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

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