lp_windows.go

     1  // Copyright 2010 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 exec
     6  
     7  import (
     8  	"errors"
     9  	"io/fs"
    10  	"os"
    11  	"path/filepath"
    12  	"strings"
    13  	"syscall"
    14  )
    15  
    16  // ErrNotFound is the error resulting if a path search failed to find an executable file.
    17  var ErrNotFound = errors.New("executable file not found in %PATH%")
    18  
    19  func chkStat(file string) error {
    20  	d, err := os.Stat(file)
    21  	if err != nil {
    22  		return err
    23  	}
    24  	if d.IsDir() {
    25  		return fs.ErrPermission
    26  	}
    27  	return nil
    28  }
    29  
    30  func hasExt(file string) bool {
    31  	i := strings.LastIndex(file, ".")
    32  	if i < 0 {
    33  		return false
    34  	}
    35  	return strings.LastIndexAny(file, `:\/`) < i
    36  }
    37  
    38  func findExecutable(file string, exts []string) (string, error) {
    39  	if len(exts) == 0 {
    40  		return file, chkStat(file)
    41  	}
    42  	if hasExt(file) {
    43  		if chkStat(file) == nil {
    44  			return file, nil
    45  		}
    46  		// Keep checking exts below, so that programs with weird names
    47  		// like "foo.bat.exe" will resolve instead of failing.
    48  	}
    49  	for _, e := range exts {
    50  		if f := file + e; chkStat(f) == nil {
    51  			return f, nil
    52  		}
    53  	}
    54  	if hasExt(file) {
    55  		return "", fs.ErrNotExist
    56  	}
    57  	return "", ErrNotFound
    58  }
    59  
    60  // LookPath searches for an executable named file in the
    61  // directories named by the PATH environment variable.
    62  // LookPath also uses PATHEXT environment variable to match
    63  // a suitable candidate.
    64  // If file contains a slash, it is tried directly and the PATH is not consulted.
    65  // Otherwise, on success, the result is an absolute path.
    66  //
    67  // In older versions of Go, LookPath could return a path relative to the current directory.
    68  // As of Go 1.19, LookPath will instead return that path along with an error satisfying
    69  // [errors.Is](err, [ErrDot]). See the package documentation for more details.
    70  func LookPath(file string) (string, error) {
    71  	return lookPath(file, pathExt())
    72  }
    73  
    74  // lookExtensions finds windows executable by its dir and path.
    75  // It uses LookPath to try appropriate extensions.
    76  // lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
    77  //
    78  // If the path already has an extension found in PATHEXT,
    79  // lookExtensions returns it directly without searching
    80  // for additional extensions. For example,
    81  // "C:\foo\example.com" would be returned as-is even if the
    82  // program is actually "C:\foo\example.com.exe".
    83  func lookExtensions(path, dir string) (string, error) {
    84  	if filepath.Base(path) == path {
    85  		path = "." + string(filepath.Separator) + path
    86  	}
    87  	exts := pathExt()
    88  	if ext := filepath.Ext(path); ext != "" {
    89  		for _, e := range exts {
    90  			if strings.EqualFold(ext, e) {
    91  				// Assume that path has already been resolved.
    92  				return path, nil
    93  			}
    94  		}
    95  	}
    96  	if dir == "" {
    97  		return lookPath(path, exts)
    98  	}
    99  	if filepath.VolumeName(path) != "" {
   100  		return lookPath(path, exts)
   101  	}
   102  	if len(path) > 1 && os.IsPathSeparator(path[0]) {
   103  		return lookPath(path, exts)
   104  	}
   105  	dirandpath := filepath.Join(dir, path)
   106  	// We assume that LookPath will only add file extension.
   107  	lp, err := lookPath(dirandpath, exts)
   108  	if err != nil {
   109  		return "", err
   110  	}
   111  	ext := strings.TrimPrefix(lp, dirandpath)
   112  	return path + ext, nil
   113  }
   114  
   115  func pathExt() []string {
   116  	var exts []string
   117  	x := os.Getenv(`PATHEXT`)
   118  	if x != "" {
   119  		for _, e := range strings.Split(strings.ToLower(x), `;`) {
   120  			if e == "" {
   121  				continue
   122  			}
   123  			if e[0] != '.' {
   124  				e = "." + e
   125  			}
   126  			exts = append(exts, e)
   127  		}
   128  	} else {
   129  		exts = []string{".com", ".exe", ".bat", ".cmd"}
   130  	}
   131  	return exts
   132  }
   133  
   134  // lookPath implements LookPath for the given PATHEXT list.
   135  func lookPath(file string, exts []string) (string, error) {
   136  	if strings.ContainsAny(file, `:\/`) {
   137  		f, err := findExecutable(file, exts)
   138  		if err == nil {
   139  			return f, nil
   140  		}
   141  		return "", &Error{file, err}
   142  	}
   143  
   144  	// On Windows, creating the NoDefaultCurrentDirectoryInExePath
   145  	// environment variable (with any value or no value!) signals that
   146  	// path lookups should skip the current directory.
   147  	// In theory we are supposed to call NeedCurrentDirectoryForExePathW
   148  	// "as the registry location of this environment variable can change"
   149  	// but that seems exceedingly unlikely: it would break all users who
   150  	// have configured their environment this way!
   151  	// https://docs.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-needcurrentdirectoryforexepathw
   152  	// See also go.dev/issue/43947.
   153  	var (
   154  		dotf   string
   155  		dotErr error
   156  	)
   157  	if _, found := syscall.Getenv("NoDefaultCurrentDirectoryInExePath"); !found {
   158  		if f, err := findExecutable(filepath.Join(".", file), exts); err == nil {
   159  			if execerrdot.Value() == "0" {
   160  				execerrdot.IncNonDefault()
   161  				return f, nil
   162  			}
   163  			dotf, dotErr = f, &Error{file, ErrDot}
   164  		}
   165  	}
   166  
   167  	path := os.Getenv("path")
   168  	for _, dir := range filepath.SplitList(path) {
   169  		if dir == "" {
   170  			// Skip empty entries, consistent with what PowerShell does.
   171  			// (See https://go.dev/issue/61493#issuecomment-1649724826.)
   172  			continue
   173  		}
   174  
   175  		if f, err := findExecutable(filepath.Join(dir, file), exts); err == nil {
   176  			if dotErr != nil {
   177  				// https://go.dev/issue/53536: if we resolved a relative path implicitly,
   178  				// and it is the same executable that would be resolved from the explicit %PATH%,
   179  				// prefer the explicit name for the executable (and, likely, no error) instead
   180  				// of the equivalent implicit name with ErrDot.
   181  				//
   182  				// Otherwise, return the ErrDot for the implicit path as soon as we find
   183  				// out that the explicit one doesn't match.
   184  				dotfi, dotfiErr := os.Lstat(dotf)
   185  				fi, fiErr := os.Lstat(f)
   186  				if dotfiErr != nil || fiErr != nil || !os.SameFile(dotfi, fi) {
   187  					return dotf, dotErr
   188  				}
   189  			}
   190  
   191  			if !filepath.IsAbs(f) {
   192  				if execerrdot.Value() != "0" {
   193  					// If this is the same relative path that we already found,
   194  					// dotErr is non-nil and we already checked it above.
   195  					// Otherwise, record this path as the one to which we must resolve,
   196  					// with or without a dotErr.
   197  					if dotErr == nil {
   198  						dotf, dotErr = f, &Error{file, ErrDot}
   199  					}
   200  					continue
   201  				}
   202  				execerrdot.IncNonDefault()
   203  			}
   204  			return f, nil
   205  		}
   206  	}
   207  
   208  	if dotErr != nil {
   209  		return dotf, dotErr
   210  	}
   211  	return "", &Error{file, ErrNotFound}
   212  }
   213
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