+/* Check if a given label represents a valid DNS label
+ * Return pointer to the first character after the label upon success,
+ * NULL otherwise.
+ * See RFC1035, 2.3.1
+ */
+/* We don't need to be particularly anal. For example, allowing _, hyphen
+ * at the end, or leading and trailing dots would be ok, since it
+ * can't be used for attacks. (Leading hyphen can be, if someone uses
+ * cmd "$hostname"
+ * in the script: then hostname may be treated as an option)
+ */
+static const char *valid_domain_label(const char *label)
+{
+ unsigned char ch;
+ unsigned pos = 0;
+
+ for (;;) {
+ ch = *label;
+ if ((ch|0x20) < 'a' || (ch|0x20) > 'z') {
+ if (pos == 0) {
+ /* label must begin with letter */
+ return NULL;
+ }
+ if (ch < '0' || ch > '9') {
+ if (ch == '\0' || ch == '.')
+ return label;
+ /* DNS allows only '-', but we are more permissive */
+ if (ch != '-' && ch != '_')
+ return NULL;
+ }
+ }
+ label++;
+ pos++;
+ //Do we want this?
+ //if (pos > 63) /* NS_MAXLABEL; labels must be 63 chars or less */
+ // return NULL;
+ }
+}
+
+/* Check if a given name represents a valid DNS name */
+/* See RFC1035, 2.3.1 */
+static int good_hostname(const char *name)
+{
+ //const char *start = name;
+
+ for (;;) {
+ name = valid_domain_label(name);
+ if (!name)
+ return 0;
+ if (!name[0])
+ return 1;
+ //Do we want this?
+ //return ((name - start) < 1025); /* NS_MAXDNAME */
+ name++;
+ }
+}
+