dhcpv4: implement router configuration option

RFC 2132 defines:

3.5. Router Option

   The router option specifies a list of IP addresses for routers on the
   client's subnet.  Routers SHOULD be listed in order of preference.

   The code for the router option is 3.  The minimum length for the
   router option is 4 octets, and the length MUST always be a multiple
   of 4.

    Code   Len         Address 1               Address 2
   +-----+-----+-----+-----+-----+-----+-----+-----+--
   |  3  |  n  |  a1 |  a2 |  a3 |  a4 |  a1 |  a2 |  ...
   +-----+-----+-----+-----+-----+-----+-----+-----+--

4 files changed, 34 insertions, 2 deletions

diff --git a/README b/README
index 6011b0f..b86df25 100644
--- a/README
+++ b/README
@@ -85,6 +85,8 @@ ndp		string	disabled		Neighbor Discovery Proxy
 
 dynamicdhcp	bool	1			dynamically create leases
 						for DHCPv4 and DHCPv6
+router          list    <local address>         Routers to announce
+                                                accepts IPv4 only
 dns		list	<local address>		DNS servers to announce
 						accepts IPv4 and IPv6
 domain		list	<local search domain>	Search domains to announce
diff --git a/src/config.c b/src/config.c
index 068d1a7..835db13 100644
--- a/src/config.c
+++ b/src/config.c
@@ -30,6 +30,7 @@ enum {
 	IFACE_ATTR_DHCPV4,
 	IFACE_ATTR_DHCPV6,
 	IFACE_ATTR_NDP,
+	IFACE_ATTR_ROUTER,
 	IFACE_ATTR_DNS,
 	IFACE_ATTR_DOMAIN,
 	IFACE_ATTR_FILTER_CLASS,
@@ -61,6 +62,7 @@ static const struct blobmsg_policy iface_attrs[IFACE_ATTR_MAX] = {
 	[IFACE_ATTR_DHCPV4] = { .name = "dhcpv4", .type = BLOBMSG_TYPE_STRING },
 	[IFACE_ATTR_DHCPV6] = { .name = "dhcpv6", .type = BLOBMSG_TYPE_STRING },
 	[IFACE_ATTR_NDP] = { .name = "ndp", .type = BLOBMSG_TYPE_STRING },
+	[IFACE_ATTR_ROUTER] = { .name = "router", .type = BLOBMSG_TYPE_ARRAY },
 	[IFACE_ATTR_DNS] = { .name = "dns", .type = BLOBMSG_TYPE_ARRAY },
 	[IFACE_ATTR_DOMAIN] = { .name = "domain", .type = BLOBMSG_TYPE_ARRAY },
 	[IFACE_ATTR_FILTER_CLASS] = { .name = "filter_class", .type = BLOBMSG_TYPE_STRING },
@@ -152,6 +154,7 @@ static void clean_interface(struct interface *iface)
 	free(iface->search);
 	free(iface->upstream);
 	free(iface->static_ndp);
+	free(iface->dhcpv4_router);
 	free(iface->dhcpv4_dns);
 	free(iface->dhcpv6_raw);
 	free(iface->filter_class);
@@ -409,6 +412,28 @@ int config_parse_interface(void *data, size_t len, const char *name, bool overwr
 			goto err;
 	}
 
+	if ((c = tb[IFACE_ATTR_ROUTER])) {
+		struct blob_attr *cur;
+		unsigned rem;
+
+		blobmsg_for_each_attr(cur, c, rem) {
+			if (blobmsg_type(cur) != BLOBMSG_TYPE_STRING || !blobmsg_check_attr(cur, NULL))
+				continue;
+
+			struct in_addr addr4;
+			if (inet_pton(AF_INET, blobmsg_get_string(cur), &addr4) == 1) {
+				iface->dhcpv4_router = realloc(iface->dhcpv4_router,
+						(++iface->dhcpv4_router_cnt) * sizeof(*iface->dhcpv4_router));
+				if (!iface->dhcpv4_router)
+					goto err;
+
+				iface->dhcpv4_router[iface->dhcpv4_router_cnt - 1] = addr4;
+			} else {
+				goto err;
+			}
+		}
+	}
+
 	if ((c = tb[IFACE_ATTR_DNS])) {
 		struct blob_attr *cur;
 		unsigned rem;
diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 2093ecd..7b200cd 100644
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -384,8 +384,11 @@ static void handle_dhcpv4(void *addr, void *data, size_t len,
 					len, search_buf);
 	}
 
-	dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER, 4, &ifaddr.sin_addr);
-
+	if (iface->dhcpv4_router_cnt == 0)
+		dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER, 4, &ifaddr.sin_addr);
+	else
+		dhcpv4_put(&reply, &cookie, DHCPV4_OPT_ROUTER,
+				4 * iface->dhcpv4_router_cnt, iface->dhcpv4_router);
 
 
 	if (iface->dhcpv4_dns_cnt == 0)
diff --git a/src/odhcpd.h b/src/odhcpd.h
index b2b38dc..4c0c28c 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -147,6 +147,8 @@ struct interface {
 	// DHCPv4
 	struct in_addr dhcpv4_start;
 	struct in_addr dhcpv4_end;
+	struct in_addr *dhcpv4_router;
+	size_t dhcpv4_router_cnt;
 	struct in_addr *dhcpv4_dns;
 	size_t dhcpv4_dns_cnt;
 	uint32_t dhcpv4_leasetime;