Make DNS resolution order selectable during runtime or compile time

libraries/ESP8266WiFi/examples/IPv6/IPv6.ino

@@ -1,4 +1,3 @@
-
 /*
   arduino IPv6 example
   released to public domain
@@ -27,7 +26,8 @@
 #define STAPSK  "your-password"
 #endif
 
-#define FQDN  F("www.google.com") // with both IPv4 & IPv6 addresses
+#define FQDN  F("www.google.com")  // with both IPv4 & IPv6 addresses
+#define FQDN2 F("www.yahoo.com")   // with both IPv4 & IPv6 addresses
 #define FQDN6 F("ipv6.google.com") // does not resolve in IPv4
 #define STATUSDELAY_MS 10000
 #define TCP_PORT 23
@@ -50,6 +50,21 @@ void fqdn(Print& out, const String& fqdn) {
   }
 }
 
+#if LWIP_IPV4 && LWIP_IPV6
+void fqdn_rt(Print& out, const String& fqdn, DNSResolveType resolveType) {
+  out.print(F("resolving "));
+  out.print(fqdn);
+  out.print(F(": "));
+  IPAddress result;
+  if (WiFi.hostByName(fqdn.c_str(), result, 10000, resolveType)) {
+    result.printTo(out);
+    out.println();
+  } else {
+    out.println(F("timeout or not found"));
+  }
+}
+#endif
+
 void status(Print& out) {
   out.println(F("------------------------------"));
   out.println(ESP.getFullVersion());
@@ -85,7 +100,10 @@ void status(Print& out) {
   // an example is provided with a fqdn which does not resolve with IPv4
   fqdn(out, FQDN);
   fqdn(out, FQDN6);
-
+#if LWIP_IPV4 && LWIP_IPV6
+  fqdn_rt(out, FQDN,  DNSResolveType::DNS_AddrType_IPv4_IPv6); // IPv4 before IPv6
+  fqdn_rt(out, FQDN2, DNSResolveType::DNS_AddrType_IPv6_IPv4); // IPv6 before IPv4
+#endif
   out.println(F("------------------------------"));
 }
 

libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.cpp

@@ -608,7 +608,7 @@ int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResul
 int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms)
 {
     ip_addr_t addr;
-    aResult = static_cast<uint32_t>(0);
+    aResult = static_cast<uint32_t>(INADDR_NONE);
 
     if(aResult.fromString(aHostname)) {
         // Host name is a IP address use it!
@@ -617,7 +617,61 @@ int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResul
     }
 
     DEBUG_WIFI_GENERIC("[hostByName] request IP for: %s\n", aHostname);
+#if LWIP_IPV4 && LWIP_IPV6
+    err_t err = dns_gethostbyname_addrtype(aHostname, &addr, &wifi_dns_found_callback, &aResult,LWIP_DNS_ADDRTYPE_DEFAULT);
+#else
     err_t err = dns_gethostbyname(aHostname, &addr, &wifi_dns_found_callback, &aResult);
+#endif
+    if(err == ERR_OK) {
+        aResult = IPAddress(&addr);
+    } else if(err == ERR_INPROGRESS) {
+        _dns_lookup_pending = true;
+        delay(timeout_ms);
+        // will resume on timeout or when wifi_dns_found_callback fires
+        _dns_lookup_pending = false;
+        // will return here when dns_found_callback fires
+        if(aResult.isSet()) {
+            err = ERR_OK;
+        }
+    }
+
+    if(err != 0) {
+        DEBUG_WIFI_GENERIC("[hostByName] Host: %s lookup error: %d!\n", aHostname, (int)err);
+    } else {
+        DEBUG_WIFI_GENERIC("[hostByName] Host: %s IP: %s\n", aHostname, aResult.toString().c_str());
+    }
+
+    return (err == ERR_OK) ? 1 : 0;
+}
+
+#if LWIP_IPV4 && LWIP_IPV6
+int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms, DNSResolveType resolveType)
+{
+    ip_addr_t addr;
+    err_t err;
+    aResult = static_cast<uint32_t>(INADDR_NONE);
+
+    if(aResult.fromString(aHostname)) {
+        // Host name is a IP address use it!
+        DEBUG_WIFI_GENERIC("[hostByName] Host: %s is a IP!\n", aHostname);
+        return 1;
+    }
+
+    DEBUG_WIFI_GENERIC("[hostByName] request IP for: %s\n", aHostname);
+    switch(resolveType)
+    {
+      // Use selected addrtype
+      case DNSResolveType::DNS_AddrType_IPv4:
+      case DNSResolveType::DNS_AddrType_IPv6:
+      case DNSResolveType::DNS_AddrType_IPv4_IPv6:
+      case DNSResolveType::DNS_AddrType_IPv6_IPv4:
+         err = dns_gethostbyname_addrtype(aHostname, &addr, &wifi_dns_found_callback, &aResult, (uint8_t) resolveType);
+	 break;
+      default:
+         err = dns_gethostbyname_addrtype(aHostname, &addr, &wifi_dns_found_callback, &aResult, LWIP_DNS_ADDRTYPE_DEFAULT); // If illegal type, use default.
+	 break;
+    }
+
     if(err == ERR_OK) {
         aResult = IPAddress(&addr);
     } else if(err == ERR_INPROGRESS) {
@@ -639,6 +693,7 @@ int ESP8266WiFiGenericClass::hostByName(const char* aHostname, IPAddress& aResul
 
     return (err == ERR_OK) ? 1 : 0;
 }
+#endif
 
 /**
  * DNS callback

libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.h

@@ -42,6 +42,14 @@ typedef std::shared_ptr<WiFiEventHandlerOpaque> WiFiEventHandler;
 
 typedef void (*WiFiEventCb)(WiFiEvent_t);
 
+enum class DNSResolveType: uint8_t
+{
+    DNS_AddrType_IPv4 = 0,	// LWIP_DNS_ADDRTYPE_IPV4 = 0
+    DNS_AddrType_IPv6,		// LWIP_DNS_ADDRTYPE_IPV6 = 1
+    DNS_AddrType_IPv4_IPv6,	// LWIP_DNS_ADDRTYPE_IPV4_IPV6 = 2
+    DNS_AddrType_IPv6_IPv4	// LWIP_DNS_ADDRTYPE_IPV6_IPV4 = 3
+};
+
 struct WiFiState;
 
 class ESP8266WiFiGenericClass {
@@ -113,6 +121,9 @@ class ESP8266WiFiGenericClass {
     public:
         int hostByName(const char* aHostname, IPAddress& aResult);
         int hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms);
+#if LWIP_IPV4 && LWIP_IPV6
+        int hostByName(const char* aHostname, IPAddress& aResult, uint32_t timeout_ms, DNSResolveType resolveType);
+#endif
         bool getPersistent();
 
     protected: