LEAmDNS Fixes (#5641)

- Better separation of ESP wifi thread code from user thread code
- Added a flag for 'update()'-less use (disabled by default)
- The too fast updates for service queries are fixed
- Switched fully to PolledTimeout; LEATimeFlag not needed anymore (BTW: a const 'expired()' method would be helpful)
- The device should stay visible now even after the first TTL timeout
- Improved service querying (queries five times now)
- Fixed TTL (bug introduced with Fixes 1.0)

Author: LaborEtArs

Diff for: libraries/ESP8266mDNS/src/LEAmDNS.cpp

@@ -87,21 +87,26 @@ MDNSResponder::~MDNSResponder(void) {
  */
 bool MDNSResponder::begin(const char* p_pcHostname) {
 
-    bool    bResult = false;
+    bool    bResult = (0 != m_pcHostname);
 
-    if (_setHostname(p_pcHostname)) {
-        
-        m_GotIPHandler = WiFi.onStationModeGotIP([this](const WiFiEventStationModeGotIP& pEvent) {
-            (void) pEvent;
-            _restart();
-        });
-
-        m_DisconnectedHandler = WiFi.onStationModeDisconnected([this](const WiFiEventStationModeDisconnected& pEvent) {
-            (void) pEvent;
-            _restart();
-        });
+    if (0 == m_pcHostname) {
+        if (_setHostname(p_pcHostname)) {
 
-        bResult = _restart();
+            m_GotIPHandler = WiFi.onStationModeGotIP([this](const WiFiEventStationModeGotIP& pEvent) {
+                (void) pEvent;
+                _restart();
+            });
+
+            m_DisconnectedHandler = WiFi.onStationModeDisconnected([this](const WiFiEventStationModeDisconnected& pEvent) {
+                (void) pEvent;
+                _restart();
+            });
+
+            bResult = _restart();
+        }
+    }
+    else {
+        DEBUG_EX_INFO(DEBUG_OUTPUT.printf_P(PSTR("[MDNSResponder] begin: Ignoring multiple calls (Ignored host domain: '%s')!\n"), (p_pcHostname ?: "-")););
     }
     DEBUG_EX_ERR(if (!bResult) { DEBUG_OUTPUT.printf_P(PSTR("[MDNSResponder] begin: FAILED for '%s'!\n"), (p_pcHostname ?: "-")); } );
     return bResult;

Diff for: libraries/ESP8266mDNS/src/LEAmDNS_Control.cpp

@@ -480,7 +480,6 @@ bool MDNSResponder::_parseQuery(const MDNSResponder::stcMDNS_MsgHeader& p_MsgHea
 
             sendParameter.m_bResponse = true;
             sendParameter.m_bAuthorative = true;
-            sendParameter.m_bCacheFlush = false;
 
             bResult = _sendMDNSMessage(sendParameter);
         }
@@ -1214,7 +1213,7 @@ bool MDNSResponder::_sendHostProbe(void) {
 
         //sendParameter.m_pQuestions->m_bUnicast = true;
         sendParameter.m_pQuestions->m_Header.m_Attributes.m_u16Type = DNS_RRTYPE_ANY;
-        sendParameter.m_pQuestions->m_Header.m_Attributes.m_u16Class = (/*0x8000 |*/ DNS_RRCLASS_IN);   // Unicast & INternet
+        sendParameter.m_pQuestions->m_Header.m_Attributes.m_u16Class = (0x8000 | DNS_RRCLASS_IN);   // Unicast & INternet
 
         // Add known answers
 #ifdef MDNS_IP4_SUPPORT

Diff for: libraries/ESP8266mDNS/src/LEAmDNS_Transfer.cpp

@@ -1439,8 +1439,7 @@ bool MDNSResponder::_writeMDNSAnswer_PTR_TYPE(MDNSResponder::stcMDNSService& p_r
 
     stcMDNS_RRDomain        dnssdDomain;
     stcMDNS_RRDomain        serviceDomain;
-    stcMDNS_RRAttributes    attributes(DNS_RRTYPE_PTR,
-                                       ((p_rSendParameter.m_bCacheFlush ? 0x8000 : 0) | DNS_RRCLASS_IN));   // Cache flush? & INternet
+    stcMDNS_RRAttributes    attributes(DNS_RRTYPE_PTR, DNS_RRCLASS_IN);	// No cache flush! only INternet
     bool    bResult = ((_buildDomainForDNSSD(dnssdDomain)) &&                                   // _services._dns-sd._udp.local
                        (_writeMDNSRRDomain(dnssdDomain, p_rSendParameter)) &&
                        (_writeMDNSRRAttributes(attributes, p_rSendParameter)) &&                // TYPE & CLASS
@@ -1465,8 +1464,7 @@ bool MDNSResponder::_writeMDNSAnswer_PTR_NAME(MDNSResponder::stcMDNSService& p_r
                                               MDNSResponder::stcMDNSSendParameter& p_rSendParameter) {
     DEBUG_EX_INFO(DEBUG_OUTPUT.printf_P(PSTR("[MDNSResponder] _writeMDNSAnswer_PTR_NAME\n")););
 
-    stcMDNS_RRAttributes    attributes(DNS_RRTYPE_PTR,
-                                       ((p_rSendParameter.m_bCacheFlush ? 0x8000 : 0) | DNS_RRCLASS_IN));   // Cache flush? & INternet
+    stcMDNS_RRAttributes    attributes(DNS_RRTYPE_PTR, DNS_RRCLASS_IN);	// No cache flush! only INternet
     bool    bResult = ((_writeMDNSServiceDomain(p_rService, false, false, p_rSendParameter)) && // _http._tcp.local
                        (_writeMDNSRRAttributes(attributes, p_rSendParameter)) &&                    // TYPE & CLASS
                        (_write32((p_rSendParameter.m_bUnannounce ? 0 : MDNS_SERVICE_TTL), p_rSendParameter)) && // TTL