public static void DNSNAPTRRecordLookup(string host, bool async, ref SIPDNSLookupResult lookupResult)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS NAPTR record lookup initiated for " + host + ".", null));
// Target is a hostname with no explicit port, DNS lookup for NAPTR records.
DNSResponse naptrRecordResponse = DNSManager.Lookup(host, DNSQType.NAPTR, DNS_LOOKUP_TIMEOUT, null, true, async);
if (naptrRecordResponse == null && async)
{
lookupResult.Pending = true;
}
else if (naptrRecordResponse.Timedout)
{
lookupResult.NAPTRTimedoutAt = DateTime.Now;
}
else if (naptrRecordResponse.Error == null && naptrRecordResponse.RecordNAPTR != null && naptrRecordResponse.RecordNAPTR.Length > 0)
{
foreach (RecordNAPTR naptrRecord in naptrRecordResponse.RecordNAPTR)
{
SIPDNSServiceResult sipNAPTRResult = new SIPDNSServiceResult(SIPServices.GetService(naptrRecord.Service), naptrRecord.Order, 0, naptrRecord.RR.TTL, naptrRecord.Replacement, 0, DateTime.Now);
lookupResult.AddNAPTRResult(sipNAPTRResult);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS NAPTR record found for " + host + ", result " + naptrRecord.Service + " " + naptrRecord.Replacement + ".", null));
}
}
else
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS no NAPTR records found for " + host + ".", null));
}
}
public void LookupAAAARecordMethod()
{
logger.LogDebug("--> " + System.Reflection.MethodBase.GetCurrentMethod().Name);
logger.BeginScope(System.Reflection.MethodBase.GetCurrentMethod().Name);
DNSResponse result = DNSManager.Lookup("www.google.com", QType.AAAA, 10, null, false, false);
foreach (var aaaaResult in result.RecordsAAAA)
{
logger.LogDebug($"AAAA Lookup result {aaaaResult.ToString()}.");
}
// Three's no guarantee that a particular DNS server will return AAAA records. The AppVeyor
// macos vm is hooked up to a DNS that does not return AAAA records.
// worker - 628 - 002:sipsorcery - jyl3x appveyor$ dig AAAA www.gooogle.com
//
// ; <<>> DiG 9.10.6 <<>> AAAA www.gooogle.com
// ; ; global options: +cmd
// ; ; Got answer:
// ; ; ->> HEADER << -opcode: QUERY, status: NOERROR, id: 8102
// ; ; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
//
// ; ; QUESTION SECTION:
// ; www.gooogle.com.IN AAAA
//
// ; ; Query time: 24 msec
// ; ; SERVER: 10.211.55.1#53(10.211.55.1)
// ; ; WHEN: Wed Jun 10 05:56:30 CDT 2020
// ; ; MSG SIZE rcvd: 33
//Assert.NotEmpty(result.RecordsAAAA);
//Assert.True(result.RecordsAAAA[0].Address.AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6);
}
public void LookupAnyRecordAsyncCacheTest()
{
logger.LogDebug("--> " + System.Reflection.MethodBase.GetCurrentMethod().Name);
logger.BeginScope(System.Reflection.MethodBase.GetCurrentMethod().Name);
//1.queue dns lookup for async resolution
DNSResponse result = DNSManager.Lookup("dns.google", QType.ANY, 1, null, false, true);
Assert.Null(result);
System.Threading.Thread.Sleep(500);
//2.check lookup / resolution cache for result
result = DNSManager.Lookup("dns.google", QType.ANY, 150, null, true, false);
Assert.NotNull(result);
Assert.NotEmpty(result.RecordsA);
var ipv4Addresses = from a in result.RecordsA select a.Address;
Assert.NotEmpty(ipv4Addresses);
Assert.Contains(IPSocket.ParseSocketString("8.8.8.8").Address, ipv4Addresses);
Assert.Contains(IPSocket.ParseSocketString("8.8.4.4").Address, ipv4Addresses);
Assert.NotEmpty(result.RecordsAAAA);
var ipv6Addresses = from a in result.RecordsAAAA select a.Address;
Assert.NotEmpty(ipv6Addresses);
Assert.Contains(IPSocket.ParseSocketString("2001:4860:4860::8888").Address, ipv6Addresses);
Assert.Contains(IPSocket.ParseSocketString("2001:4860:4860::8844").Address, ipv6Addresses);
}
public void LookupARecordMethod()
{
logger.LogDebug(System.Reflection.MethodBase.GetCurrentMethod().Name);
DNSResponse result = DNSManager.Lookup("www.sipsorcery.com", QType.A, 10, null, false, false);
logger.LogDebug($"Lookup result {result.RecordsA[0].Address}.");
Assert.AreEqual(result.RecordsA[0].Address.ToString(), "67.222.131.148");
}
public void LookupAAAARecordMethod()
{
logger.LogDebug(System.Reflection.MethodBase.GetCurrentMethod().Name);
DNSResponse result = DNSManager.Lookup("www.google.com", QType.AAAA, 10, null, false, false);
foreach (var aaaaResult in result.RecordsAAAA)
{
logger.LogDebug($"AAAA Lookup result {aaaaResult.ToString()}.");
}
Assert.IsTrue(result.RecordsAAAA.Length > 0);
}
public void LookupSrvRecordMethod()
{
logger.LogDebug(System.Reflection.MethodBase.GetCurrentMethod().Name);
DNSResponse result = DNSManager.Lookup(SIPDNSConstants.SRV_SIP_UDP_QUERY_PREFIX + "sipsorcery.com", QType.SRV, 10, null, false, false);
foreach (var srvResult in result.RecordSRV)
{
logger.LogDebug($"SRV Lookup result {srvResult.ToString()}.");
}
Assert.AreEqual(result.RecordSRV.Length, 1);
Assert.AreEqual(result.RecordSRV.First().TARGET, "sip.sipsorcery.com.");
}
public void LookupAAAARecordMethod()
{
logger.LogDebug("--> " + System.Reflection.MethodBase.GetCurrentMethod().Name);
logger.BeginScope(System.Reflection.MethodBase.GetCurrentMethod().Name);
DNSResponse result = DNSManager.Lookup("www.google.com", QType.AAAA, 10, null, false, false);
foreach (var aaaaResult in result.RecordsAAAA)
{
logger.LogDebug($"AAAA Lookup result {aaaaResult.ToString()}.");
}
Assert.NotEmpty(result.RecordsAAAA);
Assert.True(result.RecordsAAAA[0].Address.AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6);
}
public static SIPDNSLookupResult DNSAAAARecordLookup(string host, int port, bool async, SIPURI uri, SIPDNSLookupResult lookupResult = null)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS A record lookup requested for " + host + ".", null));
SIPDNSLookupResult result = lookupResult ?? new SIPDNSLookupResult(uri);
result.LookupError = null;
DNSResponse aaaaRecordResponse = DNSManager.Lookup(host, QType.AAAA, DNS_A_RECORD_LOOKUP_TIMEOUT, null, true, async);
if (aaaaRecordResponse == null)
{
if (async)
{
result.Pending = true;
}
}
else if (aaaaRecordResponse.Timedout)
{
result.ATimedoutAt = DateTime.Now;
}
else if (!string.IsNullOrWhiteSpace(aaaaRecordResponse.Error))
{
result.LookupError = aaaaRecordResponse.Error;
}
else if (aaaaRecordResponse.RecordsAAAA == null || aaaaRecordResponse.RecordsAAAA.Length == 0)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS no AAAA records found for " + host + ".", null));
result.LookupError = "No AAAA records found for " + host + ".";
}
else
{
SIPURI sipURI = result.URI;
foreach (RecordAAAA aRecord in aaaaRecordResponse.RecordsAAAA)
{
SIPDNSLookupEndPoint sipLookupEndPoint = new SIPDNSLookupEndPoint(new SIPEndPoint(sipURI.Protocol, new IPEndPoint(aRecord.Address, port)), aRecord.RR.TTL);
result.AddLookupResult(sipLookupEndPoint);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS AAAA record found for " + host + ", result " + sipLookupEndPoint.LookupEndPoint.ToString() + ".", null));
}
}
return(result);
}
public void LookupAnyRecordTest()
{
logger.LogDebug("--> " + System.Reflection.MethodBase.GetCurrentMethod().Name);
logger.BeginScope(System.Reflection.MethodBase.GetCurrentMethod().Name);
DNSResponse result = DNSManager.Lookup("dns.google", QType.ANY, 100, null, false, false);
Assert.NotNull(result);
Assert.NotEmpty(result.RecordsA);
var ipv4Addresses = from a in result.RecordsA select a.Address;
Assert.NotEmpty(ipv4Addresses);
Assert.Contains(IPSocket.ParseSocketString("8.8.8.8").Address, ipv4Addresses);
Assert.Contains(IPSocket.ParseSocketString("8.8.4.4").Address, ipv4Addresses);
Assert.NotEmpty(result.RecordsAAAA);
var ipv6Addresses = from a in result.RecordsAAAA select a.Address;
Assert.NotEmpty(ipv6Addresses);
Assert.Contains(IPSocket.ParseSocketString("2001:4860:4860::8888").Address, ipv6Addresses);
Assert.Contains(IPSocket.ParseSocketString("2001:4860:4860::8844").Address, ipv6Addresses);
}
public static void DNSSRVRecordLookup(SIPSchemesEnum scheme, SIPProtocolsEnum protocol, string host, bool async, ref SIPDNSLookupResult lookupResult)
{
SIPServicesEnum reqdNAPTRService = SIPServicesEnum.none;
if (scheme == SIPSchemesEnum.sip && protocol == SIPProtocolsEnum.udp)
{
reqdNAPTRService = SIPServicesEnum.sipudp;
}
else if (scheme == SIPSchemesEnum.sip && protocol == SIPProtocolsEnum.tcp)
{
reqdNAPTRService = SIPServicesEnum.siptcp;
}
else if (scheme == SIPSchemesEnum.sips && protocol == SIPProtocolsEnum.tcp)
{
reqdNAPTRService = SIPServicesEnum.sipstcp;
}
else if (scheme == SIPSchemesEnum.sip && protocol == SIPProtocolsEnum.tls)
{
reqdNAPTRService = SIPServicesEnum.siptls;
}
// If there are NAPTR records available see if there is a matching one for the SIP scheme and protocol required.
SIPDNSServiceResult naptrService = null;
if (lookupResult.SIPNAPTRResults != null && lookupResult.SIPNAPTRResults.Count > 0)
{
if (reqdNAPTRService != SIPServicesEnum.none && lookupResult.SIPNAPTRResults.ContainsKey(reqdNAPTRService))
{
naptrService = lookupResult.SIPNAPTRResults[reqdNAPTRService];
}
}
// Construct the SRV target to lookup depending on whether an NAPTR record was available or not.
string srvLookup = null;
if (naptrService != null)
{
srvLookup = naptrService.Data;
}
else
{
srvLookup = "_" + scheme.ToString() + "._" + protocol.ToString() + "." + host;
}
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup requested for " + srvLookup + ".", null));
DNSResponse srvRecordResponse = DNSManager.Lookup(srvLookup, DNSQType.SRV, DNS_LOOKUP_TIMEOUT, null, true, async);
if (srvRecordResponse == null && async)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup pending for " + srvLookup + ".", null));
lookupResult.Pending = true;
}
else if (srvRecordResponse.Timedout)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup timed out for " + srvLookup + ".", null));
lookupResult.SRVTimedoutAt = DateTime.Now;
}
else if (srvRecordResponse.Error != null)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup for " + srvLookup + " returned error of " + lookupResult.LookupError + ".", null));
}
else if (srvRecordResponse.Error == null && srvRecordResponse.RecordSRV != null && srvRecordResponse.RecordSRV.Length > 0)
{
foreach (RecordSRV srvRecord in srvRecordResponse.RecordSRV)
{
SIPDNSServiceResult sipSRVResult = new SIPDNSServiceResult(reqdNAPTRService, srvRecord.Priority, srvRecord.Weight, srvRecord.RR.TTL, srvRecord.Target, srvRecord.Port, DateTime.Now);
lookupResult.AddSRVResult(sipSRVResult);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record found for " + srvLookup + ", result " + srvRecord.Target + " " + srvRecord.Port + ".", null));
}
}
else
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS no SRV records found for " + srvLookup + ".", null));
}
}
public static void DNSSRVRecordLookup(SIPSchemesEnum scheme, SIPProtocolsEnum protocol, string host, bool async, ref SIPDNSLookupResult lookupResult)
{
SIPServicesEnum reqdNAPTRService = SIPServicesEnum.none;
if (scheme == SIPSchemesEnum.sip && protocol == SIPProtocolsEnum.udp)
{
reqdNAPTRService = SIPServicesEnum.sipudp;
}
else if (scheme == SIPSchemesEnum.sip && protocol == SIPProtocolsEnum.tcp)
{
reqdNAPTRService = SIPServicesEnum.siptcp;
}
else if (scheme == SIPSchemesEnum.sips && protocol == SIPProtocolsEnum.tcp)
{
reqdNAPTRService = SIPServicesEnum.sipstcp;
}
//rj2 2018-10-17: this looks wrong, but the www says: if sips then protocol is _tcp not _tls
else if (scheme == SIPSchemesEnum.sips && protocol == SIPProtocolsEnum.tls)
{
reqdNAPTRService = SIPServicesEnum.sipstcp;
}
else if (scheme == SIPSchemesEnum.sip && protocol == SIPProtocolsEnum.tls)
{
reqdNAPTRService = SIPServicesEnum.siptls;
}
// If there are NAPTR records available see if there is a matching one for the SIP scheme and protocol required.
// this works best (only works) if protocol in sip-uri matches sip-service of NAPTRRecord
SIPDNSServiceResult naptrService = null;
if (lookupResult.SIPNAPTRResults != null && lookupResult.SIPNAPTRResults.Count > 0)
{
if (reqdNAPTRService != SIPServicesEnum.none && lookupResult.SIPNAPTRResults.ContainsKey(reqdNAPTRService))
{
naptrService = lookupResult.SIPNAPTRResults[reqdNAPTRService];
}
}
// Construct the SRV target to lookup depending on whether an NAPTR record was available or not.
string srvLookup = null;
if (naptrService != null)
{
srvLookup = naptrService.Data;
}
else
{
if (scheme == SIPSchemesEnum.sips)
{
srvLookup = SIPDNSConstants.SRV_SIPS_TCP_QUERY_PREFIX + host;
}
else
{
srvLookup = "_" + scheme.ToString() + "._" + protocol.ToString() + "." + host;
}
}
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup requested for " + srvLookup + ".", null));
DNSResponse srvRecordResponse = DNSManager.Lookup(srvLookup, QType.SRV, DNS_LOOKUP_TIMEOUT, null, true, async);
if (srvRecordResponse == null && async)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup pending for " + srvLookup + ".", null));
lookupResult.Pending = true;
}
else if (srvRecordResponse.Timedout)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup timed out for " + srvLookup + ".", null));
lookupResult.SRVTimedoutAt = DateTime.Now;
}
else if (!string.IsNullOrWhiteSpace(srvRecordResponse.Error))
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record lookup for " + srvLookup + " returned error of " + lookupResult.LookupError + ".", null));
}
else if (string.IsNullOrWhiteSpace(srvRecordResponse.Error) && srvRecordResponse.RecordSRV != null && srvRecordResponse.RecordSRV.Length > 0)
{
foreach (RecordSRV srvRecord in srvRecordResponse.RecordSRV)
{
SIPDNSServiceResult sipSRVResult = new SIPDNSServiceResult(reqdNAPTRService, srvRecord.PRIORITY, srvRecord.WEIGHT, srvRecord.RR.TTL, srvRecord.TARGET, srvRecord.PORT, DateTime.Now);
lookupResult.AddSRVResult(sipSRVResult);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS SRV record found for " + srvLookup + ", result " + srvRecord.TARGET + " " + srvRecord.PORT + ".", null));
}
}
else
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS no SRV records found for " + srvLookup + ".", null));
}
}
public static SIPDNSLookupResult DNSNameRecordLookup(string host, int port, bool async, SIPURI uri, SIPDNSLookupResult lookupResult = null, bool?preferIPv6 = null, int recursionLevel = 0)
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS Name record lookup requested for " + host + ".", null));
SIPDNSLookupResult result = lookupResult ?? new SIPDNSLookupResult(uri);
result.LookupError = null;
if (UseANYLookups)
{
DNSResponse aRecordResponse = DNSManager.Lookup(host, QType.ANY, DNS_A_RECORD_LOOKUP_TIMEOUT, null, true, async);
if (aRecordResponse == null && async)
{
result.Pending = true;
}
else if (aRecordResponse == null)
{
}
else if (aRecordResponse.Timedout)
{
result.ATimedoutAt = DateTime.Now;
}
else if (!string.IsNullOrWhiteSpace(aRecordResponse.Error))
{
result.LookupError = aRecordResponse.Error;
}
else if ((aRecordResponse.RecordsAAAA == null || aRecordResponse.RecordsAAAA.Length == 0) && (aRecordResponse.RecordsA == null || aRecordResponse.RecordsA.Length == 0) && (aRecordResponse.RecordsCNAME == null || aRecordResponse.RecordsCNAME.Length == 0))
{
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS no CNAME, A or AAAA records found for " + host + ".", null));
result.LookupError = "No CNAME, A or AAAA records found for " + host + ".";
}
else
{
if (preferIPv6 == null)
{
preferIPv6 = SIPDNSManager.PreferIPv6NameResolution;
}
foreach (RecordCNAME aRecord in aRecordResponse.RecordsCNAME)
{
//CNAME could be another CNAME or A/AAAA Record -> max 3 levels recursive name resolution
if (recursionLevel < 3)
{
SIPDNSLookupResult resultCName = DNSNameRecordLookup(aRecord.CNAME, port, async, uri, lookupResult, preferIPv6, recursionLevel + 1);
if (resultCName != null)
{
foreach (SIPDNSLookupEndPoint ep in resultCName.EndPointResults)
{
result.AddLookupResult(ep);
}
}
}
}
if (preferIPv6 == true)
{
SIPURI sipURI = result.URI;
foreach (RecordAAAA aRecord in aRecordResponse.RecordsAAAA)
{
SIPDNSLookupEndPoint sipLookupEndPoint = new SIPDNSLookupEndPoint(new SIPEndPoint(sipURI.Protocol, new IPEndPoint(aRecord.Address, port)), aRecord.RR.TTL);
result.AddLookupResult(sipLookupEndPoint);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS AAAA record found for " + host + ", result " + sipLookupEndPoint.LookupEndPoint.ToString() + ".", null));
}
foreach (RecordA aRecord in aRecordResponse.RecordsA)
{
SIPDNSLookupEndPoint sipLookupEndPoint = new SIPDNSLookupEndPoint(new SIPEndPoint(sipURI.Protocol, new IPEndPoint(aRecord.Address, port)), aRecord.RR.TTL);
result.AddLookupResult(sipLookupEndPoint);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS A record found for " + host + ", result " + sipLookupEndPoint.LookupEndPoint.ToString() + ".", null));
}
}
else
{
SIPURI sipURI = result.URI;
foreach (RecordA aRecord in aRecordResponse.RecordsA)
{
SIPDNSLookupEndPoint sipLookupEndPoint = new SIPDNSLookupEndPoint(new SIPEndPoint(sipURI.Protocol, new IPEndPoint(aRecord.Address, port)), aRecord.RR.TTL);
result.AddLookupResult(sipLookupEndPoint);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS A record found for " + host + ", result " + sipLookupEndPoint.LookupEndPoint.ToString() + ".", null));
}
foreach (RecordAAAA aRecord in aRecordResponse.RecordsAAAA)
{
SIPDNSLookupEndPoint sipLookupEndPoint = new SIPDNSLookupEndPoint(new SIPEndPoint(sipURI.Protocol, new IPEndPoint(aRecord.Address, port)), aRecord.RR.TTL);
result.AddLookupResult(sipLookupEndPoint);
SIPMonitorLogEvent(new SIPMonitorConsoleEvent(SIPMonitorServerTypesEnum.Unknown, SIPMonitorEventTypesEnum.DNS, "SIP DNS AAAA record found for " + host + ", result " + sipLookupEndPoint.LookupEndPoint.ToString() + ".", null));
}
}
}
}
if (result.LookupError != null || result.EndPointResults == null || result.EndPointResults.Count == 0)
{
if (preferIPv6 == true)
{
result = DNSAAAARecordLookup(host, port, async, uri, lookupResult);
}
else
{
result = DNSARecordLookup(host, port, async, uri, lookupResult);
}
}
return(result);
}