mDNS: add queryHost()

libraries/ESP8266mDNS/src/LEAmDNS.cpp

@@ -671,6 +671,81 @@ namespace MDNSImplementation
         return addDynamicServiceTxt(p_hService, p_pcKey, acBuffer);
     }
 
+#ifdef MDNS_IP4_SUPPORT
+    /*
+        MDNSResponder::queryHost
+        Perform a blocking mDNS A query for a host.
+    */
+    IPAddress MDNSResponder::queryHost(const char*    p_pcHostname,
+                                       const uint32_t p_u32Timeout /*= MDNS_QUERYHOST_WAIT_TIME*/)
+    {
+        if (0 == m_pUDPContext)
+        {
+            // safeguard against misuse
+            return IPAddress();
+        }
+
+        DEBUG_EX_INFO(DEBUG_OUTPUT.printf_P(PSTR("[MDNSResponder] queryHost '%s'\n"),
+                                            (p_pcHostname ?: "-")););
+
+        IPAddress result;
+
+        stcMDNSServiceQuery* pServiceQuery = 0;
+        stcMDNS_RRDomain     hostDomain;
+
+        if ((p_pcHostname) && (os_strlen(p_pcHostname)) && (p_u32Timeout)
+            && (_removeLegacyServiceQuery()) && (_buildDomainForHost(p_pcHostname, hostDomain))
+            && ((pServiceQuery = _allocServiceQuery())))
+        {
+            pServiceQuery->m_bLegacyQuery = true;
+
+            stcMDNSServiceQuery::stcAnswer* pAnswer = new stcMDNSServiceQuery::stcAnswer;
+
+            if (pAnswer)
+            {
+                pAnswer->m_HostDomain = hostDomain;
+
+                if ((pServiceQuery->addAnswer(pAnswer))
+                    && (_sendMDNSQuery(hostDomain, DNS_RRTYPE_A)))
+                {
+                    DEBUG_EX_INFO(DEBUG_OUTPUT.printf_P(
+                        PSTR("[MDNSResponder] queryHost: Waiting up to %lu ms for answer...\n"),
+                        p_u32Timeout););
+
+                    const uint32_t start = millis();
+
+                    do
+                    {
+                        delay(1);
+
+                        const stcMDNSServiceQuery::stcAnswer::stcIP4Address* pIP4Address
+                            = pAnswer->IP4AddressAtIndex(0);
+
+                        if (pIP4Address)
+                        {
+                            result = pIP4Address->m_IPAddress;
+                            break;
+                        }
+                    } while ((millis() - start) < p_u32Timeout);
+                }
+            }
+
+            pServiceQuery->m_bAwaitingAnswers = false;
+            _removeServiceQuery(pServiceQuery);
+        }
+        else
+        {
+            if (pServiceQuery)
+                _removeServiceQuery(pServiceQuery);
+
+            DEBUG_EX_ERR(
+                DEBUG_OUTPUT.printf_P(PSTR("[MDNSResponder] queryHost: INVALID input data!\n")););
+        }
+
+        return result;
+    }
+#endif
+
     /**
         STATIC SERVICE QUERY (LEGACY)
     */

libraries/ESP8266mDNS/src/LEAmDNS.h

@@ -167,6 +167,10 @@ namespace MDNSImplementation
     Default timeout for static service queries
 */
 #define MDNS_QUERYSERVICES_WAIT_TIME 1000
+/*
+    Default timeout for static host queries
+*/
+#define MDNS_QUERYHOST_WAIT_TIME 2000
 
 /*
     Timeout for udpContext->sendtimeout()
@@ -312,6 +316,19 @@ namespace MDNSImplementation
         hMDNSTxt addDynamicServiceTxt(hMDNSService p_hService, const char* p_pcKey,
                                       int8_t p_i8Value);
 
+#ifdef MDNS_IP4_SUPPORT
+        // Resolve a host name using an mDNS A query.
+        // The ".local" suffix is appended automatically.
+        IPAddress queryHost(const char*    p_pcHostname,
+                            const uint32_t p_u32Timeout = MDNS_QUERYHOST_WAIT_TIME);
+
+        IPAddress queryHost(const String&  p_strHostname,
+                            const uint32_t p_u32Timeout = MDNS_QUERYHOST_WAIT_TIME)
+        {
+            return queryHost(p_strHostname.c_str(), p_u32Timeout);
+        }
+#endif
+
         // Perform a (static) service query. The function returns after p_u16Timeout milliseconds
         // The answers (the number of received answers is returned) can be retrieved by calling
         // - answerHostname (or hostname)