stat_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  	"internal/filepathlite"
     9  	"internal/syscall/windows"
    10  	"syscall"
    11  	"unsafe"
    12  )
    13  
    14  // Stat returns the [FileInfo] structure describing file.
    15  // If there is an error, it will be of type [*PathError].
    16  func (file *File) Stat() (FileInfo, error) {
    17  	if file == nil {
    18  		return nil, ErrInvalid
    19  	}
    20  	return statHandle(file.name, file.pfd.Sysfd)
    21  }
    22  
    23  // stat implements both Stat and Lstat of a file.
    24  func stat(funcname, name string, followSurrogates bool) (FileInfo, error) {
    25  	if len(name) == 0 {
    26  		return nil, &PathError{Op: funcname, Path: name, Err: syscall.Errno(syscall.ERROR_PATH_NOT_FOUND)}
    27  	}
    28  	namep, err := syscall.UTF16PtrFromString(fixLongPath(name))
    29  	if err != nil {
    30  		return nil, &PathError{Op: funcname, Path: name, Err: err}
    31  	}
    32  
    33  	// Try GetFileAttributesEx first, because it is faster than CreateFile.
    34  	// See https://golang.org/issues/19922#issuecomment-300031421 for details.
    35  	var fa syscall.Win32FileAttributeData
    36  	err = syscall.GetFileAttributesEx(namep, syscall.GetFileExInfoStandard, (*byte)(unsafe.Pointer(&fa)))
    37  	if err == nil && fa.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT == 0 {
    38  		// Not a surrogate for another named entity, because it isn't any kind of reparse point.
    39  		// The information we got from GetFileAttributesEx is good enough for now.
    40  		fs := newFileStatFromWin32FileAttributeData(&fa)
    41  		if err := fs.saveInfoFromPath(name); err != nil {
    42  			return nil, err
    43  		}
    44  		return fs, nil
    45  	}
    46  
    47  	// GetFileAttributesEx fails with ERROR_SHARING_VIOLATION error for
    48  	// files like c:\pagefile.sys. Use FindFirstFile for such files.
    49  	if err == windows.ERROR_SHARING_VIOLATION {
    50  		var fd syscall.Win32finddata
    51  		sh, err := syscall.FindFirstFile(namep, &fd)
    52  		if err != nil {
    53  			return nil, &PathError{Op: "FindFirstFile", Path: name, Err: err}
    54  		}
    55  		syscall.FindClose(sh)
    56  		if fd.FileAttributes&syscall.FILE_ATTRIBUTE_REPARSE_POINT == 0 {
    57  			// Not a surrogate for another named entity. FindFirstFile is good enough.
    58  			fs := newFileStatFromWin32finddata(&fd)
    59  			if err := fs.saveInfoFromPath(name); err != nil {
    60  				return nil, err
    61  			}
    62  			return fs, nil
    63  		}
    64  	}
    65  
    66  	// Use CreateFile to determine whether the file is a name surrogate and, if so,
    67  	// save information about the link target.
    68  	// Set FILE_FLAG_BACKUP_SEMANTICS so that CreateFile will create the handle
    69  	// even if name refers to a directory.
    70  	var flags uint32 = syscall.FILE_FLAG_BACKUP_SEMANTICS | syscall.FILE_FLAG_OPEN_REPARSE_POINT
    71  	h, err := syscall.CreateFile(namep, 0, 0, nil, syscall.OPEN_EXISTING, flags, 0)
    72  
    73  	if err == windows.ERROR_INVALID_PARAMETER {
    74  		// Console handles, like "\\.\con", require generic read access. See
    75  		// https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew#consoles.
    76  		// We haven't set it previously because it is normally not required
    77  		// to read attributes and some files may not allow it.
    78  		h, err = syscall.CreateFile(namep, syscall.GENERIC_READ, 0, nil, syscall.OPEN_EXISTING, flags, 0)
    79  	}
    80  	if err != nil {
    81  		// Since CreateFile failed, we can't determine whether name refers to a
    82  		// name surrogate, or some other kind of reparse point. Since we can't return a
    83  		// FileInfo with a known-accurate Mode, we must return an error.
    84  		return nil, &PathError{Op: "CreateFile", Path: name, Err: err}
    85  	}
    86  
    87  	fi, err := statHandle(name, h)
    88  	syscall.CloseHandle(h)
    89  	if err == nil && followSurrogates && fi.(*fileStat).isReparseTagNameSurrogate() {
    90  		// To obtain information about the link target, we reopen the file without
    91  		// FILE_FLAG_OPEN_REPARSE_POINT and examine the resulting handle.
    92  		// (See https://devblogs.microsoft.com/oldnewthing/20100212-00/?p=14963.)
    93  		h, err = syscall.CreateFile(namep, 0, 0, nil, syscall.OPEN_EXISTING, syscall.FILE_FLAG_BACKUP_SEMANTICS, 0)
    94  		if err != nil {
    95  			// name refers to a symlink, but we couldn't resolve the symlink target.
    96  			return nil, &PathError{Op: "CreateFile", Path: name, Err: err}
    97  		}
    98  		defer syscall.CloseHandle(h)
    99  		return statHandle(name, h)
   100  	}
   101  	return fi, err
   102  }
   103  
   104  func statHandle(name string, h syscall.Handle) (FileInfo, error) {
   105  	ft, err := syscall.GetFileType(h)
   106  	if err != nil {
   107  		return nil, &PathError{Op: "GetFileType", Path: name, Err: err}
   108  	}
   109  	switch ft {
   110  	case syscall.FILE_TYPE_PIPE, syscall.FILE_TYPE_CHAR:
   111  		return &fileStat{name: filepathlite.Base(name), filetype: ft}, nil
   112  	}
   113  	fs, err := newFileStatFromGetFileInformationByHandle(name, h)
   114  	if err != nil {
   115  		return nil, err
   116  	}
   117  	fs.filetype = ft
   118  	return fs, err
   119  }
   120  
   121  // statNolog implements Stat for Windows.
   122  func statNolog(name string) (FileInfo, error) {
   123  	return stat("Stat", name, true)
   124  }
   125  
   126  // lstatNolog implements Lstat for Windows.
   127  func lstatNolog(name string) (FileInfo, error) {
   128  	followSurrogates := false
   129  	if name != "" && IsPathSeparator(name[len(name)-1]) {
   130  		// We try to implement POSIX semantics for Lstat path resolution
   131  		// (per https://pubs.opengroup.org/onlinepubs/9699919799.2013edition/basedefs/V1_chap04.html#tag_04_12):
   132  		// symlinks before the last separator in the path must be resolved. Since
   133  		// the last separator in this case follows the last path element, we should
   134  		// follow symlinks in the last path element.
   135  		followSurrogates = true
   136  	}
   137  	return stat("Lstat", name, followSurrogates)
   138  }
   139
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