Turns out my encoding was correct after all :)

I've now split it out into it's own function for easier maintenance though.

diff --git a/dhcp.c b/dhcp.c
index 578ec1126fb394eaef85aaff7e10073d1a0c6066..0f8a1724dbf684cf4f11da19661d9cfc408ea419 100644 (file)
--- a/dhcp.c
+++ b/dhcp.c
@@ -701,13 +701,37 @@ get_option_routes(const struct dhcp_message *dhcp)
        return routes;
 }
 
+static size_t
+encode_rfc1035(const char *src, uint8_t *dst, size_t len)
+{
+       const char *c = src;
+       uint8_t *p = dst;
+       uint8_t *lp = p++;
+
+       while (c < src + len) {
+               if (*c == '\0')
+                       break;
+               if (*c == '.') {
+                       *lp = p - lp - 1;
+                       if (*lp == 0)
+                               return p - dst;
+                       lp = p++;
+               } else
+                       *p++ = (uint8_t) *c;
+               c++;
+       }
+       *lp = p - lp - 1;
+       *p++ = '\0';
+       return p - dst;
+}
+
 ssize_t
 make_message(struct dhcp_message **message,
             const struct interface *iface, const struct dhcp_lease *lease,
             uint32_t xid, uint8_t type, const struct options *options)
 {
        struct dhcp_message *dhcp;
-       uint8_t *m, *p;
+       uint8_t *m, *lp, *p;
        uint8_t *n_params = NULL;
        time_t up = uptime() - iface->start_uptime;
        uint32_t ul;
@@ -832,7 +856,8 @@ make_message(struct dhcp_message **message,
                        } else {
                                /* IETF DHC-FQDN option (81), RFC4702 */
                                *p++ = DHCP_FQDN;
-                               *p++ = options->hostname[0] + 3;
+                               lp = p;
+                               *p++ = 3;
                                /*
                                 * Flags: 0000NEOS
                                 * S: 1 => Client requests Server to update
@@ -843,19 +868,13 @@ make_message(struct dhcp_message **message,
                                 * N: 1 => Client requests Server to not
                                 *         update DNS
                                 */
-                               *p++ = (options->fqdn & 0x9);
-                               /* FIXME: We should use DNS format as 
-                                * RFC4702 claims ASCII is deprecated.
-                                * However I cannot find anything that says
-                                * what this encoding actually is, so we
-                                * use ASCII.
-                                * To flip the encoding bit, set it like so
-                                * *p++ = (options->fqdn & 0x9) | 0x4; */
+                               *p++ = (options->fqdn & 0x09) | 0x04;
                                *p++ = 0; /* from server for PTR RR */
                                *p++ = 0; /* from server for A RR if S=1 */
-                               memcpy(p, options->hostname + 1, 
-                                      options->hostname[0]);
-                               p += options->hostname[0];
+                               ul = encode_rfc1035(options->hostname + 1, p,
+                                                   options->hostname[0]);
+                               *lp += ul;
+                               p += ul;
                        }
                }