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