lix/src/libutil/file-system.cc

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

#include "environment-variables.hh"
#include "file-descriptor.hh"
#include "file-system.hh"
#include "finally.hh"
#include "logging.hh"
#include "serialise.hh"
#include "signals.hh"
#include "types.hh"
#include "users.hh"

namespace fs = std::filesystem;

namespace nix {

Path absPath(Path path, std::optional<PathView> dir, bool resolveSymlinks)
{
    if (path.empty() || path[0] != '/') {
        if (!dir) {
#ifdef __GNU__
            /* GNU (aka. GNU/Hurd) doesn't have any limitation on path
               lengths and doesn't define `PATH_MAX'.  */
            char *buf = getcwd(NULL, 0);
            if (buf == NULL)
#else
            char buf[PATH_MAX];
            if (!getcwd(buf, sizeof(buf)))
#endif
                throw SysError("cannot get cwd");
            path = concatStrings(buf, "/", path);
#ifdef __GNU__
            free(buf);
#endif
        } else
            path = concatStrings(*dir, "/", path);
    }
    return canonPath(path, resolveSymlinks);
}


Path canonPath(PathView path, bool resolveSymlinks)
{
    assert(path != "");

    std::string s;
    s.reserve(256);

    if (path[0] != '/')
        throw Error("not an absolute path: '%1%'", path);

    std::string temp;

    /* Count the number of times we follow a symlink and stop at some
       arbitrary (but high) limit to prevent infinite loops. */
    unsigned int followCount = 0, maxFollow = 1024;

    while (1) {

        /* Skip slashes. */
        while (!path.empty() && path[0] == '/') path.remove_prefix(1);
        if (path.empty()) break;

        /* Ignore `.'. */
        if (path == "." || path.substr(0, 2) == "./")
            path.remove_prefix(1);

        /* If `..', delete the last component. */
        else if (path == ".." || path.substr(0, 3) == "../")
        {
            if (!s.empty()) s.erase(s.rfind('/'));
            path.remove_prefix(2);
        }

        /* Normal component; copy it. */
        else {
            s += '/';
            if (const auto slash = path.find('/'); slash == std::string::npos) {
                s += path;
                path = {};
            } else {
                s += path.substr(0, slash);
                path = path.substr(slash);
            }

            /* If s points to a symlink, resolve it and continue from there */
            if (resolveSymlinks && isLink(s)) {
                if (++followCount >= maxFollow)
                    throw Error("infinite symlink recursion in path '%1%'", path);
                temp = concatStrings(readLink(s), path);
                path = temp;
                if (!temp.empty() && temp[0] == '/') {
                    s.clear();  /* restart for symlinks pointing to absolute path */
                } else {
                    s = dirOf(s);
                    if (s == "/") {  // we don’t want trailing slashes here, which dirOf only produces if s = /
                        s.clear();
                    }
                }
            }
        }
    }

    return s.empty() ? "/" : std::move(s);
}

Path realPath(Path const & path)
{
    // With nullptr, realpath() malloc's and returns a new c-string.
    char * resolved = realpath(path.c_str(), nullptr);
    int saved = errno;
    if (resolved == nullptr) {
        throw SysError(saved, "cannot get realpath for '%s'", path);
    }

    Finally const _free([&] { free(resolved); });

    // There's not really a from_raw_parts() for std::string.
    // The copy is not a big deal.
    Path ret(resolved);

    return ret;
}

void chmodPath(const Path & path, mode_t mode)
{
    if (chmod(path.c_str(), mode) == -1)
        throw SysError("setting permissions on '%s'", path);
}

Path dirOf(const PathView path)
{
    Path::size_type pos = path.rfind('/');
    if (pos == std::string::npos)
        return ".";
    return pos == 0 ? "/" : Path(path, 0, pos);
}


std::string_view baseNameOf(std::string_view path)
{
    if (path.empty())
        return "";

    auto last = path.size() - 1;
    if (path[last] == '/' && last > 0)
        last -= 1;

    auto pos = path.rfind('/', last);
    if (pos == std::string::npos)
        pos = 0;
    else
        pos += 1;

    return path.substr(pos, last - pos + 1);
}


std::string expandTilde(std::string_view path)
{
    // TODO: expand ~user ?
    auto tilde = path.substr(0, 2);
    if (tilde == "~/" || tilde == "~")
        return getHome() + std::string(path.substr(1));
    else
        return std::string(path);
}


bool isInDir(std::string_view path, std::string_view dir)
{
    return path.substr(0, 1) == "/"
        && path.substr(0, dir.size()) == dir
        && path.size() >= dir.size() + 2
        && path[dir.size()] == '/';
}


bool isDirOrInDir(std::string_view path, std::string_view dir)
{
    return path == dir || isInDir(path, dir);
}


struct stat stat(const Path & path)
{
    struct stat st;
    if (stat(path.c_str(), &st))
        throw SysError("getting status of '%1%'", path);
    return st;
}


struct stat lstat(const Path & path)
{
    struct stat st;
    if (lstat(path.c_str(), &st))
        throw SysError("getting status of '%1%'", path);
    return st;
}

std::optional<struct stat> maybeLstat(const Path & path)
{
    std::optional<struct stat> st{std::in_place};
    if (lstat(path.c_str(), &*st))
    {
        if (errno == ENOENT || errno == ENOTDIR)
            st.reset();
        else
            throw SysError("getting status of '%s'", path);
    }
    return st;
}

bool pathExists(const Path & path)
{
    return maybeLstat(path).has_value();
}

bool pathAccessible(const Path & path)
{
    try {
        return pathExists(path);
    } catch (SysError & e) {
        // swallow EPERM
        if (e.errNo == EPERM) return false;
        throw;
    }
}


Path readLink(const Path & path)
{
    checkInterrupt();
    std::vector<char> buf;
    for (ssize_t bufSize = PATH_MAX/4; true; bufSize += bufSize/2) {
        buf.resize(bufSize);
        ssize_t rlSize = readlink(path.c_str(), buf.data(), bufSize);
        if (rlSize == -1)
            if (errno == EINVAL)
                throw Error("'%1%' is not a symlink", path);
            else
                throw SysError("reading symbolic link '%1%'", path);
        else if (rlSize < bufSize)
            return std::string(buf.data(), rlSize);
    }
}


bool isLink(const Path & path)
{
    struct stat st = lstat(path);
    return S_ISLNK(st.st_mode);
}


DirEntries readDirectory(DIR *dir, const Path & path)
{
    DirEntries entries;
    entries.reserve(64);

    struct dirent * dirent;
    while (errno = 0, dirent = readdir(dir)) { /* sic */
        checkInterrupt();
        std::string name = dirent->d_name;
        if (name == "." || name == "..") continue;
        entries.emplace_back(name, dirent->d_ino,
#ifdef HAVE_STRUCT_DIRENT_D_TYPE
            dirent->d_type
#else
            DT_UNKNOWN
#endif
        );
    }
    if (errno) throw SysError("reading directory '%1%'", path);

    return entries;
}

DirEntries readDirectory(const Path & path)
{
    AutoCloseDir dir(opendir(path.c_str()));
    if (!dir) throw SysError("opening directory '%1%'", path);

    return readDirectory(dir.get(), path);
}


unsigned char getFileType(const Path & path)
{
    struct stat st = lstat(path);
    if (S_ISDIR(st.st_mode)) return DT_DIR;
    if (S_ISLNK(st.st_mode)) return DT_LNK;
    if (S_ISREG(st.st_mode)) return DT_REG;
    return DT_UNKNOWN;
}


std::string readFile(const Path & path)
{
    AutoCloseFD fd{open(path.c_str(), O_RDONLY | O_CLOEXEC)};
    if (!fd)
        throw SysError("opening file '%1%'", path);
    return readFile(fd.get());
}


Generator<Bytes> readFileSource(const Path & path)
{
    AutoCloseFD fd{open(path.c_str(), O_RDONLY | O_CLOEXEC)};
    if (!fd)
        throw SysError("opening file '%s'", path);
    return [](AutoCloseFD fd) -> Generator<Bytes> {
        co_yield drainFDSource(fd.get());
    }(std::move(fd));
}


void writeFile(const Path & path, std::string_view s, mode_t mode, bool sync)
{
    AutoCloseFD fd{open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT | O_CLOEXEC, mode)};
    if (!fd)
        throw SysError("opening file '%1%'", path);
    try {
        writeFull(fd.get(), s);
    } catch (Error & e) {
        e.addTrace({}, "writing file '%1%'", path);
        throw;
    }
    if (sync)
        fd.fsync();
    // Explicitly close to make sure exceptions are propagated.
    fd.close();
    if (sync)
        syncParent(path);
}


void writeFile(const Path & path, Source & source, mode_t mode, bool sync)
{
    AutoCloseFD fd{open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT | O_CLOEXEC, mode)};
    if (!fd)
        throw SysError("opening file '%1%'", path);

    std::vector<char> buf(64 * 1024);

    try {
        while (true) {
            try {
                auto n = source.read(buf.data(), buf.size());
                writeFull(fd.get(), {buf.data(), n});
            } catch (EndOfFile &) { break; }
        }
    } catch (Error & e) {
        e.addTrace({}, "writing file '%1%'", path);
        throw;
    }
    if (sync)
        fd.fsync();
    // Explicitly close to make sure exceptions are propagated.
    fd.close();
    if (sync)
        syncParent(path);
}

void syncParent(const Path & path)
{
    AutoCloseFD fd{open(dirOf(path).c_str(), O_RDONLY, 0)};
    if (!fd)
        throw SysError("opening file '%1%'", path);
    fd.fsync();
}

static void _deletePath(int parentfd, const Path & path, uint64_t & bytesFreed)
{
    checkInterrupt();

    std::string name(baseNameOf(path));

    struct stat st;
    if (fstatat(parentfd, name.c_str(), &st, AT_SYMLINK_NOFOLLOW) == -1) {
        if (errno == ENOENT) return;
        throw SysError("getting status of '%1%'", path);
    }

    if (!S_ISDIR(st.st_mode)) {
        /* We are about to delete a file. Will it likely free space? */

        switch (st.st_nlink) {
            /* Yes: last link. */
            case 1:
                bytesFreed += st.st_size;
                break;
            /* Maybe: yes, if 'auto-optimise-store' or manual optimisation
               was performed. Instead of checking for real let's assume
               it's an optimised file and space will be freed.

               In worst case we will double count on freed space for files
               with exactly two hardlinks for unoptimised packages.
             */
            case 2:
                bytesFreed += st.st_size;
                break;
            /* No: 3+ links. */
            default:
                break;
        }
    }

    if (S_ISDIR(st.st_mode)) {
        /* Make the directory accessible. */
        const auto PERM_MASK = S_IRUSR | S_IWUSR | S_IXUSR;
        if ((st.st_mode & PERM_MASK) != PERM_MASK) {
            if (fchmodat(parentfd, name.c_str(), st.st_mode | PERM_MASK, 0) == -1)
                throw SysError("chmod '%1%'", path);
        }

        int fd = openat(parentfd, path.c_str(), O_RDONLY);
        if (fd == -1)
            throw SysError("opening directory '%1%'", path);
        AutoCloseDir dir(fdopendir(fd));
        if (!dir)
            throw SysError("opening directory '%1%'", path);
        for (auto & i : readDirectory(dir.get(), path))
            _deletePath(dirfd(dir.get()), path + "/" + i.name, bytesFreed);
    }

    int flags = S_ISDIR(st.st_mode) ? AT_REMOVEDIR : 0;
    if (unlinkat(parentfd, name.c_str(), flags) == -1) {
        if (errno == ENOENT) return;
        throw SysError("cannot unlink '%1%'", path);
    }
}

static void _deletePath(const Path & path, uint64_t & bytesFreed)
{
    Path dir = dirOf(path);
    if (dir == "")
        dir = "/";

    AutoCloseFD dirfd{open(dir.c_str(), O_RDONLY)};
    if (!dirfd) {
        if (errno == ENOENT) return;
        throw SysError("opening directory '%1%'", path);
    }

    _deletePath(dirfd.get(), path, bytesFreed);
}


void deletePath(const Path & path)
{
    uint64_t dummy;
    deletePath(path, dummy);
}


void deletePath(const Path & path, uint64_t & bytesFreed)
{
    //Activity act(*logger, lvlDebug, "recursively deleting path '%1%'", path);
    bytesFreed = 0;
    _deletePath(path, bytesFreed);
}

Paths createDirs(const Path & path)
{
    Paths created;
    if (path == "/") return created;

    struct stat st;
    if (lstat(path.c_str(), &st) == -1) {
        created = createDirs(dirOf(path));
        if (mkdir(path.c_str(), 0777) == -1 && errno != EEXIST)
            throw SysError("creating directory '%1%'", path);
        st = lstat(path);
        created.push_back(path);
    }

    if (S_ISLNK(st.st_mode) && stat(path.c_str(), &st) == -1)
        throw SysError("statting symlink '%1%'", path);

    if (!S_ISDIR(st.st_mode)) throw Error("'%1%' is not a directory", path);

    return created;
}


//////////////////////////////////////////////////////////////////////

AutoDelete::AutoDelete() : del{false} {}

AutoDelete::AutoDelete(const std::string & p, bool recursive) : path(p)
{
    del = true;
    this->recursive = recursive;
}

AutoDelete::~AutoDelete()
{
    try {
        if (del) {
            if (recursive)
                deletePath(path);
            else {
                if (remove(path.c_str()) == -1)
                    throw SysError("cannot unlink '%1%'", path);
            }
        }
    } catch (...) {
        ignoreException();
    }
}

void AutoDelete::cancel()
{
    del = false;
}

void AutoDelete::reset(const Path & p, bool recursive) {
    path = p;
    this->recursive = recursive;
    del = true;
}

//////////////////////////////////////////////////////////////////////

std::string defaultTempDir() {
    return getEnvNonEmpty("TMPDIR").value_or("/tmp");
}

static Path tempName(Path tmpRoot, const Path & prefix, bool includePid,
    std::atomic<unsigned int> & counter)
{
    tmpRoot = canonPath(tmpRoot.empty() ? defaultTempDir() : tmpRoot, true);
    if (includePid)
        return fmt("%1%/%2%-%3%-%4%", tmpRoot, prefix, getpid(), counter++);
    else
        return fmt("%1%/%2%-%3%", tmpRoot, prefix, counter++);
}

Path createTempDir(const Path & tmpRoot, const Path & prefix,
    bool includePid, bool useGlobalCounter, mode_t mode)
{
    static std::atomic<unsigned int> globalCounter = 0;
    std::atomic<unsigned int> localCounter = 0;
    auto & counter(useGlobalCounter ? globalCounter : localCounter);

    while (1) {
        checkInterrupt();
        Path tmpDir = tempName(tmpRoot, prefix, includePid, counter);
        if (mkdir(tmpDir.c_str(), mode) == 0) {
#if __FreeBSD__
            /* Explicitly set the group of the directory.  This is to
               work around around problems caused by BSD's group
               ownership semantics (directories inherit the group of
               the parent).  For instance, the group of /tmp on
               FreeBSD is "wheel", so all directories created in /tmp
               will be owned by "wheel"; but if the user is not in
               "wheel", then "tar" will fail to unpack archives that
               have the setgid bit set on directories. */
            if (chown(tmpDir.c_str(), (uid_t) -1, getegid()) != 0)
                throw SysError("setting group of directory '%1%'", tmpDir);
#endif
            return tmpDir;
        }
        if (errno != EEXIST)
            throw SysError("creating directory '%1%'", tmpDir);
    }
}


std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix)
{
    Path tmpl(defaultTempDir() + "/" + prefix + ".XXXXXX");
    // Strictly speaking, this is UB, but who cares...
    // FIXME: use O_TMPFILE.
    AutoCloseFD fd(mkstemp((char *) tmpl.c_str()));
    if (!fd)
        throw SysError("creating temporary file '%s'", tmpl);
    closeOnExec(fd.get());
    return {std::move(fd), tmpl};
}

void createSymlink(const Path & target, const Path & link)
{
    if (symlink(target.c_str(), link.c_str()))
        throw SysError("creating symlink from '%1%' to '%2%'", link, target);
}

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

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

        renameFile(tmp, link);

        break;
    }
}

void setWriteTime(const fs::path & p, const struct stat & st)
{
    struct timeval times[2];
    times[0] = {
        .tv_sec = st.st_atime,
        .tv_usec = 0,
    };
    times[1] = {
        .tv_sec = st.st_mtime,
        .tv_usec = 0,
    };
    if (lutimes(p.c_str(), times) != 0)
        throw SysError("changing modification time of '%s'", p);
}

void copy(const fs::directory_entry & from, const fs::path & to, CopyFileFlags flags)
{
    // TODO: Rewrite the `is_*` to use `symlink_status()`
    auto statOfFrom = lstat(from.path().c_str());
    auto fromStatus = from.symlink_status();

    // Mark the directory as writable so that we can delete its children
    if (flags.deleteAfter && fs::is_directory(fromStatus)) {
        fs::permissions(from.path(), fs::perms::owner_write, fs::perm_options::add | fs::perm_options::nofollow);
    }


    if (fs::is_symlink(fromStatus) || fs::is_regular_file(fromStatus)) {
        auto opts = fs::copy_options::overwrite_existing;

        if (!flags.followSymlinks) {
            opts |= fs::copy_options::copy_symlinks;
        }

        fs::copy(from.path(), to, opts);
    } else if (fs::is_directory(fromStatus)) {
        fs::create_directory(to);
        for (auto & entry : fs::directory_iterator(from.path())) {
            copy(entry, to / entry.path().filename(), flags);
        }
    } else {
        throw Error("file '%s' has an unsupported type", from.path());
    }

    setWriteTime(to, statOfFrom);
    if (flags.deleteAfter) {
        if (!fs::is_symlink(fromStatus))
            fs::permissions(from.path(), fs::perms::owner_write, fs::perm_options::add | fs::perm_options::nofollow);
        fs::remove(from.path());
    }
}


void copyFile(const Path & oldPath, const Path & newPath, CopyFileFlags flags)
{
    return copy(fs::directory_entry(fs::path(oldPath)), fs::path(newPath), flags);
}

void renameFile(const Path & oldName, const Path & newName)
{
    fs::rename(oldName, newName);
}

void moveFile(const Path & oldName, const Path & newName)
{
    try {
        renameFile(oldName, newName);
    } catch (fs::filesystem_error & e) {
        auto oldPath = fs::path(oldName);
        auto newPath = fs::path(newName);
        // For the move to be as atomic as possible, copy to a temporary
        // directory
        fs::path temp = createTempDir(newPath.parent_path(), "rename-tmp");
        Finally removeTemp = [&]() { fs::remove(temp); };
        auto tempCopyTarget = temp / "copy-target";
        if (e.code().value() == EXDEV) {
            fs::remove(newPath);
            warn("Can’t rename %s as %s, copying instead", oldName, newName);
            copy(fs::directory_entry(oldPath), tempCopyTarget, { .deleteAfter = true });
            renameFile(tempCopyTarget, newPath);
        }
    }
}

}