dns: Allow storing dnsserver per netif

src/core/dns.c

@@ -101,6 +101,10 @@
 static bool s_is_tmr_start = false;
 #endif /* ESP_LWIP_DNS_TIMERS_ONDEMAND */
 
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+static dns_setserver_callback_t s_dns_setserver_callback = NULL;
+#endif /* LWIP_DNS_SETSERVER_WITH_NETIF */
+
 #include <string.h>
 #if ESP_DNS
 #include <stdbool.h>
@@ -1769,4 +1773,27 @@ dns_gethostbyname_addrtype(const char *hostname, ip_addr_t *addr, dns_found_call
                      LWIP_DNS_ISMDNS_ARG(is_mdns));
 }
 
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+void
+dns_setserver_with_netif(struct netif* netif, u8_t numdns, const ip_addr_t *dnsserver)
+{
+  if (s_dns_setserver_callback) {
+    s_dns_setserver_callback(netif, numdns, dnsserver);
+  } else {
+    dns_setserver(numdns, dnsserver);
+  }
+}
+
+err_t
+dns_setserver_callback(dns_setserver_callback_t callback)
+{
+  if (s_dns_setserver_callback) {
+    /* fail if the callback has been set already */
+    return ERR_ARG;
+  }
+  s_dns_setserver_callback = callback;  /* support only one time configuration */
+  return ERR_OK;
+}
+#endif /* LWIP_DNS_SETSERVER_WITH_NETIF */
+
 #endif /* LWIP_DNS */

src/core/ipv4/dhcp.c

@@ -777,7 +777,11 @@ dhcp_handle_ack(struct netif *netif, struct dhcp_msg *msg_in)
     }
 #endif
     ip_addr_set_ip4_u32_val(dns_addr, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_DNS_SERVER + n)));
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+    dns_setserver_with_netif(netif, n, &dns_addr);
+#else
     dns_setserver(n, &dns_addr);
+#endif
   }
 #endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
 }

src/core/ipv6/dhcp6.c

@@ -547,7 +547,12 @@ dhcp6_handle_config_reply(struct netif *netif, struct pbuf *p_msg_in)
       }
       ip6_addr_assign_zone(dns_addr6, IP6_UNKNOWN, netif);
       /* @todo: do we need a different offset than DHCP(v4)? */
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+      dns_setserver_with_netif(netif, n, &dns_addr);
+#else
       dns_setserver(n, &dns_addr);
+#endif
+
     }
   }
   /* @ todo: parse and set Domain Search List */

src/core/ipv6/nd6.c

@@ -780,14 +780,23 @@ nd6_input(struct pbuf *p, struct netif *inp)
 
             if (htonl(rdnss_opt->lifetime) > 0) {
               /* TODO implement Lifetime > 0 */
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+              dns_setserver_with_netif(inp, rdnss_server_idx++, &rdnss_address);
+#else
               dns_setserver(rdnss_server_idx++, &rdnss_address);
+#endif
+
             } else {
               /* TODO implement DNS removal in dns.c */
               u8_t s;
               for (s = 0; s < DNS_MAX_SERVERS; s++) {
                 const ip_addr_t *addr = dns_getserver(s);
                 if(ip_addr_cmp(addr, &rdnss_address)) {
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+                  dns_setserver_with_netif(inp, s, NULL);
+#else
                   dns_setserver(s, NULL);
+#endif
                 }
               }
             }

src/include/lwip/dns.h

@@ -122,6 +122,12 @@ err_t          dns_local_addhost(const char *hostname, const ip_addr_t *addr);
 #endif /* DNS_LOCAL_HOSTLIST_IS_DYNAMIC */
 #endif /* DNS_LOCAL_HOSTLIST */
 
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+typedef void (*dns_setserver_callback_t)(struct netif* netif, u8_t numdns, const ip_addr_t *dnsserver);
+void            dns_setserver_with_netif(struct netif* netif, u8_t numdns, const ip_addr_t *dnsserver);
+err_t           dns_setserver_callback(dns_setserver_callback_t callback);
+#endif /* LWIP_DNS_SETSERVER_WITH_NETIF */
+
 #ifdef __cplusplus
 }
 #endif

src/include/lwip/opt.h

@@ -1161,6 +1161,20 @@
 #define DNS_LOCAL_HOSTLIST              0
 #endif /* DNS_LOCAL_HOSTLIST */
 
+/** LWIP_DNS_SETSERVER_WITH_NETIF: If this is turned on, the dns_setserver_with_netif() is enabled and called
+ * from all internal modules (instead of dns_setserver()) allowing to setup a user callback to collect DNS server
+ * information acquired by the related network interface.
+ * This could be used to overcome the LWIP limitation of using DNS servers
+ * globally, which could in some cases overwrite distinct DNS server information of one netif by another.
+ * If you want to use this option, you would have to set LWIP_DNS_SETSERVER_WITH_NETIF=1 and:
+ * 1) Register DNS setserver callback using dns_setserver_callback() and collect the DNS server information
+ * in the callback and store it separately for each netif.
+ * 2) Restore the actual DNS server information using dns_setserver() before every DNS lookup.
+ * */
+#if !defined LWIP_DNS_SETSERVER_WITH_NETIF || defined __DOXYGEN__
+#define LWIP_DNS_SETSERVER_WITH_NETIF   0
+#endif /* LWIP_DNS_SETSERVER_WITH_NETIF */
+
 /** If this is turned on, the local host-list can be dynamically changed
  *  at runtime. */
 #if !defined DNS_LOCAL_HOSTLIST_IS_DYNAMIC || defined __DOXYGEN__

src/netif/ppp/ppp.c

@@ -1109,12 +1109,23 @@ int cifproxyarp(ppp_pcb *pcb, u32_t his_adr) {
  */
 int sdns(ppp_pcb *pcb, u32_t ns1, u32_t ns2) {
   ip_addr_t ns;
+#if !LWIP_DNS_SETSERVER_WITH_NETIF
   LWIP_UNUSED_ARG(pcb);
+#endif
 
   ip_addr_set_ip4_u32_val(ns, ns1);
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+  dns_setserver_with_netif(pcb->netif, 0, &ns);
+#else
   dns_setserver(0, &ns);
+#endif
+
   ip_addr_set_ip4_u32_val(ns, ns2);
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+  dns_setserver_with_netif(pcb->netif, 1, &ns);
+#else
   dns_setserver(1, &ns);
+#endif
   return 1;
 }
 
@@ -1125,17 +1136,27 @@ int sdns(ppp_pcb *pcb, u32_t ns1, u32_t ns2) {
 int cdns(ppp_pcb *pcb, u32_t ns1, u32_t ns2) {
   const ip_addr_t *nsa;
   ip_addr_t nsb;
+#if !LWIP_DNS_SETSERVER_WITH_NETIF
   LWIP_UNUSED_ARG(pcb);
+#endif
 
   nsa = dns_getserver(0);
   ip_addr_set_ip4_u32_val(nsb, ns1);
   if (ip_addr_cmp(nsa, &nsb)) {
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+    dns_setserver_with_netif(pcb->netif, 0, IP_ADDR_ANY);
+#else
     dns_setserver(0, IP_ADDR_ANY);
+#endif
   }
   nsa = dns_getserver(1);
   ip_addr_set_ip4_u32_val(nsb, ns2);
   if (ip_addr_cmp(nsa, &nsb)) {
+#if LWIP_DNS_SETSERVER_WITH_NETIF
+    dns_setserver_with_netif(pcb->netif, 1, IP_ADDR_ANY);
+#else
     dns_setserver(1, IP_ADDR_ANY);
+#endif
   }
   return 1;
 }