
.. _fs:

File system operations
======================

libuv provides a wide variety of cross-platform sync and async file system
operations. All functions defined in this document take a callback, which is
allowed to be NULL. If the callback is NULL the request is completed synchronously,
otherwise it will be performed asynchronously.

All file operations are run on the threadpool. See :ref:`threadpool` for information
on the threadpool size.


Data types
----------

.. c:type:: uv_fs_t

    File system request type.

.. c:type:: uv_timespec_t

    Portable equivalent of ``struct timespec``.

    ::

        typedef struct {
            long tv_sec;
            long tv_nsec;
        } uv_timespec_t;

.. c:type:: uv_stat_t

    Portable equivalent of ``struct stat``.

    ::

        typedef struct {
            uint64_t st_dev;
            uint64_t st_mode;
            uint64_t st_nlink;
            uint64_t st_uid;
            uint64_t st_gid;
            uint64_t st_rdev;
            uint64_t st_ino;
            uint64_t st_size;
            uint64_t st_blksize;
            uint64_t st_blocks;
            uint64_t st_flags;
            uint64_t st_gen;
            uv_timespec_t st_atim;
            uv_timespec_t st_mtim;
            uv_timespec_t st_ctim;
            uv_timespec_t st_birthtim;
        } uv_stat_t;

.. c:type:: uv_fs_type

    File system request type.

    ::

        typedef enum {
            UV_FS_UNKNOWN = -1,
            UV_FS_CUSTOM,
            UV_FS_OPEN,
            UV_FS_CLOSE,
            UV_FS_READ,
            UV_FS_WRITE,
            UV_FS_SENDFILE,
            UV_FS_STAT,
            UV_FS_LSTAT,
            UV_FS_FSTAT,
            UV_FS_FTRUNCATE,
            UV_FS_UTIME,
            UV_FS_FUTIME,
            UV_FS_ACCESS,
            UV_FS_CHMOD,
            UV_FS_FCHMOD,
            UV_FS_FSYNC,
            UV_FS_FDATASYNC,
            UV_FS_UNLINK,
            UV_FS_RMDIR,
            UV_FS_MKDIR,
            UV_FS_MKDTEMP,
            UV_FS_RENAME,
            UV_FS_SCANDIR,
            UV_FS_LINK,
            UV_FS_SYMLINK,
            UV_FS_READLINK,
            UV_FS_CHOWN,
            UV_FS_FCHOWN,
            UV_FS_REALPATH,
            UV_FS_COPYFILE,
            UV_FS_LCHOWN
        } uv_fs_type;

.. c:type:: uv_dirent_t

    Cross platform (reduced) equivalent of ``struct dirent``.
    Used in :c:func:`uv_fs_scandir_next`.

    ::

        typedef enum {
            UV_DIRENT_UNKNOWN,
            UV_DIRENT_FILE,
            UV_DIRENT_DIR,
            UV_DIRENT_LINK,
            UV_DIRENT_FIFO,
            UV_DIRENT_SOCKET,
            UV_DIRENT_CHAR,
            UV_DIRENT_BLOCK
        } uv_dirent_type_t;

        typedef struct uv_dirent_s {
            const char* name;
            uv_dirent_type_t type;
        } uv_dirent_t;


Public members
^^^^^^^^^^^^^^

.. c:member:: uv_loop_t* uv_fs_t.loop

    Loop that started this request and where completion will be reported.
    Readonly.

.. c:member:: uv_fs_type uv_fs_t.fs_type

    FS request type.

.. c:member:: const char* uv_fs_t.path

    Path affecting the request.

.. c:member:: ssize_t uv_fs_t.result

    Result of the request. < 0 means error, success otherwise. On requests such
    as :c:func:`uv_fs_read` or :c:func:`uv_fs_write` it indicates the amount of
    data that was read or written, respectively.

.. c:member:: uv_stat_t uv_fs_t.statbuf

    Stores the result of :c:func:`uv_fs_stat` and other stat requests.

.. c:member:: void* uv_fs_t.ptr

    Stores the result of :c:func:`uv_fs_readlink` and
    :c:func:`uv_fs_realpath` and serves as an alias to `statbuf`.

.. seealso:: The :c:type:`uv_req_t` members also apply.


API
---

.. c:function:: void uv_fs_req_cleanup(uv_fs_t* req)

    Cleanup request. Must be called after a request is finished to deallocate
    any memory libuv might have allocated.

.. c:function:: int uv_fs_close(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb)

    Equivalent to :man:`close(2)`.

.. c:function:: int uv_fs_open(uv_loop_t* loop, uv_fs_t* req, const char* path, int flags, int mode, uv_fs_cb cb)

    Equivalent to :man:`open(2)`.

    .. note::
        On Windows libuv uses `CreateFileW` and thus the file is always opened
        in binary mode. Because of this the O_BINARY and O_TEXT flags are not
        supported.

.. c:function:: int uv_fs_read(uv_loop_t* loop, uv_fs_t* req, uv_file file, const uv_buf_t bufs[], unsigned int nbufs, int64_t offset, uv_fs_cb cb)

    Equivalent to :man:`preadv(2)`.

.. c:function:: int uv_fs_unlink(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb)

    Equivalent to :man:`unlink(2)`.

.. c:function:: int uv_fs_write(uv_loop_t* loop, uv_fs_t* req, uv_file file, const uv_buf_t bufs[], unsigned int nbufs, int64_t offset, uv_fs_cb cb)

    Equivalent to :man:`pwritev(2)`.

.. c:function:: int uv_fs_mkdir(uv_loop_t* loop, uv_fs_t* req, const char* path, int mode, uv_fs_cb cb)

    Equivalent to :man:`mkdir(2)`.

    .. note::
        `mode` is currently not implemented on Windows.

.. c:function:: int uv_fs_mkdtemp(uv_loop_t* loop, uv_fs_t* req, const char* tpl, uv_fs_cb cb)

    Equivalent to :man:`mkdtemp(3)`.

    .. note::
        The result can be found as a null terminated string at `req->path`.

.. c:function:: int uv_fs_rmdir(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb)

    Equivalent to :man:`rmdir(2)`.

.. c:function:: int uv_fs_scandir(uv_loop_t* loop, uv_fs_t* req, const char* path, int flags, uv_fs_cb cb)
.. c:function:: int uv_fs_scandir_next(uv_fs_t* req, uv_dirent_t* ent)

    Equivalent to :man:`scandir(3)`, with a slightly different API. Once the callback
    for the request is called, the user can use :c:func:`uv_fs_scandir_next` to
    get `ent` populated with the next directory entry data. When there are no
    more entries ``UV_EOF`` will be returned.

    .. note::
        Unlike `scandir(3)`, this function does not return the "." and ".." entries.

    .. note::
        On Linux, getting the type of an entry is only supported by some file systems (btrfs, ext2,
        ext3 and ext4 at the time of this writing), check the :man:`getdents(2)` man page.

.. c:function:: int uv_fs_stat(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb)
.. c:function:: int uv_fs_fstat(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb)
.. c:function:: int uv_fs_lstat(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb)

    Equivalent to :man:`stat(2)`, :man:`fstat(2)` and :man:`lstat(2)` respectively.

.. c:function:: int uv_fs_rename(uv_loop_t* loop, uv_fs_t* req, const char* path, const char* new_path, uv_fs_cb cb)

    Equivalent to :man:`rename(2)`.

.. c:function:: int uv_fs_fsync(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb)

    Equivalent to :man:`fsync(2)`.

    .. note::
        For AIX, `uv_fs_fsync` returns `UV_EBADF` on file descriptors referencing
        non regular files.

.. c:function:: int uv_fs_fdatasync(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_fs_cb cb)

    Equivalent to :man:`fdatasync(2)`.

.. c:function:: int uv_fs_ftruncate(uv_loop_t* loop, uv_fs_t* req, uv_file file, int64_t offset, uv_fs_cb cb)

    Equivalent to :man:`ftruncate(2)`.

.. c:function:: int uv_fs_copyfile(uv_loop_t* loop, uv_fs_t* req, const char* path, const char* new_path, int flags, uv_fs_cb cb)

    Copies a file from `path` to `new_path`. Supported `flags` are described below.

    - `UV_FS_COPYFILE_EXCL`: If present, `uv_fs_copyfile()` will fail with
      `UV_EEXIST` if the destination path already exists. The default behavior
      is to overwrite the destination if it exists.
    - `UV_FS_COPYFILE_FICLONE`: If present, `uv_fs_copyfile()` will attempt to
      create a copy-on-write reflink. If the underlying platform does not
      support copy-on-write, then a fallback copy mechanism is used.
    - `UV_FS_COPYFILE_FICLONE_FORCE`: If present, `uv_fs_copyfile()` will
      attempt to create a copy-on-write reflink. If the underlying platform does
      not support copy-on-write, then an error is returned.

    .. warning::
        If the destination path is created, but an error occurs while copying
        the data, then the destination path is removed. There is a brief window
        of time between closing and removing the file where another process
        could access the file.

    .. versionadded:: 1.14.0

    .. versionchanged:: 1.20.0 `UV_FS_COPYFILE_FICLONE` and
        `UV_FS_COPYFILE_FICLONE_FORCE` are supported.

.. c:function:: int uv_fs_sendfile(uv_loop_t* loop, uv_fs_t* req, uv_file out_fd, uv_file in_fd, int64_t in_offset, size_t length, uv_fs_cb cb)

    Limited equivalent to :man:`sendfile(2)`.

.. c:function:: int uv_fs_access(uv_loop_t* loop, uv_fs_t* req, const char* path, int mode, uv_fs_cb cb)

    Equivalent to :man:`access(2)` on Unix. Windows uses ``GetFileAttributesW()``.

.. c:function:: int uv_fs_chmod(uv_loop_t* loop, uv_fs_t* req, const char* path, int mode, uv_fs_cb cb)
.. c:function:: int uv_fs_fchmod(uv_loop_t* loop, uv_fs_t* req, uv_file file, int mode, uv_fs_cb cb)

    Equivalent to :man:`chmod(2)` and :man:`fchmod(2)` respectively.

.. c:function:: int uv_fs_utime(uv_loop_t* loop, uv_fs_t* req, const char* path, double atime, double mtime, uv_fs_cb cb)
.. c:function:: int uv_fs_futime(uv_loop_t* loop, uv_fs_t* req, uv_file file, double atime, double mtime, uv_fs_cb cb)

    Equivalent to :man:`utime(2)` and :man:`futime(2)` respectively.

    .. note::
      AIX: This function only works for AIX 7.1 and newer. It can still be called on older
      versions but will return ``UV_ENOSYS``.

    .. versionchanged:: 1.10.0 sub-second precission is supported on Windows

.. c:function:: int uv_fs_link(uv_loop_t* loop, uv_fs_t* req, const char* path, const char* new_path, uv_fs_cb cb)

    Equivalent to :man:`link(2)`.

.. c:function:: int uv_fs_symlink(uv_loop_t* loop, uv_fs_t* req, const char* path, const char* new_path, int flags, uv_fs_cb cb)

    Equivalent to :man:`symlink(2)`.

    .. note::
        On Windows the `flags` parameter can be specified to control how the symlink will
        be created:

            * ``UV_FS_SYMLINK_DIR``: indicates that `path` points to a directory.

            * ``UV_FS_SYMLINK_JUNCTION``: request that the symlink is created
              using junction points.

.. c:function:: int uv_fs_readlink(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb)

    Equivalent to :man:`readlink(2)`.
    The resulting string is stored in `req->ptr`.

.. c:function:: int uv_fs_realpath(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_fs_cb cb)

    Equivalent to :man:`realpath(3)` on Unix. Windows uses `GetFinalPathNameByHandle <https://msdn.microsoft.com/en-us/library/windows/desktop/aa364962(v=vs.85).aspx>`_.
    The resulting string is stored in `req->ptr`.

    .. warning::
        This function has certain platform-specific caveats that were discovered when used in Node.

        * macOS and other BSDs: this function will fail with UV_ELOOP if more than 32 symlinks are
          found while resolving the given path.  This limit is hardcoded and cannot be sidestepped.
        * Windows: while this function works in the common case, there are a number of corner cases
          where it doesn't:

          - Paths in ramdisk volumes created by tools which sidestep the Volume Manager (such as ImDisk)
            cannot be resolved.
          - Inconsistent casing when using drive letters.
          - Resolved path bypasses subst'd drives.

        While this function can still be used, it's not recommended if scenarios such as the
        above need to be supported.

        The background story and some more details on these issues can be checked
        `here <https://github.com/nodejs/node/issues/7726>`_.

    .. note::
      This function is not implemented on Windows XP and Windows Server 2003.
      On these systems, UV_ENOSYS is returned.

    .. versionadded:: 1.8.0

.. c:function:: int uv_fs_chown(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_uid_t uid, uv_gid_t gid, uv_fs_cb cb)
.. c:function:: int uv_fs_fchown(uv_loop_t* loop, uv_fs_t* req, uv_file file, uv_uid_t uid, uv_gid_t gid, uv_fs_cb cb)
.. c:function:: int uv_fs_lchown(uv_loop_t* loop, uv_fs_t* req, const char* path, uv_uid_t uid, uv_gid_t gid, uv_fs_cb cb)

    Equivalent to :man:`chown(2)`, :man:`fchown(2)` and :man:`lchown(2)` respectively.

    .. note::
        These functions are not implemented on Windows.

    .. versionchanged:: 1.21.0 implemented uv_fs_lchown

.. c:function:: uv_fs_type uv_fs_get_type(const uv_fs_t* req)

    Returns `req->fs_type`.

    .. versionadded:: 1.19.0

.. c:function:: ssize_t uv_fs_get_result(const uv_fs_t* req)

    Returns `req->result`.

    .. versionadded:: 1.19.0

.. c:function:: void* uv_fs_get_ptr(const uv_fs_t* req)

    Returns `req->ptr`.

    .. versionadded:: 1.19.0

.. c:function:: const char* uv_fs_get_path(const uv_fs_t* req)

    Returns `req->path`.

    .. versionadded:: 1.19.0

.. c:function:: uv_stat_t* uv_fs_get_statbuf(uv_fs_t* req)

    Returns `&req->statbuf`.

    .. versionadded:: 1.19.0

.. seealso:: The :c:type:`uv_req_t` API functions also apply.

Helper functions
----------------

.. c:function:: uv_os_fd_t uv_get_osfhandle(int fd)

   For a file descriptor in the C runtime, get the OS-dependent handle.
   On UNIX, returns the ``fd`` intact. On Windows, this calls `_get_osfhandle <https://msdn.microsoft.com/en-us/library/ks2530z6.aspx>`_.
   Note that the return value is still owned by the C runtime,
   any attempts to close it or to use it after closing the fd may lead to malfunction.

    .. versionadded:: 1.12.0

.. c:function:: int uv_open_osfhandle(uv_os_fd_t os_fd)

   For a OS-dependent handle, get the file descriptor in the C runtime.
   On UNIX, returns the ``os_fd`` intact. On Windows, this calls `_open_osfhandle <https://msdn.microsoft.com/en-us/library/bdts1c9x.aspx>`_.
   Note that the return value is still owned by the CRT,
   any attempts to close it or to use it after closing the handle may lead to malfunction.

    .. versionadded:: 1.23.0

File open constants
-------------------

.. c:macro:: UV_FS_O_APPEND

    The file is opened in append mode. Before each write, the file offset is
    positioned at the end of the file.

.. c:macro:: UV_FS_O_CREAT

    The file is created if it does not already exist.

.. c:macro:: UV_FS_O_DIRECT

    File I/O is done directly to and from user-space buffers, which must be
    aligned. Buffer size and address should be a multiple of the physical sector
    size of the block device.

    .. note::
        `UV_FS_O_DIRECT` is supported on Linux, and on Windows via
        `FILE_FLAG_NO_BUFFERING <https://msdn.microsoft.com/en-us/library/windows/desktop/cc644950.aspx>`_.
        `UV_FS_O_DIRECT` is not supported on macOS.

.. c:macro:: UV_FS_O_DIRECTORY

    If the path is not a directory, fail the open.

    .. note::
        `UV_FS_O_DIRECTORY` is not supported on Windows.

.. c:macro:: UV_FS_O_DSYNC

    The file is opened for synchronous I/O. Write operations will complete once
    all data and a minimum of metadata are flushed to disk.

    .. note::
        `UV_FS_O_DSYNC` is supported on Windows via
        `FILE_FLAG_WRITE_THROUGH <https://msdn.microsoft.com/en-us/library/windows/desktop/cc644950.aspx>`_.

.. c:macro:: UV_FS_O_EXCL

    If the `O_CREAT` flag is set and the file already exists, fail the open.

    .. note::
        In general, the behavior of `O_EXCL` is undefined if it is used without
        `O_CREAT`. There is one exception: on Linux 2.6 and later, `O_EXCL` can
        be used without `O_CREAT` if pathname refers to a block device. If the
        block device is in use by the system (e.g., mounted), the open will fail
        with the error `EBUSY`.

.. c:macro:: UV_FS_O_EXLOCK

    Atomically obtain an exclusive lock.

    .. note::
        `UV_FS_O_EXLOCK` is only supported on macOS and Windows.

    .. versionchanged:: 1.17.0 support is added for Windows.

.. c:macro:: UV_FS_O_NOATIME

    Do not update the file access time when the file is read.

    .. note::
        `UV_FS_O_NOATIME` is not supported on Windows.

.. c:macro:: UV_FS_O_NOCTTY

    If the path identifies a terminal device, opening the path will not cause
    that terminal to become the controlling terminal for the process (if the
    process does not already have one).

    .. note::
        `UV_FS_O_NOCTTY` is not supported on Windows.

.. c:macro:: UV_FS_O_NOFOLLOW

    If the path is a symbolic link, fail the open.

    .. note::
        `UV_FS_O_NOFOLLOW` is not supported on Windows.

.. c:macro:: UV_FS_O_NONBLOCK

    Open the file in nonblocking mode if possible.

    .. note::
        `UV_FS_O_NONBLOCK` is not supported on Windows.

.. c:macro:: UV_FS_O_RANDOM

    Access is intended to be random. The system can use this as a hint to
    optimize file caching.

    .. note::
        `UV_FS_O_RANDOM` is only supported on Windows via
        `FILE_FLAG_RANDOM_ACCESS <https://msdn.microsoft.com/en-us/library/windows/desktop/aa363858.aspx>`_.

.. c:macro:: UV_FS_O_RDONLY

    Open the file for read-only access.

.. c:macro:: UV_FS_O_RDWR

    Open the file for read-write access.

.. c:macro:: UV_FS_O_SEQUENTIAL

    Access is intended to be sequential from beginning to end. The system can
    use this as a hint to optimize file caching.

    .. note::
        `UV_FS_O_SEQUENTIAL` is only supported on Windows via
        `FILE_FLAG_SEQUENTIAL_SCAN <https://msdn.microsoft.com/en-us/library/windows/desktop/aa363858.aspx>`_.

.. c:macro:: UV_FS_O_SHORT_LIVED

    The file is temporary and should not be flushed to disk if possible.

    .. note::
        `UV_FS_O_SHORT_LIVED` is only supported on Windows via
        `FILE_ATTRIBUTE_TEMPORARY <https://msdn.microsoft.com/en-us/library/windows/desktop/aa363858.aspx>`_.

.. c:macro:: UV_FS_O_SYMLINK

    Open the symbolic link itself rather than the resource it points to.

.. c:macro:: UV_FS_O_SYNC

    The file is opened for synchronous I/O. Write operations will complete once
    all data and all metadata are flushed to disk.

    .. note::
        `UV_FS_O_SYNC` is supported on Windows via
        `FILE_FLAG_WRITE_THROUGH <https://msdn.microsoft.com/en-us/library/windows/desktop/cc644950.aspx>`_.

.. c:macro:: UV_FS_O_TEMPORARY

    The file is temporary and should not be flushed to disk if possible.

    .. note::
        `UV_FS_O_TEMPORARY` is only supported on Windows via
        `FILE_ATTRIBUTE_TEMPORARY <https://msdn.microsoft.com/en-us/library/windows/desktop/aa363858.aspx>`_.

.. c:macro:: UV_FS_O_TRUNC

    If the file exists and is a regular file, and the file is opened
    successfully for write access, its length shall be truncated to zero.

.. c:macro:: UV_FS_O_WRONLY

    Open the file for write-only access.
