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 "internal/bytealg" 17 "internal/filepathlite" 18 "io/fs" 19 "os" 20 "slices" 21 ) 22 23 const ( 24 Separator = os.PathSeparator 25 ListSeparator = os.PathListSeparator 26 ) 27 28 // Clean returns the shortest path name equivalent to path 29 // by purely lexical processing. It applies the following rules 30 // iteratively until no further processing can be done: 31 // 32 // 1. Replace multiple [Separator] elements with a single one. 33 // 2. Eliminate each . path name element (the current directory). 34 // 3. Eliminate each inner .. path name element (the parent directory) 35 // along with the non-.. element that precedes it. 36 // 4. Eliminate .. elements that begin a rooted path: 37 // that is, replace "/.." by "/" at the beginning of a path, 38 // assuming Separator is '/'. 39 // 40 // The returned path ends in a slash only if it represents a root directory, 41 // such as "/" on Unix or `C:\` on Windows. 42 // 43 // Finally, any occurrences of slash are replaced by Separator. 44 // 45 // If the result of this process is an empty string, Clean 46 // returns the string ".". 47 // 48 // On Windows, Clean does not modify the volume name other than to replace 49 // occurrences of "/" with `\`. 50 // For example, Clean("//host/share/../x") returns `\\host\share\x`. 51 // 52 // See also Rob Pike, “Lexical File Names in Plan 9 or 53 // Getting Dot-Dot Right,” 54 // https://9p.io/sys/doc/lexnames.html 55 func Clean(path string) string { 56 return filepathlite.Clean(path) 57 } 58 59 // IsLocal reports whether path, using lexical analysis only, has all of these properties: 60 // 61 // - is within the subtree rooted at the directory in which path is evaluated 62 // - is not an absolute path 63 // - is not empty 64 // - on Windows, is not a reserved name such as "NUL" 65 // 66 // If IsLocal(path) returns true, then 67 // Join(base, path) will always produce a path contained within base and 68 // Clean(path) will always produce an unrooted path with no ".." path elements. 69 // 70 // IsLocal is a purely lexical operation. 71 // In particular, it does not account for the effect of any symbolic links 72 // that may exist in the filesystem. 73 func IsLocal(path string) bool { 74 return filepathlite.IsLocal(path) 75 } 76 77 // Localize converts a slash-separated path into an operating system path. 78 // The input path must be a valid path as reported by [io/fs.ValidPath]. 79 // 80 // Localize returns an error if the path cannot be represented by the operating system. 81 // For example, the path a\b is rejected on Windows, on which \ is a separator 82 // character and cannot be part of a filename. 83 // 84 // The path returned by Localize will always be local, as reported by IsLocal. 85 func Localize(path string) (string, error) { 86 return filepathlite.Localize(path) 87 } 88 89 // ToSlash returns the result of replacing each separator character 90 // in path with a slash ('/') character. Multiple separators are 91 // replaced by multiple slashes. 92 func ToSlash(path string) string { 93 return filepathlite.ToSlash(path) 94 } 95 96 // FromSlash returns the result of replacing each slash ('/') character 97 // in path with a separator character. Multiple slashes are replaced 98 // by multiple separators. 99 // 100 // See also the Localize function, which converts a slash-separated path 101 // as used by the io/fs package to an operating system path. 102 func FromSlash(path string) string { 103 return filepathlite.FromSlash(path) 104 } 105 106 // SplitList splits a list of paths joined by the OS-specific [ListSeparator], 107 // usually found in PATH or GOPATH environment variables. 108 // Unlike strings.Split, SplitList returns an empty slice when passed an empty 109 // string. 110 func SplitList(path string) []string { 111 return splitList(path) 112 } 113 114 // Split splits path immediately following the final [Separator], 115 // separating it into a directory and file name component. 116 // If there is no Separator in path, Split returns an empty dir 117 // and file set to path. 118 // The returned values have the property that path = dir+file. 119 func Split(path string) (dir, file string) { 120 return filepathlite.Split(path) 121 } 122 123 // Join joins any number of path elements into a single path, 124 // separating them with an OS specific [Separator]. Empty elements 125 // are ignored. The result is Cleaned. However, if the argument 126 // list is empty or all its elements are empty, Join returns 127 // an empty string. 128 // On Windows, the result will only be a UNC path if the first 129 // non-empty element is a UNC path. 130 func Join(elem ...string) string { 131 return join(elem) 132 } 133 134 // Ext returns the file name extension used by path. 135 // The extension is the suffix beginning at the final dot 136 // in the final element of path; it is empty if there is 137 // no dot. 138 func Ext(path string) string { 139 return filepathlite.Ext(path) 140 } 141 142 // EvalSymlinks returns the path name after the evaluation of any symbolic 143 // links. 144 // If path is relative the result will be relative to the current directory, 145 // unless one of the components is an absolute symbolic link. 146 // EvalSymlinks calls [Clean] on the result. 147 func EvalSymlinks(path string) (string, error) { 148 return evalSymlinks(path) 149 } 150 151 // IsAbs reports whether the path is absolute. 152 func IsAbs(path string) bool { 153 return filepathlite.IsAbs(path) 154 } 155 156 // Abs returns an absolute representation of path. 157 // If the path is not absolute it will be joined with the current 158 // working directory to turn it into an absolute path. The absolute 159 // path name for a given file is not guaranteed to be unique. 160 // Abs calls [Clean] on the result. 161 func Abs(path string) (string, error) { 162 return abs(path) 163 } 164 165 func unixAbs(path string) (string, error) { 166 if IsAbs(path) { 167 return Clean(path), nil 168 } 169 wd, err := os.Getwd() 170 if err != nil { 171 return "", err 172 } 173 return Join(wd, path), nil 174 } 175 176 // Rel returns a relative path that is lexically equivalent to targPath when 177 // joined to basePath with an intervening separator. That is, 178 // [Join](basePath, Rel(basePath, targPath)) is equivalent to targPath itself. 179 // 180 // The returned path will always be relative to basePath, even if basePath and 181 // targPath share no elements. Rel calls [Clean] on the result. 182 // 183 // An error is returned if targPath can't be made relative to basePath 184 // or if knowing the current working directory would be necessary to compute it. 185 func Rel(basePath, targPath string) (string, error) { 186 baseVol := VolumeName(basePath) 187 targVol := VolumeName(targPath) 188 base := Clean(basePath) 189 targ := Clean(targPath) 190 if sameWord(targ, base) { 191 return ".", nil 192 } 193 base = base[len(baseVol):] 194 targ = targ[len(targVol):] 195 if base == "." { 196 base = "" 197 } else if base == "" && filepathlite.VolumeNameLen(baseVol) > 2 /* isUNC */ { 198 // Treat any targetpath matching `\\host\share` basePath as absolute path. 199 base = string(Separator) 200 } 201 202 // Can't use IsAbs - `\a` and `a` are both relative in Windows. 203 baseSlashed := len(base) > 0 && base[0] == Separator 204 targSlashed := len(targ) > 0 && targ[0] == Separator 205 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) { 206 return "", errors.New("Rel: can't make " + targPath + " relative to " + basePath) 207 } 208 // Position base[b0:bi] and targ[t0:ti] at the first differing elements. 209 bl := len(base) 210 tl := len(targ) 211 var b0, bi, t0, ti int 212 for { 213 for bi < bl && base[bi] != Separator { 214 bi++ 215 } 216 for ti < tl && targ[ti] != Separator { 217 ti++ 218 } 219 if !sameWord(targ[t0:ti], base[b0:bi]) { 220 break 221 } 222 if bi < bl { 223 bi++ 224 } 225 if ti < tl { 226 ti++ 227 } 228 b0 = bi 229 t0 = ti 230 } 231 if base[b0:bi] == ".." { 232 return "", errors.New("Rel: can't make " + targPath + " relative to " + basePath) 233 } 234 if b0 != bl { 235 // Base elements left. Must go up before going down. 236 seps := bytealg.CountString(base[b0:bl], Separator) 237 size := 2 + seps*3 238 if tl != t0 { 239 size += 1 + tl - t0 240 } 241 buf := make([]byte, size) 242 n := copy(buf, "..") 243 for i := 0; i < seps; i++ { 244 buf[n] = Separator 245 copy(buf[n+1:], "..") 246 n += 3 247 } 248 if t0 != tl { 249 buf[n] = Separator 250 copy(buf[n+1:], targ[t0:]) 251 } 252 return Clean(string(buf)), nil 253 } 254 return targ[t0:], nil 255 } 256 257 // SkipDir is used as a return value from [WalkFunc] to indicate that 258 // the directory named in the call is to be skipped. It is not returned 259 // as an error by any function. 260 var SkipDir error = fs.SkipDir 261 262 // SkipAll is used as a return value from [WalkFunc] to indicate that 263 // all remaining files and directories are to be skipped. It is not returned 264 // as an error by any function. 265 var SkipAll error = fs.SkipAll 266 267 // WalkFunc is the type of the function called by [Walk] to visit each 268 // file or directory. 269 // 270 // The path argument contains the argument to Walk as a prefix. 271 // That is, if Walk is called with root argument "dir" and finds a file 272 // named "a" in that directory, the walk function will be called with 273 // argument "dir/a". 274 // 275 // The directory and file are joined with Join, which may clean the 276 // directory name: if Walk is called with the root argument "x/../dir" 277 // and finds a file named "a" in that directory, the walk function will 278 // be called with argument "dir/a", not "x/../dir/a". 279 // 280 // The info argument is the fs.FileInfo for the named path. 281 // 282 // The error result returned by the function controls how Walk continues. 283 // If the function returns the special value [SkipDir], Walk skips the 284 // current directory (path if info.IsDir() is true, otherwise path's 285 // parent directory). If the function returns the special value [SkipAll], 286 // Walk skips all remaining files and directories. Otherwise, if the function 287 // returns a non-nil error, Walk stops entirely and returns that error. 288 // 289 // The err argument reports an error related to path, signaling that Walk 290 // will not walk into that directory. The function can decide how to 291 // handle that error; as described earlier, returning the error will 292 // cause Walk to stop walking the entire tree. 293 // 294 // Walk calls the function with a non-nil err argument in two cases. 295 // 296 // First, if an [os.Lstat] on the root directory or any directory or file 297 // in the tree fails, Walk calls the function with path set to that 298 // directory or file's path, info set to nil, and err set to the error 299 // from os.Lstat. 300 // 301 // Second, if a directory's Readdirnames method fails, Walk calls the 302 // function with path set to the directory's path, info, set to an 303 // [fs.FileInfo] describing the directory, and err set to the error from 304 // Readdirnames. 305 type WalkFunc func(path string, info fs.FileInfo, err error) error 306 307 var lstat = os.Lstat // for testing 308 309 // walkDir recursively descends path, calling walkDirFn. 310 func walkDir(path string, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error { 311 if err := walkDirFn(path, d, nil); err != nil || !d.IsDir() { 312 if err == SkipDir && d.IsDir() { 313 // Successfully skipped directory. 314 err = nil 315 } 316 return err 317 } 318 319 dirs, err := os.ReadDir(path) 320 if err != nil { 321 // Second call, to report ReadDir error. 322 err = walkDirFn(path, d, err) 323 if err != nil { 324 if err == SkipDir && d.IsDir() { 325 err = nil 326 } 327 return err 328 } 329 } 330 331 for _, d1 := range dirs { 332 path1 := Join(path, d1.Name()) 333 if err := walkDir(path1, d1, walkDirFn); err != nil { 334 if err == SkipDir { 335 break 336 } 337 return err 338 } 339 } 340 return nil 341 } 342 343 // walk recursively descends path, calling walkFn. 344 func walk(path string, info fs.FileInfo, walkFn WalkFunc) error { 345 if !info.IsDir() { 346 return walkFn(path, info, nil) 347 } 348 349 names, err := readDirNames(path) 350 err1 := walkFn(path, info, err) 351 // If err != nil, walk can't walk into this directory. 352 // err1 != nil means walkFn want walk to skip this directory or stop walking. 353 // Therefore, if one of err and err1 isn't nil, walk will return. 354 if err != nil || err1 != nil { 355 // The caller's behavior is controlled by the return value, which is decided 356 // by walkFn. walkFn may ignore err and return nil. 357 // If walkFn returns SkipDir or SkipAll, it will be handled by the caller. 358 // So walk should return whatever walkFn returns. 359 return err1 360 } 361 362 for _, name := range names { 363 filename := Join(path, name) 364 fileInfo, err := lstat(filename) 365 if err != nil { 366 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir { 367 return err 368 } 369 } else { 370 err = walk(filename, fileInfo, walkFn) 371 if err != nil { 372 if !fileInfo.IsDir() || err != SkipDir { 373 return err 374 } 375 } 376 } 377 } 378 return nil 379 } 380 381 // WalkDir walks the file tree rooted at root, calling fn for each file or 382 // directory in the tree, including root. 383 // 384 // All errors that arise visiting files and directories are filtered by fn: 385 // see the [fs.WalkDirFunc] documentation for details. 386 // 387 // The files are walked in lexical order, which makes the output deterministic 388 // but requires WalkDir to read an entire directory into memory before proceeding 389 // to walk that directory. 390 // 391 // WalkDir does not follow symbolic links. 392 // 393 // WalkDir calls fn with paths that use the separator character appropriate 394 // for the operating system. This is unlike [io/fs.WalkDir], which always 395 // uses slash separated paths. 396 func WalkDir(root string, fn fs.WalkDirFunc) error { 397 info, err := os.Lstat(root) 398 if err != nil { 399 err = fn(root, nil, err) 400 } else { 401 err = walkDir(root, fs.FileInfoToDirEntry(info), fn) 402 } 403 if err == SkipDir || err == SkipAll { 404 return nil 405 } 406 return err 407 } 408 409 // Walk walks the file tree rooted at root, calling fn for each file or 410 // directory in the tree, including root. 411 // 412 // All errors that arise visiting files and directories are filtered by fn: 413 // see the [WalkFunc] documentation for details. 414 // 415 // The files are walked in lexical order, which makes the output deterministic 416 // but requires Walk to read an entire directory into memory before proceeding 417 // to walk that directory. 418 // 419 // Walk does not follow symbolic links. 420 // 421 // Walk is less efficient than [WalkDir], introduced in Go 1.16, 422 // which avoids calling os.Lstat on every visited file or directory. 423 func Walk(root string, fn WalkFunc) error { 424 info, err := os.Lstat(root) 425 if err != nil { 426 err = fn(root, nil, err) 427 } else { 428 err = walk(root, info, fn) 429 } 430 if err == SkipDir || err == SkipAll { 431 return nil 432 } 433 return err 434 } 435 436 // readDirNames reads the directory named by dirname and returns 437 // a sorted list of directory entry names. 438 func readDirNames(dirname string) ([]string, error) { 439 f, err := os.Open(dirname) 440 if err != nil { 441 return nil, err 442 } 443 names, err := f.Readdirnames(-1) 444 f.Close() 445 if err != nil { 446 return nil, err 447 } 448 slices.Sort(names) 449 return names, nil 450 } 451 452 // Base returns the last element of path. 453 // Trailing path separators are removed before extracting the last element. 454 // If the path is empty, Base returns ".". 455 // If the path consists entirely of separators, Base returns a single separator. 456 func Base(path string) string { 457 return filepathlite.Base(path) 458 } 459 460 // Dir returns all but the last element of path, typically the path's directory. 461 // After dropping the final element, Dir calls [Clean] on the path and trailing 462 // slashes are removed. 463 // If the path is empty, Dir returns ".". 464 // If the path consists entirely of separators, Dir returns a single separator. 465 // The returned path does not end in a separator unless it is the root directory. 466 func Dir(path string) string { 467 return filepathlite.Dir(path) 468 } 469 470 // VolumeName returns leading volume name. 471 // Given "C:\foo\bar" it returns "C:" on Windows. 472 // Given "\\host\share\foo" it returns "\\host\share". 473 // On other platforms it returns "". 474 func VolumeName(path string) string { 475 return filepathlite.VolumeName(path) 476 } 477