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 "slices" 19 "sort" 20 "strings" 21 ) 22 23 // A lazybuf is a lazily constructed path buffer. 24 // It supports append, reading previously appended bytes, 25 // and retrieving the final string. It does not allocate a buffer 26 // to hold the output until that output diverges from s. 27 type lazybuf struct { 28 path string 29 buf []byte 30 w int 31 volAndPath string 32 volLen int 33 } 34 35 func (b *lazybuf) index(i int) byte { 36 if b.buf != nil { 37 return b.buf[i] 38 } 39 return b.path[i] 40 } 41 42 func (b *lazybuf) append(c byte) { 43 if b.buf == nil { 44 if b.w < len(b.path) && b.path[b.w] == c { 45 b.w++ 46 return 47 } 48 b.buf = make([]byte, len(b.path)) 49 copy(b.buf, b.path[:b.w]) 50 } 51 b.buf[b.w] = c 52 b.w++ 53 } 54 55 func (b *lazybuf) prepend(prefix ...byte) { 56 b.buf = slices.Insert(b.buf, 0, prefix...) 57 b.w += len(prefix) 58 } 59 60 func (b *lazybuf) string() string { 61 if b.buf == nil { 62 return b.volAndPath[:b.volLen+b.w] 63 } 64 return b.volAndPath[:b.volLen] + string(b.buf[:b.w]) 65 } 66 67 const ( 68 Separator = os.PathSeparator 69 ListSeparator = os.PathListSeparator 70 ) 71 72 // Clean returns the shortest path name equivalent to path 73 // by purely lexical processing. It applies the following rules 74 // iteratively until no further processing can be done: 75 // 76 // 1. Replace multiple [Separator] elements with a single one. 77 // 2. Eliminate each . path name element (the current directory). 78 // 3. Eliminate each inner .. path name element (the parent directory) 79 // along with the non-.. element that precedes it. 80 // 4. Eliminate .. elements that begin a rooted path: 81 // that is, replace "/.." by "/" at the beginning of a path, 82 // assuming Separator is '/'. 83 // 84 // The returned path ends in a slash only if it represents a root directory, 85 // such as "/" on Unix or `C:\` on Windows. 86 // 87 // Finally, any occurrences of slash are replaced by Separator. 88 // 89 // If the result of this process is an empty string, Clean 90 // returns the string ".". 91 // 92 // On Windows, Clean does not modify the volume name other than to replace 93 // occurrences of "/" with `\`. 94 // For example, Clean("//host/share/../x") returns `\\host\share\x`. 95 // 96 // See also Rob Pike, “Lexical File Names in Plan 9 or 97 // Getting Dot-Dot Right,” 98 // https://9p.io/sys/doc/lexnames.html 99 func Clean(path string) string { 100 originalPath := path 101 volLen := volumeNameLen(path) 102 path = path[volLen:] 103 if path == "" { 104 if volLen > 1 && os.IsPathSeparator(originalPath[0]) && os.IsPathSeparator(originalPath[1]) { 105 // should be UNC 106 return FromSlash(originalPath) 107 } 108 return originalPath + "." 109 } 110 rooted := os.IsPathSeparator(path[0]) 111 112 // Invariants: 113 // reading from path; r is index of next byte to process. 114 // writing to buf; w is index of next byte to write. 115 // dotdot is index in buf where .. must stop, either because 116 // it is the leading slash or it is a leading ../../.. prefix. 117 n := len(path) 118 out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen} 119 r, dotdot := 0, 0 120 if rooted { 121 out.append(Separator) 122 r, dotdot = 1, 1 123 } 124 125 for r < n { 126 switch { 127 case os.IsPathSeparator(path[r]): 128 // empty path element 129 r++ 130 case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])): 131 // . element 132 r++ 133 case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])): 134 // .. element: remove to last separator 135 r += 2 136 switch { 137 case out.w > dotdot: 138 // can backtrack 139 out.w-- 140 for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) { 141 out.w-- 142 } 143 case !rooted: 144 // cannot backtrack, but not rooted, so append .. element. 145 if out.w > 0 { 146 out.append(Separator) 147 } 148 out.append('.') 149 out.append('.') 150 dotdot = out.w 151 } 152 default: 153 // real path element. 154 // add slash if needed 155 if rooted && out.w != 1 || !rooted && out.w != 0 { 156 out.append(Separator) 157 } 158 // copy element 159 for ; r < n && !os.IsPathSeparator(path[r]); r++ { 160 out.append(path[r]) 161 } 162 } 163 } 164 165 // Turn empty string into "." 166 if out.w == 0 { 167 out.append('.') 168 } 169 170 postClean(&out) // avoid creating absolute paths on Windows 171 return FromSlash(out.string()) 172 } 173 174 // IsLocal reports whether path, using lexical analysis only, has all of these properties: 175 // 176 // - is within the subtree rooted at the directory in which path is evaluated 177 // - is not an absolute path 178 // - is not empty 179 // - on Windows, is not a reserved name such as "NUL" 180 // 181 // If IsLocal(path) returns true, then 182 // Join(base, path) will always produce a path contained within base and 183 // Clean(path) will always produce an unrooted path with no ".." path elements. 184 // 185 // IsLocal is a purely lexical operation. 186 // In particular, it does not account for the effect of any symbolic links 187 // that may exist in the filesystem. 188 func IsLocal(path string) bool { 189 return isLocal(path) 190 } 191 192 func unixIsLocal(path string) bool { 193 if IsAbs(path) || path == "" { 194 return false 195 } 196 hasDots := false 197 for p := path; p != ""; { 198 var part string 199 part, p, _ = strings.Cut(p, "/") 200 if part == "." || part == ".." { 201 hasDots = true 202 break 203 } 204 } 205 if hasDots { 206 path = Clean(path) 207 } 208 if path == ".." || strings.HasPrefix(path, "../") { 209 return false 210 } 211 return true 212 } 213 214 // ToSlash returns the result of replacing each separator character 215 // in path with a slash ('/') character. Multiple separators are 216 // replaced by multiple slashes. 217 func ToSlash(path string) string { 218 if Separator == '/' { 219 return path 220 } 221 return strings.ReplaceAll(path, string(Separator), "/") 222 } 223 224 // FromSlash returns the result of replacing each slash ('/') character 225 // in path with a separator character. Multiple slashes are replaced 226 // by multiple separators. 227 func FromSlash(path string) string { 228 if Separator == '/' { 229 return path 230 } 231 return strings.ReplaceAll(path, "/", string(Separator)) 232 } 233 234 // SplitList splits a list of paths joined by the OS-specific [ListSeparator], 235 // usually found in PATH or GOPATH environment variables. 236 // Unlike strings.Split, SplitList returns an empty slice when passed an empty 237 // string. 238 func SplitList(path string) []string { 239 return splitList(path) 240 } 241 242 // Split splits path immediately following the final [Separator], 243 // separating it into a directory and file name component. 244 // If there is no Separator in path, Split returns an empty dir 245 // and file set to path. 246 // The returned values have the property that path = dir+file. 247 func Split(path string) (dir, file string) { 248 vol := VolumeName(path) 249 i := len(path) - 1 250 for i >= len(vol) && !os.IsPathSeparator(path[i]) { 251 i-- 252 } 253 return path[:i+1], path[i+1:] 254 } 255 256 // Join joins any number of path elements into a single path, 257 // separating them with an OS specific [Separator]. Empty elements 258 // are ignored. The result is Cleaned. However, if the argument 259 // list is empty or all its elements are empty, Join returns 260 // an empty string. 261 // On Windows, the result will only be a UNC path if the first 262 // non-empty element is a UNC path. 263 func Join(elem ...string) string { 264 return join(elem) 265 } 266 267 // Ext returns the file name extension used by path. 268 // The extension is the suffix beginning at the final dot 269 // in the final element of path; it is empty if there is 270 // no dot. 271 func Ext(path string) string { 272 for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- { 273 if path[i] == '.' { 274 return path[i:] 275 } 276 } 277 return "" 278 } 279 280 // EvalSymlinks returns the path name after the evaluation of any symbolic 281 // links. 282 // If path is relative the result will be relative to the current directory, 283 // unless one of the components is an absolute symbolic link. 284 // EvalSymlinks calls [Clean] on the result. 285 func EvalSymlinks(path string) (string, error) { 286 return evalSymlinks(path) 287 } 288 289 // Abs returns an absolute representation of path. 290 // If the path is not absolute it will be joined with the current 291 // working directory to turn it into an absolute path. The absolute 292 // path name for a given file is not guaranteed to be unique. 293 // Abs calls [Clean] on the result. 294 func Abs(path string) (string, error) { 295 return abs(path) 296 } 297 298 func unixAbs(path string) (string, error) { 299 if IsAbs(path) { 300 return Clean(path), nil 301 } 302 wd, err := os.Getwd() 303 if err != nil { 304 return "", err 305 } 306 return Join(wd, path), nil 307 } 308 309 // Rel returns a relative path that is lexically equivalent to targpath when 310 // joined to basepath with an intervening separator. That is, 311 // [Join](basepath, Rel(basepath, targpath)) is equivalent to targpath itself. 312 // On success, the returned path will always be relative to basepath, 313 // even if basepath and targpath share no elements. 314 // An error is returned if targpath can't be made relative to basepath or if 315 // knowing the current working directory would be necessary to compute it. 316 // Rel calls [Clean] on the result. 317 func Rel(basepath, targpath string) (string, error) { 318 baseVol := VolumeName(basepath) 319 targVol := VolumeName(targpath) 320 base := Clean(basepath) 321 targ := Clean(targpath) 322 if sameWord(targ, base) { 323 return ".", nil 324 } 325 base = base[len(baseVol):] 326 targ = targ[len(targVol):] 327 if base == "." { 328 base = "" 329 } else if base == "" && volumeNameLen(baseVol) > 2 /* isUNC */ { 330 // Treat any targetpath matching `\\host\share` basepath as absolute path. 331 base = string(Separator) 332 } 333 334 // Can't use IsAbs - `\a` and `a` are both relative in Windows. 335 baseSlashed := len(base) > 0 && base[0] == Separator 336 targSlashed := len(targ) > 0 && targ[0] == Separator 337 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) { 338 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 339 } 340 // Position base[b0:bi] and targ[t0:ti] at the first differing elements. 341 bl := len(base) 342 tl := len(targ) 343 var b0, bi, t0, ti int 344 for { 345 for bi < bl && base[bi] != Separator { 346 bi++ 347 } 348 for ti < tl && targ[ti] != Separator { 349 ti++ 350 } 351 if !sameWord(targ[t0:ti], base[b0:bi]) { 352 break 353 } 354 if bi < bl { 355 bi++ 356 } 357 if ti < tl { 358 ti++ 359 } 360 b0 = bi 361 t0 = ti 362 } 363 if base[b0:bi] == ".." { 364 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 365 } 366 if b0 != bl { 367 // Base elements left. Must go up before going down. 368 seps := strings.Count(base[b0:bl], string(Separator)) 369 size := 2 + seps*3 370 if tl != t0 { 371 size += 1 + tl - t0 372 } 373 buf := make([]byte, size) 374 n := copy(buf, "..") 375 for i := 0; i < seps; i++ { 376 buf[n] = Separator 377 copy(buf[n+1:], "..") 378 n += 3 379 } 380 if t0 != tl { 381 buf[n] = Separator 382 copy(buf[n+1:], targ[t0:]) 383 } 384 return string(buf), nil 385 } 386 return targ[t0:], nil 387 } 388 389 // SkipDir is used as a return value from [WalkFunc] to indicate that 390 // the directory named in the call is to be skipped. It is not returned 391 // as an error by any function. 392 var SkipDir error = fs.SkipDir 393 394 // SkipAll is used as a return value from [WalkFunc] to indicate that 395 // all remaining files and directories are to be skipped. It is not returned 396 // as an error by any function. 397 var SkipAll error = fs.SkipAll 398 399 // WalkFunc is the type of the function called by [Walk] to visit each 400 // file or directory. 401 // 402 // The path argument contains the argument to Walk as a prefix. 403 // That is, if Walk is called with root argument "dir" and finds a file 404 // named "a" in that directory, the walk function will be called with 405 // argument "dir/a". 406 // 407 // The directory and file are joined with Join, which may clean the 408 // directory name: if Walk is called with the root argument "x/../dir" 409 // and finds a file named "a" in that directory, the walk function will 410 // be called with argument "dir/a", not "x/../dir/a". 411 // 412 // The info argument is the fs.FileInfo for the named path. 413 // 414 // The error result returned by the function controls how Walk continues. 415 // If the function returns the special value [SkipDir], Walk skips the 416 // current directory (path if info.IsDir() is true, otherwise path's 417 // parent directory). If the function returns the special value [SkipAll], 418 // Walk skips all remaining files and directories. Otherwise, if the function 419 // returns a non-nil error, Walk stops entirely and returns that error. 420 // 421 // The err argument reports an error related to path, signaling that Walk 422 // will not walk into that directory. The function can decide how to 423 // handle that error; as described earlier, returning the error will 424 // cause Walk to stop walking the entire tree. 425 // 426 // Walk calls the function with a non-nil err argument in two cases. 427 // 428 // First, if an [os.Lstat] on the root directory or any directory or file 429 // in the tree fails, Walk calls the function with path set to that 430 // directory or file's path, info set to nil, and err set to the error 431 // from os.Lstat. 432 // 433 // Second, if a directory's Readdirnames method fails, Walk calls the 434 // function with path set to the directory's path, info, set to an 435 // [fs.FileInfo] describing the directory, and err set to the error from 436 // Readdirnames. 437 type WalkFunc func(path string, info fs.FileInfo, err error) error 438 439 var lstat = os.Lstat // for testing 440 441 // walkDir recursively descends path, calling walkDirFn. 442 func walkDir(path string, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error { 443 if err := walkDirFn(path, d, nil); err != nil || !d.IsDir() { 444 if err == SkipDir && d.IsDir() { 445 // Successfully skipped directory. 446 err = nil 447 } 448 return err 449 } 450 451 dirs, err := os.ReadDir(path) 452 if err != nil { 453 // Second call, to report ReadDir error. 454 err = walkDirFn(path, d, err) 455 if err != nil { 456 if err == SkipDir && d.IsDir() { 457 err = nil 458 } 459 return err 460 } 461 } 462 463 for _, d1 := range dirs { 464 path1 := Join(path, d1.Name()) 465 if err := walkDir(path1, d1, walkDirFn); err != nil { 466 if err == SkipDir { 467 break 468 } 469 return err 470 } 471 } 472 return nil 473 } 474 475 // walk recursively descends path, calling walkFn. 476 func walk(path string, info fs.FileInfo, walkFn WalkFunc) error { 477 if !info.IsDir() { 478 return walkFn(path, info, nil) 479 } 480 481 names, err := readDirNames(path) 482 err1 := walkFn(path, info, err) 483 // If err != nil, walk can't walk into this directory. 484 // err1 != nil means walkFn want walk to skip this directory or stop walking. 485 // Therefore, if one of err and err1 isn't nil, walk will return. 486 if err != nil || err1 != nil { 487 // The caller's behavior is controlled by the return value, which is decided 488 // by walkFn. walkFn may ignore err and return nil. 489 // If walkFn returns SkipDir or SkipAll, it will be handled by the caller. 490 // So walk should return whatever walkFn returns. 491 return err1 492 } 493 494 for _, name := range names { 495 filename := Join(path, name) 496 fileInfo, err := lstat(filename) 497 if err != nil { 498 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir { 499 return err 500 } 501 } else { 502 err = walk(filename, fileInfo, walkFn) 503 if err != nil { 504 if !fileInfo.IsDir() || err != SkipDir { 505 return err 506 } 507 } 508 } 509 } 510 return nil 511 } 512 513 // WalkDir walks the file tree rooted at root, calling fn for each file or 514 // directory in the tree, including root. 515 // 516 // All errors that arise visiting files and directories are filtered by fn: 517 // see the [fs.WalkDirFunc] documentation for details. 518 // 519 // The files are walked in lexical order, which makes the output deterministic 520 // but requires WalkDir to read an entire directory into memory before proceeding 521 // to walk that directory. 522 // 523 // WalkDir does not follow symbolic links. 524 // 525 // WalkDir calls fn with paths that use the separator character appropriate 526 // for the operating system. This is unlike [io/fs.WalkDir], which always 527 // uses slash separated paths. 528 func WalkDir(root string, fn fs.WalkDirFunc) error { 529 info, err := os.Lstat(root) 530 if err != nil { 531 err = fn(root, nil, err) 532 } else { 533 err = walkDir(root, fs.FileInfoToDirEntry(info), fn) 534 } 535 if err == SkipDir || err == SkipAll { 536 return nil 537 } 538 return err 539 } 540 541 // Walk walks the file tree rooted at root, calling fn for each file or 542 // directory in the tree, including root. 543 // 544 // All errors that arise visiting files and directories are filtered by fn: 545 // see the [WalkFunc] documentation for details. 546 // 547 // The files are walked in lexical order, which makes the output deterministic 548 // but requires Walk to read an entire directory into memory before proceeding 549 // to walk that directory. 550 // 551 // Walk does not follow symbolic links. 552 // 553 // Walk is less efficient than [WalkDir], introduced in Go 1.16, 554 // which avoids calling os.Lstat on every visited file or directory. 555 func Walk(root string, fn WalkFunc) error { 556 info, err := os.Lstat(root) 557 if err != nil { 558 err = fn(root, nil, err) 559 } else { 560 err = walk(root, info, fn) 561 } 562 if err == SkipDir || err == SkipAll { 563 return nil 564 } 565 return err 566 } 567 568 // readDirNames reads the directory named by dirname and returns 569 // a sorted list of directory entry names. 570 func readDirNames(dirname string) ([]string, error) { 571 f, err := os.Open(dirname) 572 if err != nil { 573 return nil, err 574 } 575 names, err := f.Readdirnames(-1) 576 f.Close() 577 if err != nil { 578 return nil, err 579 } 580 sort.Strings(names) 581 return names, nil 582 } 583 584 // Base returns the last element of path. 585 // Trailing path separators are removed before extracting the last element. 586 // If the path is empty, Base returns ".". 587 // If the path consists entirely of separators, Base returns a single separator. 588 func Base(path string) string { 589 if path == "" { 590 return "." 591 } 592 // Strip trailing slashes. 593 for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) { 594 path = path[0 : len(path)-1] 595 } 596 // Throw away volume name 597 path = path[len(VolumeName(path)):] 598 // Find the last element 599 i := len(path) - 1 600 for i >= 0 && !os.IsPathSeparator(path[i]) { 601 i-- 602 } 603 if i >= 0 { 604 path = path[i+1:] 605 } 606 // If empty now, it had only slashes. 607 if path == "" { 608 return string(Separator) 609 } 610 return path 611 } 612 613 // Dir returns all but the last element of path, typically the path's directory. 614 // After dropping the final element, Dir calls [Clean] on the path and trailing 615 // slashes are removed. 616 // If the path is empty, Dir returns ".". 617 // If the path consists entirely of separators, Dir returns a single separator. 618 // The returned path does not end in a separator unless it is the root directory. 619 func Dir(path string) string { 620 vol := VolumeName(path) 621 i := len(path) - 1 622 for i >= len(vol) && !os.IsPathSeparator(path[i]) { 623 i-- 624 } 625 dir := Clean(path[len(vol) : i+1]) 626 if dir == "." && len(vol) > 2 { 627 // must be UNC 628 return vol 629 } 630 return vol + dir 631 } 632 633 // VolumeName returns leading volume name. 634 // Given "C:\foo\bar" it returns "C:" on Windows. 635 // Given "\\host\share\foo" it returns "\\host\share". 636 // On other platforms it returns "". 637 func VolumeName(path string) string { 638 return FromSlash(path[:volumeNameLen(path)]) 639 } 640