nix-super/src/libutil/filesystem.cc

#include <sys/time.h>
#include <filesystem>

#include "util.hh"
#include "types.hh"

namespace fs = std::filesystem;

namespace nix {

void createSymlink(const Path & target, const Path & link,
    std::optional<time_t> mtime)
{
    if (symlink(target.c_str(), link.c_str()))
        throw SysError("creating symlink from '%1%' to '%2%'", link, target);
    if (mtime) {
        struct timeval times[2];
        times[0].tv_sec = *mtime;
        times[0].tv_usec = 0;
        times[1].tv_sec = *mtime;
        times[1].tv_usec = 0;
        if (lutimes(link.c_str(), times))
            throw SysError("setting time of symlink '%s'", link);
    }
}

void replaceSymlink(const Path & target, const Path & link,
    std::optional<time_t> mtime)
{
    for (unsigned int n = 0; true; n++) {
        Path tmp = canonPath(fmt("%s/.%d_%s", dirOf(link), n, baseNameOf(link)));

        try {
            createSymlink(target, tmp, mtime);
        } catch (SysError & e) {
            if (e.errNo == EEXIST) continue;
            throw;
        }

        moveFile(tmp, link);

        break;
    }
}

void moveFile(const Path & oldName, const Path & newName)
{
    auto oldPath = fs::path(oldName);
    auto newPath = fs::path(newName);
    try {
        fs::rename(oldPath, newPath);
    } catch (fs::filesystem_error & e) {
        if (e.code().value() == EXDEV) {
            fs::copy(oldName, newName, fs::copy_options::copy_symlinks);
            fs::remove_all(oldName);
        }
    }
}

}