Source file src/path/filepath/path.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 filepath implements utility routines for manipulating filename paths
     6  // in a way compatible with the target operating system-defined file paths.
     7  //
     8  // The filepath package uses either forward slashes or backslashes,
     9  // depending on the operating system. To process paths such as URLs
    10  // that always use forward slashes regardless of the operating
    11  // system, see the path package.
    12  package filepath
    13  
    14  import (
    15  	"errors"
    16  	"io/fs"
    17  	"os"
    18  	"sort"
    19  	"strings"
    20  )
    21  
    22  // A lazybuf is a lazily constructed path buffer.
    23  // It supports append, reading previously appended bytes,
    24  // and retrieving the final string. It does not allocate a buffer
    25  // to hold the output until that output diverges from s.
    26  type lazybuf struct {
    27  	path       string
    28  	buf        []byte
    29  	w          int
    30  	volAndPath string
    31  	volLen     int
    32  }
    33  
    34  func (b *lazybuf) index(i int) byte {
    35  	if b.buf != nil {
    36  		return b.buf[i]
    37  	}
    38  	return b.path[i]
    39  }
    40  
    41  func (b *lazybuf) append(c byte) {
    42  	if b.buf == nil {
    43  		if b.w < len(b.path) && b.path[b.w] == c {
    44  			b.w++
    45  			return
    46  		}
    47  		b.buf = make([]byte, len(b.path))
    48  		copy(b.buf, b.path[:b.w])
    49  	}
    50  	b.buf[b.w] = c
    51  	b.w++
    52  }
    53  
    54  func (b *lazybuf) string() string {
    55  	if b.buf == nil {
    56  		return b.volAndPath[:b.volLen+b.w]
    57  	}
    58  	return b.volAndPath[:b.volLen] + string(b.buf[:b.w])
    59  }
    60  
    61  const (
    62  	Separator     = os.PathSeparator
    63  	ListSeparator = os.PathListSeparator
    64  )
    65  
    66  // Clean returns the shortest path name equivalent to path
    67  // by purely lexical processing. It applies the following rules
    68  // iteratively until no further processing can be done:
    69  //
    70  //	1. Replace multiple Separator elements with a single one.
    71  //	2. Eliminate each . path name element (the current directory).
    72  //	3. Eliminate each inner .. path name element (the parent directory)
    73  //	   along with the non-.. element that precedes it.
    74  //	4. Eliminate .. elements that begin a rooted path:
    75  //	   that is, replace "/.." by "/" at the beginning of a path,
    76  //	   assuming Separator is '/'.
    77  //
    78  // The returned path ends in a slash only if it represents a root directory,
    79  // such as "/" on Unix or `C:\` on Windows.
    80  //
    81  // Finally, any occurrences of slash are replaced by Separator.
    82  //
    83  // If the result of this process is an empty string, Clean
    84  // returns the string ".".
    85  //
    86  // See also Rob Pike, ``Lexical File Names in Plan 9 or
    87  // Getting Dot-Dot Right,''
    88  // https://9p.io/sys/doc/lexnames.html
    89  func Clean(path string) string {
    90  	originalPath := path
    91  	volLen := volumeNameLen(path)
    92  	path = path[volLen:]
    93  	if path == "" {
    94  		if volLen > 1 && originalPath[1] != ':' {
    95  			// should be UNC
    96  			return FromSlash(originalPath)
    97  		}
    98  		return originalPath + "."
    99  	}
   100  	rooted := os.IsPathSeparator(path[0])
   101  
   102  	// Invariants:
   103  	//	reading from path; r is index of next byte to process.
   104  	//	writing to buf; w is index of next byte to write.
   105  	//	dotdot is index in buf where .. must stop, either because
   106  	//		it is the leading slash or it is a leading ../../.. prefix.
   107  	n := len(path)
   108  	out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen}
   109  	r, dotdot := 0, 0
   110  	if rooted {
   111  		out.append(Separator)
   112  		r, dotdot = 1, 1
   113  	}
   114  
   115  	for r < n {
   116  		switch {
   117  		case os.IsPathSeparator(path[r]):
   118  			// empty path element
   119  			r++
   120  		case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
   121  			// . element
   122  			r++
   123  		case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
   124  			// .. element: remove to last separator
   125  			r += 2
   126  			switch {
   127  			case out.w > dotdot:
   128  				// can backtrack
   129  				out.w--
   130  				for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) {
   131  					out.w--
   132  				}
   133  			case !rooted:
   134  				// cannot backtrack, but not rooted, so append .. element.
   135  				if out.w > 0 {
   136  					out.append(Separator)
   137  				}
   138  				out.append('.')
   139  				out.append('.')
   140  				dotdot = out.w
   141  			}
   142  		default:
   143  			// real path element.
   144  			// add slash if needed
   145  			if rooted && out.w != 1 || !rooted && out.w != 0 {
   146  				out.append(Separator)
   147  			}
   148  			// copy element
   149  			for ; r < n && !os.IsPathSeparator(path[r]); r++ {
   150  				out.append(path[r])
   151  			}
   152  		}
   153  	}
   154  
   155  	// Turn empty string into "."
   156  	if out.w == 0 {
   157  		out.append('.')
   158  	}
   159  
   160  	return FromSlash(out.string())
   161  }
   162  
   163  // ToSlash returns the result of replacing each separator character
   164  // in path with a slash ('/') character. Multiple separators are
   165  // replaced by multiple slashes.
   166  func ToSlash(path string) string {
   167  	if Separator == '/' {
   168  		return path
   169  	}
   170  	return strings.ReplaceAll(path, string(Separator), "/")
   171  }
   172  
   173  // FromSlash returns the result of replacing each slash ('/') character
   174  // in path with a separator character. Multiple slashes are replaced
   175  // by multiple separators.
   176  func FromSlash(path string) string {
   177  	if Separator == '/' {
   178  		return path
   179  	}
   180  	return strings.ReplaceAll(path, "/", string(Separator))
   181  }
   182  
   183  // SplitList splits a list of paths joined by the OS-specific ListSeparator,
   184  // usually found in PATH or GOPATH environment variables.
   185  // Unlike strings.Split, SplitList returns an empty slice when passed an empty
   186  // string.
   187  func SplitList(path string) []string {
   188  	return splitList(path)
   189  }
   190  
   191  // Split splits path immediately following the final Separator,
   192  // separating it into a directory and file name component.
   193  // If there is no Separator in path, Split returns an empty dir
   194  // and file set to path.
   195  // The returned values have the property that path = dir+file.
   196  func Split(path string) (dir, file string) {
   197  	vol := VolumeName(path)
   198  	i := len(path) - 1
   199  	for i >= len(vol) && !os.IsPathSeparator(path[i]) {
   200  		i--
   201  	}
   202  	return path[:i+1], path[i+1:]
   203  }
   204  
   205  // Join joins any number of path elements into a single path,
   206  // separating them with an OS specific Separator. Empty elements
   207  // are ignored. The result is Cleaned. However, if the argument
   208  // list is empty or all its elements are empty, Join returns
   209  // an empty string.
   210  // On Windows, the result will only be a UNC path if the first
   211  // non-empty element is a UNC path.
   212  func Join(elem ...string) string {
   213  	return join(elem)
   214  }
   215  
   216  // Ext returns the file name extension used by path.
   217  // The extension is the suffix beginning at the final dot
   218  // in the final element of path; it is empty if there is
   219  // no dot.
   220  func Ext(path string) string {
   221  	for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- {
   222  		if path[i] == '.' {
   223  			return path[i:]
   224  		}
   225  	}
   226  	return ""
   227  }
   228  
   229  // EvalSymlinks returns the path name after the evaluation of any symbolic
   230  // links.
   231  // If path is relative the result will be relative to the current directory,
   232  // unless one of the components is an absolute symbolic link.
   233  // EvalSymlinks calls Clean on the result.
   234  func EvalSymlinks(path string) (string, error) {
   235  	return evalSymlinks(path)
   236  }
   237  
   238  // Abs returns an absolute representation of path.
   239  // If the path is not absolute it will be joined with the current
   240  // working directory to turn it into an absolute path. The absolute
   241  // path name for a given file is not guaranteed to be unique.
   242  // Abs calls Clean on the result.
   243  func Abs(path string) (string, error) {
   244  	return abs(path)
   245  }
   246  
   247  func unixAbs(path string) (string, error) {
   248  	if IsAbs(path) {
   249  		return Clean(path), nil
   250  	}
   251  	wd, err := os.Getwd()
   252  	if err != nil {
   253  		return "", err
   254  	}
   255  	return Join(wd, path), nil
   256  }
   257  
   258  // Rel returns a relative path that is lexically equivalent to targpath when
   259  // joined to basepath with an intervening separator. That is,
   260  // Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
   261  // On success, the returned path will always be relative to basepath,
   262  // even if basepath and targpath share no elements.
   263  // An error is returned if targpath can't be made relative to basepath or if
   264  // knowing the current working directory would be necessary to compute it.
   265  // Rel calls Clean on the result.
   266  func Rel(basepath, targpath string) (string, error) {
   267  	baseVol := VolumeName(basepath)
   268  	targVol := VolumeName(targpath)
   269  	base := Clean(basepath)
   270  	targ := Clean(targpath)
   271  	if sameWord(targ, base) {
   272  		return ".", nil
   273  	}
   274  	base = base[len(baseVol):]
   275  	targ = targ[len(targVol):]
   276  	if base == "." {
   277  		base = ""
   278  	} else if base == "" && volumeNameLen(baseVol) > 2 /* isUNC */ {
   279  		// Treat any targetpath matching `\\host\share` basepath as absolute path.
   280  		base = string(Separator)
   281  	}
   282  
   283  	// Can't use IsAbs - `\a` and `a` are both relative in Windows.
   284  	baseSlashed := len(base) > 0 && base[0] == Separator
   285  	targSlashed := len(targ) > 0 && targ[0] == Separator
   286  	if baseSlashed != targSlashed || !sameWord(baseVol, targVol) {
   287  		return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
   288  	}
   289  	// Position base[b0:bi] and targ[t0:ti] at the first differing elements.
   290  	bl := len(base)
   291  	tl := len(targ)
   292  	var b0, bi, t0, ti int
   293  	for {
   294  		for bi < bl && base[bi] != Separator {
   295  			bi++
   296  		}
   297  		for ti < tl && targ[ti] != Separator {
   298  			ti++
   299  		}
   300  		if !sameWord(targ[t0:ti], base[b0:bi]) {
   301  			break
   302  		}
   303  		if bi < bl {
   304  			bi++
   305  		}
   306  		if ti < tl {
   307  			ti++
   308  		}
   309  		b0 = bi
   310  		t0 = ti
   311  	}
   312  	if base[b0:bi] == ".." {
   313  		return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
   314  	}
   315  	if b0 != bl {
   316  		// Base elements left. Must go up before going down.
   317  		seps := strings.Count(base[b0:bl], string(Separator))
   318  		size := 2 + seps*3
   319  		if tl != t0 {
   320  			size += 1 + tl - t0
   321  		}
   322  		buf := make([]byte, size)
   323  		n := copy(buf, "..")
   324  		for i := 0; i < seps; i++ {
   325  			buf[n] = Separator
   326  			copy(buf[n+1:], "..")
   327  			n += 3
   328  		}
   329  		if t0 != tl {
   330  			buf[n] = Separator
   331  			copy(buf[n+1:], targ[t0:])
   332  		}
   333  		return string(buf), nil
   334  	}
   335  	return targ[t0:], nil
   336  }
   337  
   338  // SkipDir is used as a return value from WalkFuncs to indicate that
   339  // the directory named in the call is to be skipped. It is not returned
   340  // as an error by any function.
   341  var SkipDir error = fs.SkipDir
   342  
   343  // WalkFunc is the type of the function called by Walk to visit each
   344  // file or directory.
   345  //
   346  // The path argument contains the argument to Walk as a prefix.
   347  // That is, if Walk is called with root argument "dir" and finds a file
   348  // named "a" in that directory, the walk function will be called with
   349  // argument "dir/a".
   350  //
   351  // The directory and file are joined with Join, which may clean the
   352  // directory name: if Walk is called with the root argument "x/../dir"
   353  // and finds a file named "a" in that directory, the walk function will
   354  // be called with argument "dir/a", not "x/../dir/a".
   355  //
   356  // The info argument is the fs.FileInfo for the named path.
   357  //
   358  // The error result returned by the function controls how Walk continues.
   359  // If the function returns the special value SkipDir, Walk skips the
   360  // current directory (path if info.IsDir() is true, otherwise path's
   361  // parent directory). Otherwise, if the function returns a non-nil error,
   362  // Walk stops entirely and returns that error.
   363  //
   364  // The err argument reports an error related to path, signaling that Walk
   365  // will not walk into that directory. The function can decide how to
   366  // handle that error; as described earlier, returning the error will
   367  // cause Walk to stop walking the entire tree.
   368  //
   369  // Walk calls the function with a non-nil err argument in two cases.
   370  //
   371  // First, if an os.Lstat on the root directory or any directory or file
   372  // in the tree fails, Walk calls the function with path set to that
   373  // directory or file's path, info set to nil, and err set to the error
   374  // from os.Lstat.
   375  //
   376  // Second, if a directory's Readdirnames method fails, Walk calls the
   377  // function with path set to the directory's path, info, set to an
   378  // fs.FileInfo describing the directory, and err set to the error from
   379  // Readdirnames.
   380  type WalkFunc func(path string, info fs.FileInfo, err error) error
   381  
   382  var lstat = os.Lstat // for testing
   383  
   384  // walkDir recursively descends path, calling walkDirFn.
   385  func walkDir(path string, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error {
   386  	if err := walkDirFn(path, d, nil); err != nil || !d.IsDir() {
   387  		if err == SkipDir && d.IsDir() {
   388  			// Successfully skipped directory.
   389  			err = nil
   390  		}
   391  		return err
   392  	}
   393  
   394  	dirs, err := readDir(path)
   395  	if err != nil {
   396  		// Second call, to report ReadDir error.
   397  		err = walkDirFn(path, d, err)
   398  		if err != nil {
   399  			return err
   400  		}
   401  	}
   402  
   403  	for _, d1 := range dirs {
   404  		path1 := Join(path, d1.Name())
   405  		if err := walkDir(path1, d1, walkDirFn); err != nil {
   406  			if err == SkipDir {
   407  				break
   408  			}
   409  			return err
   410  		}
   411  	}
   412  	return nil
   413  }
   414  
   415  // walk recursively descends path, calling walkFn.
   416  func walk(path string, info fs.FileInfo, walkFn WalkFunc) error {
   417  	if !info.IsDir() {
   418  		return walkFn(path, info, nil)
   419  	}
   420  
   421  	names, err := readDirNames(path)
   422  	err1 := walkFn(path, info, err)
   423  	// If err != nil, walk can't walk into this directory.
   424  	// err1 != nil means walkFn want walk to skip this directory or stop walking.
   425  	// Therefore, if one of err and err1 isn't nil, walk will return.
   426  	if err != nil || err1 != nil {
   427  		// The caller's behavior is controlled by the return value, which is decided
   428  		// by walkFn. walkFn may ignore err and return nil.
   429  		// If walkFn returns SkipDir, it will be handled by the caller.
   430  		// So walk should return whatever walkFn returns.
   431  		return err1
   432  	}
   433  
   434  	for _, name := range names {
   435  		filename := Join(path, name)
   436  		fileInfo, err := lstat(filename)
   437  		if err != nil {
   438  			if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
   439  				return err
   440  			}
   441  		} else {
   442  			err = walk(filename, fileInfo, walkFn)
   443  			if err != nil {
   444  				if !fileInfo.IsDir() || err != SkipDir {
   445  					return err
   446  				}
   447  			}
   448  		}
   449  	}
   450  	return nil
   451  }
   452  
   453  // WalkDir walks the file tree rooted at root, calling fn for each file or
   454  // directory in the tree, including root.
   455  //
   456  // All errors that arise visiting files and directories are filtered by fn:
   457  // see the fs.WalkDirFunc documentation for details.
   458  //
   459  // The files are walked in lexical order, which makes the output deterministic
   460  // but requires WalkDir to read an entire directory into memory before proceeding
   461  // to walk that directory.
   462  //
   463  // WalkDir does not follow symbolic links.
   464  func WalkDir(root string, fn fs.WalkDirFunc) error {
   465  	info, err := os.Lstat(root)
   466  	if err != nil {
   467  		err = fn(root, nil, err)
   468  	} else {
   469  		err = walkDir(root, &statDirEntry{info}, fn)
   470  	}
   471  	if err == SkipDir {
   472  		return nil
   473  	}
   474  	return err
   475  }
   476  
   477  type statDirEntry struct {
   478  	info fs.FileInfo
   479  }
   480  
   481  func (d *statDirEntry) Name() string               { return d.info.Name() }
   482  func (d *statDirEntry) IsDir() bool                { return d.info.IsDir() }
   483  func (d *statDirEntry) Type() fs.FileMode          { return d.info.Mode().Type() }
   484  func (d *statDirEntry) Info() (fs.FileInfo, error) { return d.info, nil }
   485  
   486  // Walk walks the file tree rooted at root, calling fn for each file or
   487  // directory in the tree, including root.
   488  //
   489  // All errors that arise visiting files and directories are filtered by fn:
   490  // see the WalkFunc documentation for details.
   491  //
   492  // The files are walked in lexical order, which makes the output deterministic
   493  // but requires Walk to read an entire directory into memory before proceeding
   494  // to walk that directory.
   495  //
   496  // Walk does not follow symbolic links.
   497  //
   498  // Walk is less efficient than WalkDir, introduced in Go 1.16,
   499  // which avoids calling os.Lstat on every visited file or directory.
   500  func Walk(root string, fn WalkFunc) error {
   501  	info, err := os.Lstat(root)
   502  	if err != nil {
   503  		err = fn(root, nil, err)
   504  	} else {
   505  		err = walk(root, info, fn)
   506  	}
   507  	if err == SkipDir {
   508  		return nil
   509  	}
   510  	return err
   511  }
   512  
   513  // readDir reads the directory named by dirname and returns
   514  // a sorted list of directory entries.
   515  func readDir(dirname string) ([]fs.DirEntry, error) {
   516  	f, err := os.Open(dirname)
   517  	if err != nil {
   518  		return nil, err
   519  	}
   520  	dirs, err := f.ReadDir(-1)
   521  	f.Close()
   522  	if err != nil {
   523  		return nil, err
   524  	}
   525  	sort.Slice(dirs, func(i, j int) bool { return dirs[i].Name() < dirs[j].Name() })
   526  	return dirs, nil
   527  }
   528  
   529  // readDirNames reads the directory named by dirname and returns
   530  // a sorted list of directory entry names.
   531  func readDirNames(dirname string) ([]string, error) {
   532  	f, err := os.Open(dirname)
   533  	if err != nil {
   534  		return nil, err
   535  	}
   536  	names, err := f.Readdirnames(-1)
   537  	f.Close()
   538  	if err != nil {
   539  		return nil, err
   540  	}
   541  	sort.Strings(names)
   542  	return names, nil
   543  }
   544  
   545  // Base returns the last element of path.
   546  // Trailing path separators are removed before extracting the last element.
   547  // If the path is empty, Base returns ".".
   548  // If the path consists entirely of separators, Base returns a single separator.
   549  func Base(path string) string {
   550  	if path == "" {
   551  		return "."
   552  	}
   553  	// Strip trailing slashes.
   554  	for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) {
   555  		path = path[0 : len(path)-1]
   556  	}
   557  	// Throw away volume name
   558  	path = path[len(VolumeName(path)):]
   559  	// Find the last element
   560  	i := len(path) - 1
   561  	for i >= 0 && !os.IsPathSeparator(path[i]) {
   562  		i--
   563  	}
   564  	if i >= 0 {
   565  		path = path[i+1:]
   566  	}
   567  	// If empty now, it had only slashes.
   568  	if path == "" {
   569  		return string(Separator)
   570  	}
   571  	return path
   572  }
   573  
   574  // Dir returns all but the last element of path, typically the path's directory.
   575  // After dropping the final element, Dir calls Clean on the path and trailing
   576  // slashes are removed.
   577  // If the path is empty, Dir returns ".".
   578  // If the path consists entirely of separators, Dir returns a single separator.
   579  // The returned path does not end in a separator unless it is the root directory.
   580  func Dir(path string) string {
   581  	vol := VolumeName(path)
   582  	i := len(path) - 1
   583  	for i >= len(vol) && !os.IsPathSeparator(path[i]) {
   584  		i--
   585  	}
   586  	dir := Clean(path[len(vol) : i+1])
   587  	if dir == "." && len(vol) > 2 {
   588  		// must be UNC
   589  		return vol
   590  	}
   591  	return vol + dir
   592  }
   593  
   594  // VolumeName returns leading volume name.
   595  // Given "C:\foo\bar" it returns "C:" on Windows.
   596  // Given "\\host\share\foo" it returns "\\host\share".
   597  // On other platforms it returns "".
   598  func VolumeName(path string) string {
   599  	return path[:volumeNameLen(path)]
   600  }
   601  

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