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