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