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