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 "os" 17 "sort" 18 "strings" 19 ) 20 21 // A lazybuf is a lazily constructed path buffer. 22 // It supports append, reading previously appended bytes, 23 // and retrieving the final string. It does not allocate a buffer 24 // to hold the output until that output diverges from s. 25 type lazybuf struct { 26 path string 27 buf []byte 28 w int 29 volAndPath string 30 volLen int 31 } 32 33 func (b *lazybuf) index(i int) byte { 34 if b.buf != nil { 35 return b.buf[i] 36 } 37 return b.path[i] 38 } 39 40 func (b *lazybuf) append(c byte) { 41 if b.buf == nil { 42 if b.w < len(b.path) && b.path[b.w] == c { 43 b.w++ 44 return 45 } 46 b.buf = make([]byte, len(b.path)) 47 copy(b.buf, b.path[:b.w]) 48 } 49 b.buf[b.w] = c 50 b.w++ 51 } 52 53 func (b *lazybuf) string() string { 54 if b.buf == nil { 55 return b.volAndPath[:b.volLen+b.w] 56 } 57 return b.volAndPath[:b.volLen] + string(b.buf[:b.w]) 58 } 59 60 const ( 61 Separator = os.PathSeparator 62 ListSeparator = os.PathListSeparator 63 ) 64 65 // Clean returns the shortest path name equivalent to path 66 // by purely lexical processing. It applies the following rules 67 // iteratively until no further processing can be done: 68 // 69 // 1. Replace multiple Separator elements with a single one. 70 // 2. Eliminate each . path name element (the current directory). 71 // 3. Eliminate each inner .. path name element (the parent directory) 72 // along with the non-.. element that precedes it. 73 // 4. Eliminate .. elements that begin a rooted path: 74 // that is, replace "/.." by "/" at the beginning of a path, 75 // assuming Separator is '/'. 76 // 77 // The returned path ends in a slash only if it represents a root directory, 78 // such as "/" on Unix or `C:\` on Windows. 79 // 80 // Finally, any occurrences of slash are replaced by Separator. 81 // 82 // If the result of this process is an empty string, Clean 83 // returns the string ".". 84 // 85 // See also Rob Pike, ``Lexical File Names in Plan 9 or 86 // Getting Dot-Dot Right,'' 87 // https://9p.io/sys/doc/lexnames.html 88 func Clean(path string) string { 89 originalPath := path 90 volLen := volumeNameLen(path) 91 path = path[volLen:] 92 if path == "" { 93 if volLen > 1 && originalPath[1] != ':' { 94 // should be UNC 95 return FromSlash(originalPath) 96 } 97 return originalPath + "." 98 } 99 rooted := os.IsPathSeparator(path[0]) 100 101 // Invariants: 102 // reading from path; r is index of next byte to process. 103 // writing to buf; w is index of next byte to write. 104 // dotdot is index in buf where .. must stop, either because 105 // it is the leading slash or it is a leading ../../.. prefix. 106 n := len(path) 107 out := lazybuf{path: path, volAndPath: originalPath, volLen: volLen} 108 r, dotdot := 0, 0 109 if rooted { 110 out.append(Separator) 111 r, dotdot = 1, 1 112 } 113 114 for r < n { 115 switch { 116 case os.IsPathSeparator(path[r]): 117 // empty path element 118 r++ 119 case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])): 120 // . element 121 r++ 122 case path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])): 123 // .. element: remove to last separator 124 r += 2 125 switch { 126 case out.w > dotdot: 127 // can backtrack 128 out.w-- 129 for out.w > dotdot && !os.IsPathSeparator(out.index(out.w)) { 130 out.w-- 131 } 132 case !rooted: 133 // cannot backtrack, but not rooted, so append .. element. 134 if out.w > 0 { 135 out.append(Separator) 136 } 137 out.append('.') 138 out.append('.') 139 dotdot = out.w 140 } 141 default: 142 // real path element. 143 // add slash if needed 144 if rooted && out.w != 1 || !rooted && out.w != 0 { 145 out.append(Separator) 146 } 147 // copy element 148 for ; r < n && !os.IsPathSeparator(path[r]); r++ { 149 out.append(path[r]) 150 } 151 } 152 } 153 154 // Turn empty string into "." 155 if out.w == 0 { 156 out.append('.') 157 } 158 159 return FromSlash(out.string()) 160 } 161 162 // ToSlash returns the result of replacing each separator character 163 // in path with a slash ('/') character. Multiple separators are 164 // replaced by multiple slashes. 165 func ToSlash(path string) string { 166 if Separator == '/' { 167 return path 168 } 169 return strings.ReplaceAll(path, string(Separator), "/") 170 } 171 172 // FromSlash returns the result of replacing each slash ('/') character 173 // in path with a separator character. Multiple slashes are replaced 174 // by multiple separators. 175 func FromSlash(path string) string { 176 if Separator == '/' { 177 return path 178 } 179 return strings.ReplaceAll(path, "/", string(Separator)) 180 } 181 182 // SplitList splits a list of paths joined by the OS-specific ListSeparator, 183 // usually found in PATH or GOPATH environment variables. 184 // Unlike strings.Split, SplitList returns an empty slice when passed an empty 185 // string. 186 func SplitList(path string) []string { 187 return splitList(path) 188 } 189 190 // Split splits path immediately following the final Separator, 191 // separating it into a directory and file name component. 192 // If there is no Separator in path, Split returns an empty dir 193 // and file set to path. 194 // The returned values have the property that path = dir+file. 195 func Split(path string) (dir, file string) { 196 vol := VolumeName(path) 197 i := len(path) - 1 198 for i >= len(vol) && !os.IsPathSeparator(path[i]) { 199 i-- 200 } 201 return path[:i+1], path[i+1:] 202 } 203 204 // Join joins any number of path elements into a single path, adding 205 // a Separator if necessary. Join calls Clean on the result; in particular, 206 // all empty strings are ignored. 207 // On Windows, the result is a UNC path if and only if the first path 208 // element is a UNC path. 209 func Join(elem ...string) string { 210 return join(elem) 211 } 212 213 // Ext returns the file name extension used by path. 214 // The extension is the suffix beginning at the final dot 215 // in the final element of path; it is empty if there is 216 // no dot. 217 func Ext(path string) string { 218 for i := len(path) - 1; i >= 0 && !os.IsPathSeparator(path[i]); i-- { 219 if path[i] == '.' { 220 return path[i:] 221 } 222 } 223 return "" 224 } 225 226 // EvalSymlinks returns the path name after the evaluation of any symbolic 227 // links. 228 // If path is relative the result will be relative to the current directory, 229 // unless one of the components is an absolute symbolic link. 230 // EvalSymlinks calls Clean on the result. 231 func EvalSymlinks(path string) (string, error) { 232 return evalSymlinks(path) 233 } 234 235 // Abs returns an absolute representation of path. 236 // If the path is not absolute it will be joined with the current 237 // working directory to turn it into an absolute path. The absolute 238 // path name for a given file is not guaranteed to be unique. 239 // Abs calls Clean on the result. 240 func Abs(path string) (string, error) { 241 return abs(path) 242 } 243 244 func unixAbs(path string) (string, error) { 245 if IsAbs(path) { 246 return Clean(path), nil 247 } 248 wd, err := os.Getwd() 249 if err != nil { 250 return "", err 251 } 252 return Join(wd, path), nil 253 } 254 255 // Rel returns a relative path that is lexically equivalent to targpath when 256 // joined to basepath with an intervening separator. That is, 257 // Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself. 258 // On success, the returned path will always be relative to basepath, 259 // even if basepath and targpath share no elements. 260 // An error is returned if targpath can't be made relative to basepath or if 261 // knowing the current working directory would be necessary to compute it. 262 // Rel calls Clean on the result. 263 func Rel(basepath, targpath string) (string, error) { 264 baseVol := VolumeName(basepath) 265 targVol := VolumeName(targpath) 266 base := Clean(basepath) 267 targ := Clean(targpath) 268 if sameWord(targ, base) { 269 return ".", nil 270 } 271 base = base[len(baseVol):] 272 targ = targ[len(targVol):] 273 if base == "." { 274 base = "" 275 } 276 // Can't use IsAbs - `\a` and `a` are both relative in Windows. 277 baseSlashed := len(base) > 0 && base[0] == Separator 278 targSlashed := len(targ) > 0 && targ[0] == Separator 279 if baseSlashed != targSlashed || !sameWord(baseVol, targVol) { 280 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 281 } 282 // Position base[b0:bi] and targ[t0:ti] at the first differing elements. 283 bl := len(base) 284 tl := len(targ) 285 var b0, bi, t0, ti int 286 for { 287 for bi < bl && base[bi] != Separator { 288 bi++ 289 } 290 for ti < tl && targ[ti] != Separator { 291 ti++ 292 } 293 if !sameWord(targ[t0:ti], base[b0:bi]) { 294 break 295 } 296 if bi < bl { 297 bi++ 298 } 299 if ti < tl { 300 ti++ 301 } 302 b0 = bi 303 t0 = ti 304 } 305 if base[b0:bi] == ".." { 306 return "", errors.New("Rel: can't make " + targpath + " relative to " + basepath) 307 } 308 if b0 != bl { 309 // Base elements left. Must go up before going down. 310 seps := strings.Count(base[b0:bl], string(Separator)) 311 size := 2 + seps*3 312 if tl != t0 { 313 size += 1 + tl - t0 314 } 315 buf := make([]byte, size) 316 n := copy(buf, "..") 317 for i := 0; i < seps; i++ { 318 buf[n] = Separator 319 copy(buf[n+1:], "..") 320 n += 3 321 } 322 if t0 != tl { 323 buf[n] = Separator 324 copy(buf[n+1:], targ[t0:]) 325 } 326 return string(buf), nil 327 } 328 return targ[t0:], nil 329 } 330 331 // SkipDir is used as a return value from WalkFuncs to indicate that 332 // the directory named in the call is to be skipped. It is not returned 333 // as an error by any function. 334 var SkipDir = errors.New("skip this directory") 335 336 // WalkFunc is the type of the function called for each file or directory 337 // visited by Walk. The path argument contains the argument to Walk as a 338 // prefix; that is, if Walk is called with "dir", which is a directory 339 // containing the file "a", the walk function will be called with argument 340 // "dir/a". The info argument is the os.FileInfo for the named path. 341 // 342 // If there was a problem walking to the file or directory named by path, the 343 // incoming error will describe the problem and the function can decide how 344 // to handle that error (and Walk will not descend into that directory). In the 345 // case of an error, the info argument will be nil. If an error is returned, 346 // processing stops. The sole exception is when the function returns the special 347 // value SkipDir. If the function returns SkipDir when invoked on a directory, 348 // Walk skips the directory's contents entirely. If the function returns SkipDir 349 // when invoked on a non-directory file, Walk skips the remaining files in the 350 // containing directory. 351 type WalkFunc func(path string, info os.FileInfo, err error) error 352 353 var lstat = os.Lstat // for testing 354 355 // walk recursively descends path, calling walkFn. 356 func walk(path string, info os.FileInfo, walkFn WalkFunc) error { 357 if !info.IsDir() { 358 return walkFn(path, info, nil) 359 } 360 361 names, err := readDirNames(path) 362 err1 := walkFn(path, info, err) 363 // If err != nil, walk can't walk into this directory. 364 // err1 != nil means walkFn want walk to skip this directory or stop walking. 365 // Therefore, if one of err and err1 isn't nil, walk will return. 366 if err != nil || err1 != nil { 367 // The caller's behavior is controlled by the return value, which is decided 368 // by walkFn. walkFn may ignore err and return nil. 369 // If walkFn returns SkipDir, it will be handled by the caller. 370 // So walk should return whatever walkFn returns. 371 return err1 372 } 373 374 for _, name := range names { 375 filename := Join(path, name) 376 fileInfo, err := lstat(filename) 377 if err != nil { 378 if err := walkFn(filename, fileInfo, err); err != nil && err != SkipDir { 379 return err 380 } 381 } else { 382 err = walk(filename, fileInfo, walkFn) 383 if err != nil { 384 if !fileInfo.IsDir() || err != SkipDir { 385 return err 386 } 387 } 388 } 389 } 390 return nil 391 } 392 393 // Walk walks the file tree rooted at root, calling walkFn for each file or 394 // directory in the tree, including root. All errors that arise visiting files 395 // and directories are filtered by walkFn. The files are walked in lexical 396 // order, which makes the output deterministic but means that for very 397 // large directories Walk can be inefficient. 398 // Walk does not follow symbolic links. 399 func Walk(root string, walkFn WalkFunc) error { 400 info, err := os.Lstat(root) 401 if err != nil { 402 err = walkFn(root, nil, err) 403 } else { 404 err = walk(root, info, walkFn) 405 } 406 if err == SkipDir { 407 return nil 408 } 409 return err 410 } 411 412 // readDirNames reads the directory named by dirname and returns 413 // a sorted list of directory entries. 414 func readDirNames(dirname string) ([]string, error) { 415 f, err := os.Open(dirname) 416 if err != nil { 417 return nil, err 418 } 419 names, err := f.Readdirnames(-1) 420 f.Close() 421 if err != nil { 422 return nil, err 423 } 424 sort.Strings(names) 425 return names, nil 426 } 427 428 // Base returns the last element of path. 429 // Trailing path separators are removed before extracting the last element. 430 // If the path is empty, Base returns ".". 431 // If the path consists entirely of separators, Base returns a single separator. 432 func Base(path string) string { 433 if path == "" { 434 return "." 435 } 436 // Strip trailing slashes. 437 for len(path) > 0 && os.IsPathSeparator(path[len(path)-1]) { 438 path = path[0 : len(path)-1] 439 } 440 // Throw away volume name 441 path = path[len(VolumeName(path)):] 442 // Find the last element 443 i := len(path) - 1 444 for i >= 0 && !os.IsPathSeparator(path[i]) { 445 i-- 446 } 447 if i >= 0 { 448 path = path[i+1:] 449 } 450 // If empty now, it had only slashes. 451 if path == "" { 452 return string(Separator) 453 } 454 return path 455 } 456 457 // Dir returns all but the last element of path, typically the path's directory. 458 // After dropping the final element, Dir calls Clean on the path and trailing 459 // slashes are removed. 460 // If the path is empty, Dir returns ".". 461 // If the path consists entirely of separators, Dir returns a single separator. 462 // The returned path does not end in a separator unless it is the root directory. 463 func Dir(path string) string { 464 vol := VolumeName(path) 465 i := len(path) - 1 466 for i >= len(vol) && !os.IsPathSeparator(path[i]) { 467 i-- 468 } 469 dir := Clean(path[len(vol) : i+1]) 470 if dir == "." && len(vol) > 2 { 471 // must be UNC 472 return vol 473 } 474 return vol + dir 475 } 476 477 // VolumeName returns leading volume name. 478 // Given "C:\foo\bar" it returns "C:" on Windows. 479 // Given "\\host\share\foo" it returns "\\host\share". 480 // On other platforms it returns "". 481 func VolumeName(path string) string { 482 return path[:volumeNameLen(path)] 483 } 484