rebuild -I nixos-config="$repo_root/configuration.nix" "$@"

Shouldn't nixos-rebuild switch reuse the same build artifact as produced by nixos-rebuild build? Why is it trying and failing to build something else?

[samuela]

Also may be worth noting that I get this error on many different github URLs, not limited to any specific one:

❯ sudo ./rebuild.sh switch
unpacking 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz' into the Git cache...
warning: error: unable to download 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz': Timeout was reached (28) Resolving timed out after 15000 milliseconds; retrying in 336 ms

[samuela]

This reproduces on nix-2.34pre20251217_b6add8dc which is the latest nixVersions.git in nixpkgs at the time of writing.

nixpkgs on  master took 1m12s
❯ git log -1 --oneline
0ec0edf1d56a (HEAD -> master, upstream/master, upstream/HEAD) kdePackages.plasma-wayland-protocols: 1.19.0 -> 1.20.0 (#479723)

❯ echo "$(nix build ~/dev/nixpkgs#nixVersions.git --print-out-paths --no-link)/bin/nix-build"
/nix/store/pwk9i70lab04808d5sk7was5khc69ixw-nix-2.34pre20251217_b6add8dc-man
/nix/store/kr0x3cjk2m7v82s4pxc4pzaf4nfrny1q-nix-2.34pre20251217_b6add8dc/bin/nix-build

❯ cd ~/dev/nixos-config

nixos-config on  main [$!?] took 30s 
❯ /nix/store/kr0x3cjk2m7v82s4pxc4pzaf4nfrny1q-nix-2.34pre20251217_b6add8dc/bin/nix-build ~/dev/nixpkgs/nixos/ -A system
unpacking 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz' into the Git cache...
warning: error: unable to download 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz': Timeout was reached (28) Resolving timed out after 15001 milliseconds; retrying in 293 ms
^C

[samuela]

more verbose logging:

❯ /nix/store/kr0x3cjk2m7v82s4pxc4pzaf4nfrny1q-nix-2.34pre20251217_b6add8dc/bin/nix-build -vvvv ~/dev/nixpkgs/nixos/ -A system
...
unpacking 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz' into the Git cache...
downloading 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz'...
starting download of https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz
curl: Couldn't find host github.com in the /etc/nix/netrc file; using defaults
curl: Resolving timed out after 15000 milliseconds
curl: closing connection #0
finished download of 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz'; curl status = 28, HTTP status = 0, body = 0 bytes, duration = 15.00 s
warning: error: unable to download 'https://github.com/NixOS/nixos-hardware/archive/9154f4569b6cdfd3c595851a6ba51bfaa472d9f3.tar.gz': Timeout was reached (28) Resolving timed out after 15000 milliseconds; retrying in 342 ms

[samuela]

Come to think of it does using a different nix cli version really make a difference here if the nix-daemon processes are still running the old version?

[samuela]

Is there a way to configure the DNS resolution timeout in nix?

[samuela]

Turns out to be my garbage netgear wifi router. It was timing out on AAAA lookups. Fix in samuela/nixos-config@50a1bd9 for anyone who's curious.

[xokdvium]

I wonder if there's a way to get more information on the error out of libcurl to make it easier to diagnose.

[xokdvium]

Does look like it's possible: https://curl.se/libcurl/c/CURLINFO_NAMELOOKUP_TIME.html. I can try poking around for improving the error message it include that information

[xokdvium]

@samuela, mind if I reopen so we can repurpose the issue for error message improvements?

[samuela]

@xokdvium Thanks for taking a look! Reopened and changed the title