fix(dns): Use getaddrinfo for DNS, to fix some IPv6 issues

Replace hostbyname with getaddrinfo for better IPv6 support. The API is also
simpler, as it has no callbacks (they are handled internally). Allows
dual-stack networks to connect to IPv6-only destinations.

Still does not work for IPv6-only networks, as IPv6 DNS is not enabled in the
pre-built ESP-IDF libraries.

Author: sgryphon

Diff for: libraries/Network/src/NetworkEvents.cpp

@@ -55,7 +55,7 @@ NetworkEvents::~NetworkEvents(){
 	}
 }
 
-static uint32_t _initial_bits = NET_DNS_IDLE_BIT;
+static uint32_t _initial_bits = 0;
 
 bool NetworkEvents::initNetworkEvents(){
     if(!_arduino_event_group){

Diff for: libraries/Network/src/NetworkEvents.h

@@ -28,9 +28,6 @@ static const int WIFI_SCANNING_BIT = BIT0;
 static const int WIFI_SCAN_DONE_BIT= BIT1;
 #endif
 
-static const int NET_DNS_IDLE_BIT  = BIT2;
-static const int NET_DNS_DONE_BIT  = BIT3;
-
 #define NET_HAS_IP6_GLOBAL_BIT 0
 
 ESP_EVENT_DECLARE_BASE(ARDUINO_EVENTS);

Diff for: libraries/Network/src/NetworkManager.cpp

@@ -5,11 +5,11 @@
  */
 #include "NetworkManager.h"
 #include "NetworkInterface.h"
+#include "IPAddress.h"
 #include "esp_netif.h"
-#include "lwip/ip_addr.h"
 #include "lwip/dns.h"
-#include "esp32-hal-log.h"
 #include "esp_mac.h"
+#include "netdb.h"
 
 NetworkManager::NetworkManager(){
 
@@ -36,54 +36,16 @@ bool NetworkManager::begin(){
     return initialized;
 }
 
-typedef struct gethostbynameParameters {
-    const char *hostname;
-    ip_addr_t addr;
-    uint8_t addr_type;
-    int result;
-} gethostbynameParameters_t;
-
-/**
- * DNS callback
- * @param name
- * @param ipaddr
- * @param callback_arg
- */
-static void wifi_dns_found_callback(const char *name, const ip_addr_t *ipaddr, void *callback_arg)
-{
-    gethostbynameParameters_t *parameters = static_cast<gethostbynameParameters_t *>(callback_arg);
-    if(ipaddr) {
-        if(parameters->result == 0){
-            memcpy(&(parameters->addr), ipaddr, sizeof(ip_addr_t));
-            parameters->result = 1;
-        }
-    } else {
-        parameters->result = -1;
-    }
-    Network.setStatusBits(NET_DNS_DONE_BIT);
-}
-
-/**
- * Callback to execute dns_gethostbyname in lwIP's TCP/IP context
- * @param param Parameters for dns_gethostbyname call
- */
-static esp_err_t wifi_gethostbyname_tcpip_ctx(void *param)
-{
-    gethostbynameParameters_t *parameters = static_cast<gethostbynameParameters_t *>(param);
-    return dns_gethostbyname_addrtype(parameters->hostname, &parameters->addr, &wifi_dns_found_callback, parameters, parameters->addr_type);
-}
-
 /**
  * Resolve the given hostname to an IP address.
  * @param aHostname     Name to be resolved
  * @param aResult       IPAddress structure to store the returned IP address
  * @return 1 if aIPAddrString was successfully converted to an IP address,
  *          else error code
  */
-int NetworkManager::hostByName(const char* aHostname, IPAddress& aResult, bool preferV6)
+int NetworkManager::hostByName(const char* aHostname, IPAddress& aResult)
 {
     err_t err = ERR_OK;
-    gethostbynameParameters_t params;
 
     // This should generally check if we have a global address assigned to one of the interfaces.
     // If such address is not assigned, there is no point in trying to get V6 from DNS as we will not be able to reach it.
@@ -97,32 +59,41 @@ int NetworkManager::hostByName(const char* aHostname, IPAddress& aResult, bool p
     }
 
     aResult = static_cast<uint32_t>(0);
-    params.hostname = aHostname;
-    params.addr_type = (preferV6 || hasGlobalV6)?LWIP_DNS_ADDRTYPE_IPV6_IPV4:LWIP_DNS_ADDRTYPE_IPV4;
-    params.result = 0;
-    aResult.to_ip_addr_t(&(params.addr));
-
-    if (!aResult.fromString(aHostname)) {
-        Network.waitStatusBits(NET_DNS_IDLE_BIT, 16000);
-        Network.clearStatusBits(NET_DNS_IDLE_BIT | NET_DNS_DONE_BIT);
-
-        err = esp_netif_tcpip_exec(wifi_gethostbyname_tcpip_ctx, &params);
-        if (err == ERR_OK) {
-            aResult.from_ip_addr_t(&(params.addr));
-        } else if (err == ERR_INPROGRESS) {
-            Network.waitStatusBits(NET_DNS_DONE_BIT, 15000);  //real internal timeout in lwip library is 14[s]
-            Network.clearStatusBits(NET_DNS_DONE_BIT);
-            if (params.result == 1) {
-                aResult.from_ip_addr_t(&(params.addr));
-                err = ERR_OK;
-            }
-        }
-        Network.setStatusBits(NET_DNS_IDLE_BIT);
+
+    // First check if the host parses as a literal address
+    if (aResult.fromString(aHostname)) {
+        return 1;
     }
-    if (err == ERR_OK) {
+
+    const char *servname = "0";
+    struct addrinfo *res;
+    const struct addrinfo hints = {
+        .ai_family = AF_UNSPEC,
+        .ai_socktype = SOCK_STREAM,
+    };
+    err = lwip_getaddrinfo(aHostname, servname, &hints, &res);
+    if (err == ERR_OK)
+    {
+        if (res->ai_family == AF_INET6)
+        {
+            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)res->ai_addr;
+            // As an array of u8_t
+            aResult = IPAddress(IPv6, ipv6->sin6_addr.s6_addr);
+            log_d("DNS found IPv6 %s", aResult.toString().c_str());
+        }
+        else
+        {
+            struct sockaddr_in *ipv4 = (struct sockaddr_in *)res->ai_addr;
+            // As a single u32_t
+            aResult = IPAddress(ipv4->sin_addr.s_addr);
+            log_d("DNS found IPv4 %s", aResult.toString().c_str());
+        }
+
+        lwip_freeaddrinfo(res);
         return 1;
     }
-    log_e("DNS Failed for '%s' with error '%d' and result '%d'", aHostname, err, params.result);
+
+    log_e("DNS Failed for '%s' with error '%d'", aHostname, err);
     return err;
 }