1 files changed, 52 insertions, 0 deletions
diff --git a/src/lib9/cleanname.c b/src/lib9/cleanname.c
new file mode 100644
index 00000000..cfcb4822
--- /dev/null
+++ b/src/lib9/cleanname.c
@@ -0,0 +1,52 @@
+#include <u.h>
+#include <libc.h>
+
+/*
+ * In place, rewrite name to compress multiple /, eliminate ., and process ..
+ */
+#define SEP(x)	((x)=='/' || (x) == 0)
+char*
+cleanname(char *name)
+{
+	char *p, *q, *dotdot;
+	int rooted;
+
+	rooted = name[0] == '/';
+
+	/*
+	 * invariants:
+	 *	p points at beginning of path element we're considering.
+	 *	q points just past the last path element we wrote (no slash).
+	 *	dotdot points just past the point where .. cannot backtrack
+	 *		any further (no slash).
+	 */
+	p = q = dotdot = name+rooted;
+	while(*p) {
+		if(p[0] == '/')	/* null element */
+			p++;
+		else if(p[0] == '.' && SEP(p[1]))
+			p += 1;	/* don't count the separator in case it is nul */
+		else if(p[0] == '.' && p[1] == '.' && SEP(p[2])) {
+			p += 2;
+			if(q > dotdot) {	/* can backtrack */
+				while(--q > dotdot && *q != '/')
+					;
+			} else if(!rooted) {	/* /.. is / but ./../ is .. */
+				if(q != name)
+					*q++ = '/';
+				*q++ = '.';
+				*q++ = '.';
+				dotdot = q;
+			}
+		} else {	/* real path element */
+			if(q != name+rooted)
+				*q++ = '/';
+			while((*q = *p) != '/' && *q != 0)
+				p++, q++;
+		}
+	}
+	if(q == name)	/* empty string is really ``.'' */
+		*q++ = '.';
+	*q = '\0';
+	return name;
+}