1 files changed, 96 insertions, 0 deletions
diff --git a/path.c b/path.c
index 496123c..5983255 100644
--- a/path.c
+++ b/path.c
@@ -343,3 +343,99 @@ const char *make_relative_path(const char *abs, const char *base)
 	strcpy(buf, abs + baselen);
 	return buf;
 }
+
+/*
+ * path = absolute path
+ * buf = buffer of at least max(2, strlen(path)+1) bytes
+ * It is okay if buf == path, but they should not overlap otherwise.
+ *
+ * Performs the following normalizations on path, storing the result in buf:
+ * - Removes trailing slashes.
+ * - Removes empty components.
+ * - Removes "." components.
+ * - Removes ".." components, and the components the precede them.
+ * "" and paths that contain only slashes are normalized to "/".
+ * Returns the length of the output.
+ *
+ * Note that this function is purely textual.  It does not follow symlinks,
+ * verify the existence of the path, or make any system calls.
+ */
+int normalize_absolute_path(char *buf, const char *path)
+{
+	const char *comp_start = path, *comp_end = path;
+	char *dst = buf;
+	int comp_len;
+	assert(buf);
+	assert(path);
+
+	while (*comp_start) {
+		assert(*comp_start == '/');
+		while (*++comp_end && *comp_end != '/')
+			; /* nothing */
+		comp_len = comp_end - comp_start;
+
+		if (!strncmp("/",  comp_start, comp_len) ||
+		    !strncmp("/.", comp_start, comp_len))
+			goto next;
+
+		if (!strncmp("/..", comp_start, comp_len)) {
+			while (dst > buf && *--dst != '/')
+				; /* nothing */
+			goto next;
+		}
+
+		memcpy(dst, comp_start, comp_len);
+		dst += comp_len;
+	next:
+		comp_start = comp_end;
+	}
+
+	if (dst == buf)
+		*dst++ = '/';
+
+	*dst = '\0';
+	return dst - buf;
+}
+
+/*
+ * path = Canonical absolute path
+ * prefix_list = Colon-separated list of absolute paths
+ *
+ * Determines, for each path in parent_list, whether the "prefix" really
+ * is an ancestor directory of path.  Returns the length of the longest
+ * ancestor directory, excluding any trailing slashes, or -1 if no prefix
+ * is an ancestor.  (Note that this means 0 is returned if prefix_list is
+ * "/".) "/foo" is not considered an ancestor of "/foobar".  Directories
+ * are not considered to be their own ancestors.  path must be in a
+ * canonical form: empty components, or "." or ".." components are not
+ * allowed.  prefix_list may be null, which is like "".
+ */
+int longest_ancestor_length(const char *path, const char *prefix_list)
+{
+	char buf[PATH_MAX+1];
+	const char *ceil, *colon;
+	int len, max_len = -1;
+
+	if (prefix_list == NULL || !strcmp(path, "/"))
+		return -1;
+
+	for (colon = ceil = prefix_list; *colon; ceil = colon+1) {
+		for (colon = ceil; *colon && *colon != ':'; colon++);
+		len = colon - ceil;
+		if (len == 0 || len > PATH_MAX || !is_absolute_path(ceil))
+			continue;
+		strlcpy(buf, ceil, len+1);
+		len = normalize_absolute_path(buf, buf);
+		/* Strip "trailing slashes" from "/". */
+		if (len == 1)
+			len = 0;
+
+		if (!strncmp(path, buf, len) &&
+		    path[len] == '/' &&
+		    len > max_len) {
+			max_len = len;
+		}
+	}
+
+	return max_len;
+}