file_windows.go

Documentation: os

     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/poll"
    10  	"internal/syscall/windows"
    11  	"runtime"
    12  	"syscall"
    13  	"unicode/utf16"
    14  	"unsafe"
    15  )
    16  
    17  // file is the real representation of *File.
    18  // The extra level of indirection ensures that no clients of os
    19  // can overwrite this data, which could cause the finalizer
    20  // to close the wrong file descriptor.
    21  type file struct {
    22  	pfd        poll.FD
    23  	name       string
    24  	dirinfo    *dirInfo // nil unless directory being read
    25  	appendMode bool     // whether file is opened for appending
    26  }
    27  
    28  // Fd returns the Windows handle referencing the open file.
    29  // If f is closed, the file descriptor becomes invalid.
    30  // If f is garbage collected, a finalizer may close the file descriptor,
    31  // making it invalid; see runtime.SetFinalizer for more information on when
    32  // a finalizer might be run. On Unix systems this will cause the SetDeadline
    33  // methods to stop working.
    34  func (file *File) Fd() uintptr {
    35  	if file == nil {
    36  		return uintptr(syscall.InvalidHandle)
    37  	}
    38  	return uintptr(file.pfd.Sysfd)
    39  }
    40  
    41  // newFile returns a new File with the given file handle and name.
    42  // Unlike NewFile, it does not check that h is syscall.InvalidHandle.
    43  func newFile(h syscall.Handle, name string, kind string) *File {
    44  	if kind == "file" {
    45  		var m uint32
    46  		if syscall.GetConsoleMode(h, &m) == nil {
    47  			kind = "console"
    48  		}
    49  		if t, err := syscall.GetFileType(h); err == nil && t == syscall.FILE_TYPE_PIPE {
    50  			kind = "pipe"
    51  		}
    52  	}
    53  
    54  	f := &File{&file{
    55  		pfd: poll.FD{
    56  			Sysfd:         h,
    57  			IsStream:      true,
    58  			ZeroReadIsEOF: true,
    59  		},
    60  		name: name,
    61  	}}
    62  	runtime.SetFinalizer(f.file, (*file).close)
    63  
    64  	// Ignore initialization errors.
    65  	// Assume any problems will show up in later I/O.
    66  	f.pfd.Init(kind, false)
    67  
    68  	return f
    69  }
    70  
    71  // newConsoleFile creates new File that will be used as console.
    72  func newConsoleFile(h syscall.Handle, name string) *File {
    73  	return newFile(h, name, "console")
    74  }
    75  
    76  // NewFile returns a new File with the given file descriptor and
    77  // name. The returned value will be nil if fd is not a valid file
    78  // descriptor.
    79  func NewFile(fd uintptr, name string) *File {
    80  	h := syscall.Handle(fd)
    81  	if h == syscall.InvalidHandle {
    82  		return nil
    83  	}
    84  	return newFile(h, name, "file")
    85  }
    86  
    87  // Auxiliary information if the File describes a directory
    88  type dirInfo struct {
    89  	data     syscall.Win32finddata
    90  	needdata bool
    91  	path     string
    92  	isempty  bool // set if FindFirstFile returns ERROR_FILE_NOT_FOUND
    93  }
    94  
    95  func epipecheck(file *File, e error) {
    96  }
    97  
    98  // DevNull is the name of the operating system's ``null device.''
    99  // On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
   100  const DevNull = "NUL"
   101  
   102  func (f *file) isdir() bool { return f != nil && f.dirinfo != nil }
   103  
   104  func openFile(name string, flag int, perm FileMode) (file *File, err error) {
   105  	r, e := syscall.Open(fixLongPath(name), flag|syscall.O_CLOEXEC, syscallMode(perm))
   106  	if e != nil {
   107  		return nil, e
   108  	}
   109  	return newFile(r, name, "file"), nil
   110  }
   111  
   112  func openDir(name string) (file *File, err error) {
   113  	var mask string
   114  
   115  	path := fixLongPath(name)
   116  
   117  	if len(path) == 2 && path[1] == ':' { // it is a drive letter, like C:
   118  		mask = path + `*`
   119  	} else if len(path) > 0 {
   120  		lc := path[len(path)-1]
   121  		if lc == '/' || lc == '\\' {
   122  			mask = path + `*`
   123  		} else {
   124  			mask = path + `\*`
   125  		}
   126  	} else {
   127  		mask = `\*`
   128  	}
   129  	maskp, e := syscall.UTF16PtrFromString(mask)
   130  	if e != nil {
   131  		return nil, e
   132  	}
   133  	d := new(dirInfo)
   134  	r, e := syscall.FindFirstFile(maskp, &d.data)
   135  	if e != nil {
   136  		// FindFirstFile returns ERROR_FILE_NOT_FOUND when
   137  		// no matching files can be found. Then, if directory
   138  		// exists, we should proceed.
   139  		if e != syscall.ERROR_FILE_NOT_FOUND {
   140  			return nil, e
   141  		}
   142  		var fa syscall.Win32FileAttributeData
   143  		pathp, e := syscall.UTF16PtrFromString(path)
   144  		if e != nil {
   145  			return nil, e
   146  		}
   147  		e = syscall.GetFileAttributesEx(pathp, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
   148  		if e != nil {
   149  			return nil, e
   150  		}
   151  		if fa.FileAttributes&syscall.FILE_ATTRIBUTE_DIRECTORY == 0 {
   152  			return nil, e
   153  		}
   154  		d.isempty = true
   155  	}
   156  	d.path = path
   157  	if !isAbs(d.path) {
   158  		d.path, e = syscall.FullPath(d.path)
   159  		if e != nil {
   160  			return nil, e
   161  		}
   162  	}
   163  	f := newFile(r, name, "dir")
   164  	f.dirinfo = d
   165  	return f, nil
   166  }
   167  
   168  // openFileNolog is the Windows implementation of OpenFile.
   169  func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
   170  	if name == "" {
   171  		return nil, &PathError{Op: "open", Path: name, Err: syscall.ENOENT}
   172  	}
   173  	r, errf := openFile(name, flag, perm)
   174  	if errf == nil {
   175  		return r, nil
   176  	}
   177  	r, errd := openDir(name)
   178  	if errd == nil {
   179  		if flag&O_WRONLY != 0 || flag&O_RDWR != 0 {
   180  			r.Close()
   181  			return nil, &PathError{Op: "open", Path: name, Err: syscall.EISDIR}
   182  		}
   183  		return r, nil
   184  	}
   185  	return nil, &PathError{Op: "open", Path: name, Err: errf}
   186  }
   187  
   188  func (file *file) close() error {
   189  	if file == nil {
   190  		return syscall.EINVAL
   191  	}
   192  	if file.isdir() && file.dirinfo.isempty {
   193  		// "special" empty directories
   194  		return nil
   195  	}
   196  	var err error
   197  	if e := file.pfd.Close(); e != nil {
   198  		if e == poll.ErrFileClosing {
   199  			e = ErrClosed
   200  		}
   201  		err = &PathError{Op: "close", Path: file.name, Err: e}
   202  	}
   203  
   204  	// no need for a finalizer anymore
   205  	runtime.SetFinalizer(file, nil)
   206  	return err
   207  }
   208  
   209  // seek sets the offset for the next Read or Write on file to offset, interpreted
   210  // according to whence: 0 means relative to the origin of the file, 1 means
   211  // relative to the current offset, and 2 means relative to the end.
   212  // It returns the new offset and an error, if any.
   213  func (f *File) seek(offset int64, whence int) (ret int64, err error) {
   214  	ret, err = f.pfd.Seek(offset, whence)
   215  	runtime.KeepAlive(f)
   216  	return ret, err
   217  }
   218  
   219  // Truncate changes the size of the named file.
   220  // If the file is a symbolic link, it changes the size of the link's target.
   221  func Truncate(name string, size int64) error {
   222  	f, e := OpenFile(name, O_WRONLY|O_CREATE, 0666)
   223  	if e != nil {
   224  		return e
   225  	}
   226  	defer f.Close()
   227  	e1 := f.Truncate(size)
   228  	if e1 != nil {
   229  		return e1
   230  	}
   231  	return nil
   232  }
   233  
   234  // Remove removes the named file or directory.
   235  // If there is an error, it will be of type *PathError.
   236  func Remove(name string) error {
   237  	p, e := syscall.UTF16PtrFromString(fixLongPath(name))
   238  	if e != nil {
   239  		return &PathError{Op: "remove", Path: name, Err: e}
   240  	}
   241  
   242  	// Go file interface forces us to know whether
   243  	// name is a file or directory. Try both.
   244  	e = syscall.DeleteFile(p)
   245  	if e == nil {
   246  		return nil
   247  	}
   248  	e1 := syscall.RemoveDirectory(p)
   249  	if e1 == nil {
   250  		return nil
   251  	}
   252  
   253  	// Both failed: figure out which error to return.
   254  	if e1 != e {
   255  		a, e2 := syscall.GetFileAttributes(p)
   256  		if e2 != nil {
   257  			e = e2
   258  		} else {
   259  			if a&syscall.FILE_ATTRIBUTE_DIRECTORY != 0 {
   260  				e = e1
   261  			} else if a&syscall.FILE_ATTRIBUTE_READONLY != 0 {
   262  				if e1 = syscall.SetFileAttributes(p, a&^syscall.FILE_ATTRIBUTE_READONLY); e1 == nil {
   263  					if e = syscall.DeleteFile(p); e == nil {
   264  						return nil
   265  					}
   266  				}
   267  			}
   268  		}
   269  	}
   270  	return &PathError{Op: "remove", Path: name, Err: e}
   271  }
   272  
   273  func rename(oldname, newname string) error {
   274  	e := windows.Rename(fixLongPath(oldname), fixLongPath(newname))
   275  	if e != nil {
   276  		return &LinkError{"rename", oldname, newname, e}
   277  	}
   278  	return nil
   279  }
   280  
   281  // Pipe returns a connected pair of Files; reads from r return bytes written to w.
   282  // It returns the files and an error, if any. The Windows handles underlying
   283  // the returned files are marked as inheritable by child processes.
   284  func Pipe() (r *File, w *File, err error) {
   285  	var p [2]syscall.Handle
   286  	e := syscall.Pipe(p[:])
   287  	if e != nil {
   288  		return nil, nil, NewSyscallError("pipe", e)
   289  	}
   290  	return newFile(p[0], "|0", "pipe"), newFile(p[1], "|1", "pipe"), nil
   291  }
   292  
   293  func tempDir() string {
   294  	n := uint32(syscall.MAX_PATH)
   295  	for {
   296  		b := make([]uint16, n)
   297  		n, _ = syscall.GetTempPath(uint32(len(b)), &b[0])
   298  		if n > uint32(len(b)) {
   299  			continue
   300  		}
   301  		if n == 3 && b[1] == ':' && b[2] == '\\' {
   302  			// Do nothing for path, like C:\.
   303  		} else if n > 0 && b[n-1] == '\\' {
   304  			// Otherwise remove terminating \.
   305  			n--
   306  		}
   307  		return string(utf16.Decode(b[:n]))
   308  	}
   309  }
   310  
   311  // Link creates newname as a hard link to the oldname file.
   312  // If there is an error, it will be of type *LinkError.
   313  func Link(oldname, newname string) error {
   314  	n, err := syscall.UTF16PtrFromString(fixLongPath(newname))
   315  	if err != nil {
   316  		return &LinkError{"link", oldname, newname, err}
   317  	}
   318  	o, err := syscall.UTF16PtrFromString(fixLongPath(oldname))
   319  	if err != nil {
   320  		return &LinkError{"link", oldname, newname, err}
   321  	}
   322  	err = syscall.CreateHardLink(n, o, 0)
   323  	if err != nil {
   324  		return &LinkError{"link", oldname, newname, err}
   325  	}
   326  	return nil
   327  }
   328  
   329  // Symlink creates newname as a symbolic link to oldname.
   330  // On Windows, a symlink to a non-existent oldname creates a file symlink;
   331  // if oldname is later created as a directory the symlink will not work.
   332  // If there is an error, it will be of type *LinkError.
   333  func Symlink(oldname, newname string) error {
   334  	// '/' does not work in link's content
   335  	oldname = fromSlash(oldname)
   336  
   337  	// need the exact location of the oldname when it's relative to determine if it's a directory
   338  	destpath := oldname
   339  	if v := volumeName(oldname); v == "" {
   340  		if len(oldname) > 0 && IsPathSeparator(oldname[0]) {
   341  			// oldname is relative to the volume containing newname.
   342  			if v = volumeName(newname); v != "" {
   343  				// Prepend the volume explicitly, because it may be different from the
   344  				// volume of the current working directory.
   345  				destpath = v + oldname
   346  			}
   347  		} else {
   348  			// oldname is relative to newname.
   349  			destpath = dirname(newname) + `\` + oldname
   350  		}
   351  	}
   352  
   353  	fi, err := Stat(destpath)
   354  	isdir := err == nil && fi.IsDir()
   355  
   356  	n, err := syscall.UTF16PtrFromString(fixLongPath(newname))
   357  	if err != nil {
   358  		return &LinkError{"symlink", oldname, newname, err}
   359  	}
   360  	o, err := syscall.UTF16PtrFromString(fixLongPath(oldname))
   361  	if err != nil {
   362  		return &LinkError{"symlink", oldname, newname, err}
   363  	}
   364  
   365  	var flags uint32 = windows.SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
   366  	if isdir {
   367  		flags |= syscall.SYMBOLIC_LINK_FLAG_DIRECTORY
   368  	}
   369  	err = syscall.CreateSymbolicLink(n, o, flags)
   370  	if err != nil {
   371  		// the unprivileged create flag is unsupported
   372  		// below Windows 10 (1703, v10.0.14972). retry without it.
   373  		flags &^= windows.SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
   374  		err = syscall.CreateSymbolicLink(n, o, flags)
   375  		if err != nil {
   376  			return &LinkError{"symlink", oldname, newname, err}
   377  		}
   378  	}
   379  	return nil
   380  }
   381  
   382  // openSymlink calls CreateFile Windows API with FILE_FLAG_OPEN_REPARSE_POINT
   383  // parameter, so that Windows does not follow symlink, if path is a symlink.
   384  // openSymlink returns opened file handle.
   385  func openSymlink(path string) (syscall.Handle, error) {
   386  	p, err := syscall.UTF16PtrFromString(path)
   387  	if err != nil {
   388  		return 0, err
   389  	}
   390  	attrs := uint32(syscall.FILE_FLAG_BACKUP_SEMANTICS)
   391  	// Use FILE_FLAG_OPEN_REPARSE_POINT, otherwise CreateFile will follow symlink.
   392  	// See https://docs.microsoft.com/en-us/windows/desktop/FileIO/symbolic-link-effects-on-file-systems-functions#createfile-and-createfiletransacted
   393  	attrs |= syscall.FILE_FLAG_OPEN_REPARSE_POINT
   394  	h, err := syscall.CreateFile(p, 0, 0, nil, syscall.OPEN_EXISTING, attrs, 0)
   395  	if err != nil {
   396  		return 0, err
   397  	}
   398  	return h, nil
   399  }
   400  
   401  // normaliseLinkPath converts absolute paths returned by
   402  // DeviceIoControl(h, FSCTL_GET_REPARSE_POINT, ...)
   403  // into paths acceptable by all Windows APIs.
   404  // For example, it coverts
   405  //  \??\C:\foo\bar into C:\foo\bar
   406  //  \??\UNC\foo\bar into \\foo\bar
   407  //  \??\Volume{abc}\ into C:\
   408  func normaliseLinkPath(path string) (string, error) {
   409  	if len(path) < 4 || path[:4] != `\??\` {
   410  		// unexpected path, return it as is
   411  		return path, nil
   412  	}
   413  	// we have path that start with \??\
   414  	s := path[4:]
   415  	switch {
   416  	case len(s) >= 2 && s[1] == ':': // \??\C:\foo\bar
   417  		return s, nil
   418  	case len(s) >= 4 && s[:4] == `UNC\`: // \??\UNC\foo\bar
   419  		return `\\` + s[4:], nil
   420  	}
   421  
   422  	// handle paths, like \??\Volume{abc}\...
   423  
   424  	err := windows.LoadGetFinalPathNameByHandle()
   425  	if err != nil {
   426  		// we must be using old version of Windows
   427  		return "", err
   428  	}
   429  
   430  	h, err := openSymlink(path)
   431  	if err != nil {
   432  		return "", err
   433  	}
   434  	defer syscall.CloseHandle(h)
   435  
   436  	buf := make([]uint16, 100)
   437  	for {
   438  		n, err := windows.GetFinalPathNameByHandle(h, &buf[0], uint32(len(buf)), windows.VOLUME_NAME_DOS)
   439  		if err != nil {
   440  			return "", err
   441  		}
   442  		if n < uint32(len(buf)) {
   443  			break
   444  		}
   445  		buf = make([]uint16, n)
   446  	}
   447  	s = syscall.UTF16ToString(buf)
   448  	if len(s) > 4 && s[:4] == `\\?\` {
   449  		s = s[4:]
   450  		if len(s) > 3 && s[:3] == `UNC` {
   451  			// return path like \\server\share\...
   452  			return `\` + s[3:], nil
   453  		}
   454  		return s, nil
   455  	}
   456  	return "", errors.New("GetFinalPathNameByHandle returned unexpected path: " + s)
   457  }
   458  
   459  func readlink(path string) (string, error) {
   460  	h, err := openSymlink(path)
   461  	if err != nil {
   462  		return "", err
   463  	}
   464  	defer syscall.CloseHandle(h)
   465  
   466  	rdbbuf := make([]byte, syscall.MAXIMUM_REPARSE_DATA_BUFFER_SIZE)
   467  	var bytesReturned uint32
   468  	err = syscall.DeviceIoControl(h, syscall.FSCTL_GET_REPARSE_POINT, nil, 0, &rdbbuf[0], uint32(len(rdbbuf)), &bytesReturned, nil)
   469  	if err != nil {
   470  		return "", err
   471  	}
   472  
   473  	rdb := (*windows.REPARSE_DATA_BUFFER)(unsafe.Pointer(&rdbbuf[0]))
   474  	switch rdb.ReparseTag {
   475  	case syscall.IO_REPARSE_TAG_SYMLINK:
   476  		rb := (*windows.SymbolicLinkReparseBuffer)(unsafe.Pointer(&rdb.DUMMYUNIONNAME))
   477  		s := rb.Path()
   478  		if rb.Flags&windows.SYMLINK_FLAG_RELATIVE != 0 {
   479  			return s, nil
   480  		}
   481  		return normaliseLinkPath(s)
   482  	case windows.IO_REPARSE_TAG_MOUNT_POINT:
   483  		return normaliseLinkPath((*windows.MountPointReparseBuffer)(unsafe.Pointer(&rdb.DUMMYUNIONNAME)).Path())
   484  	default:
   485  		// the path is not a symlink or junction but another type of reparse
   486  		// point
   487  		return "", syscall.ENOENT
   488  	}
   489  }
   490  
   491  // Readlink returns the destination of the named symbolic link.
   492  // If there is an error, it will be of type *PathError.
   493  func Readlink(name string) (string, error) {
   494  	s, err := readlink(fixLongPath(name))
   495  	if err != nil {
   496  		return "", &PathError{Op: "readlink", Path: name, Err: err}
   497  	}
   498  	return s, nil
   499  }
   500
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