isValidPath getHydraPath getHydraDBPath openHydraDB

    isValidPath queryPathInfo
    getHydraPath getHydraDBPath openHydraDB

}
sub queryPathInfo {
    my $path = shift;
    # !!! like above, this breaks abstraction.  What we really need is
    # Perl bindings for libstore :-)
    open FH, "</nix/var/nix/db/info/" . basename $path
        or die "cannot open info file for $path";
    my $hash;
    my $deriver;
    my @refs = ();
    while (<FH>) {
        if (/^Hash: (\S+)$/) {
            $hash = $1;
        }
        elsif (/^Deriver: (\S+)$/) {
            $deriver = $1;
        }
        elsif (/^References: (.*)$/) {
            @refs = split / /, $1;
        }
    }
    close FH;
    die unless defined $hash;
    return ($hash, $deriver, \@refs);

use IO::Pipe;
use POSIX qw(dup2);

use Hydra::Helper::Nix;

        my @refs = split '\n', `nix-store --query --references $path`;
        die "cannot query references of `$path': $?" if $? != 0;

        my ($hash, $deriver, $refs) = queryPathInfo $path;

        my $hash = `nix-store --query --hash $path`
            or die "cannot query hash of `$path': $?";
        chomp $hash;

        my $deriver = `nix-store --query --deriver $path`
            or die "cannot query deriver of `$path': $?";
        chomp $deriver;
        

            (scalar @refs > 0 ? "  References: @refs\n" : "") .
            ($deriver ne "unknown-deriver" ? "  Deriver: $deriver\n" : "") .

            (scalar @{$refs} > 0 ? "  References: @{$refs}\n" : "") .
            (defined $deriver ? "  Deriver: $deriver\n" : "") .