public DnsHeader(Byte[] bytes, UInt32 offset)
{
id = (UInt16)((bytes[offset] << 8) |
(bytes[offset + 1]));
thirdByte = bytes[offset + 2];
fourthByte = bytes[offset + 3];
isResponseFlag = (bytes[offset + 2] & 0x80) != 0;
opCode = (DnsOpCode)((bytes[offset + 2] >> 3) & 0xF);
rCode = (DnsRCode)(bytes[offset + 3] & 0xF);
qdCount = (UInt16)((bytes[offset + 4] << 8) |
(bytes[offset + 5]));
anCount = (UInt16)((bytes[offset + 6] << 8) |
(bytes[offset + 7]));
nsCount = (UInt16)((bytes[offset + 8] << 8) |
(bytes[offset + 9]));
arCount = (UInt16)((bytes[offset + 10] << 8) |
(bytes[offset + 11]));
}
void ProcessResponse(SimpleResolverEventArgs args, DnsResponse response, EndPoint server_ep)
{
DnsRCode status = response.Header.RCode;
if (status != 0)
{
if (args.PTRAddress != null)
{
// PTR query failed -> no error, we have the IP
return;
}
args.ResolverError = (ResolverError)status;
return;
}
// TODO: verify IP of the server is in our list and the same one that got the query
IPEndPoint ep = (IPEndPoint)server_ep;
if (ep.Port != 53)
{
args.ResolverError = ResolverError.ResponseHeaderError;
args.ErrorMessage = "Port";
return;
}
DnsHeader header = response.Header;
if (!header.IsQuery)
{
args.ResolverError = ResolverError.ResponseHeaderError;
args.ErrorMessage = "IsQuery";
return;
}
// TODO: handle Truncation. Retry with bigger buffer?
if (header.QuestionCount > 1)
{
args.ResolverError = ResolverError.ResponseHeaderError;
args.ErrorMessage = "QuestionCount";
return;
}
ReadOnlyCollection <DnsQuestion> q = response.GetQuestions();
if (q.Count != 1)
{
args.ResolverError = ResolverError.ResponseHeaderError;
args.ErrorMessage = "QuestionCount 2";
return;
}
DnsQuestion question = q [0];
/* The answer might have dot at the end, etc...
* if (String.Compare (question.Name, args.HostName) != 0) {
* args.ResolverError = ResolverError.ResponseHeaderError;
* args.ErrorMessage = "HostName - " + question.Name + " != " + args.HostName;
* return;
* }
*/
DnsQType t = question.Type;
if (t != DnsQType.A && t != DnsQType.AAAA && t != DnsQType.PTR)
{
args.ResolverError = ResolverError.ResponseHeaderError;
args.ErrorMessage = "QType " + question.Type;
return;
}
if (question.Class != DnsQClass.IN)
{
args.ResolverError = ResolverError.ResponseHeaderError;
args.ErrorMessage = "QClass " + question.Class;
return;
}
ReadOnlyCollection <DnsResourceRecord> records = response.GetAnswers();
if (records.Count == 0)
{
if (args.PTRAddress != null)
{
// PTR query failed -> no error
return;
}
args.ResolverError = ResolverError.NameError; // is this ok?
args.ErrorMessage = "NoAnswers";
return;
}
List <string> aliases = null;
List <IPAddress> addresses = null;
foreach (DnsResourceRecord r in records)
{
if (r.Class != DnsClass.IN)
{
continue;
}
if (r.Type == DnsType.A || r.Type == DnsType.AAAA)
{
if (addresses == null)
{
addresses = new List <IPAddress> ();
}
addresses.Add(((DnsResourceRecordIPAddress)r).Address);
}
else if (r.Type == DnsType.CNAME)
{
if (aliases == null)
{
aliases = new List <string> ();
}
aliases.Add(((DnsResourceRecordCName)r).CName);
}
else if (r.Type == DnsType.PTR)
{
args.HostEntry.HostName = ((DnsResourceRecordPTR)r).DName;
args.HostEntry.Aliases = aliases == null ? EmptyStrings : aliases.ToArray();
args.HostEntry.AddressList = EmptyAddresses;
return;
}
}
IPHostEntry entry = args.HostEntry ?? new IPHostEntry();
if (entry.HostName == null && aliases != null && aliases.Count > 0)
{
entry.HostName = aliases [0];
aliases.RemoveAt(0);
}
entry.Aliases = aliases == null ? EmptyStrings : aliases.ToArray();
entry.AddressList = addresses == null ? EmptyAddresses : addresses.ToArray();
args.HostEntry = entry;
if ((question.Type == DnsQType.A || question.Type == DnsQType.AAAA) && entry.AddressList == EmptyAddresses)
{
args.ResolverError = ResolverError.NameError;
args.ErrorMessage = "No addresses in response";
}
else if (question.Type == DnsQType.PTR && entry.HostName == null)
{
args.ResolverError = ResolverError.NameError;
args.ErrorMessage = "No PTR in response";
}
}
