fsys.go

     1  // Package fsys is an abstraction for reading files that
     2  // allows for virtual overlays on top of the files on disk.
     3  package fsys
     4  
     5  import (
     6  	"encoding/json"
     7  	"errors"
     8  	"fmt"
     9  	"io/fs"
    10  	"io/ioutil"
    11  	"os"
    12  	"path/filepath"
    13  	"runtime"
    14  	"sort"
    15  	"strings"
    16  	"time"
    17  )
    18  
    19  // OverlayFile is the path to a text file in the OverlayJSON format.
    20  // It is the value of the -overlay flag.
    21  var OverlayFile string
    22  
    23  // OverlayJSON is the format overlay files are expected to be in.
    24  // The Replace map maps from overlaid paths to replacement paths:
    25  // the Go command will forward all reads trying to open
    26  // each overlaid path to its replacement path, or consider the overlaid
    27  // path not to exist if the replacement path is empty.
    28  type OverlayJSON struct {
    29  	Replace map[string]string
    30  }
    31  
    32  type node struct {
    33  	actualFilePath string           // empty if a directory
    34  	children       map[string]*node // path element → file or directory
    35  }
    36  
    37  func (n *node) isDir() bool {
    38  	return n.actualFilePath == "" && n.children != nil
    39  }
    40  
    41  func (n *node) isDeleted() bool {
    42  	return n.actualFilePath == "" && n.children == nil
    43  }
    44  
    45  // TODO(matloob): encapsulate these in an io/fs-like interface
    46  var overlay map[string]*node // path -> file or directory node
    47  var cwd string               // copy of base.Cwd() to avoid dependency
    48  
    49  // Canonicalize a path for looking it up in the overlay.
    50  // Important: filepath.Join(cwd, path) doesn't always produce
    51  // the correct absolute path if path is relative, because on
    52  // Windows producing the correct absolute path requires making
    53  // a syscall. So this should only be used when looking up paths
    54  // in the overlay, or canonicalizing the paths in the overlay.
    55  func canonicalize(path string) string {
    56  	if path == "" {
    57  		return ""
    58  	}
    59  	if filepath.IsAbs(path) {
    60  		return filepath.Clean(path)
    61  	}
    62  
    63  	if v := filepath.VolumeName(cwd); v != "" && path[0] == filepath.Separator {
    64  		// On Windows filepath.Join(cwd, path) doesn't always work. In general
    65  		// filepath.Abs needs to make a syscall on Windows. Elsewhere in cmd/go
    66  		// use filepath.Join(cwd, path), but cmd/go specifically supports Windows
    67  		// paths that start with "\" which implies the path is relative to the
    68  		// volume of the working directory. See golang.org/issue/8130.
    69  		return filepath.Join(v, path)
    70  	}
    71  
    72  	// Make the path absolute.
    73  	return filepath.Join(cwd, path)
    74  }
    75  
    76  // Init initializes the overlay, if one is being used.
    77  func Init(wd string) error {
    78  	if overlay != nil {
    79  		// already initialized
    80  		return nil
    81  	}
    82  
    83  	cwd = wd
    84  
    85  	if OverlayFile == "" {
    86  		return nil
    87  	}
    88  
    89  	b, err := os.ReadFile(OverlayFile)
    90  	if err != nil {
    91  		return fmt.Errorf("reading overlay file: %v", err)
    92  	}
    93  
    94  	var overlayJSON OverlayJSON
    95  	if err := json.Unmarshal(b, &overlayJSON); err != nil {
    96  		return fmt.Errorf("parsing overlay JSON: %v", err)
    97  	}
    98  
    99  	return initFromJSON(overlayJSON)
   100  }
   101  
   102  func initFromJSON(overlayJSON OverlayJSON) error {
   103  	// Canonicalize the paths in the overlay map.
   104  	// Use reverseCanonicalized to check for collisions:
   105  	// no two 'from' paths should canonicalize to the same path.
   106  	overlay = make(map[string]*node)
   107  	reverseCanonicalized := make(map[string]string) // inverse of canonicalize operation, to check for duplicates
   108  	// Build a table of file and directory nodes from the replacement map.
   109  
   110  	// Remove any potential non-determinism from iterating over map by sorting it.
   111  	replaceFrom := make([]string, 0, len(overlayJSON.Replace))
   112  	for k := range overlayJSON.Replace {
   113  		replaceFrom = append(replaceFrom, k)
   114  	}
   115  	sort.Strings(replaceFrom)
   116  
   117  	for _, from := range replaceFrom {
   118  		to := overlayJSON.Replace[from]
   119  		// Canonicalize paths and check for a collision.
   120  		if from == "" {
   121  			return fmt.Errorf("empty string key in overlay file Replace map")
   122  		}
   123  		cfrom := canonicalize(from)
   124  		if to != "" {
   125  			// Don't canonicalize "", meaning to delete a file, because then it will turn into ".".
   126  			to = canonicalize(to)
   127  		}
   128  		if otherFrom, seen := reverseCanonicalized[cfrom]; seen {
   129  			return fmt.Errorf(
   130  				"paths %q and %q both canonicalize to %q in overlay file Replace map", otherFrom, from, cfrom)
   131  		}
   132  		reverseCanonicalized[cfrom] = from
   133  		from = cfrom
   134  
   135  		// Create node for overlaid file.
   136  		dir, base := filepath.Dir(from), filepath.Base(from)
   137  		if n, ok := overlay[from]; ok {
   138  			// All 'from' paths in the overlay are file paths. Since the from paths
   139  			// are in a map, they are unique, so if the node already exists we added
   140  			// it below when we create parent directory nodes. That is, that
   141  			// both a file and a path to one of its parent directories exist as keys
   142  			// in the Replace map.
   143  			//
   144  			// This only applies if the overlay directory has any files or directories
   145  			// in it: placeholder directories that only contain deleted files don't
   146  			// count. They are safe to be overwritten with actual files.
   147  			for _, f := range n.children {
   148  				if !f.isDeleted() {
   149  					return fmt.Errorf("invalid overlay: path %v is used as both file and directory", from)
   150  				}
   151  			}
   152  		}
   153  		overlay[from] = &node{actualFilePath: to}
   154  
   155  		// Add parent directory nodes to overlay structure.
   156  		childNode := overlay[from]
   157  		for {
   158  			dirNode := overlay[dir]
   159  			if dirNode == nil || dirNode.isDeleted() {
   160  				dirNode = &node{children: make(map[string]*node)}
   161  				overlay[dir] = dirNode
   162  			}
   163  			if childNode.isDeleted() {
   164  				// Only create one parent for a deleted file:
   165  				// the directory only conditionally exists if
   166  				// there are any non-deleted children, so
   167  				// we don't create their parents.
   168  				if dirNode.isDir() {
   169  					dirNode.children[base] = childNode
   170  				}
   171  				break
   172  			}
   173  			if !dirNode.isDir() {
   174  				// This path already exists as a file, so it can't be a parent
   175  				// directory. See comment at error above.
   176  				return fmt.Errorf("invalid overlay: path %v is used as both file and directory", dir)
   177  			}
   178  			dirNode.children[base] = childNode
   179  			parent := filepath.Dir(dir)
   180  			if parent == dir {
   181  				break // reached the top; there is no parent
   182  			}
   183  			dir, base = parent, filepath.Base(dir)
   184  			childNode = dirNode
   185  		}
   186  	}
   187  
   188  	return nil
   189  }
   190  
   191  // IsDir returns true if path is a directory on disk or in the
   192  // overlay.
   193  func IsDir(path string) (bool, error) {
   194  	path = canonicalize(path)
   195  
   196  	if _, ok := parentIsOverlayFile(path); ok {
   197  		return false, nil
   198  	}
   199  
   200  	if n, ok := overlay[path]; ok {
   201  		return n.isDir(), nil
   202  	}
   203  
   204  	fi, err := os.Stat(path)
   205  	if err != nil {
   206  		return false, err
   207  	}
   208  
   209  	return fi.IsDir(), nil
   210  }
   211  
   212  // parentIsOverlayFile returns whether name or any of
   213  // its parents are files in the overlay, and the first parent found,
   214  // including name itself, that's a file in the overlay.
   215  func parentIsOverlayFile(name string) (string, bool) {
   216  	if overlay != nil {
   217  		// Check if name can't possibly be a directory because
   218  		// it or one of its parents is overlaid with a file.
   219  		// TODO(matloob): Maybe save this to avoid doing it every time?
   220  		prefix := name
   221  		for {
   222  			node := overlay[prefix]
   223  			if node != nil && !node.isDir() {
   224  				return prefix, true
   225  			}
   226  			parent := filepath.Dir(prefix)
   227  			if parent == prefix {
   228  				break
   229  			}
   230  			prefix = parent
   231  		}
   232  	}
   233  
   234  	return "", false
   235  }
   236  
   237  // errNotDir is used to communicate from ReadDir to IsDirWithGoFiles
   238  // that the argument is not a directory, so that IsDirWithGoFiles doesn't
   239  // return an error.
   240  var errNotDir = errors.New("not a directory")
   241  
   242  // readDir reads a dir on disk, returning an error that is errNotDir if the dir is not a directory.
   243  // Unfortunately, the error returned by ioutil.ReadDir if dir is not a directory
   244  // can vary depending on the OS (Linux, Mac, Windows return ENOTDIR; BSD returns EINVAL).
   245  func readDir(dir string) ([]fs.FileInfo, error) {
   246  	fis, err := ioutil.ReadDir(dir)
   247  	if err == nil {
   248  		return fis, nil
   249  	}
   250  
   251  	if os.IsNotExist(err) {
   252  		return nil, err
   253  	}
   254  	if dirfi, staterr := os.Stat(dir); staterr == nil && !dirfi.IsDir() {
   255  		return nil, &fs.PathError{Op: "ReadDir", Path: dir, Err: errNotDir}
   256  	}
   257  	return nil, err
   258  }
   259  
   260  // ReadDir provides a slice of fs.FileInfo entries corresponding
   261  // to the overlaid files in the directory.
   262  func ReadDir(dir string) ([]fs.FileInfo, error) {
   263  	dir = canonicalize(dir)
   264  	if _, ok := parentIsOverlayFile(dir); ok {
   265  		return nil, &fs.PathError{Op: "ReadDir", Path: dir, Err: errNotDir}
   266  	}
   267  
   268  	dirNode := overlay[dir]
   269  	if dirNode == nil {
   270  		return readDir(dir)
   271  	}
   272  	if dirNode.isDeleted() {
   273  		return nil, &fs.PathError{Op: "ReadDir", Path: dir, Err: fs.ErrNotExist}
   274  	}
   275  	diskfis, err := readDir(dir)
   276  	if err != nil && !os.IsNotExist(err) && !errors.Is(err, errNotDir) {
   277  		return nil, err
   278  	}
   279  
   280  	// Stat files in overlay to make composite list of fileinfos
   281  	files := make(map[string]fs.FileInfo)
   282  	for _, f := range diskfis {
   283  		files[f.Name()] = f
   284  	}
   285  	for name, to := range dirNode.children {
   286  		switch {
   287  		case to.isDir():
   288  			files[name] = fakeDir(name)
   289  		case to.isDeleted():
   290  			delete(files, name)
   291  		default:
   292  			// This is a regular file.
   293  			f, err := os.Lstat(to.actualFilePath)
   294  			if err != nil {
   295  				files[name] = missingFile(name)
   296  				continue
   297  			} else if f.IsDir() {
   298  				return nil, fmt.Errorf("for overlay of %q to %q: overlay Replace entries can't point to dirctories",
   299  					filepath.Join(dir, name), to.actualFilePath)
   300  			}
   301  			// Add a fileinfo for the overlaid file, so that it has
   302  			// the original file's name, but the overlaid file's metadata.
   303  			files[name] = fakeFile{name, f}
   304  		}
   305  	}
   306  	sortedFiles := diskfis[:0]
   307  	for _, f := range files {
   308  		sortedFiles = append(sortedFiles, f)
   309  	}
   310  	sort.Slice(sortedFiles, func(i, j int) bool { return sortedFiles[i].Name() < sortedFiles[j].Name() })
   311  	return sortedFiles, nil
   312  }
   313  
   314  // OverlayPath returns the path to the overlaid contents of the
   315  // file, the empty string if the overlay deletes the file, or path
   316  // itself if the file is not in the overlay, the file is a directory
   317  // in the overlay, or there is no overlay.
   318  // It returns true if the path is overlaid with a regular file
   319  // or deleted, and false otherwise.
   320  func OverlayPath(path string) (string, bool) {
   321  	if p, ok := overlay[canonicalize(path)]; ok && !p.isDir() {
   322  		return p.actualFilePath, ok
   323  	}
   324  
   325  	return path, false
   326  }
   327  
   328  // Open opens the file at or overlaid on the given path.
   329  func Open(path string) (*os.File, error) {
   330  	return OpenFile(path, os.O_RDONLY, 0)
   331  }
   332  
   333  // OpenFile opens the file at or overlaid on the given path with the flag and perm.
   334  func OpenFile(path string, flag int, perm os.FileMode) (*os.File, error) {
   335  	cpath := canonicalize(path)
   336  	if node, ok := overlay[cpath]; ok {
   337  		// Opening a file in the overlay.
   338  		if node.isDir() {
   339  			return nil, &fs.PathError{Op: "OpenFile", Path: path, Err: errors.New("fsys.OpenFile doesn't support opening directories yet")}
   340  		}
   341  		// We can't open overlaid paths for write.
   342  		if perm != os.FileMode(os.O_RDONLY) {
   343  			return nil, &fs.PathError{Op: "OpenFile", Path: path, Err: errors.New("overlaid files can't be opened for write")}
   344  		}
   345  		return os.OpenFile(node.actualFilePath, flag, perm)
   346  	}
   347  	if parent, ok := parentIsOverlayFile(filepath.Dir(cpath)); ok {
   348  		// The file is deleted explicitly in the Replace map,
   349  		// or implicitly because one of its parent directories was
   350  		// replaced by a file.
   351  		return nil, &fs.PathError{
   352  			Op:   "Open",
   353  			Path: path,
   354  			Err:  fmt.Errorf("file %s does not exist: parent directory %s is replaced by a file in overlay", path, parent),
   355  		}
   356  	}
   357  	return os.OpenFile(cpath, flag, perm)
   358  }
   359  
   360  // IsDirWithGoFiles reports whether dir is a directory containing Go files
   361  // either on disk or in the overlay.
   362  func IsDirWithGoFiles(dir string) (bool, error) {
   363  	fis, err := ReadDir(dir)
   364  	if os.IsNotExist(err) || errors.Is(err, errNotDir) {
   365  		return false, nil
   366  	}
   367  	if err != nil {
   368  		return false, err
   369  	}
   370  
   371  	var firstErr error
   372  	for _, fi := range fis {
   373  		if fi.IsDir() {
   374  			continue
   375  		}
   376  
   377  		// TODO(matloob): this enforces that the "from" in the map
   378  		// has a .go suffix, but the actual destination file
   379  		// doesn't need to have a .go suffix. Is this okay with the
   380  		// compiler?
   381  		if !strings.HasSuffix(fi.Name(), ".go") {
   382  			continue
   383  		}
   384  		if fi.Mode().IsRegular() {
   385  			return true, nil
   386  		}
   387  
   388  		// fi is the result of an Lstat, so it doesn't follow symlinks.
   389  		// But it's okay if the file is a symlink pointing to a regular
   390  		// file, so use os.Stat to follow symlinks and check that.
   391  		actualFilePath, _ := OverlayPath(filepath.Join(dir, fi.Name()))
   392  		fi, err := os.Stat(actualFilePath)
   393  		if err == nil && fi.Mode().IsRegular() {
   394  			return true, nil
   395  		}
   396  		if err != nil && firstErr == nil {
   397  			firstErr = err
   398  		}
   399  	}
   400  
   401  	// No go files found in directory.
   402  	return false, firstErr
   403  }
   404  
   405  // walk recursively descends path, calling walkFn. Copied, with some
   406  // modifications from path/filepath.walk.
   407  func walk(path string, info fs.FileInfo, walkFn filepath.WalkFunc) error {
   408  	if !info.IsDir() {
   409  		return walkFn(path, info, nil)
   410  	}
   411  
   412  	fis, readErr := ReadDir(path)
   413  	walkErr := walkFn(path, info, readErr)
   414  	// If readErr != nil, walk can't walk into this directory.
   415  	// walkErr != nil means walkFn want walk to skip this directory or stop walking.
   416  	// Therefore, if one of readErr and walkErr isn't nil, walk will return.
   417  	if readErr != nil || walkErr != nil {
   418  		// The caller's behavior is controlled by the return value, which is decided
   419  		// by walkFn. walkFn may ignore readErr and return nil.
   420  		// If walkFn returns SkipDir, it will be handled by the caller.
   421  		// So walk should return whatever walkFn returns.
   422  		return walkErr
   423  	}
   424  
   425  	for _, fi := range fis {
   426  		filename := filepath.Join(path, fi.Name())
   427  		if walkErr = walk(filename, fi, walkFn); walkErr != nil {
   428  			if !fi.IsDir() || walkErr != filepath.SkipDir {
   429  				return walkErr
   430  			}
   431  		}
   432  	}
   433  	return nil
   434  }
   435  
   436  // Walk walks the file tree rooted at root, calling walkFn for each file or
   437  // directory in the tree, including root.
   438  func Walk(root string, walkFn filepath.WalkFunc) error {
   439  	info, err := Lstat(root)
   440  	if err != nil {
   441  		err = walkFn(root, nil, err)
   442  	} else {
   443  		err = walk(root, info, walkFn)
   444  	}
   445  	if err == filepath.SkipDir {
   446  		return nil
   447  	}
   448  	return err
   449  }
   450  
   451  // lstat implements a version of os.Lstat that operates on the overlay filesystem.
   452  func Lstat(path string) (fs.FileInfo, error) {
   453  	return overlayStat(path, os.Lstat, "lstat")
   454  }
   455  
   456  // Stat implements a version of os.Stat that operates on the overlay filesystem.
   457  func Stat(path string) (fs.FileInfo, error) {
   458  	return overlayStat(path, os.Stat, "stat")
   459  }
   460  
   461  // overlayStat implements lstat or Stat (depending on whether os.Lstat or os.Stat is passed in).
   462  func overlayStat(path string, osStat func(string) (fs.FileInfo, error), opName string) (fs.FileInfo, error) {
   463  	cpath := canonicalize(path)
   464  
   465  	if _, ok := parentIsOverlayFile(filepath.Dir(cpath)); ok {
   466  		return nil, &fs.PathError{Op: opName, Path: cpath, Err: fs.ErrNotExist}
   467  	}
   468  
   469  	node, ok := overlay[cpath]
   470  	if !ok {
   471  		// The file or directory is not overlaid.
   472  		return osStat(path)
   473  	}
   474  
   475  	switch {
   476  	case node.isDeleted():
   477  		return nil, &fs.PathError{Op: "lstat", Path: cpath, Err: fs.ErrNotExist}
   478  	case node.isDir():
   479  		return fakeDir(filepath.Base(path)), nil
   480  	default:
   481  		fi, err := osStat(node.actualFilePath)
   482  		if err != nil {
   483  			return nil, err
   484  		}
   485  		return fakeFile{name: filepath.Base(path), real: fi}, nil
   486  	}
   487  }
   488  
   489  // fakeFile provides an fs.FileInfo implementation for an overlaid file,
   490  // so that the file has the name of the overlaid file, but takes all
   491  // other characteristics of the replacement file.
   492  type fakeFile struct {
   493  	name string
   494  	real fs.FileInfo
   495  }
   496  
   497  func (f fakeFile) Name() string       { return f.name }
   498  func (f fakeFile) Size() int64        { return f.real.Size() }
   499  func (f fakeFile) Mode() fs.FileMode  { return f.real.Mode() }
   500  func (f fakeFile) ModTime() time.Time { return f.real.ModTime() }
   501  func (f fakeFile) IsDir() bool        { return f.real.IsDir() }
   502  func (f fakeFile) Sys() any           { return f.real.Sys() }
   503  
   504  // missingFile provides an fs.FileInfo for an overlaid file where the
   505  // destination file in the overlay doesn't exist. It returns zero values
   506  // for the fileInfo methods other than Name, set to the file's name, and Mode
   507  // set to ModeIrregular.
   508  type missingFile string
   509  
   510  func (f missingFile) Name() string       { return string(f) }
   511  func (f missingFile) Size() int64        { return 0 }
   512  func (f missingFile) Mode() fs.FileMode  { return fs.ModeIrregular }
   513  func (f missingFile) ModTime() time.Time { return time.Unix(0, 0) }
   514  func (f missingFile) IsDir() bool        { return false }
   515  func (f missingFile) Sys() any           { return nil }
   516  
   517  // fakeDir provides an fs.FileInfo implementation for directories that are
   518  // implicitly created by overlaid files. Each directory in the
   519  // path of an overlaid file is considered to exist in the overlay filesystem.
   520  type fakeDir string
   521  
   522  func (f fakeDir) Name() string       { return string(f) }
   523  func (f fakeDir) Size() int64        { return 0 }
   524  func (f fakeDir) Mode() fs.FileMode  { return fs.ModeDir | 0500 }
   525  func (f fakeDir) ModTime() time.Time { return time.Unix(0, 0) }
   526  func (f fakeDir) IsDir() bool        { return true }
   527  func (f fakeDir) Sys() any           { return nil }
   528  
   529  // Glob is like filepath.Glob but uses the overlay file system.
   530  func Glob(pattern string) (matches []string, err error) {
   531  	// Check pattern is well-formed.
   532  	if _, err := filepath.Match(pattern, ""); err != nil {
   533  		return nil, err
   534  	}
   535  	if !hasMeta(pattern) {
   536  		if _, err = Lstat(pattern); err != nil {
   537  			return nil, nil
   538  		}
   539  		return []string{pattern}, nil
   540  	}
   541  
   542  	dir, file := filepath.Split(pattern)
   543  	volumeLen := 0
   544  	if runtime.GOOS == "windows" {
   545  		volumeLen, dir = cleanGlobPathWindows(dir)
   546  	} else {
   547  		dir = cleanGlobPath(dir)
   548  	}
   549  
   550  	if !hasMeta(dir[volumeLen:]) {
   551  		return glob(dir, file, nil)
   552  	}
   553  
   554  	// Prevent infinite recursion. See issue 15879.
   555  	if dir == pattern {
   556  		return nil, filepath.ErrBadPattern
   557  	}
   558  
   559  	var m []string
   560  	m, err = Glob(dir)
   561  	if err != nil {
   562  		return
   563  	}
   564  	for _, d := range m {
   565  		matches, err = glob(d, file, matches)
   566  		if err != nil {
   567  			return
   568  		}
   569  	}
   570  	return
   571  }
   572  
   573  // cleanGlobPath prepares path for glob matching.
   574  func cleanGlobPath(path string) string {
   575  	switch path {
   576  	case "":
   577  		return "."
   578  	case string(filepath.Separator):
   579  		// do nothing to the path
   580  		return path
   581  	default:
   582  		return path[0 : len(path)-1] // chop off trailing separator
   583  	}
   584  }
   585  
   586  func volumeNameLen(path string) int {
   587  	isSlash := func(c uint8) bool {
   588  		return c == '\\' || c == '/'
   589  	}
   590  	if len(path) < 2 {
   591  		return 0
   592  	}
   593  	// with drive letter
   594  	c := path[0]
   595  	if path[1] == ':' && ('a' <= c && c <= 'z' || 'A' <= c && c <= 'Z') {
   596  		return 2
   597  	}
   598  	// is it UNC? https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx
   599  	if l := len(path); l >= 5 && isSlash(path[0]) && isSlash(path[1]) &&
   600  		!isSlash(path[2]) && path[2] != '.' {
   601  		// first, leading `\\` and next shouldn't be `\`. its server name.
   602  		for n := 3; n < l-1; n++ {
   603  			// second, next '\' shouldn't be repeated.
   604  			if isSlash(path[n]) {
   605  				n++
   606  				// third, following something characters. its share name.
   607  				if !isSlash(path[n]) {
   608  					if path[n] == '.' {
   609  						break
   610  					}
   611  					for ; n < l; n++ {
   612  						if isSlash(path[n]) {
   613  							break
   614  						}
   615  					}
   616  					return n
   617  				}
   618  				break
   619  			}
   620  		}
   621  	}
   622  	return 0
   623  }
   624  
   625  // cleanGlobPathWindows is windows version of cleanGlobPath.
   626  func cleanGlobPathWindows(path string) (prefixLen int, cleaned string) {
   627  	vollen := volumeNameLen(path)
   628  	switch {
   629  	case path == "":
   630  		return 0, "."
   631  	case vollen+1 == len(path) && os.IsPathSeparator(path[len(path)-1]): // /, \, C:\ and C:/
   632  		// do nothing to the path
   633  		return vollen + 1, path
   634  	case vollen == len(path) && len(path) == 2: // C:
   635  		return vollen, path + "." // convert C: into C:.
   636  	default:
   637  		if vollen >= len(path) {
   638  			vollen = len(path) - 1
   639  		}
   640  		return vollen, path[0 : len(path)-1] // chop off trailing separator
   641  	}
   642  }
   643  
   644  // glob searches for files matching pattern in the directory dir
   645  // and appends them to matches. If the directory cannot be
   646  // opened, it returns the existing matches. New matches are
   647  // added in lexicographical order.
   648  func glob(dir, pattern string, matches []string) (m []string, e error) {
   649  	m = matches
   650  	fi, err := Stat(dir)
   651  	if err != nil {
   652  		return // ignore I/O error
   653  	}
   654  	if !fi.IsDir() {
   655  		return // ignore I/O error
   656  	}
   657  
   658  	list, err := ReadDir(dir)
   659  	if err != nil {
   660  		return // ignore I/O error
   661  	}
   662  
   663  	var names []string
   664  	for _, info := range list {
   665  		names = append(names, info.Name())
   666  	}
   667  	sort.Strings(names)
   668  
   669  	for _, n := range names {
   670  		matched, err := filepath.Match(pattern, n)
   671  		if err != nil {
   672  			return m, err
   673  		}
   674  		if matched {
   675  			m = append(m, filepath.Join(dir, n))
   676  		}
   677  	}
   678  	return
   679  }
   680  
   681  // hasMeta reports whether path contains any of the magic characters
   682  // recognized by filepath.Match.
   683  func hasMeta(path string) bool {
   684  	magicChars := `*?[`
   685  	if runtime.GOOS != "windows" {
   686  		magicChars = `*?[\`
   687  	}
   688  	return strings.ContainsAny(path, magicChars)
   689  }
   690
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