path_windows.go

     1  // Copyright 2022 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 safefilepath
     6  
     7  import (
     8  	"syscall"
     9  	"unicode/utf8"
    10  )
    11  
    12  func fromFS(path string) (string, error) {
    13  	if !utf8.ValidString(path) {
    14  		return "", errInvalidPath
    15  	}
    16  	for len(path) > 1 && path[0] == '/' && path[1] == '/' {
    17  		path = path[1:]
    18  	}
    19  	containsSlash := false
    20  	for p := path; p != ""; {
    21  		// Find the next path element.
    22  		i := 0
    23  		for i < len(p) && p[i] != '/' {
    24  			switch p[i] {
    25  			case 0, '\\', ':':
    26  				return "", errInvalidPath
    27  			}
    28  			i++
    29  		}
    30  		part := p[:i]
    31  		if i < len(p) {
    32  			containsSlash = true
    33  			p = p[i+1:]
    34  		} else {
    35  			p = ""
    36  		}
    37  		if IsReservedName(part) {
    38  			return "", errInvalidPath
    39  		}
    40  	}
    41  	if containsSlash {
    42  		// We can't depend on strings, so substitute \ for / manually.
    43  		buf := []byte(path)
    44  		for i, b := range buf {
    45  			if b == '/' {
    46  				buf[i] = '\\'
    47  			}
    48  		}
    49  		path = string(buf)
    50  	}
    51  	return path, nil
    52  }
    53  
    54  // IsReservedName reports if name is a Windows reserved device name.
    55  // It does not detect names with an extension, which are also reserved on some Windows versions.
    56  //
    57  // For details, search for PRN in
    58  // https://docs.microsoft.com/en-us/windows/desktop/fileio/naming-a-file.
    59  func IsReservedName(name string) bool {
    60  	// Device names can have arbitrary trailing characters following a dot or colon.
    61  	base := name
    62  	for i := 0; i < len(base); i++ {
    63  		switch base[i] {
    64  		case ':', '.':
    65  			base = base[:i]
    66  		}
    67  	}
    68  	// Trailing spaces in the last path element are ignored.
    69  	for len(base) > 0 && base[len(base)-1] == ' ' {
    70  		base = base[:len(base)-1]
    71  	}
    72  	if !isReservedBaseName(base) {
    73  		return false
    74  	}
    75  	if len(base) == len(name) {
    76  		return true
    77  	}
    78  	// The path element is a reserved name with an extension.
    79  	// Some Windows versions consider this a reserved name,
    80  	// while others do not. Use FullPath to see if the name is
    81  	// reserved.
    82  	if p, _ := syscall.FullPath(name); len(p) >= 4 && p[:4] == `\\.\` {
    83  		return true
    84  	}
    85  	return false
    86  }
    87  
    88  func isReservedBaseName(name string) bool {
    89  	if len(name) == 3 {
    90  		switch string([]byte{toUpper(name[0]), toUpper(name[1]), toUpper(name[2])}) {
    91  		case "CON", "PRN", "AUX", "NUL":
    92  			return true
    93  		}
    94  	}
    95  	if len(name) >= 4 {
    96  		switch string([]byte{toUpper(name[0]), toUpper(name[1]), toUpper(name[2])}) {
    97  		case "COM", "LPT":
    98  			if len(name) == 4 && '1' <= name[3] && name[3] <= '9' {
    99  				return true
   100  			}
   101  			// Superscript ¹, ², and ³ are considered numbers as well.
   102  			switch name[3:] {
   103  			case "\u00b2", "\u00b3", "\u00b9":
   104  				return true
   105  			}
   106  			return false
   107  		}
   108  	}
   109  
   110  	// Passing CONIN$ or CONOUT$ to CreateFile opens a console handle.
   111  	// https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea#consoles
   112  	//
   113  	// While CONIN$ and CONOUT$ aren't documented as being files,
   114  	// they behave the same as CON. For example, ./CONIN$ also opens the console input.
   115  	if len(name) == 6 && name[5] == '$' && equalFold(name, "CONIN$") {
   116  		return true
   117  	}
   118  	if len(name) == 7 && name[6] == '$' && equalFold(name, "CONOUT$") {
   119  		return true
   120  	}
   121  	return false
   122  }
   123  
   124  func equalFold(a, b string) bool {
   125  	if len(a) != len(b) {
   126  		return false
   127  	}
   128  	for i := 0; i < len(a); i++ {
   129  		if toUpper(a[i]) != toUpper(b[i]) {
   130  			return false
   131  		}
   132  	}
   133  	return true
   134  }
   135  
   136  func toUpper(c byte) byte {
   137  	if 'a' <= c && c <= 'z' {
   138  		return c - ('a' - 'A')
   139  	}
   140  	return c
   141  }
   142
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