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 && os.IsPathSeparator(originalPath[0]) && os.IsPathSeparator(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: 121 // . element 122 r++ 123 case path[r] == '.' && os.IsPathSeparator(path[r+1]): 124 // ./ element 125 r++ 126 127 for r < len(path) && os.IsPathSeparator(path[r]) { 128 r++ 129 } 130 if out.w == 0 && volumeNameLen(path[r:]) > 0 { 131 // When joining prefix "." and an absolute path on Windows, 132 // the prefix should not be removed. 133 out.append('.') 134 } 135 case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])): 136 // .. element: remove to last separator 137 r += 2 138 switch { 139 case out.w > dotdot: 140 // can backtrack 141 out.w-- 142 for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) { 143 out.w-- 144 } 145 case !rooted: 146 // cannot backtrack, but not rooted, so append .. element. 147 if out.w > 0 { 148 out.append(Separator) 149 } 150 out.append('.') 151 out.append('.') 152 dotdot = out.w 153 } 154 default: 155 // real path element. 156 // add slash if needed 157 if rooted && out.w != 1 || !rooted && out.w != 0 { 158 out.append(Separator) 159 } 160 // copy element 161 for ; r < n && !os.IsPathSeparator(path[r]); r++ { 162 out.append(path[r]) 163 } 164 } 165 } 166 167 // Turn empty string into "." 168 if out.w == 0 { 169 out.append('.') 170 } 171 172 return FromSlash(out.string()) 173 } 174 175 // IsLocal reports whether path, using lexical analysis only, has all of these properties: 176 // 177 // - is within the subtree rooted at the directory in which path is evaluated 178 // - is not an absolute path 179 // - is not empty 180 // - on Windows, is not a reserved name such as "NUL" 181 // 182 // If IsLocal(path) returns true, then 183 // Join(base, path) will always produce a path contained within base and 184 // Clean(path) will always produce an unrooted path with no ".." path elements. 185 // 186 // IsLocal is a purely lexical operation. 187 // In particular, it does not account for the effect of any symbolic links 188 // that may exist in the filesystem. 189 func IsLocal(path string) bool { 190 return isLocal(path) 191 } 192 193 func unixIsLocal(path string) bool { 194 if IsAbs(path) || path == "" { 195 return false 196 } 197 hasDots := false 198 for p := path; p != ""; { 199 var part string 200 part, p, _ = strings.Cut(p, "/") 201 if part == "." || part == ".." { 202 hasDots = true 203 break 204 } 205 } 206 if hasDots { 207 path = Clean(path) 208 } 209 if path == ".." || strings.HasPrefix(path, "../") { 210 return false 211 } 212 return true 213 } 214 215 // ToSlash returns the result of replacing each separator character 216 // in path with a slash ('/') character. Multiple separators are 217 // replaced by multiple slashes. 218 func ToSlash(path string) string { 219 if Separator == '/' { 220 return path 221 } 222 return strings.ReplaceAll(path, string(Separator), "/") 223 } 224 225 // FromSlash returns the result of replacing each slash ('/') character 226 // in path with a separator character. Multiple slashes are replaced 227 // by multiple separators. 228 func FromSlash(path string) string { 229 if Separator == '/' { 230 return path 231 } 232 return strings.ReplaceAll(path, "/", string(Separator)) 233 } 234 235 // SplitList splits a list of paths joined by the OS-specific ListSeparator, 236 // usually found in PATH or GOPATH environment variables. 237 // Unlike strings.Split, SplitList returns an empty slice when passed an empty 238 // string. 239 func SplitList(path string) []string { 240 return splitList(path) 241 } 242 243 // Split splits path immediately following the final Separator, 244 // separating it into a directory and file name component. 245 // If there is no Separator in path, Split returns an empty dir 246 // and file set to path. 247 // The returned values have the property that path = dir+file. 248 func Split(path string) (dir, file string) { 249 vol := VolumeName(path) 250 i := len(path) - 1 251 for i >= len(vol) && !os.IsPathSeparator(path[i]) { 252 i-- 253 } 254 return path[:i+1], path[i+1:] 255 } 256 257 // Join joins any number of path elements into a single path, 258 // separating them with an OS specific Separator. Empty elements 259 // are ignored. The result is Cleaned. However, if the argument 260 // list is empty or all its elements are empty, Join returns 261 // an empty string. 262 // On Windows, the result will only be a UNC path if the first 263 // non-empty element is a UNC path. 264 func Join(elem ...string) string { 265 return join(elem) 266 } 267 268 // Ext returns the file name extension used by path. 269 // The extension is the suffix beginning at the final dot 270 // in the final element of path; it is empty if there is 271 // no dot. 272 func Ext(path string) string { 273 for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- { 274 if path[i] == '.' { 275 return path[i:] 276 } 277 } 278 return "" 279 } 280 281 // EvalSymlinks returns the path name after the evaluation of any symbolic 282 // links. 283 // If path is relative the result will be relative to the current directory, 284 // unless one of the components is an absolute symbolic link. 285 // EvalSymlinks calls Clean on the result. 286 func EvalSymlinks(path string) (string, error) { 287 return evalSymlinks(path) 288 } 289 290 // Abs returns an absolute representation of path. 291 // If the path is not absolute it will be joined with the current 292 // working directory to turn it into an absolute path. The absolute 293 // path name for a given file is not guaranteed to be unique. 294 // Abs calls Clean on the result. 295 func Abs(path string) (string, error) { 296 return abs(path) 297 } 298 299 func unixAbs(path string) (string, error) { 300 if IsAbs(path) { 301 return Clean(path), nil 302 } 303 wd, err := os.Getwd() 304 if err != nil { 305 return "", err 306 } 307 return Join(wd, path), nil 308 } 309 310 // Rel returns a relative path that is lexically equivalent to targpath when 311 // joined to basepath with an intervening separator. That is, 312 // Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself. 313 // On success, the returned path will always be relative to basepath, 314 // even if basepath and targpath share no elements. 315 // An error is returned if targpath can't be made relative to basepath or if 316 // knowing the current working directory would be necessary to compute it. 317 // Rel calls Clean on the result. 318 func Rel(basepath, targpath string) (string, error) { 319 baseVol := VolumeName(basepath) 320 targVol := VolumeName(targpath) 321 base := Clean(basepath) 322 targ := Clean(targpath) 323 if sameWord(targ, base) { 324 return ".", nil 325 } 326 base = base[len(baseVol):] 327 targ = targ[len(targVol):] 328 if base == "." { 329 base = "" 330 } else if base == "" && volumeNameLen(baseVol) > 2 /* isUNC */ { 331 // Treat any targetpath matching `\\host\share` basepath as absolute path. 332 base = string(Separator) 333 } 334 335 // Can't use IsAbs - `\a` and `a` are both relative in Windows. 336 baseSlashed := len(base) > 0 && base[0] == Separator 337 targSlashed := len(targ) > 0 && targ[0] == Separator 338 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) { 339 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 340 } 341 // Position base[b0:bi] and targ[t0:ti] at the first differing elements. 342 bl := len(base) 343 tl := len(targ) 344 var b0, bi, t0, ti int 345 for { 346 for bi < bl && base[bi] != Separator { 347 bi++ 348 } 349 for ti < tl && targ[ti] != Separator { 350 ti++ 351 } 352 if !sameWord(targ[t0:ti], base[b0:bi]) { 353 break 354 } 355 if bi < bl { 356 bi++ 357 } 358 if ti < tl { 359 ti++ 360 } 361 b0 = bi 362 t0 = ti 363 } 364 if base[b0:bi] == ".." { 365 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 366 } 367 if b0 != bl { 368 // Base elements left. Must go up before going down. 369 seps := strings.Count(base[b0:bl], string(Separator)) 370 size := 2 + seps*3 371 if tl != t0 { 372 size += 1 + tl - t0 373 } 374 buf := make([]byte, size) 375 n := copy(buf, "..") 376 for i := 0; i < seps; i++ { 377 buf[n] = Separator 378 copy(buf[n+1:], "..") 379 n += 3 380 } 381 if t0 != tl { 382 buf[n] = Separator 383 copy(buf[n+1:], targ[t0:]) 384 } 385 return string(buf), nil 386 } 387 return targ[t0:], nil 388 } 389 390 // SkipDir is used as a return value from WalkFuncs to indicate that 391 // the directory named in the call is to be skipped. It is not returned 392 // as an error by any function. 393 var SkipDir error = fs.SkipDir 394 395 // SkipAll is used as a return value from WalkFuncs to indicate that 396 // all remaining files and directories are to be skipped. It is not returned 397 // as an error by any function. 398 var SkipAll error = fs.SkipAll 399 400 // WalkFunc is the type of the function called by Walk to visit each 401 // file or directory. 402 // 403 // The path argument contains the argument to Walk as a prefix. 404 // That is, if Walk is called with root argument "dir" and finds a file 405 // named "a" in that directory, the walk function will be called with 406 // argument "dir/a". 407 // 408 // The directory and file are joined with Join, which may clean the 409 // directory name: if Walk is called with the root argument "x/../dir" 410 // and finds a file named "a" in that directory, the walk function will 411 // be called with argument "dir/a", not "x/../dir/a". 412 // 413 // The info argument is the fs.FileInfo for the named path. 414 // 415 // The error result returned by the function controls how Walk continues. 416 // If the function returns the special value SkipDir, Walk skips the 417 // current directory (path if info.IsDir() is true, otherwise path's 418 // parent directory). If the function returns the special value SkipAll, 419 // Walk skips all remaining files and directories. Otherwise, if the function 420 // returns a non-nil error, Walk stops entirely and returns that error. 421 // 422 // The err argument reports an error related to path, signaling that Walk 423 // will not walk into that directory. The function can decide how to 424 // handle that error; as described earlier, returning the error will 425 // cause Walk to stop walking the entire tree. 426 // 427 // Walk calls the function with a non-nil err argument in two cases. 428 // 429 // First, if an os.Lstat on the root directory or any directory or file 430 // in the tree fails, Walk calls the function with path set to that 431 // directory or file's path, info set to nil, and err set to the error 432 // from os.Lstat. 433 // 434 // Second, if a directory's Readdirnames method fails, Walk calls the 435 // function with path set to the directory's path, info, set to an 436 // fs.FileInfo describing the directory, and err set to the error from 437 // Readdirnames. 438 type WalkFunc func(path string, info fs.FileInfo, err error) error 439 440 var lstat = os.Lstat // for testing 441 442 // walkDir recursively descends path, calling walkDirFn. 443 func walkDir(path string, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error { 444 if err := walkDirFn(path, d, nil); err != nil || !d.IsDir() { 445 if err == SkipDir && d.IsDir() { 446 // Successfully skipped directory. 447 err = nil 448 } 449 return err 450 } 451 452 dirs, err := readDir(path) 453 if err != nil { 454 // Second call, to report ReadDir error. 455 err = walkDirFn(path, d, err) 456 if err != nil { 457 if err == SkipDir && d.IsDir() { 458 err = nil 459 } 460 return err 461 } 462 } 463 464 for _, d1 := range dirs { 465 path1 := Join(path, d1.Name()) 466 if err := walkDir(path1, d1, walkDirFn); err != nil { 467 if err == SkipDir { 468 break 469 } 470 return err 471 } 472 } 473 return nil 474 } 475 476 // walk recursively descends path, calling walkFn. 477 func walk(path string, info fs.FileInfo, walkFn WalkFunc) error { 478 if !info.IsDir() { 479 return walkFn(path, info, nil) 480 } 481 482 names, err := readDirNames(path) 483 err1 := walkFn(path, info, err) 484 // If err != nil, walk can't walk into this directory. 485 // err1 != nil means walkFn want walk to skip this directory or stop walking. 486 // Therefore, if one of err and err1 isn't nil, walk will return. 487 if err != nil || err1 != nil { 488 // The caller's behavior is controlled by the return value, which is decided 489 // by walkFn. walkFn may ignore err and return nil. 490 // If walkFn returns SkipDir or SkipAll, it will be handled by the caller. 491 // So walk should return whatever walkFn returns. 492 return err1 493 } 494 495 for _, name := range names { 496 filename := Join(path, name) 497 fileInfo, err := lstat(filename) 498 if err != nil { 499 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir { 500 return err 501 } 502 } else { 503 err = walk(filename, fileInfo, walkFn) 504 if err != nil { 505 if !fileInfo.IsDir() || err != SkipDir { 506 return err 507 } 508 } 509 } 510 } 511 return nil 512 } 513 514 // WalkDir walks the file tree rooted at root, calling fn for each file or 515 // directory in the tree, including root. 516 // 517 // All errors that arise visiting files and directories are filtered by fn: 518 // see the fs.WalkDirFunc documentation for details. 519 // 520 // The files are walked in lexical order, which makes the output deterministic 521 // but requires WalkDir to read an entire directory into memory before proceeding 522 // to walk that directory. 523 // 524 // WalkDir does not follow symbolic links. 525 // 526 // WalkDir calls fn with paths that use the separator character appropriate 527 // for the operating system. This is unlike [io/fs.WalkDir], which always 528 // uses slash separated paths. 529 func WalkDir(root string, fn fs.WalkDirFunc) error { 530 info, err := os.Lstat(root) 531 if err != nil { 532 err = fn(root, nil, err) 533 } else { 534 err = walkDir(root, &statDirEntry{info}, fn) 535 } 536 if err == SkipDir || err == SkipAll { 537 return nil 538 } 539 return err 540 } 541 542 type statDirEntry struct { 543 info fs.FileInfo 544 } 545 546 func (d *statDirEntry) Name() string { return d.info.Name() } 547 func (d *statDirEntry) IsDir() bool { return d.info.IsDir() } 548 func (d *statDirEntry) Type() fs.FileMode { return d.info.Mode().Type() } 549 func (d *statDirEntry) Info() (fs.FileInfo, error) { return d.info, nil } 550 551 // Walk walks the file tree rooted at root, calling fn for each file or 552 // directory in the tree, including root. 553 // 554 // All errors that arise visiting files and directories are filtered by fn: 555 // see the WalkFunc documentation for details. 556 // 557 // The files are walked in lexical order, which makes the output deterministic 558 // but requires Walk to read an entire directory into memory before proceeding 559 // to walk that directory. 560 // 561 // Walk does not follow symbolic links. 562 // 563 // Walk is less efficient than WalkDir, introduced in Go 1.16, 564 // which avoids calling os.Lstat on every visited file or directory. 565 func Walk(root string, fn WalkFunc) error { 566 info, err := os.Lstat(root) 567 if err != nil { 568 err = fn(root, nil, err) 569 } else { 570 err = walk(root, info, fn) 571 } 572 if err == SkipDir || err == SkipAll { 573 return nil 574 } 575 return err 576 } 577 578 // readDir reads the directory named by dirname and returns 579 // a sorted list of directory entries. 580 func readDir(dirname string) ([]fs.DirEntry, error) { 581 f, err := os.Open(dirname) 582 if err != nil { 583 return nil, err 584 } 585 dirs, err := f.ReadDir(-1) 586 f.Close() 587 if err != nil { 588 return nil, err 589 } 590 sort.Slice(dirs, func(i, j int) bool { return dirs[i].Name() < dirs[j].Name() }) 591 return dirs, nil 592 } 593 594 // readDirNames reads the directory named by dirname and returns 595 // a sorted list of directory entry names. 596 func readDirNames(dirname string) ([]string, error) { 597 f, err := os.Open(dirname) 598 if err != nil { 599 return nil, err 600 } 601 names, err := f.Readdirnames(-1) 602 f.Close() 603 if err != nil { 604 return nil, err 605 } 606 sort.Strings(names) 607 return names, nil 608 } 609 610 // Base returns the last element of path. 611 // Trailing path separators are removed before extracting the last element. 612 // If the path is empty, Base returns ".". 613 // If the path consists entirely of separators, Base returns a single separator. 614 func Base(path string) string { 615 if path == "" { 616 return "." 617 } 618 // Strip trailing slashes. 619 for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) { 620 path = path[0 : len(path)-1] 621 } 622 // Throw away volume name 623 path = path[len(VolumeName(path)):] 624 // Find the last element 625 i := len(path) - 1 626 for i >= 0 && !os.IsPathSeparator(path[i]) { 627 i-- 628 } 629 if i >= 0 { 630 path = path[i+1:] 631 } 632 // If empty now, it had only slashes. 633 if path == "" { 634 return string(Separator) 635 } 636 return path 637 } 638 639 // Dir returns all but the last element of path, typically the path's directory. 640 // After dropping the final element, Dir calls Clean on the path and trailing 641 // slashes are removed. 642 // If the path is empty, Dir returns ".". 643 // If the path consists entirely of separators, Dir returns a single separator. 644 // The returned path does not end in a separator unless it is the root directory. 645 func Dir(path string) string { 646 vol := VolumeName(path) 647 i := len(path) - 1 648 for i >= len(vol) && !os.IsPathSeparator(path[i]) { 649 i-- 650 } 651 dir := Clean(path[len(vol) : i+1]) 652 if dir == "." && len(vol) > 2 { 653 // must be UNC 654 return vol 655 } 656 return vol + dir 657 } 658 659 // VolumeName returns leading volume name. 660 // Given "C:\foo\bar" it returns "C:" on Windows. 661 // Given "\\host\share\foo" it returns "\\host\share". 662 // On other platforms it returns "". 663 func VolumeName(path string) string { 664 return FromSlash(path[:volumeNameLen(path)]) 665 } 666