1 #include <u.h>
2 #include <libc.h>
3 
4 /*
5  * In place, rewrite name to compress multiple /, eliminate ., and process ..
6  */
7 #define SEP(x)	((x)=='/' || (x) == 0)
8 char*
9 cleanname(char *name)
10 {
11 	char *p, *q, *dotdot;
12 	int rooted;
13 
14 	rooted = name[0] == '/';
15 
16 	/*
17 	 * invariants:
18 	 *	p points at beginning of path element we're considering.
19 	 *	q points just past the last path element we wrote (no slash).
20 	 *	dotdot points just past the point where .. cannot backtrack
21 	 *		any further (no slash).
22 	 */
23 	p = q = dotdot = name+rooted;
24 	while(*p) {
25 		if(p[0] == '/')	/* null element */
26 			p++;
27 		else if(p[0] == '.' && SEP(p[1]))
28 			p += 1;	/* don't count the separator in case it is nul */
29 		else if(p[0] == '.' && p[1] == '.' && SEP(p[2])) {
30 			p += 2;
31 			if(q > dotdot) {	/* can backtrack */
32 				while(--q > dotdot && *q != '/')
33 					;
34 			} else if(!rooted) {	/* /.. is / but ./../ is .. */
35 				if(q != name)
36 					*q++ = '/';
37 				*q++ = '.';
38 				*q++ = '.';
39 				dotdot = q;
40 			}
41 		} else {	/* real path element */
42 			if(q != name+rooted)
43 				*q++ = '/';
44 			while((*q = *p) != '/' && *q != 0)
45 				p++, q++;
46 		}
47 	}
48 	if(q == name)	/* empty string is really ``.'' */
49 		*q++ = '.';
50 	*q = '\0';
51 	return name;
52 }