file_windows.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package os
     6  
     7  import (
     8  	"errors"
     9  	"internal/filepathlite"
    10  	"internal/godebug"
    11  	"internal/poll"
    12  	"internal/syscall/windows"
    13  	"runtime"
    14  	"sync"
    15  	"sync/atomic"
    16  	"syscall"
    17  	"unsafe"
    18  )
    19  
    20  // This matches the value in syscall/syscall_windows.go.
    21  const _UTIME_OMIT = -1
    22  
    23  // file is the real representation of *File.
    24  // The extra level of indirection ensures that no clients of os
    25  // can overwrite this data, which could cause the finalizer
    26  // to close the wrong file descriptor.
    27  type file struct {
    28  	pfd        poll.FD
    29  	name       string
    30  	dirinfo    atomic.Pointer[dirInfo] // nil unless directory being read
    31  	appendMode bool                    // whether file is opened for appending
    32  }
    33  
    34  // Fd returns the Windows handle referencing the open file.
    35  // If f is closed, the file descriptor becomes invalid.
    36  // If f is garbage collected, a finalizer may close the file descriptor,
    37  // making it invalid; see [runtime.SetFinalizer] for more information on when
    38  // a finalizer might be run. On Unix systems this will cause the [File.SetDeadline]
    39  // methods to stop working.
    40  func (file *File) Fd() uintptr {
    41  	if file == nil {
    42  		return uintptr(syscall.InvalidHandle)
    43  	}
    44  	return uintptr(file.pfd.Sysfd)
    45  }
    46  
    47  // newFile returns a new File with the given file handle and name.
    48  // Unlike NewFile, it does not check that h is syscall.InvalidHandle.
    49  func newFile(h syscall.Handle, name string, kind string) *File {
    50  	if kind == "file" {
    51  		var m uint32
    52  		if syscall.GetConsoleMode(h, &m) == nil {
    53  			kind = "console"
    54  		}
    55  		if t, err := syscall.GetFileType(h); err == nil && t == syscall.FILE_TYPE_PIPE {
    56  			kind = "pipe"
    57  		}
    58  	}
    59  
    60  	f := &File{&file{
    61  		pfd: poll.FD{
    62  			Sysfd:         h,
    63  			IsStream:      true,
    64  			ZeroReadIsEOF: true,
    65  		},
    66  		name: name,
    67  	}}
    68  	runtime.SetFinalizer(f.file, (*file).close)
    69  
    70  	// Ignore initialization errors.
    71  	// Assume any problems will show up in later I/O.
    72  	f.pfd.Init(kind, false)
    73  
    74  	return f
    75  }
    76  
    77  // newConsoleFile creates new File that will be used as console.
    78  func newConsoleFile(h syscall.Handle, name string) *File {
    79  	return newFile(h, name, "console")
    80  }
    81  
    82  // NewFile returns a new File with the given file descriptor and
    83  // name. The returned value will be nil if fd is not a valid file
    84  // descriptor.
    85  func NewFile(fd uintptr, name string) *File {
    86  	h := syscall.Handle(fd)
    87  	if h == syscall.InvalidHandle {
    88  		return nil
    89  	}
    90  	return newFile(h, name, "file")
    91  }
    92  
    93  func epipecheck(file *File, e error) {
    94  }
    95  
    96  // DevNull is the name of the operating system's “null device.”
    97  // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
    98  const DevNull = "NUL"
    99  
   100  // openFileNolog is the Windows implementation of OpenFile.
   101  func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
   102  	if name == "" {
   103  		return nil, &PathError{Op: "open", Path: name, Err: syscall.ENOENT}
   104  	}
   105  	path := fixLongPath(name)
   106  	r, e := syscall.Open(path, flag|syscall.O_CLOEXEC, syscallMode(perm))
   107  	if e != nil {
   108  		// We should return EISDIR when we are trying to open a directory with write access.
   109  		if e == syscall.ERROR_ACCESS_DENIED && (flag&O_WRONLY != 0 || flag&O_RDWR != 0) {
   110  			pathp, e1 := syscall.UTF16PtrFromString(path)
   111  			if e1 == nil {
   112  				var fa syscall.Win32FileAttributeData
   113  				e1 = syscall.GetFileAttributesEx(pathp, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
   114  				if e1 == nil && fa.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
   115  					e = syscall.EISDIR
   116  				}
   117  			}
   118  		}
   119  		return nil, &PathError{Op: "open", Path: name, Err: e}
   120  	}
   121  	return newFile(r, name, "file"), nil
   122  }
   123  
   124  func openDirNolog(name string) (*File, error) {
   125  	return openFileNolog(name, O_RDONLY, 0)
   126  }
   127  
   128  func (file *file) close() error {
   129  	if file == nil {
   130  		return syscall.EINVAL
   131  	}
   132  	if info := file.dirinfo.Swap(nil); info != nil {
   133  		info.close()
   134  	}
   135  	var err error
   136  	if e := file.pfd.Close(); e != nil {
   137  		if e == poll.ErrFileClosing {
   138  			e = ErrClosed
   139  		}
   140  		err = &PathError{Op: "close", Path: file.name, Err: e}
   141  	}
   142  
   143  	// no need for a finalizer anymore
   144  	runtime.SetFinalizer(file, nil)
   145  	return err
   146  }
   147  
   148  // seek sets the offset for the next Read or Write on file to offset, interpreted
   149  // according to whence: 0 means relative to the origin of the file, 1 means
   150  // relative to the current offset, and 2 means relative to the end.
   151  // It returns the new offset and an error, if any.
   152  func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   153  	if info := f.dirinfo.Swap(nil); info != nil {
   154  		// Free cached dirinfo, so we allocate a new one if we
   155  		// access this file as a directory again. See #35767 and #37161.
   156  		info.close()
   157  	}
   158  	ret, err = f.pfd.Seek(offset, whence)
   159  	runtime.KeepAlive(f)
   160  	return ret, err
   161  }
   162  
   163  // Truncate changes the size of the named file.
   164  // If the file is a symbolic link, it changes the size of the link's target.
   165  func Truncate(name string, size int64) error {
   166  	f, e := OpenFile(name, O_WRONLY, 0666)
   167  	if e != nil {
   168  		return e
   169  	}
   170  	defer f.Close()
   171  	e1 := f.Truncate(size)
   172  	if e1 != nil {
   173  		return e1
   174  	}
   175  	return nil
   176  }
   177  
   178  // Remove removes the named file or directory.
   179  // If there is an error, it will be of type *PathError.
   180  func Remove(name string) error {
   181  	p, e := syscall.UTF16PtrFromString(fixLongPath(name))
   182  	if e != nil {
   183  		return &PathError{Op: "remove", Path: name, Err: e}
   184  	}
   185  
   186  	// Go file interface forces us to know whether
   187  	// name is a file or directory. Try both.
   188  	e = syscall.DeleteFile(p)
   189  	if e == nil {
   190  		return nil
   191  	}
   192  	e1 := syscall.RemoveDirectory(p)
   193  	if e1 == nil {
   194  		return nil
   195  	}
   196  
   197  	// Both failed: figure out which error to return.
   198  	if e1 != e {
   199  		a, e2 := syscall.GetFileAttributes(p)
   200  		if e2 != nil {
   201  			e = e2
   202  		} else {
   203  			if a&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
   204  				e = e1
   205  			} else if a&syscall.FILE_ATTRIBUTE_READONLY != 0 {
   206  				if e1 = syscall.SetFileAttributes(p, a&^syscall.FILE_ATTRIBUTE_READONLY); e1 == nil {
   207  					if e = syscall.DeleteFile(p); e == nil {
   208  						return nil
   209  					}
   210  				}
   211  			}
   212  		}
   213  	}
   214  	return &PathError{Op: "remove", Path: name, Err: e}
   215  }
   216  
   217  func rename(oldname, newname string) error {
   218  	e := windows.Rename(fixLongPath(oldname), fixLongPath(newname))
   219  	if e != nil {
   220  		return &LinkError{"rename", oldname, newname, e}
   221  	}
   222  	return nil
   223  }
   224  
   225  // Pipe returns a connected pair of Files; reads from r return bytes written to w.
   226  // It returns the files and an error, if any. The Windows handles underlying
   227  // the returned files are marked as inheritable by child processes.
   228  func Pipe() (r *File, w *File, err error) {
   229  	var p [2]syscall.Handle
   230  	e := syscall.Pipe(p[:])
   231  	if e != nil {
   232  		return nil, nil, NewSyscallError("pipe", e)
   233  	}
   234  	return newFile(p[0], "|0", "pipe"), newFile(p[1], "|1", "pipe"), nil
   235  }
   236  
   237  var (
   238  	useGetTempPath2Once sync.Once
   239  	useGetTempPath2     bool
   240  )
   241  
   242  func tempDir() string {
   243  	useGetTempPath2Once.Do(func() {
   244  		useGetTempPath2 = (windows.ErrorLoadingGetTempPath2() == nil)
   245  	})
   246  	getTempPath := syscall.GetTempPath
   247  	if useGetTempPath2 {
   248  		getTempPath = windows.GetTempPath2
   249  	}
   250  	n := uint32(syscall.MAX_PATH)
   251  	for {
   252  		b := make([]uint16, n)
   253  		n, _ = getTempPath(uint32(len(b)), &b[0])
   254  		if n > uint32(len(b)) {
   255  			continue
   256  		}
   257  		if n == 3 && b[1] == ':' && b[2] == '\\' {
   258  			// Do nothing for path, like C:\.
   259  		} else if n > 0 && b[n-1] == '\\' {
   260  			// Otherwise remove terminating \.
   261  			n--
   262  		}
   263  		return syscall.UTF16ToString(b[:n])
   264  	}
   265  }
   266  
   267  // Link creates newname as a hard link to the oldname file.
   268  // If there is an error, it will be of type *LinkError.
   269  func Link(oldname, newname string) error {
   270  	n, err := syscall.UTF16PtrFromString(fixLongPath(newname))
   271  	if err != nil {
   272  		return &LinkError{"link", oldname, newname, err}
   273  	}
   274  	o, err := syscall.UTF16PtrFromString(fixLongPath(oldname))
   275  	if err != nil {
   276  		return &LinkError{"link", oldname, newname, err}
   277  	}
   278  	err = syscall.CreateHardLink(n, o, 0)
   279  	if err != nil {
   280  		return &LinkError{"link", oldname, newname, err}
   281  	}
   282  	return nil
   283  }
   284  
   285  // Symlink creates newname as a symbolic link to oldname.
   286  // On Windows, a symlink to a non-existent oldname creates a file symlink;
   287  // if oldname is later created as a directory the symlink will not work.
   288  // If there is an error, it will be of type *LinkError.
   289  func Symlink(oldname, newname string) error {
   290  	// '/' does not work in link's content
   291  	oldname = filepathlite.FromSlash(oldname)
   292  
   293  	// need the exact location of the oldname when it's relative to determine if it's a directory
   294  	destpath := oldname
   295  	if v := filepathlite.VolumeName(oldname); v == "" {
   296  		if len(oldname) > 0 && IsPathSeparator(oldname[0]) {
   297  			// oldname is relative to the volume containing newname.
   298  			if v = filepathlite.VolumeName(newname); v != "" {
   299  				// Prepend the volume explicitly, because it may be different from the
   300  				// volume of the current working directory.
   301  				destpath = v + oldname
   302  			}
   303  		} else {
   304  			// oldname is relative to newname.
   305  			destpath = dirname(newname) + `\` + oldname
   306  		}
   307  	}
   308  
   309  	fi, err := Stat(destpath)
   310  	isdir := err == nil && fi.IsDir()
   311  
   312  	n, err := syscall.UTF16PtrFromString(fixLongPath(newname))
   313  	if err != nil {
   314  		return &LinkError{"symlink", oldname, newname, err}
   315  	}
   316  	var o *uint16
   317  	if filepathlite.IsAbs(oldname) {
   318  		o, err = syscall.UTF16PtrFromString(fixLongPath(oldname))
   319  	} else {
   320  		// Do not use fixLongPath on oldname for relative symlinks,
   321  		// as it would turn the name into an absolute path thus making
   322  		// an absolute symlink instead.
   323  		// Notice that CreateSymbolicLinkW does not fail for relative
   324  		// symlinks beyond MAX_PATH, so this does not prevent the
   325  		// creation of an arbitrary long path name.
   326  		o, err = syscall.UTF16PtrFromString(oldname)
   327  	}
   328  	if err != nil {
   329  		return &LinkError{"symlink", oldname, newname, err}
   330  	}
   331  
   332  	var flags uint32 = windows.SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
   333  	if isdir {
   334  		flags |= syscall.SYMBOLIC_LINK_FLAG_DIRECTORY
   335  	}
   336  	err = syscall.CreateSymbolicLink(n, o, flags)
   337  	if err != nil {
   338  		// the unprivileged create flag is unsupported
   339  		// below Windows 10 (1703, v10.0.14972). retry without it.
   340  		flags &^= windows.SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
   341  		err = syscall.CreateSymbolicLink(n, o, flags)
   342  		if err != nil {
   343  			return &LinkError{"symlink", oldname, newname, err}
   344  		}
   345  	}
   346  	return nil
   347  }
   348  
   349  // openSymlink calls CreateFile Windows API with FILE_FLAG_OPEN_REPARSE_POINT
   350  // parameter, so that Windows does not follow symlink, if path is a symlink.
   351  // openSymlink returns opened file handle.
   352  func openSymlink(path string) (syscall.Handle, error) {
   353  	p, err := syscall.UTF16PtrFromString(path)
   354  	if err != nil {
   355  		return 0, err
   356  	}
   357  	attrs := uint32(syscall.FILE_FLAG_BACKUP_SEMANTICS)
   358  	// Use FILE_FLAG_OPEN_REPARSE_POINT, otherwise CreateFile will follow symlink.
   359  	// See https://docs.microsoft.com/en-us/windows/desktop/FileIO/symbolic-link-effects-on-file-systems-functions#createfile-and-createfiletransacted
   360  	attrs |= syscall.FILE_FLAG_OPEN_REPARSE_POINT
   361  	h, err := syscall.CreateFile(p, 0, 0, nil, syscall.OPEN_EXISTING, attrs, 0)
   362  	if err != nil {
   363  		return 0, err
   364  	}
   365  	return h, nil
   366  }
   367  
   368  var winreadlinkvolume = godebug.New("winreadlinkvolume")
   369  
   370  // normaliseLinkPath converts absolute paths returned by
   371  // DeviceIoControl(h, FSCTL_GET_REPARSE_POINT, ...)
   372  // into paths acceptable by all Windows APIs.
   373  // For example, it converts
   374  //
   375  //	\??\C:\foo\bar into C:\foo\bar
   376  //	\??\UNC\foo\bar into \\foo\bar
   377  //	\??\Volume{abc}\ into \\?\Volume{abc}\
   378  func normaliseLinkPath(path string) (string, error) {
   379  	if len(path) < 4 || path[:4] != `\??\` {
   380  		// unexpected path, return it as is
   381  		return path, nil
   382  	}
   383  	// we have path that start with \??\
   384  	s := path[4:]
   385  	switch {
   386  	case len(s) >= 2 && s[1] == ':': // \??\C:\foo\bar
   387  		return s, nil
   388  	case len(s) >= 4 && s[:4] == `UNC\`: // \??\UNC\foo\bar
   389  		return `\\` + s[4:], nil
   390  	}
   391  
   392  	// \??\Volume{abc}\
   393  	if winreadlinkvolume.Value() != "0" {
   394  		return `\\?\` + path[4:], nil
   395  	}
   396  	winreadlinkvolume.IncNonDefault()
   397  
   398  	h, err := openSymlink(path)
   399  	if err != nil {
   400  		return "", err
   401  	}
   402  	defer syscall.CloseHandle(h)
   403  
   404  	buf := make([]uint16, 100)
   405  	for {
   406  		n, err := windows.GetFinalPathNameByHandle(h, &buf[0], uint32(len(buf)), windows.VOLUME_NAME_DOS)
   407  		if err != nil {
   408  			return "", err
   409  		}
   410  		if n < uint32(len(buf)) {
   411  			break
   412  		}
   413  		buf = make([]uint16, n)
   414  	}
   415  	s = syscall.UTF16ToString(buf)
   416  	if len(s) > 4 && s[:4] == `\\?\` {
   417  		s = s[4:]
   418  		if len(s) > 3 && s[:3] == `UNC` {
   419  			// return path like \\server\share\...
   420  			return `\` + s[3:], nil
   421  		}
   422  		return s, nil
   423  	}
   424  	return "", errors.New("GetFinalPathNameByHandle returned unexpected path: " + s)
   425  }
   426  
   427  func readReparseLink(path string) (string, error) {
   428  	h, err := openSymlink(path)
   429  	if err != nil {
   430  		return "", err
   431  	}
   432  	defer syscall.CloseHandle(h)
   433  
   434  	rdbbuf := make([]byte, syscall.MAXIMUM_REPARSE_DATA_BUFFER_SIZE)
   435  	var bytesReturned uint32
   436  	err = syscall.DeviceIoControl(h, syscall.FSCTL_GET_REPARSE_POINT, nil, 0, &rdbbuf[0], uint32(len(rdbbuf)), &bytesReturned, nil)
   437  	if err != nil {
   438  		return "", err
   439  	}
   440  
   441  	rdb := (*windows.REPARSE_DATA_BUFFER)(unsafe.Pointer(&rdbbuf[0]))
   442  	switch rdb.ReparseTag {
   443  	case syscall.IO_REPARSE_TAG_SYMLINK:
   444  		rb := (*windows.SymbolicLinkReparseBuffer)(unsafe.Pointer(&rdb.DUMMYUNIONNAME))
   445  		s := rb.Path()
   446  		if rb.Flags&windows.SYMLINK_FLAG_RELATIVE != 0 {
   447  			return s, nil
   448  		}
   449  		return normaliseLinkPath(s)
   450  	case windows.IO_REPARSE_TAG_MOUNT_POINT:
   451  		return normaliseLinkPath((*windows.MountPointReparseBuffer)(unsafe.Pointer(&rdb.DUMMYUNIONNAME)).Path())
   452  	default:
   453  		// the path is not a symlink or junction but another type of reparse
   454  		// point
   455  		return "", syscall.ENOENT
   456  	}
   457  }
   458  
   459  func readlink(name string) (string, error) {
   460  	s, err := readReparseLink(fixLongPath(name))
   461  	if err != nil {
   462  		return "", &PathError{Op: "readlink", Path: name, Err: err}
   463  	}
   464  	return s, nil
   465  }
   466
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