1 files changed, 136 insertions, 0 deletions
diff --git a/src/pkg/path/path.go b/src/pkg/path/path.go
new file mode 100644
index 000000000..a7e2c26c3
--- /dev/null
+++ b/src/pkg/path/path.go
@@ -0,0 +1,136 @@
+// 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 ""
+}
+