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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	package filepath
     8	
     9	import (
    10		"errors"
    11		"os"
    12		"sort"
    13		"strings"
    14	)
    15	
    16	// A lazybuf is a lazily constructed path buffer.
    17	// It supports append, reading previously appended bytes,
    18	// and retrieving the final string. It does not allocate a buffer
    19	// to hold the output until that output diverges from s.
    20	type lazybuf struct {
    21		path       string
    22		buf        []byte
    23		w          int
    24		volAndPath string
    25		volLen     int
    26	}
    27	
    28	func (b *lazybuf) index(i int) byte {
    29		if b.buf != nil {
    30			return b.buf[i]
    31		}
    32		return b.path[i]
    33	}
    34	
    35	func (b *lazybuf) append(c byte) {
    36		if b.buf == nil {
    37			if b.w < len(b.path) && b.path[b.w] == c {
    38				b.w++
    39				return
    40			}
    41			b.buf = make([]byte, len(b.path))
    42			copy(b.buf, b.path[:b.w])
    43		}
    44		b.buf[b.w] = c
    45		b.w++
    46	}
    47	
    48	func (b *lazybuf) string() string {
    49		if b.buf == nil {
    50			return b.volAndPath[:b.volLen+b.w]
    51		}
    52		return b.volAndPath[:b.volLen] + string(b.buf[:b.w])
    53	}
    54	
    55	const (
    56		Separator     = os.PathSeparator
    57		ListSeparator = os.PathListSeparator
    58	)
    59	
    60	// Clean returns the shortest path name equivalent to path
    61	// by purely lexical processing. It applies the following rules
    62	// iteratively until no further processing can be done:
    63	//
    64	//	1. Replace multiple Separator elements with a single one.
    65	//	2. Eliminate each . path name element (the current directory).
    66	//	3. Eliminate each inner .. path name element (the parent directory)
    67	//	   along with the non-.. element that precedes it.
    68	//	4. Eliminate .. elements that begin a rooted path:
    69	//	   that is, replace "/.." by "/" at the beginning of a path,
    70	//	   assuming Separator is '/'.
    71	//
    72	// The returned path ends in a slash only if it represents a root directory,
    73	// such as "/" on Unix or `C:\` on Windows.
    74	//
    75	// Finally, any occurrences of slash are replaced by Separator.
    76	//
    77	// If the result of this process is an empty string, Clean
    78	// returns the string ".".
    79	//
    80	// See also Rob Pike, ``Lexical File Names in Plan 9 or
    81	// Getting Dot-Dot Right,''
    82	// https://9p.io/sys/doc/lexnames.html
    83	func Clean(path string) string {
    84		originalPath := path
    85		volLen := volumeNameLen(path)
    86		path = path[volLen:]
    87		if path == "" {
    88			if volLen > 1 && originalPath[1] != ':' {
    89				// should be UNC
    90				return FromSlash(originalPath)
    91			}
    92			return originalPath + "."
    93		}
    94		rooted := os.IsPathSeparator(path[0])
    95	
    96		// Invariants:
    97		//	reading from path; r is index of next byte to process.
    98		//	writing to buf; w is index of next byte to write.
    99		//	dotdot is index in buf where .. must stop, either because
   100		//		it is the leading slash or it is a leading ../../.. prefix.
   101		n := len(path)
   102		out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen}
   103		r, dotdot := 0, 0
   104		if rooted {
   105			out.append(Separator)
   106			r, dotdot = 1, 1
   107		}
   108	
   109		for r < n {
   110			switch {
   111			case os.IsPathSeparator(path[r]):
   112				// empty path element
   113				r++
   114			case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
   115				// . element
   116				r++
   117			case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
   118				// .. element: remove to last separator
   119				r += 2
   120				switch {
   121				case out.w > dotdot:
   122					// can backtrack
   123					out.w--
   124					for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) {
   125						out.w--
   126					}
   127				case !rooted:
   128					// cannot backtrack, but not rooted, so append .. element.
   129					if out.w > 0 {
   130						out.append(Separator)
   131					}
   132					out.append('.')
   133					out.append('.')
   134					dotdot = out.w
   135				}
   136			default:
   137				// real path element.
   138				// add slash if needed
   139				if rooted && out.w != 1 || !rooted && out.w != 0 {
   140					out.append(Separator)
   141				}
   142				// copy element
   143				for ; r < n && !os.IsPathSeparator(path[r]); r++ {
   144					out.append(path[r])
   145				}
   146			}
   147		}
   148	
   149		// Turn empty string into "."
   150		if out.w == 0 {
   151			out.append('.')
   152		}
   153	
   154		return FromSlash(out.string())
   155	}
   156	
   157	// ToSlash returns the result of replacing each separator character
   158	// in path with a slash ('/') character. Multiple separators are
   159	// replaced by multiple slashes.
   160	func ToSlash(path string) string {
   161		if Separator == '/' {
   162			return path
   163		}
   164		return strings.Replace(path, string(Separator), "/", -1)
   165	}
   166	
   167	// FromSlash returns the result of replacing each slash ('/') character
   168	// in path with a separator character. Multiple slashes are replaced
   169	// by multiple separators.
   170	func FromSlash(path string) string {
   171		if Separator == '/' {
   172			return path
   173		}
   174		return strings.Replace(path, "/", string(Separator), -1)
   175	}
   176	
   177	// SplitList splits a list of paths joined by the OS-specific ListSeparator,
   178	// usually found in PATH or GOPATH environment variables.
   179	// Unlike strings.Split, SplitList returns an empty slice when passed an empty
   180	// string. SplitList does not replace slash characters in the returned paths.
   181	func SplitList(path string) []string {
   182		return splitList(path)
   183	}
   184	
   185	// Split splits path immediately following the final Separator,
   186	// separating it into a directory and file name component.
   187	// If there is no Separator in path, Split returns an empty dir
   188	// and file set to path.
   189	// The returned values have the property that path = dir+file.
   190	func Split(path string) (dir, file string) {
   191		vol := VolumeName(path)
   192		i := len(path) - 1
   193		for i >= len(vol) && !os.IsPathSeparator(path[i]) {
   194			i--
   195		}
   196		return path[:i+1], path[i+1:]
   197	}
   198	
   199	// Join joins any number of path elements into a single path, adding
   200	// a Separator if necessary. Join calls Clean on the result; in particular,
   201	// all empty strings are ignored.
   202	// On Windows, the result is a UNC path if and only if the first path
   203	// element is a UNC path.
   204	func Join(elem ...string) string {
   205		return join(elem)
   206	}
   207	
   208	// Ext returns the file name extension used by path.
   209	// The extension is the suffix beginning at the final dot
   210	// in the final element of path; it is empty if there is
   211	// no dot.
   212	func Ext(path string) string {
   213		for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- {
   214			if path[i] == '.' {
   215				return path[i:]
   216			}
   217		}
   218		return ""
   219	}
   220	
   221	// EvalSymlinks returns the path name after the evaluation of any symbolic
   222	// links.
   223	// If path is relative the result will be relative to the current directory,
   224	// unless one of the components is an absolute symbolic link.
   225	// EvalSymlinks calls Clean on the result.
   226	func EvalSymlinks(path string) (string, error) {
   227		return evalSymlinks(path)
   228	}
   229	
   230	// Abs returns an absolute representation of path.
   231	// If the path is not absolute it will be joined with the current
   232	// working directory to turn it into an absolute path. The absolute
   233	// path name for a given file is not guaranteed to be unique.
   234	// Abs calls Clean on the result.
   235	func Abs(path string) (string, error) {
   236		return abs(path)
   237	}
   238	
   239	func unixAbs(path string) (string, error) {
   240		if IsAbs(path) {
   241			return Clean(path), nil
   242		}
   243		wd, err := os.Getwd()
   244		if err != nil {
   245			return "", err
   246		}
   247		return Join(wd, path), nil
   248	}
   249	
   250	// Rel returns a relative path that is lexically equivalent to targpath when
   251	// joined to basepath with an intervening separator. That is,
   252	// Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
   253	// On success, the returned path will always be relative to basepath,
   254	// even if basepath and targpath share no elements.
   255	// An error is returned if targpath can't be made relative to basepath or if
   256	// knowing the current working directory would be necessary to compute it.
   257	// Rel calls Clean on the result.
   258	func Rel(basepath, targpath string) (string, error) {
   259		baseVol := VolumeName(basepath)
   260		targVol := VolumeName(targpath)
   261		base := Clean(basepath)
   262		targ := Clean(targpath)
   263		if sameWord(targ, base) {
   264			return ".", nil
   265		}
   266		base = base[len(baseVol):]
   267		targ = targ[len(targVol):]
   268		if base == "." {
   269			base = ""
   270		}
   271		// Can't use IsAbs - `\a` and `a` are both relative in Windows.
   272		baseSlashed := len(base) > 0 && base[0] == Separator
   273		targSlashed := len(targ) > 0 && targ[0] == Separator
   274		if baseSlashed != targSlashed || !sameWord(baseVol, targVol) {
   275			return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
   276		}
   277		// Position base[b0:bi] and targ[t0:ti] at the first differing elements.
   278		bl := len(base)
   279		tl := len(targ)
   280		var b0, bi, t0, ti int
   281		for {
   282			for bi < bl && base[bi] != Separator {
   283				bi++
   284			}
   285			for ti < tl && targ[ti] != Separator {
   286				ti++
   287			}
   288			if !sameWord(targ[t0:ti], base[b0:bi]) {
   289				break
   290			}
   291			if bi < bl {
   292				bi++
   293			}
   294			if ti < tl {
   295				ti++
   296			}
   297			b0 = bi
   298			t0 = ti
   299		}
   300		if base[b0:bi] == ".." {
   301			return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath)
   302		}
   303		if b0 != bl {
   304			// Base elements left. Must go up before going down.
   305			seps := strings.Count(base[b0:bl], string(Separator))
   306			size := 2 + seps*3
   307			if tl != t0 {
   308				size += 1 + tl - t0
   309			}
   310			buf := make([]byte, size)
   311			n := copy(buf, "..")
   312			for i := 0; i < seps; i++ {
   313				buf[n] = Separator
   314				copy(buf[n+1:], "..")
   315				n += 3
   316			}
   317			if t0 != tl {
   318				buf[n] = Separator
   319				copy(buf[n+1:], targ[t0:])
   320			}
   321			return string(buf), nil
   322		}
   323		return targ[t0:], nil
   324	}
   325	
   326	// SkipDir is used as a return value from WalkFuncs to indicate that
   327	// the directory named in the call is to be skipped. It is not returned
   328	// as an error by any function.
   329	var SkipDir = errors.New("skip this directory")
   330	
   331	// WalkFunc is the type of the function called for each file or directory
   332	// visited by Walk. The path argument contains the argument to Walk as a
   333	// prefix; that is, if Walk is called with "dir", which is a directory
   334	// containing the file "a", the walk function will be called with argument
   335	// "dir/a". The info argument is the os.FileInfo for the named path.
   336	//
   337	// If there was a problem walking to the file or directory named by path, the
   338	// incoming error will describe the problem and the function can decide how
   339	// to handle that error (and Walk will not descend into that directory). If
   340	// an error is returned, processing stops. The sole exception is when the function
   341	// returns the special value SkipDir. If the function returns SkipDir when invoked
   342	// on a directory, Walk skips the directory's contents entirely.
   343	// If the function returns SkipDir when invoked on a non-directory file,
   344	// Walk skips the remaining files in the containing directory.
   345	type WalkFunc func(path string, info os.FileInfo, err error) error
   346	
   347	var lstat = os.Lstat // for testing
   348	
   349	// walk recursively descends path, calling w.
   350	func walk(path string, info os.FileInfo, walkFn WalkFunc) error {
   351		err := walkFn(path, info, nil)
   352		if err != nil {
   353			if info.IsDir() && err == SkipDir {
   354				return nil
   355			}
   356			return err
   357		}
   358	
   359		if !info.IsDir() {
   360			return nil
   361		}
   362	
   363		names, err := readDirNames(path)
   364		if err != nil {
   365			return walkFn(path, info, err)
   366		}
   367	
   368		for _, name := range names {
   369			filename := Join(path, name)
   370			fileInfo, err := lstat(filename)
   371			if err != nil {
   372				if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
   373					return err
   374				}
   375			} else {
   376				err = walk(filename, fileInfo, walkFn)
   377				if err != nil {
   378					if !fileInfo.IsDir() || err != SkipDir {
   379						return err
   380					}
   381				}
   382			}
   383		}
   384		return nil
   385	}
   386	
   387	// Walk walks the file tree rooted at root, calling walkFn for each file or
   388	// directory in the tree, including root. All errors that arise visiting files
   389	// and directories are filtered by walkFn. The files are walked in lexical
   390	// order, which makes the output deterministic but means that for very
   391	// large directories Walk can be inefficient.
   392	// Walk does not follow symbolic links.
   393	func Walk(root string, walkFn WalkFunc) error {
   394		info, err := os.Lstat(root)
   395		if err != nil {
   396			return walkFn(root, nil, err)
   397		}
   398		return walk(root, info, walkFn)
   399	}
   400	
   401	// readDirNames reads the directory named by dirname and returns
   402	// a sorted list of directory entries.
   403	func readDirNames(dirname string) ([]string, error) {
   404		f, err := os.Open(dirname)
   405		if err != nil {
   406			return nil, err
   407		}
   408		names, err := f.Readdirnames(-1)
   409		f.Close()
   410		if err != nil {
   411			return nil, err
   412		}
   413		sort.Strings(names)
   414		return names, nil
   415	}
   416	
   417	// Base returns the last element of path.
   418	// Trailing path separators are removed before extracting the last element.
   419	// If the path is empty, Base returns ".".
   420	// If the path consists entirely of separators, Base returns a single separator.
   421	func Base(path string) string {
   422		if path == "" {
   423			return "."
   424		}
   425		// Strip trailing slashes.
   426		for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) {
   427			path = path[0 : len(path)-1]
   428		}
   429		// Throw away volume name
   430		path = path[len(VolumeName(path)):]
   431		// Find the last element
   432		i := len(path) - 1
   433		for i >= 0 && !os.IsPathSeparator(path[i]) {
   434			i--
   435		}
   436		if i >= 0 {
   437			path = path[i+1:]
   438		}
   439		// If empty now, it had only slashes.
   440		if path == "" {
   441			return string(Separator)
   442		}
   443		return path
   444	}
   445	
   446	// Dir returns all but the last element of path, typically the path's directory.
   447	// After dropping the final element, Dir calls Clean on the path and trailing
   448	// slashes are removed.
   449	// If the path is empty, Dir returns ".".
   450	// If the path consists entirely of separators, Dir returns a single separator.
   451	// The returned path does not end in a separator unless it is the root directory.
   452	func Dir(path string) string {
   453		vol := VolumeName(path)
   454		i := len(path) - 1
   455		for i >= len(vol) && !os.IsPathSeparator(path[i]) {
   456			i--
   457		}
   458		dir := Clean(path[len(vol) : i+1])
   459		return vol + dir
   460	}
   461	
   462	// VolumeName returns leading volume name.
   463	// Given "C:\foo\bar" it returns "C:" on Windows.
   464	// Given "\\host\share\foo" it returns "\\host\share".
   465	// On other platforms it returns "".
   466	func VolumeName(path string) string {
   467		return path[:volumeNameLen(path)]
   468	}
   469	

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