internal static DnsMessageBase CreateByFlag(byte[] data, DnsServer.SelectTsigKey tsigKeySelector, byte[] originalMac)
{
int flagPosition = 2;
ushort flags = ParseUShort(data, ref flagPosition);
DnsMessageBase res;
switch ((OperationCode)((flags & 0x7800) >> 11))
{
case OperationCode.Update:
res = new DnsUpdateMessage();
break;
default:
res = new DnsMessage();
break;
}
res.ParseInternal(data, tsigKeySelector, originalMac);
return(res);
}
private void EndUdpReceive(IAsyncResult ar)
{
try
{
lock (_udpListener)
{
_hasActiveUdpListener = false;
}
StartUdpListen();
IPEndPoint endpoint;
byte[] buffer = _udpListener.EndReceive(ar, out endpoint);
DnsMessageBase query;
byte[] originalMac;
try
{
query = DnsMessageBase.CreateByFlag(buffer, TsigKeySelector, null);
originalMac = (query.TSigOptions == null) ? null : query.TSigOptions.Mac;
}
catch (Exception e)
{
throw new Exception("Error parsing dns query", e);
}
DnsMessageBase response;
try
{
response = ProcessMessage(query, endpoint.Address, ProtocolType.Udp);
}
catch (Exception ex)
{
OnExceptionThrown(ex);
response = null;
}
if (response == null)
{
response = query;
query.IsQuery = false;
query.ReturnCode = ReturnCode.ServerFailure;
}
int length = response.Encode(false, originalMac, out buffer);
#region Truncating
DnsMessage message = response as DnsMessage;
if (message != null)
{
int maxLength = 512;
if (query.IsEDnsEnabled && message.IsEDnsEnabled)
{
maxLength = Math.Max(512, (int)message.EDnsOptions.UdpPayloadSize);
}
while (length > maxLength)
{
// First step: remove data from additional records except the opt record
if ((message.IsEDnsEnabled && (message.AdditionalRecords.Count > 1)) || (!message.IsEDnsEnabled && (message.AdditionalRecords.Count > 0)))
{
for (int i = message.AdditionalRecords.Count - 1; i >= 0; i--)
{
if (message.AdditionalRecords[i].RecordType != RecordType.Opt)
{
message.AdditionalRecords.RemoveAt(i);
}
}
length = message.Encode(false, originalMac, out buffer);
continue;
}
int savedLength = 0;
if (message.AuthorityRecords.Count > 0)
{
for (int i = message.AuthorityRecords.Count - 1; i >= 0; i--)
{
savedLength += message.AuthorityRecords[i].MaximumLength;
message.AuthorityRecords.RemoveAt(i);
if ((length - savedLength) < maxLength)
{
break;
}
}
message.IsTruncated = true;
length = message.Encode(false, originalMac, out buffer);
continue;
}
if (message.AnswerRecords.Count > 0)
{
for (int i = message.AnswerRecords.Count - 1; i >= 0; i--)
{
savedLength += message.AnswerRecords[i].MaximumLength;
message.AnswerRecords.RemoveAt(i);
if ((length - savedLength) < maxLength)
{
break;
}
}
message.IsTruncated = true;
length = message.Encode(false, originalMac, out buffer);
continue;
}
if (message.Questions.Count > 0)
{
for (int i = message.Questions.Count - 1; i >= 0; i--)
{
savedLength += message.Questions[i].MaximumLength;
message.Questions.RemoveAt(i);
if ((length - savedLength) < maxLength)
{
break;
}
}
message.IsTruncated = true;
length = message.Encode(false, originalMac, out buffer);
}
}
}
#endregion
_udpListener.BeginSend(buffer, 0, length, endpoint, EndUdpSend, null);
}
catch (Exception e)
{
HandleUdpException(e);
}
}