/// <summary>
/// Attempts a lookup from cache.
/// </summary>
/// <param name="uri"></param>
/// <param name="startQuery"></param>
/// <param name="preferIPv6"></param>
/// <returns></returns>
private static SIPEndPoint SIPLookupFromCache(
SIPURI uri,
QueryType startQuery,
bool preferIPv6)
{
SIPEndPoint result = null;
QueryType queryType = startQuery;
string host = uri.MAddrOrHostAddress;
int port = SIPConstants.GetDefaultPort(uri.Protocol);
if (ushort.TryParse(uri.HostPort, out var uriPort))
{
port = uriPort;
}
bool isDone = false;
while (!isDone)
{
switch (queryType)
{
case QueryType.SRV:
var srvProtocol = SIPServices.GetSRVProtocolForSIPURI(uri);
string serviceHost = DnsQueryExtensions.ConcatServiceName(uri.MAddrOrHostAddress, uri.Scheme.ToString(), srvProtocol.ToString());
var srvResult = _lookupClient.QueryCache(serviceHost, QueryType.SRV);
(var srvHost, var srvPort) = GetHostAndPortFromSrvResult(srvResult);
if (srvHost != null)
{
host = srvHost;
port = srvPort != 0 ? srvPort : port;
}
queryType = preferIPv6 ? QueryType.AAAA : QueryType.A;
break;
case QueryType.AAAA:
var aaaaResult = _lookupClient.QueryCache(host, UseANYLookups ? QueryType.ANY : QueryType.AAAA, QueryClass.IN);
if (aaaaResult?.Answers?.Count > 0)
{
result = GetFromLookupResult(uri.Protocol, aaaaResult.Answers.OrderByDescending(x => x.RecordType).First(), port);
isDone = true;
}
else
{
queryType = QueryType.A;
}
break;
default:
// A record lookup.
var aResult = _lookupClient.QueryCache(host, QueryType.A, QueryClass.IN);
if (aResult != null)
{
if (aResult.Answers?.Count > 0)
{
result = GetFromLookupResult(uri.Protocol, aResult.Answers.First(), port);
}
else
{
// We got a result back but it was empty indicating an unresolvable host or
// some other DNS error condition.
result = SIPEndPoint.Empty;
}
}
isDone = true;
break;
}
}
return(result);
}