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 "sort" 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 // On success, the returned path will always be relative to basepath, 180 // even if basepath and targpath share no elements. 181 // An error is returned if targpath can't be made relative to basepath or if 182 // knowing the current working directory would be necessary to compute it. 183 // Rel calls [Clean] on the result. 184 func Rel(basepath, targpath string) (string, error) { 185 baseVol := VolumeName(basepath) 186 targVol := VolumeName(targpath) 187 base := Clean(basepath) 188 targ := Clean(targpath) 189 if sameWord(targ, base) { 190 return ".", nil 191 } 192 base = base[len(baseVol):] 193 targ = targ[len(targVol):] 194 if base == "." { 195 base = "" 196 } else if base == "" && filepathlite.VolumeNameLen(baseVol) > 2 /* isUNC */ { 197 // Treat any targetpath matching `\\host\share` basepath as absolute path. 198 base = string(Separator) 199 } 200 201 // Can't use IsAbs - `\a` and `a` are both relative in Windows. 202 baseSlashed := len(base) > 0 && base[0] == Separator 203 targSlashed := len(targ) > 0 && targ[0] == Separator 204 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) { 205 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 206 } 207 // Position base[b0:bi] and targ[t0:ti] at the first differing elements. 208 bl := len(base) 209 tl := len(targ) 210 var b0, bi, t0, ti int 211 for { 212 for bi < bl && base[bi] != Separator { 213 bi++ 214 } 215 for ti < tl && targ[ti] != Separator { 216 ti++ 217 } 218 if !sameWord(targ[t0:ti], base[b0:bi]) { 219 break 220 } 221 if bi < bl { 222 bi++ 223 } 224 if ti < tl { 225 ti++ 226 } 227 b0 = bi 228 t0 = ti 229 } 230 if base[b0:bi] == ".." { 231 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 232 } 233 if b0 != bl { 234 // Base elements left. Must go up before going down. 235 seps := bytealg.CountString(base[b0:bl], Separator) 236 size := 2 + seps*3 237 if tl != t0 { 238 size += 1 + tl - t0 239 } 240 buf := make([]byte, size) 241 n := copy(buf, "..") 242 for i := 0; i < seps; i++ { 243 buf[n] = Separator 244 copy(buf[n+1:], "..") 245 n += 3 246 } 247 if t0 != tl { 248 buf[n] = Separator 249 copy(buf[n+1:], targ[t0:]) 250 } 251 return string(buf), nil 252 } 253 return targ[t0:], nil 254 } 255 256 // SkipDir is used as a return value from [WalkFunc] to indicate that 257 // the directory named in the call is to be skipped. It is not returned 258 // as an error by any function. 259 var SkipDir error = fs.SkipDir 260 261 // SkipAll is used as a return value from [WalkFunc] to indicate that 262 // all remaining files and directories are to be skipped. It is not returned 263 // as an error by any function. 264 var SkipAll error = fs.SkipAll 265 266 // WalkFunc is the type of the function called by [Walk] to visit each 267 // file or directory. 268 // 269 // The path argument contains the argument to Walk as a prefix. 270 // That is, if Walk is called with root argument "dir" and finds a file 271 // named "a" in that directory, the walk function will be called with 272 // argument "dir/a". 273 // 274 // The directory and file are joined with Join, which may clean the 275 // directory name: if Walk is called with the root argument "x/../dir" 276 // and finds a file named "a" in that directory, the walk function will 277 // be called with argument "dir/a", not "x/../dir/a". 278 // 279 // The info argument is the fs.FileInfo for the named path. 280 // 281 // The error result returned by the function controls how Walk continues. 282 // If the function returns the special value [SkipDir], Walk skips the 283 // current directory (path if info.IsDir() is true, otherwise path's 284 // parent directory). If the function returns the special value [SkipAll], 285 // Walk skips all remaining files and directories. Otherwise, if the function 286 // returns a non-nil error, Walk stops entirely and returns that error. 287 // 288 // The err argument reports an error related to path, signaling that Walk 289 // will not walk into that directory. The function can decide how to 290 // handle that error; as described earlier, returning the error will 291 // cause Walk to stop walking the entire tree. 292 // 293 // Walk calls the function with a non-nil err argument in two cases. 294 // 295 // First, if an [os.Lstat] on the root directory or any directory or file 296 // in the tree fails, Walk calls the function with path set to that 297 // directory or file's path, info set to nil, and err set to the error 298 // from os.Lstat. 299 // 300 // Second, if a directory's Readdirnames method fails, Walk calls the 301 // function with path set to the directory's path, info, set to an 302 // [fs.FileInfo] describing the directory, and err set to the error from 303 // Readdirnames. 304 type WalkFunc func(path string, info fs.FileInfo, err error) error 305 306 var lstat = os.Lstat // for testing 307 308 // walkDir recursively descends path, calling walkDirFn. 309 func walkDir(path string, d fs.DirEntry, walkDirFn fs.WalkDirFunc) error { 310 if err := walkDirFn(path, d, nil); err != nil || !d.IsDir() { 311 if err == SkipDir && d.IsDir() { 312 // Successfully skipped directory. 313 err = nil 314 } 315 return err 316 } 317 318 dirs, err := os.ReadDir(path) 319 if err != nil { 320 // Second call, to report ReadDir error. 321 err = walkDirFn(path, d, err) 322 if err != nil { 323 if err == SkipDir && d.IsDir() { 324 err = nil 325 } 326 return err 327 } 328 } 329 330 for _, d1 := range dirs { 331 path1 := Join(path, d1.Name()) 332 if err := walkDir(path1, d1, walkDirFn); err != nil { 333 if err == SkipDir { 334 break 335 } 336 return err 337 } 338 } 339 return nil 340 } 341 342 // walk recursively descends path, calling walkFn. 343 func walk(path string, info fs.FileInfo, walkFn WalkFunc) error { 344 if !info.IsDir() { 345 return walkFn(path, info, nil) 346 } 347 348 names, err := readDirNames(path) 349 err1 := walkFn(path, info, err) 350 // If err != nil, walk can't walk into this directory. 351 // err1 != nil means walkFn want walk to skip this directory or stop walking. 352 // Therefore, if one of err and err1 isn't nil, walk will return. 353 if err != nil || err1 != nil { 354 // The caller's behavior is controlled by the return value, which is decided 355 // by walkFn. walkFn may ignore err and return nil. 356 // If walkFn returns SkipDir or SkipAll, it will be handled by the caller. 357 // So walk should return whatever walkFn returns. 358 return err1 359 } 360 361 for _, name := range names { 362 filename := Join(path, name) 363 fileInfo, err := lstat(filename) 364 if err != nil { 365 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir { 366 return err 367 } 368 } else { 369 err = walk(filename, fileInfo, walkFn) 370 if err != nil { 371 if !fileInfo.IsDir() || err != SkipDir { 372 return err 373 } 374 } 375 } 376 } 377 return nil 378 } 379 380 // WalkDir walks the file tree rooted at root, calling fn for each file or 381 // directory in the tree, including root. 382 // 383 // All errors that arise visiting files and directories are filtered by fn: 384 // see the [fs.WalkDirFunc] documentation for details. 385 // 386 // The files are walked in lexical order, which makes the output deterministic 387 // but requires WalkDir to read an entire directory into memory before proceeding 388 // to walk that directory. 389 // 390 // WalkDir does not follow symbolic links. 391 // 392 // WalkDir calls fn with paths that use the separator character appropriate 393 // for the operating system. This is unlike [io/fs.WalkDir], which always 394 // uses slash separated paths. 395 func WalkDir(root string, fn fs.WalkDirFunc) error { 396 info, err := os.Lstat(root) 397 if err != nil { 398 err = fn(root, nil, err) 399 } else { 400 err = walkDir(root, fs.FileInfoToDirEntry(info), fn) 401 } 402 if err == SkipDir || err == SkipAll { 403 return nil 404 } 405 return err 406 } 407 408 // Walk walks the file tree rooted at root, calling fn for each file or 409 // directory in the tree, including root. 410 // 411 // All errors that arise visiting files and directories are filtered by fn: 412 // see the [WalkFunc] documentation for details. 413 // 414 // The files are walked in lexical order, which makes the output deterministic 415 // but requires Walk to read an entire directory into memory before proceeding 416 // to walk that directory. 417 // 418 // Walk does not follow symbolic links. 419 // 420 // Walk is less efficient than [WalkDir], introduced in Go 1.16, 421 // which avoids calling os.Lstat on every visited file or directory. 422 func Walk(root string, fn WalkFunc) error { 423 info, err := os.Lstat(root) 424 if err != nil { 425 err = fn(root, nil, err) 426 } else { 427 err = walk(root, info, fn) 428 } 429 if err == SkipDir || err == SkipAll { 430 return nil 431 } 432 return err 433 } 434 435 // readDirNames reads the directory named by dirname and returns 436 // a sorted list of directory entry names. 437 func readDirNames(dirname string) ([]string, error) { 438 f, err := os.Open(dirname) 439 if err != nil { 440 return nil, err 441 } 442 names, err := f.Readdirnames(-1) 443 f.Close() 444 if err != nil { 445 return nil, err 446 } 447 sort.Strings(names) 448 return names, nil 449 } 450 451 // Base returns the last element of path. 452 // Trailing path separators are removed before extracting the last element. 453 // If the path is empty, Base returns ".". 454 // If the path consists entirely of separators, Base returns a single separator. 455 func Base(path string) string { 456 return filepathlite.Base(path) 457 } 458 459 // Dir returns all but the last element of path, typically the path's directory. 460 // After dropping the final element, Dir calls [Clean] on the path and trailing 461 // slashes are removed. 462 // If the path is empty, Dir returns ".". 463 // If the path consists entirely of separators, Dir returns a single separator. 464 // The returned path does not end in a separator unless it is the root directory. 465 func Dir(path string) string { 466 return filepathlite.Dir(path) 467 } 468 469 // VolumeName returns leading volume name. 470 // Given "C:\foo\bar" it returns "C:" on Windows. 471 // Given "\\host\share\foo" it returns "\\host\share". 472 // On other platforms it returns "". 473 func VolumeName(path string) string { 474 return filepathlite.VolumeName(path) 475 } 476