netutils/dhcpc: parse DHCP NTP server option

Request DHCP option 42 and store the returned IPv4 NTP server
addresses in struct dhcpc_state for later consumers.

Signed-off-by: Jerry Ma <masc2008@gmail.com>

Author: masc2008

include/netutils/dhcpc.h

@@ -55,6 +55,10 @@
 #  define CONFIG_NETDB_DNSSERVER_NAMESERVERS 1
 #endif
 
+#if !defined(CONFIG_NETUTILS_DHCPC_NTP_SERVER_NUM)
+#  define CONFIG_NETUTILS_DHCPC_NTP_SERVER_NUM 1
+#endif
+
 /****************************************************************************
  * Public Types
  ****************************************************************************/
@@ -66,6 +70,8 @@ struct dhcpc_state
   struct in_addr netmask;
   struct in_addr dnsaddr[CONFIG_NETDB_DNSSERVER_NAMESERVERS];
   uint8_t        num_dnsaddr;     /* Number of DNS addresses received */
+  struct in_addr ntpaddr[CONFIG_NETUTILS_DHCPC_NTP_SERVER_NUM];
+  uint8_t        num_ntpaddr;     /* Number of NTP addresses received */
   struct in_addr default_router;
   uint32_t       lease_time;      /* Lease expires in this number of seconds */
   uint32_t       renewal_time;    /* Seconds to transition to RENEW state(T1) */

netutils/dhcpc/dhcpc.c

@@ -91,6 +91,7 @@
 #define DHCP_OPTION_ROUTER      3
 #define DHCP_OPTION_DNS_SERVER  6
 #define DHCP_OPTION_HOST_NAME   12
+#define DHCP_OPTION_NTP_SERVER  42
 #define DHCP_OPTION_REQ_IPADDR  50
 #define DHCP_OPTION_LEASE_TIME  51
 #define DHCP_OPTION_MSG_TYPE    53
@@ -210,10 +211,11 @@ static FAR uint8_t *dhcpc_addclientid(FAR uint8_t *clientid,
 static FAR uint8_t *dhcpc_addreqoptions(FAR uint8_t *optptr)
 {
   *optptr++ = DHCP_OPTION_REQ_LIST;
-  *optptr++ = 3;
+  *optptr++ = 4;
   *optptr++ = DHCP_OPTION_SUBNET_MASK;
   *optptr++ = DHCP_OPTION_ROUTER;
   *optptr++ = DHCP_OPTION_DNS_SERVER;
+  *optptr++ = DHCP_OPTION_NTP_SERVER;
   return optptr;
 }
 
@@ -411,6 +413,39 @@ static uint8_t dhcpc_parseoptions(FAR struct dhcpc_state *presult,
               }
             break;
 
+          case DHCP_OPTION_NTP_SERVER:
+
+            /* Get the NTP server addresses in network order.
+             * DHCP option 42 can contain multiple IPv4 addresses,
+             * each 4 bytes long.
+             */
+
+            if (optptr + 2 <= end)
+              {
+                uint8_t optlen = *(optptr + 1);
+                uint8_t num_ntp = optlen / 4;
+                uint8_t i;
+
+                if (num_ntp > CONFIG_NETUTILS_DHCPC_NTP_SERVER_NUM)
+                  {
+                    num_ntp = CONFIG_NETUTILS_DHCPC_NTP_SERVER_NUM;
+                  }
+
+                presult->num_ntpaddr = 0;
+                for (i = 0; i < num_ntp && (optptr + 2 + i * 4 + 4) <= end;
+                     i++)
+                  {
+                    memcpy(&presult->ntpaddr[i].s_addr, optptr + 2 + i * 4,
+                           4);
+                    presult->num_ntpaddr++;
+                  }
+              }
+            else
+              {
+                nerr("Packet too short (NTP address missing)\n");
+              }
+            break;
+
           case DHCP_OPTION_MSG_TYPE:
 
             /* Get message type */