fs.rs.html -- source
Description: Source to the Rust file `src\libstd\sys\windows\fs.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::os::windows::prelude::*;

    use crate::ffi::OsString;
    use crate::fmt;
    use crate::io::{self, Error, SeekFrom, IoSlice, IoSliceMut};
    use crate::mem;
    use crate::path::{Path, PathBuf};
    use crate::ptr;
    use crate::slice;
    use crate::sync::Arc;
    use crate::sys::handle::Handle;
    use crate::sys::time::SystemTime;
    use crate::sys::{c, cvt};
    use crate::sys_common::FromInner;

    use super::to_u16s;

    pub struct File { handle: Handle }

    #[derive(Clone)]
    pub struct FileAttr {
        attributes: c::DWORD,
        creation_time: c::FILETIME,
        last_access_time: c::FILETIME,
        last_write_time: c::FILETIME,
        file_size: u64,
        reparse_tag: c::DWORD,
        volume_serial_number: Option<u32>,
        number_of_links: Option<u32>,
        file_index: Option<u64>,
    }

    #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
    pub struct FileType {
        attributes: c::DWORD,
        reparse_tag: c::DWORD,
    }

    pub struct ReadDir {
        handle: FindNextFileHandle,
        root: Arc<PathBuf>,
        first: Option<c::WIN32_FIND_DATAW>,
    }

    struct FindNextFileHandle(c::HANDLE);

    unsafe impl Send for FindNextFileHandle {}
    unsafe impl Sync for FindNextFileHandle {}

    pub struct DirEntry {
        root: Arc<PathBuf>,
        data: c::WIN32_FIND_DATAW,
    }

    #[derive(Clone, Debug)]
    pub struct OpenOptions {
        // generic
        read: bool,
        write: bool,
        append: bool,
        truncate: bool,
        create: bool,
        create_new: bool,
        // system-specific
        custom_flags: u32,
        access_mode: Option<c::DWORD>,
        attributes: c::DWORD,
        share_mode: c::DWORD,
        security_qos_flags: c::DWORD,
        security_attributes: usize, // FIXME: should be a reference
    }

    #[derive(Clone, PartialEq, Eq, Debug)]
    pub struct FilePermissions { attrs: c::DWORD }

    #[derive(Debug)]
    pub struct DirBuilder;

    impl fmt::Debug for ReadDir {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            // This will only be called from std::fs::ReadDir, which will add a "ReadDir()" frame.
            // Thus the result will be e g 'ReadDir("C:\")'
            fmt::Debug::fmt(&*self.root, f)
        }
    }

    impl Iterator for ReadDir {
        type Item = io::Result<DirEntry>;
        fn next(&mut self) -> Option<io::Result<DirEntry>> {
            if let Some(first) = self.first.take() {
                if let Some(e) = DirEntry::new(&self.root, &first) {
                    return Some(Ok(e));
                }
            }
            unsafe {
                let mut wfd = mem::zeroed();
                loop {
                    if c::FindNextFileW(self.handle.0, &mut wfd) == 0 {
                        if c::GetLastError() == c::ERROR_NO_MORE_FILES {
                            return None
                        } else {
                            return Some(Err(Error::last_os_error()))
                        }
                    }
                    if let Some(e) = DirEntry::new(&self.root, &wfd) {
                        return Some(Ok(e))
                    }
                }
            }
        }
    }

    impl Drop for FindNextFileHandle {
        fn drop(&mut self) {
            let r = unsafe { c::FindClose(self.0) };
            debug_assert!(r != 0);
        }
    }

    impl DirEntry {
        fn new(root: &Arc<PathBuf>, wfd: &c::WIN32_FIND_DATAW) -> Option<DirEntry> {
            match &wfd.cFileName[0..3] {
                // check for '.' and '..'
                &[46, 0, ..] |
                &[46, 46, 0, ..] => return None,
                _ => {}
            }

            Some(DirEntry {
                root: root.clone(),
                data: *wfd,
            })
        }

        pub fn path(&self) -> PathBuf {
            self.root.join(&self.file_name())
        }

        pub fn file_name(&self) -> OsString {
            let filename = super::truncate_utf16_at_nul(&self.data.cFileName);
            OsString::from_wide(filename)
        }

        pub fn file_type(&self) -> io::Result<FileType> {
            Ok(FileType::new(self.data.dwFileAttributes,
                             /* reparse_tag = */ self.data.dwReserved0))
        }

        pub fn metadata(&self) -> io::Result<FileAttr> {
            Ok(FileAttr {
                attributes: self.data.dwFileAttributes,
                creation_time: self.data.ftCreationTime,
                last_access_time: self.data.ftLastAccessTime,
                last_write_time: self.data.ftLastWriteTime,
                file_size: ((self.data.nFileSizeHigh as u64) << 32) | (self.data.nFileSizeLow as u64),
                reparse_tag: if self.data.dwFileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0 {
                        // reserved unless this is a reparse point
                        self.data.dwReserved0
                    } else {
                        0
                    },
                volume_serial_number: None,
                number_of_links: None,
                file_index: None,
            })
        }
    }

    impl OpenOptions {
        pub fn new() -> OpenOptions {
            OpenOptions {
                // generic
                read: false,
                write: false,
                append: false,
                truncate: false,
                create: false,
                create_new: false,
                // system-specific
                custom_flags: 0,
                access_mode: None,
                share_mode: c::FILE_SHARE_READ | c::FILE_SHARE_WRITE | c::FILE_SHARE_DELETE,
                attributes: 0,
                security_qos_flags: 0,
                security_attributes: 0,
            }
        }

        pub fn read(&mut self, read: bool) { self.read = read; }
        pub fn write(&mut self, write: bool) { self.write = write; }
        pub fn append(&mut self, append: bool) { self.append = append; }
        pub fn truncate(&mut self, truncate: bool) { self.truncate = truncate; }
        pub fn create(&mut self, create: bool) { self.create = create; }
        pub fn create_new(&mut self, create_new: bool) { self.create_new = create_new; }

        pub fn custom_flags(&mut self, flags: u32) { self.custom_flags = flags; }
        pub fn access_mode(&mut self, access_mode: u32) { self.access_mode = Some(access_mode); }
        pub fn share_mode(&mut self, share_mode: u32) { self.share_mode = share_mode; }
        pub fn attributes(&mut self, attrs: u32) { self.attributes = attrs; }
        pub fn security_qos_flags(&mut self, flags: u32) {
            // We have to set `SECURITY_SQOS_PRESENT` here, because one of the valid flags we can
            // receive is `SECURITY_ANONYMOUS = 0x0`, which we can't check for later on.
            self.security_qos_flags = flags | c::SECURITY_SQOS_PRESENT;
        }
        pub fn security_attributes(&mut self, attrs: c::LPSECURITY_ATTRIBUTES) {
            self.security_attributes = attrs as usize;
        }

        fn get_access_mode(&self) -> io::Result<c::DWORD> {
            const ERROR_INVALID_PARAMETER: i32 = 87;

            match (self.read, self.write, self.append, self.access_mode) {
                (.., Some(mode)) => Ok(mode),
                (true,  false, false, None) => Ok(c::GENERIC_READ),
                (false, true,  false, None) => Ok(c::GENERIC_WRITE),
                (true,  true,  false, None) => Ok(c::GENERIC_READ | c::GENERIC_WRITE),
                (false, _,     true,  None) => Ok(c::FILE_GENERIC_WRITE & !c::FILE_WRITE_DATA),
                (true,  _,     true,  None) => Ok(c::GENERIC_READ |
                                                  (c::FILE_GENERIC_WRITE & !c::FILE_WRITE_DATA)),
                (false, false, false, None) => Err(Error::from_raw_os_error(ERROR_INVALID_PARAMETER)),
            }
        }

        fn get_creation_mode(&self) -> io::Result<c::DWORD> {
            const ERROR_INVALID_PARAMETER: i32 = 87;

            match (self.write, self.append) {
                (true, false) => {}
                (false, false) =>
                    if self.truncate || self.create || self.create_new {
                        return Err(Error::from_raw_os_error(ERROR_INVALID_PARAMETER));
                    },
                (_, true) =>
                    if self.truncate && !self.create_new {
                        return Err(Error::from_raw_os_error(ERROR_INVALID_PARAMETER));
                    },
            }

            Ok(match (self.create, self.truncate, self.create_new) {
                    (false, false, false) => c::OPEN_EXISTING,
                    (true,  false, false) => c::OPEN_ALWAYS,
                    (false, true,  false) => c::TRUNCATE_EXISTING,
                    (true,  true,  false) => c::CREATE_ALWAYS,
                    (_,      _,    true)  => c::CREATE_NEW,
               })
        }

        fn get_flags_and_attributes(&self) -> c::DWORD {
            self.custom_flags |
            self.attributes |
            self.security_qos_flags |
            if self.create_new { c::FILE_FLAG_OPEN_REPARSE_POINT } else { 0 }
        }
    }

    impl File {
        pub fn open(path: &Path, opts: &OpenOptions) -> io::Result<File> {
            let path = to_u16s(path)?;
            let handle = unsafe {
                c::CreateFileW(path.as_ptr(),
                               opts.get_access_mode()?,
                               opts.share_mode,
                               opts.security_attributes as *mut _,
                               opts.get_creation_mode()?,
                               opts.get_flags_and_attributes(),
                               ptr::null_mut())
            };
            if handle == c::INVALID_HANDLE_VALUE {
                Err(Error::last_os_error())
            } else {
                Ok(File { handle: Handle::new(handle) })
            }
        }

        pub fn fsync(&self) -> io::Result<()> {
            cvt(unsafe { c::FlushFileBuffers(self.handle.raw()) })?;
            Ok(())
        }

        pub fn datasync(&self) -> io::Result<()> { self.fsync() }

        pub fn truncate(&self, size: u64) -> io::Result<()> {
            let mut info = c::FILE_END_OF_FILE_INFO {
                EndOfFile: size as c::LARGE_INTEGER,
            };
            let size = mem::size_of_val(&info);
            cvt(unsafe {
                c::SetFileInformationByHandle(self.handle.raw(),
                                              c::FileEndOfFileInfo,
                                              &mut info as *mut _ as *mut _,
                                              size as c::DWORD)
            })?;
            Ok(())
        }

        #[cfg(not(target_vendor = "uwp"))]
        pub fn file_attr(&self) -> io::Result<FileAttr> {
            unsafe {
                let mut info: c::BY_HANDLE_FILE_INFORMATION = mem::zeroed();
                cvt(c::GetFileInformationByHandle(self.handle.raw(), &mut info))?;
                let mut reparse_tag = 0;
                if info.dwFileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0 {
                    let mut b = [0; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
                    if let Ok((_, buf)) = self.reparse_point(&mut b) {
                        reparse_tag = buf.ReparseTag;
                    }
                }
                Ok(FileAttr {
                    attributes: info.dwFileAttributes,
                    creation_time: info.ftCreationTime,
                    last_access_time: info.ftLastAccessTime,
                    last_write_time: info.ftLastWriteTime,
                    file_size: (info.nFileSizeLow as u64) | ((info.nFileSizeHigh as u64) << 32),
                    reparse_tag,
                    volume_serial_number: Some(info.dwVolumeSerialNumber),
                    number_of_links: Some(info.nNumberOfLinks),
                    file_index: Some((info.nFileIndexLow as u64) |
                                     ((info.nFileIndexHigh as u64) << 32)),
                })
            }
        }

        #[cfg(target_vendor = "uwp")]
        pub fn file_attr(&self) -> io::Result<FileAttr> {
            unsafe {
                let mut info: c::FILE_BASIC_INFO = mem::zeroed();
                let size = mem::size_of_val(&info);
                cvt(c::GetFileInformationByHandleEx(self.handle.raw(),
                                                  c::FileBasicInfo,
                                                  &mut info as *mut _ as *mut libc::c_void,
                                                  size as c::DWORD))?;
                let mut attr = FileAttr {
                    attributes: info.FileAttributes,
                    creation_time: c::FILETIME {
                        dwLowDateTime: info.CreationTime as c::DWORD,
                        dwHighDateTime: (info.CreationTime >> 32) as c::DWORD,
                    },
                    last_access_time: c::FILETIME {
                        dwLowDateTime: info.LastAccessTime as c::DWORD,
                        dwHighDateTime: (info.LastAccessTime >> 32) as c::DWORD,
                    },
                    last_write_time: c::FILETIME {
                        dwLowDateTime: info.LastWriteTime as c::DWORD,
                        dwHighDateTime: (info.LastWriteTime >> 32) as c::DWORD,
                    },
                    file_size: 0,
                    reparse_tag: 0,
                    volume_serial_number: None,
                    number_of_links: None,
                    file_index: None,
                };
                let mut info: c::FILE_STANDARD_INFO = mem::zeroed();
                let size = mem::size_of_val(&info);
                cvt(c::GetFileInformationByHandleEx(self.handle.raw(),
                                                    c::FileStandardInfo,
                                                    &mut info as *mut _ as *mut libc::c_void,
                                                    size as c::DWORD))?;
                attr.file_size = info.AllocationSize as u64;
                attr.number_of_links = Some(info.NumberOfLinks);
                if attr.file_type().is_reparse_point() {
                    let mut b = [0; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
                    if let Ok((_, buf)) = self.reparse_point(&mut b) {
                        attr.reparse_tag = buf.ReparseTag;
                    }
                }
                Ok(attr)
            }
        }

        pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
            self.handle.read(buf)
        }

        pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
            self.handle.read_vectored(bufs)
        }

        pub fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
            self.handle.read_at(buf, offset)
        }

        pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
            self.handle.write(buf)
        }

        pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
            self.handle.write_vectored(bufs)
        }

        pub fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
            self.handle.write_at(buf, offset)
        }

        pub fn flush(&self) -> io::Result<()> { Ok(()) }

        pub fn seek(&self, pos: SeekFrom) -> io::Result<u64> {
            let (whence, pos) = match pos {
                // Casting to `i64` is fine, `SetFilePointerEx` reinterprets this
                // integer as `u64`.
                SeekFrom::Start(n) => (c::FILE_BEGIN, n as i64),
                SeekFrom::End(n) => (c::FILE_END, n),
                SeekFrom::Current(n) => (c::FILE_CURRENT, n),
            };
            let pos = pos as c::LARGE_INTEGER;
            let mut newpos = 0;
            cvt(unsafe {
                c::SetFilePointerEx(self.handle.raw(), pos,
                                    &mut newpos, whence)
            })?;
            Ok(newpos as u64)
        }

        pub fn duplicate(&self) -> io::Result<File> {
            Ok(File {
                handle: self.handle.duplicate(0, false, c::DUPLICATE_SAME_ACCESS)?,
            })
        }

        pub fn handle(&self) -> &Handle { &self.handle }

        pub fn into_handle(self) -> Handle { self.handle }

        fn reparse_point<'a>(&self,
                             space: &'a mut [u8; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE])
                             -> io::Result<(c::DWORD, &'a c::REPARSE_DATA_BUFFER)> {
            unsafe {
                let mut bytes = 0;
                cvt({
                    c::DeviceIoControl(self.handle.raw(),
                                       c::FSCTL_GET_REPARSE_POINT,
                                       ptr::null_mut(),
                                       0,
                                       space.as_mut_ptr() as *mut _,
                                       space.len() as c::DWORD,
                                       &mut bytes,
                                       ptr::null_mut())
                })?;
                Ok((bytes, &*(space.as_ptr() as *const c::REPARSE_DATA_BUFFER)))
            }
        }

        fn readlink(&self) -> io::Result<PathBuf> {
            let mut space = [0u8; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
            let (_bytes, buf) = self.reparse_point(&mut space)?;
            unsafe {
                let (path_buffer, subst_off, subst_len, relative) = match buf.ReparseTag {
                    c::IO_REPARSE_TAG_SYMLINK => {
                        let info: *const c::SYMBOLIC_LINK_REPARSE_BUFFER =
                            &buf.rest as *const _ as *const _;
                        (&(*info).PathBuffer as *const _ as *const u16,
                         (*info).SubstituteNameOffset / 2,
                         (*info).SubstituteNameLength / 2,
                         (*info).Flags & c::SYMLINK_FLAG_RELATIVE != 0)
                    },
                    c::IO_REPARSE_TAG_MOUNT_POINT => {
                        let info: *const c::MOUNT_POINT_REPARSE_BUFFER =
                            &buf.rest as *const _ as *const _;
                        (&(*info).PathBuffer as *const _ as *const u16,
                         (*info).SubstituteNameOffset / 2,
                         (*info).SubstituteNameLength / 2,
                         false)
                    },
                    _ => return Err(io::Error::new(io::ErrorKind::Other,
                                                   "Unsupported reparse point type"))
                };
                let subst_ptr = path_buffer.offset(subst_off as isize);
                let mut subst = slice::from_raw_parts(subst_ptr, subst_len as usize);
                // Absolute paths start with an NT internal namespace prefix `\??\`
                // We should not let it leak through.
                if !relative && subst.starts_with(&[92u16, 63u16, 63u16, 92u16]) {
                    subst = &subst[4..];
                }
                Ok(PathBuf::from(OsString::from_wide(subst)))
            }
        }

        pub fn set_permissions(&self, perm: FilePermissions) -> io::Result<()> {
            let mut info = c::FILE_BASIC_INFO {
                CreationTime: 0,
                LastAccessTime: 0,
                LastWriteTime: 0,
                ChangeTime: 0,
                FileAttributes: perm.attrs,
            };
            let size = mem::size_of_val(&info);
            cvt(unsafe {
                c::SetFileInformationByHandle(self.handle.raw(),
                                              c::FileBasicInfo,
                                              &mut info as *mut _ as *mut _,
                                              size as c::DWORD)
            })?;
            Ok(())
        }
    }

    impl FromInner<c::HANDLE> for File {
        fn from_inner(handle: c::HANDLE) -> File {
            File { handle: Handle::new(handle) }
        }
    }

    impl fmt::Debug for File {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            // FIXME(#24570): add more info here (e.g., mode)
            let mut b = f.debug_struct("File");
            b.field("handle", &self.handle.raw());
            if let Ok(path) = get_path(&self) {
                b.field("path", &path);
            }
            b.finish()
        }
    }

    impl FileAttr {
        pub fn size(&self) -> u64 {
            self.file_size
        }

        pub fn perm(&self) -> FilePermissions {
            FilePermissions { attrs: self.attributes }
        }

        pub fn attrs(&self) -> u32 {
            self.attributes
        }

        pub fn file_type(&self) -> FileType {
            FileType::new(self.attributes, self.reparse_tag)
        }

        pub fn modified(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(self.last_write_time))
        }

        pub fn accessed(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(self.last_access_time))
        }

        pub fn created(&self) -> io::Result<SystemTime> {
            Ok(SystemTime::from(self.creation_time))
        }

        pub fn modified_u64(&self) -> u64 {
            to_u64(&self.last_write_time)
        }

        pub fn accessed_u64(&self) -> u64 {
            to_u64(&self.last_access_time)
        }

        pub fn created_u64(&self) -> u64 {
            to_u64(&self.creation_time)
        }

        pub fn volume_serial_number(&self) -> Option<u32> {
            self.volume_serial_number
        }

        pub fn number_of_links(&self) -> Option<u32> {
            self.number_of_links
        }

        pub fn file_index(&self) -> Option<u64> {
            self.file_index
        }
    }

    fn to_u64(ft: &c::FILETIME) -> u64 {
        (ft.dwLowDateTime as u64) | ((ft.dwHighDateTime as u64) << 32)
    }

    impl FilePermissions {
        pub fn readonly(&self) -> bool {
            self.attrs & c::FILE_ATTRIBUTE_READONLY != 0
        }

        pub fn set_readonly(&mut self, readonly: bool) {
            if readonly {
                self.attrs |= c::FILE_ATTRIBUTE_READONLY;
            } else {
                self.attrs &= !c::FILE_ATTRIBUTE_READONLY;
            }
        }
    }

    impl FileType {
        fn new(attrs: c::DWORD, reparse_tag: c::DWORD) -> FileType {
            FileType {
                attributes: attrs,
                reparse_tag: reparse_tag,
            }
        }
        pub fn is_dir(&self) -> bool {
            !self.is_symlink() && self.is_directory()
        }
        pub fn is_file(&self) -> bool {
            !self.is_symlink() && !self.is_directory()
        }
        pub fn is_symlink(&self) -> bool {
            self.is_reparse_point() && self.is_reparse_tag_name_surrogate()
        }
        pub fn is_symlink_dir(&self) -> bool {
            self.is_symlink() && self.is_directory()
        }
        pub fn is_symlink_file(&self) -> bool {
            self.is_symlink() && !self.is_directory()
        }
        fn is_directory(&self) -> bool {
            self.attributes & c::FILE_ATTRIBUTE_DIRECTORY != 0
        }
        fn is_reparse_point(&self) -> bool {
            self.attributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0
        }
        fn is_reparse_tag_name_surrogate(&self) -> bool {
            self.reparse_tag & 0x20000000 != 0
        }
    }

    impl DirBuilder {
        pub fn new() -> DirBuilder { DirBuilder }

        pub fn mkdir(&self, p: &Path) -> io::Result<()> {
            let p = to_u16s(p)?;
            cvt(unsafe {
                c::CreateDirectoryW(p.as_ptr(), ptr::null_mut())
            })?;
            Ok(())
        }
    }

    pub fn readdir(p: &Path) -> io::Result<ReadDir> {
        let root = p.to_path_buf();
        let star = p.join("*");
        let path = to_u16s(&star)?;

        unsafe {
            let mut wfd = mem::zeroed();
            let find_handle = c::FindFirstFileW(path.as_ptr(), &mut wfd);
            if find_handle != c::INVALID_HANDLE_VALUE {
                Ok(ReadDir {
                    handle: FindNextFileHandle(find_handle),
                    root: Arc::new(root),
                    first: Some(wfd),
                })
            } else {
                Err(Error::last_os_error())
            }
        }
    }

    pub fn unlink(p: &Path) -> io::Result<()> {
        let p_u16s = to_u16s(p)?;
        cvt(unsafe { c::DeleteFileW(p_u16s.as_ptr()) })?;
        Ok(())
    }

    pub fn rename(old: &Path, new: &Path) -> io::Result<()> {
        let old = to_u16s(old)?;
        let new = to_u16s(new)?;
        cvt(unsafe {
            c::MoveFileExW(old.as_ptr(), new.as_ptr(), c::MOVEFILE_REPLACE_EXISTING)
        })?;
        Ok(())
    }

    pub fn rmdir(p: &Path) -> io::Result<()> {
        let p = to_u16s(p)?;
        cvt(unsafe { c::RemoveDirectoryW(p.as_ptr()) })?;
        Ok(())
    }

    pub fn remove_dir_all(path: &Path) -> io::Result<()> {
        let filetype = lstat(path)?.file_type();
        if filetype.is_symlink() {
            // On Windows symlinks to files and directories are removed differently.
            // rmdir only deletes dir symlinks and junctions, not file symlinks.
            rmdir(path)
        } else {
            remove_dir_all_recursive(path)
        }
    }

    fn remove_dir_all_recursive(path: &Path) -> io::Result<()> {
        for child in readdir(path)? {
            let child = child?;
            let child_type = child.file_type()?;
            if child_type.is_dir() {
                remove_dir_all_recursive(&child.path())?;
            } else if child_type.is_symlink_dir() {
                rmdir(&child.path())?;
            } else {
                unlink(&child.path())?;
            }
        }
        rmdir(path)
    }

    pub fn readlink(path: &Path) -> io::Result<PathBuf> {
        // Open the link with no access mode, instead of generic read.
        // By default FILE_LIST_DIRECTORY is denied for the junction "C:\Documents and Settings", so
        // this is needed for a common case.
        let mut opts = OpenOptions::new();
        opts.access_mode(0);
        opts.custom_flags(c::FILE_FLAG_OPEN_REPARSE_POINT |
                          c::FILE_FLAG_BACKUP_SEMANTICS);
        let file = File::open(&path, &opts)?;
        file.readlink()
    }

    pub fn symlink(src: &Path, dst: &Path) -> io::Result<()> {
        symlink_inner(src, dst, false)
    }

    pub fn symlink_inner(src: &Path, dst: &Path, dir: bool) -> io::Result<()> {
        let src = to_u16s(src)?;
        let dst = to_u16s(dst)?;
        let flags = if dir { c::SYMBOLIC_LINK_FLAG_DIRECTORY } else { 0 };
        // Formerly, symlink creation required the SeCreateSymbolicLink privilege. For the Windows 10
        // Creators Update, Microsoft loosened this to allow unprivileged symlink creation if the
        // computer is in Developer Mode, but SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE must be
        // added to dwFlags to opt into this behaviour.
        let result = cvt(unsafe {
            c::CreateSymbolicLinkW(dst.as_ptr(), src.as_ptr(),
                                   flags | c::SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE) as c::BOOL
        });
        if let Err(err) = result {
            if err.raw_os_error() == Some(c::ERROR_INVALID_PARAMETER as i32) {
                // Older Windows objects to SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE,
                // so if we encounter ERROR_INVALID_PARAMETER, retry without that flag.
                cvt(unsafe {
                    c::CreateSymbolicLinkW(dst.as_ptr(), src.as_ptr(), flags) as c::BOOL
                })?;
            } else {
                return Err(err);
            }
        }
        Ok(())
    }

    #[cfg(not(target_vendor = "uwp"))]
    pub fn link(src: &Path, dst: &Path) -> io::Result<()> {
        let src = to_u16s(src)?;
        let dst = to_u16s(dst)?;
        cvt(unsafe {
            c::CreateHardLinkW(dst.as_ptr(), src.as_ptr(), ptr::null_mut())
        })?;
        Ok(())
    }

    #[cfg(target_vendor = "uwp")]
    pub fn link(_src: &Path, _dst: &Path) -> io::Result<()> {
        return Err(io::Error::new(io::ErrorKind::Other,
                                "hard link are not supported on UWP"));
    }

    pub fn stat(path: &Path) -> io::Result<FileAttr> {
        let mut opts = OpenOptions::new();
        // No read or write permissions are necessary
        opts.access_mode(0);
        // This flag is so we can open directories too
        opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS);
        let file = File::open(path, &opts)?;
        file.file_attr()
    }

    pub fn lstat(path: &Path) -> io::Result<FileAttr> {
        let mut opts = OpenOptions::new();
        // No read or write permissions are necessary
        opts.access_mode(0);
        opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS | c::FILE_FLAG_OPEN_REPARSE_POINT);
        let file = File::open(path, &opts)?;
        file.file_attr()
    }

    pub fn set_perm(p: &Path, perm: FilePermissions) -> io::Result<()> {
        let p = to_u16s(p)?;
        unsafe {
            cvt(c::SetFileAttributesW(p.as_ptr(), perm.attrs))?;
            Ok(())
        }
    }

    fn get_path(f: &File) -> io::Result<PathBuf> {
        super::fill_utf16_buf(|buf, sz| unsafe {
            c::GetFinalPathNameByHandleW(f.handle.raw(), buf, sz,
                                         c::VOLUME_NAME_DOS)
        }, |buf| {
            PathBuf::from(OsString::from_wide(buf))
        })
    }

    pub fn canonicalize(p: &Path) -> io::Result<PathBuf> {
        let mut opts = OpenOptions::new();
        // No read or write permissions are necessary
        opts.access_mode(0);
        // This flag is so we can open directories too
        opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS);
        let f = File::open(p, &opts)?;
        get_path(&f)
    }

    pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
        unsafe extern "system" fn callback(
            _TotalFileSize: c::LARGE_INTEGER,
            _TotalBytesTransferred: c::LARGE_INTEGER,
            _StreamSize: c::LARGE_INTEGER,
            StreamBytesTransferred: c::LARGE_INTEGER,
            dwStreamNumber: c::DWORD,
            _dwCallbackReason: c::DWORD,
            _hSourceFile: c::HANDLE,
            _hDestinationFile: c::HANDLE,
            lpData: c::LPVOID,
        ) -> c::DWORD {
            if dwStreamNumber == 1 {*(lpData as *mut i64) = StreamBytesTransferred;}
            c::PROGRESS_CONTINUE
        }
        let pfrom = to_u16s(from)?;
        let pto = to_u16s(to)?;
        let mut size = 0i64;
        cvt(unsafe {
            c::CopyFileExW(pfrom.as_ptr(), pto.as_ptr(), Some(callback),
                           &mut size as *mut _ as *mut _, ptr::null_mut(), 0)
        })?;
        Ok(size as u64)
    }

    #[allow(dead_code)]
    pub fn symlink_junction<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()> {
        symlink_junction_inner(src.as_ref(), dst.as_ref())
    }

    // Creating a directory junction on windows involves dealing with reparse
    // points and the DeviceIoControl function, and this code is a skeleton of
    // what can be found here:
    //
    // http://www.flexhex.com/docs/articles/hard-links.phtml
    #[allow(dead_code)]
    fn symlink_junction_inner(target: &Path, junction: &Path) -> io::Result<()> {
        let d = DirBuilder::new();
        d.mkdir(&junction)?;

        let mut opts = OpenOptions::new();
        opts.write(true);
        opts.custom_flags(c::FILE_FLAG_OPEN_REPARSE_POINT |
                          c::FILE_FLAG_BACKUP_SEMANTICS);
        let f = File::open(junction, &opts)?;
        let h = f.handle().raw();

        unsafe {
            let mut data = [0u8; c::MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
            let db = data.as_mut_ptr()
                        as *mut c::REPARSE_MOUNTPOINT_DATA_BUFFER;
            let buf = &mut (*db).ReparseTarget as *mut c::WCHAR;
            let mut i = 0;
            // FIXME: this conversion is very hacky
            let v = br"\??\";
            let v = v.iter().map(|x| *x as u16);
            for c in v.chain(target.as_os_str().encode_wide()) {
                *buf.offset(i) = c;
                i += 1;
            }
            *buf.offset(i) = 0;
            i += 1;
            (*db).ReparseTag = c::IO_REPARSE_TAG_MOUNT_POINT;
            (*db).ReparseTargetMaximumLength = (i * 2) as c::WORD;
            (*db).ReparseTargetLength = ((i - 1) * 2) as c::WORD;
            (*db).ReparseDataLength =
                    (*db).ReparseTargetLength as c::DWORD + 12;

            let mut ret = 0;
            cvt(c::DeviceIoControl(h as *mut _,
                                   c::FSCTL_SET_REPARSE_POINT,
                                   data.as_ptr() as *mut _,
                                   (*db).ReparseDataLength + 8,
                                   ptr::null_mut(), 0,
                                   &mut ret,
                                   ptr::null_mut())).map(|_| ())
        }
    }