invalid dns cache entry after ttl expires

Log ttl after receive dns query and invalid dns cache entry when ttl expires.

Signed-off-by: liangchaozhong <liangchaozhong@xiaomi.com>

libs/libc/netdb/lib_dns.h

@@ -222,6 +222,7 @@ int dns_query(FAR const char *hostname, FAR union dns_addr_u *addr,
  *   hostname - The hostname string to be cached.
  *   addr     - The IP addresses associated with the hostname.
  *   naddr    - The count of the IP addresses.
+ *   ttl      - The TTL of the IP addresses.
  *
  * Returned Value:
  *   None
@@ -230,7 +231,8 @@ int dns_query(FAR const char *hostname, FAR union dns_addr_u *addr,
 
 #if CONFIG_NETDB_DNSCLIENT_ENTRIES > 0
 void dns_save_answer(FAR const char *hostname,
-                     FAR const union dns_addr_u *addr, int naddr);
+                     FAR const union dns_addr_u *addr, int naddr,
+                     uint32_t ttl);
 #endif
 
 /****************************************************************************

libs/libc/netdb/lib_dnscache.c

@@ -53,6 +53,7 @@ struct dns_cache_s
   char              name[CONFIG_NETDB_DNSCLIENT_NAMESIZE];
   uint8_t           naddr;      /* How many addresses per name */
   union dns_addr_u  addr[CONFIG_NETDB_MAX_IPADDR];
+  uint32_t          ttl;
 };
 
 /****************************************************************************
@@ -84,6 +85,7 @@ static struct dns_cache_s g_dns_cache[CONFIG_NETDB_DNSCLIENT_ENTRIES];
  *   hostname - The hostname string to be cached.
  *   addr     - The IP addresses associated with the hostname.
  *   naddr    - The count of the IP addresses.
+ *   ttl      - The TTL of the IP addresses.
  *
  * Returned Value:
  *   None
@@ -91,7 +93,8 @@ static struct dns_cache_s g_dns_cache[CONFIG_NETDB_DNSCLIENT_ENTRIES];
  ****************************************************************************/
 
 void dns_save_answer(FAR const char *hostname,
-                     FAR const union dns_addr_u *addr, int naddr)
+                     FAR const union dns_addr_u *addr, int naddr,
+                     uint32_t ttl)
 {
   FAR struct dns_cache_s *entry;
 #if CONFIG_NETDB_DNSCLIENT_LIFESEC > 0
@@ -145,6 +148,7 @@ void dns_save_answer(FAR const char *hostname,
   strlcpy(entry->name, hostname, CONFIG_NETDB_DNSCLIENT_NAMESIZE);
   memcpy(&entry->addr, addr, naddr * sizeof(*addr));
   entry->naddr = naddr;
+  entry->ttl = ttl;
 
   /* Save the updated head index */
 
@@ -242,7 +246,8 @@ int dns_find_answer(FAR const char *hostname, FAR union dns_addr_u *addr,
        */
 
       elapsed = (uint32_t)now.tv_sec - (uint32_t)entry->ctime;
-      if (ret >= 0 && elapsed > CONFIG_NETDB_DNSCLIENT_LIFESEC)
+      if (ret >= 0 &&
+          (elapsed > CONFIG_NETDB_DNSCLIENT_LIFESEC || elapsed > entry->ttl))
         {
           /* This entry has expired.  Increment the tail index to exclude
            * this entry on future traversals.

libs/libc/netdb/lib_dnsquery.c

@@ -90,6 +90,7 @@ struct dns_query_s
   FAR const char *hostname;       /* Hostname to lookup */
   FAR union dns_addr_u *addr;     /* Location to return host address */
   FAR int *naddr;                 /* Number of returned addresses */
+  uint32_t ttl;                   /* Time to Live, unit:s */
 };
 
 /* Query info to check response against. */
@@ -325,7 +326,8 @@ static int dns_send_query(int sd, FAR const char *name,
  ****************************************************************************/
 
 static int dns_recv_response(int sd, FAR union dns_addr_u *addr, int naddr,
-                             FAR struct dns_query_info_s *qinfo)
+                             FAR struct dns_query_info_s *qinfo,
+                             uint32_t *ttl)
 {
   FAR uint8_t *nameptr;
   FAR uint8_t *namestart;
@@ -475,6 +477,10 @@ static int dns_recv_response(int sd, FAR union dns_addr_u *addr, int naddr,
             NTOHS(ans->type), NTOHS(ans->class),
             (NTOHS(ans->ttl[0]) << 16) | NTOHS(ans->ttl[1]),
             NTOHS(ans->len));
+      if (ttl)
+        {
+          *ttl = (NTOHS(ans->ttl[0]) << 16) | NTOHS(ans->ttl[1]);
+        }
 
       /* Check for IPv4/6 address type and Internet class. Others are
        * discarded.
@@ -612,7 +618,7 @@ static int dns_query_callback(FAR void *arg, FAR struct sockaddr *addr,
           /* Obtain the IPv6 response */
 
           ret = dns_recv_response(sd, &query->addr[next],
-                                  *query->naddr - next, &qinfo);
+                                  *query->naddr - next, &qinfo, &query->ttl);
           if (ret >= 0)
             {
               next += ret;
@@ -641,7 +647,7 @@ static int dns_query_callback(FAR void *arg, FAR struct sockaddr *addr,
           /* Obtain the IPv4 response */
 
           ret = dns_recv_response(sd, &query->addr[next],
-                                  *query->naddr - next, &qinfo);
+                                  *query->naddr - next, &qinfo, &query->ttl);
           if (ret >= 0)
             {
               next += ret;
@@ -659,7 +665,7 @@ static int dns_query_callback(FAR void *arg, FAR struct sockaddr *addr,
 #if CONFIG_NETDB_DNSCLIENT_ENTRIES > 0
           /* Save the answer in the DNS cache */
 
-          dns_save_answer(query->hostname, query->addr, next);
+          dns_save_answer(query->hostname, query->addr, next, query->ttl);
 #endif
           /* Return 1 to indicate to (1) stop the traversal, and (2)
            * indicate that the address was found.