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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The path package implements utility routines for manipulating
// slash-separated filename paths.
package path
import "io"
// Clean returns the shortest path name equivalent to path
// by purely lexical processing. It applies the following rules
// iteratively until no further processing can be done:
//
// 1. Replace multiple slashes with a single slash.
// 2. Eliminate each . path name element (the current directory).
// 3. Eliminate each inner .. path name element (the parent directory)
// along with the non-.. element that precedes it.
// 4. Eliminate .. elements that begin a rooted path:
// that is, replace "/.." by "/" at the beginning of a path.
//
// If the result of this process is an empty string, Clean
// returns the string ".".
//
// See also Rob Pike, ``Lexical File Names in Plan 9 or
// Getting Dot-Dot right,''
// http://plan9.bell-labs.com/sys/doc/lexnames.html
func Clean(path string) string {
if path == "" {
return "."
}
rooted := path[0] == '/';
n := len(path);
// Invariants:
// reading from path; r is index of next byte to process.
// writing to buf; w is index of next byte to write.
// dotdot is index in buf where .. must stop, either because
// it is the leading slash or it is a leading ../../.. prefix.
buf := io.StringBytes(path);
r, w, dotdot := 0, 0, 0;
if rooted {
r, w, dotdot = 1, 1, 1;
}
for r < n {
switch {
case path[r] == '/':
// empty path element
r++;
case path[r] == '.' && (r+1 == n || path[r+1] == '/'):
// . element
r++;
case path[r] == '.' && path[r+1] == '.' && (r+2 == n || path[r+2] == '/'):
// .. element: remove to last /
r += 2;
switch {
case w > dotdot:
// can backtrack
w--;
for w > dotdot && buf[w] != '/' {
w--;
}
case !rooted:
// cannot backtrack, but not rooted, so append .. element.
if w > 0 {
buf[w] = '/';
w++;
}
buf[w] = '.';
w++;
buf[w] = '.';
w++;
dotdot = w;
}
default:
// real path element.
// add slash if needed
if rooted && w != 1 || !rooted && w != 0 {
buf[w] = '/';
w++;
}
// copy element
for ; r < n && path[r] != '/'; r++ {
buf[w] = path[r];
w++;
}
}
}
// Turn empty string into "."
if w == 0 {
buf[w] = '.';
w++;
}
return string(buf[0:w]);
}
// Split splits path immediately following the final slash,
// separating it into a directory and file name component.
// If there is no slash in path, DirFile returns an empty dir and
// file set to path.
func Split(path string) (dir, file string) {
for i := len(path)-1; i >= 0; i-- {
if path[i] == '/' {
return path[0:i+1], path[i+1:len(path)];
}
}
return "", path
}
// Join joins dir and file into a single path, adding a separating
// slash if necessary. If dir is empty, it returns file.
func Join(dir, file string) string {
if dir == "" {
return file;
}
return Clean(dir + "/" + file);
}
// Ext returns the file name extension used by path.
// The extension is the suffix beginning at the final dot
// in the final slash-separated element of path;
// it is empty if there is no dot.
func Ext(path string) string {
dot := -1;
for i := len(path)-1; i >= 0 && path[i] != '/'; i-- {
if path[i] == '.' {
return path[i:len(path)];
}
}
return ""
}
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