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Source file src/pkg/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	// If the result of this process is an empty string, Clean
    76	// returns the string ".".
    77	//
    78	// See also Rob Pike, ``Lexical File Names in Plan 9 or
    79	// Getting Dot-Dot Right,''
    80	// http://plan9.bell-labs.com/sys/doc/lexnames.html
    81	func Clean(path string) string {
    82		originalPath := path
    83		volLen := volumeNameLen(path)
    84		path = path[volLen:]
    85		if path == "" {
    86			if volLen > 1 && originalPath[1] != ':' {
    87				// should be UNC
    88				return FromSlash(originalPath)
    89			}
    90			return originalPath + "."
    91		}
    92		rooted := os.IsPathSeparator(path[0])
    93	
    94		// Invariants:
    95		//	reading from path; r is index of next byte to process.
    96		//	writing to buf; w is index of next byte to write.
    97		//	dotdot is index in buf where .. must stop, either because
    98		//		it is the leading slash or it is a leading ../../.. prefix.
    99		n := len(path)
   100		out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen}
   101		r, dotdot := 0, 0
   102		if rooted {
   103			out.append(Separator)
   104			r, dotdot = 1, 1
   105		}
   106	
   107		for r < n {
   108			switch {
   109			case os.IsPathSeparator(path[r]):
   110				// empty path element
   111				r++
   112			case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
   113				// . element
   114				r++
   115			case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
   116				// .. element: remove to last separator
   117				r += 2
   118				switch {
   119				case out.w > dotdot:
   120					// can backtrack
   121					out.w--
   122					for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) {
   123						out.w--
   124					}
   125				case !rooted:
   126					// cannot backtrack, but not rooted, so append .. element.
   127					if out.w > 0 {
   128						out.append(Separator)
   129					}
   130					out.append('.')
   131					out.append('.')
   132					dotdot = out.w
   133				}
   134			default:
   135				// real path element.
   136				// add slash if needed
   137				if rooted && out.w != 1 || !rooted && out.w != 0 {
   138					out.append(Separator)
   139				}
   140				// copy element
   141				for ; r < n && !os.IsPathSeparator(path[r]); r++ {
   142					out.append(path[r])
   143				}
   144			}
   145		}
   146	
   147		// Turn empty string into "."
   148		if out.w == 0 {
   149			out.append('.')
   150		}
   151	
   152		return FromSlash(out.string())
   153	}
   154	
   155	// ToSlash returns the result of replacing each separator character
   156	// in path with a slash ('/') character. Multiple separators are
   157	// replaced by multiple slashes.
   158	func ToSlash(path string) string {
   159		if Separator == '/' {
   160			return path
   161		}
   162		return strings.Replace(path, string(Separator), "/", -1)
   163	}
   164	
   165	// FromSlash returns the result of replacing each slash ('/') character
   166	// in path with a separator character. Multiple slashes are replaced
   167	// by multiple separators.
   168	func FromSlash(path string) string {
   169		if Separator == '/' {
   170			return path
   171		}
   172		return strings.Replace(path, "/", string(Separator), -1)
   173	}
   174	
   175	// SplitList splits a list of paths joined by the OS-specific ListSeparator,
   176	// usually found in PATH or GOPATH environment variables.
   177	// Unlike strings.Split, SplitList returns an empty slice when passed an empty string.
   178	func SplitList(path string) []string {
   179		return splitList(path)
   180	}
   181	
   182	// Split splits path immediately following the final Separator,
   183	// separating it into a directory and file name component.
   184	// If there is no Separator in path, Split returns an empty dir
   185	// and file set to path.
   186	// The returned values have the property that path = dir+file.
   187	func Split(path string) (dir, file string) {
   188		vol := VolumeName(path)
   189		i := len(path) - 1
   190		for i >= len(vol) && !os.IsPathSeparator(path[i]) {
   191			i--
   192		}
   193		return path[:i+1], path[i+1:]
   194	}
   195	
   196	// Join joins any number of path elements into a single path, adding
   197	// a Separator if necessary. The result is Cleaned, in particular
   198	// all empty strings are ignored.
   199	func Join(elem ...string) string {
   200		for i, e := range elem {
   201			if e != "" {
   202				return Clean(strings.Join(elem[i:], string(Separator)))
   203			}
   204		}
   205		return ""
   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	func EvalSymlinks(path string) (string, error) {
   226		return evalSymlinks(path)
   227	}
   228	
   229	// Abs returns an absolute representation of path.
   230	// If the path is not absolute it will be joined with the current
   231	// working directory to turn it into an absolute path.  The absolute
   232	// path name for a given file is not guaranteed to be unique.
   233	func Abs(path string) (string, error) {
   234		if IsAbs(path) {
   235			return Clean(path), nil
   236		}
   237		wd, err := os.Getwd()
   238		if err != nil {
   239			return "", err
   240		}
   241		return Join(wd, path), nil
   242	}
   243	
   244	// Rel returns a relative path that is lexically equivalent to targpath when
   245	// joined to basepath with an intervening separator. That is,
   246	// Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
   247	// On success, the returned path will always be relative to basepath,
   248	// even if basepath and targpath share no elements.
   249	// An error is returned if targpath can't be made relative to basepath or if
   250	// knowing the current working directory would be necessary to compute it.
   251	func Rel(basepath, targpath string) (string, error) {
   252		baseVol := VolumeName(basepath)
   253		targVol := VolumeName(targpath)
   254		base := Clean(basepath)
   255		targ := Clean(targpath)
   256		if targ == base {
   257			return ".", nil
   258		}
   259		base = base[len(baseVol):]
   260		targ = targ[len(targVol):]
   261		if base == "." {
   262			base = ""
   263		}
   264		// Can't use IsAbs - `\a` and `a` are both relative in Windows.
   265		baseSlashed := len(base) > 0 && base[0] == Separator
   266		targSlashed := len(targ) > 0 && targ[0] == Separator
   267		if baseSlashed != targSlashed || baseVol != targVol {
   268			return "", errors.New("Rel: can't make " + targ + " relative to " + base)
   269		}
   270		// Position base[b0:bi] and targ[t0:ti] at the first differing elements.
   271		bl := len(base)
   272		tl := len(targ)
   273		var b0, bi, t0, ti int
   274		for {
   275			for bi < bl && base[bi] != Separator {
   276				bi++
   277			}
   278			for ti < tl && targ[ti] != Separator {
   279				ti++
   280			}
   281			if targ[t0:ti] != base[b0:bi] {
   282				break
   283			}
   284			if bi < bl {
   285				bi++
   286			}
   287			if ti < tl {
   288				ti++
   289			}
   290			b0 = bi
   291			t0 = ti
   292		}
   293		if base[b0:bi] == ".." {
   294			return "", errors.New("Rel: can't make " + targ + " relative to " + base)
   295		}
   296		if b0 != bl {
   297			// Base elements left. Must go up before going down.
   298			seps := strings.Count(base[b0:bl], string(Separator))
   299			size := 2 + seps*3
   300			if tl != t0 {
   301				size += 1 + tl - t0
   302			}
   303			buf := make([]byte, size)
   304			n := copy(buf, "..")
   305			for i := 0; i < seps; i++ {
   306				buf[n] = Separator
   307				copy(buf[n+1:], "..")
   308				n += 3
   309			}
   310			if t0 != tl {
   311				buf[n] = Separator
   312				copy(buf[n+1:], targ[t0:])
   313			}
   314			return string(buf), nil
   315		}
   316		return targ[t0:], nil
   317	}
   318	
   319	// SkipDir is used as a return value from WalkFuncs to indicate that
   320	// the directory named in the call is to be skipped. It is not returned
   321	// as an error by any function.
   322	var SkipDir = errors.New("skip this directory")
   323	
   324	// WalkFunc is the type of the function called for each file or directory
   325	// visited by Walk. The path argument contains the argument to Walk as a
   326	// prefix; that is, if Walk is called with "dir", which is a directory
   327	// containing the file "a", the walk function will be called with argument
   328	// "dir/a". The info argument is the os.FileInfo for the named path.
   329	//
   330	// If there was a problem walking to the file or directory named by path, the
   331	// incoming error will describe the problem and the function can decide how
   332	// to handle that error (and Walk will not descend into that directory). If
   333	// an error is returned, processing stops. The sole exception is that if path
   334	// is a directory and the function returns the special value SkipDir, the
   335	// contents of the directory are skipped and processing continues as usual on
   336	// the next file.
   337	type WalkFunc func(path string, info os.FileInfo, err error) error
   338	
   339	var lstat = os.Lstat // for testing
   340	
   341	// walk recursively descends path, calling w.
   342	func walk(path string, info os.FileInfo, walkFn WalkFunc) error {
   343		err := walkFn(path, info, nil)
   344		if err != nil {
   345			if info.IsDir() && err == SkipDir {
   346				return nil
   347			}
   348			return err
   349		}
   350	
   351		if !info.IsDir() {
   352			return nil
   353		}
   354	
   355		names, err := readDirNames(path)
   356		if err != nil {
   357			return walkFn(path, info, err)
   358		}
   359	
   360		for _, name := range names {
   361			filename := Join(path, name)
   362			fileInfo, err := lstat(filename)
   363			if err != nil {
   364				if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir {
   365					return err
   366				}
   367			} else {
   368				err = walk(filename, fileInfo, walkFn)
   369				if err != nil {
   370					if !fileInfo.IsDir() || err != SkipDir {
   371						return err
   372					}
   373				}
   374			}
   375		}
   376		return nil
   377	}
   378	
   379	// Walk walks the file tree rooted at root, calling walkFn for each file or
   380	// directory in the tree, including root. All errors that arise visiting files
   381	// and directories are filtered by walkFn. The files are walked in lexical
   382	// order, which makes the output deterministic but means that for very
   383	// large directories Walk can be inefficient.
   384	// Walk does not follow symbolic links.
   385	func Walk(root string, walkFn WalkFunc) error {
   386		info, err := os.Lstat(root)
   387		if err != nil {
   388			return walkFn(root, nil, err)
   389		}
   390		return walk(root, info, walkFn)
   391	}
   392	
   393	// readDirNames reads the directory named by dirname and returns
   394	// a sorted list of directory entries.
   395	func readDirNames(dirname string) ([]string, error) {
   396		f, err := os.Open(dirname)
   397		if err != nil {
   398			return nil, err
   399		}
   400		names, err := f.Readdirnames(-1)
   401		f.Close()
   402		if err != nil {
   403			return nil, err
   404		}
   405		sort.Strings(names)
   406		return names, nil
   407	}
   408	
   409	// Base returns the last element of path.
   410	// Trailing path separators are removed before extracting the last element.
   411	// If the path is empty, Base returns ".".
   412	// If the path consists entirely of separators, Base returns a single separator.
   413	func Base(path string) string {
   414		if path == "" {
   415			return "."
   416		}
   417		// Strip trailing slashes.
   418		for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) {
   419			path = path[0 : len(path)-1]
   420		}
   421		// Throw away volume name
   422		path = path[len(VolumeName(path)):]
   423		// Find the last element
   424		i := len(path) - 1
   425		for i >= 0 && !os.IsPathSeparator(path[i]) {
   426			i--
   427		}
   428		if i >= 0 {
   429			path = path[i+1:]
   430		}
   431		// If empty now, it had only slashes.
   432		if path == "" {
   433			return string(Separator)
   434		}
   435		return path
   436	}
   437	
   438	// Dir returns all but the last element of path, typically the path's directory.
   439	// After dropping the final element, the path is Cleaned and trailing
   440	// slashes are removed.
   441	// If the path is empty, Dir returns ".".
   442	// If the path consists entirely of separators, Dir returns a single separator.
   443	// The returned path does not end in a separator unless it is the root directory.
   444	func Dir(path string) string {
   445		vol := VolumeName(path)
   446		i := len(path) - 1
   447		for i >= len(vol) && !os.IsPathSeparator(path[i]) {
   448			i--
   449		}
   450		dir := Clean(path[len(vol) : i+1])
   451		last := len(dir) - 1
   452		if last > 0 && os.IsPathSeparator(dir[last]) {
   453			dir = dir[:last]
   454		}
   455		if dir == "" {
   456			dir = "."
   457		}
   458		return vol + dir
   459	}
   460	
   461	// VolumeName returns leading volume name.
   462	// Given "C:\foo\bar" it returns "C:" under windows.
   463	// Given "\\host\share\foo" it returns "\\host\share".
   464	// On other platforms it returns "".
   465	func VolumeName(path string) (v string) {
   466		return path[:volumeNameLen(path)]
   467	}
   468	

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