AsyncUDP: Added lastErr helper variable (#4789)

The variable is useful when debugging AsyncUDP send problems.
The upper application can read and analyze the error reason.

libraries/AsyncUDP/src/AsyncUDP.cpp

@@ -479,6 +479,7 @@ AsyncUDP::AsyncUDP()
 {
     _pcb = NULL;
     _connected = false;
+	_lastErr = ERR_OK;
     _handler = NULL;
 }
 
@@ -517,8 +518,8 @@ bool AsyncUDP::connect(const ip_addr_t *addr, uint16_t port)
     }
     close();
     UDP_MUTEX_LOCK();
-    err_t err = _udp_connect(_pcb, addr, port);
-    if(err != ERR_OK) {
+    _lastErr = _udp_connect(_pcb, addr, port);
+    if(_lastErr != ERR_OK) {
         UDP_MUTEX_UNLOCK();
         return false;
     }
@@ -646,7 +647,7 @@ size_t AsyncUDP::writeTo(const uint8_t * data, size_t len, const ip_addr_t * add
     if(len > CONFIG_TCP_MSS) {
         len = CONFIG_TCP_MSS;
     }
-    err_t err = ERR_OK;
+    _lastErr = ERR_OK;
     pbuf* pbt = pbuf_alloc(PBUF_TRANSPORT, len, PBUF_RAM);
     if(pbt != NULL) {
         uint8_t* dst = reinterpret_cast<uint8_t*>(pbt->payload);
@@ -656,16 +657,16 @@ size_t AsyncUDP::writeTo(const uint8_t * data, size_t len, const ip_addr_t * add
             void * nif = NULL;
             tcpip_adapter_get_netif((tcpip_adapter_if_t)tcpip_if, &nif);
             if(!nif){
-                err = _udp_sendto(_pcb, pbt, addr, port);
+                _lastErr = _udp_sendto(_pcb, pbt, addr, port);
             } else {
-                err = _udp_sendto_if(_pcb, pbt, addr, port, (struct netif *)nif);
+                _lastErr = _udp_sendto_if(_pcb, pbt, addr, port, (struct netif *)nif);
             }
         } else {
-            err = _udp_sendto(_pcb, pbt, addr, port);
+            _lastErr = _udp_sendto(_pcb, pbt, addr, port);
         }
         UDP_MUTEX_UNLOCK();
         pbuf_free(pbt);
-        if(err < ERR_OK) {
+        if(_lastErr < ERR_OK) {
             return 0;
         }
         return len;
@@ -870,6 +871,10 @@ bool AsyncUDP::connected()
     return _connected;
 }
 
+esp_err_t AsyncUDP::lastErr() {
+	return _lastErr;
+}
+
 void AsyncUDP::onPacket(AuPacketHandlerFunctionWithArg cb, void * arg)
 {
     onPacket(std::bind(cb, arg, std::placeholders::_1));

libraries/AsyncUDP/src/AsyncUDP.h

@@ -95,6 +95,7 @@ protected:
     udp_pcb *_pcb;
     //xSemaphoreHandle _lock;
     bool _connected;
+	esp_err_t _lastErr;
     AuPacketHandlerFunction _handler;
 
     bool _init();
@@ -144,6 +145,7 @@ public:
     IPAddress listenIP();
     IPv6Address listenIPv6();
     bool connected();
+	esp_err_t lastErr();
     operator bool();
 
     static void _s_recv(void *arg, udp_pcb *upcb, pbuf *p, const ip_addr_t *addr, uint16_t port, struct netif * netif);