/// <summary>
/// Get the response data
/// </summary>
/// <returns>The response.</returns>
public int GetData(byte[] responseBuffer)
{
// Create and write the response header
var dnsMessageHeader = new DnsMessageHeader (this.Query.Header.MessageId) {
StatusCode = DnsQueryStatusCode.OK,
AdditionalAnswerCount = this.AdditionalAnswerCount,
NameServerAnswerCount = this.NameServerAnswerCount,
NormalAnswerCount = this.NormalAnswerCount,
QuestionCount = (uint)this.Query.Questions.Count,
IsAuthorativeMessage = true,
IsResponse = true,
IsTruncated = false,
RecursionDesired = false,
RecursionSupported = false
};
dnsMessageHeader.WriteHeader (responseBuffer, 0);
// After the header, copy the original request
Buffer.BlockCopy (
src: this.Query.OriginalQuestionData,
srcOffset: DnsMessageHeader.SizeInBytes,
dst: responseBuffer,
dstOffset: DnsMessageHeader.SizeInBytes,
count: this.Query.OriginalQuestionData.Length - DnsMessageHeader.SizeInBytes);
// Now write the response
var byteIndex = this.Query.OriginalQuestionData.Length;
foreach (var answer in this.Answers)
{
byteIndex += answer.WriteAnswer(responseBuffer, byteIndex);
}
// Return the number of bytes written
return byteIndex;
}
/// <summary>
/// Parse a DnsMessageHeader object from the given array
/// </summary>
/// <param name="array">Array.</param>
public static DnsMessageHeader Parse(byte[] array, int offset)
{
// TODO: check length
// HEADER: A total of 12 bytes
// 2 bytes - Message ID
byte[] messageId = new byte[2];
messageId[0] = array[offset++];
messageId[1] = array[offset++];
var dnsMessageHeader = new DnsMessageHeader(messageId);
// 1 bit - QR query response, should be set to 0
var queryHeaderByte1 = array[offset++];
var queryHeaderByte2 = array[offset++];
var isQuestion = ((queryHeaderByte1 >> 7) & 1) == 0;
if (!isQuestion)
{
// INVALID DNS query
return(null);
}
// 4 bits - Request type
dnsMessageHeader.RequestType = (DnsQueryRequestType)DnsEncoder.Parse4BitNumeric(queryHeaderByte1, 1);
// 1 bit - authorative answer
dnsMessageHeader.IsAuthorativeMessage = 1 == ((queryHeaderByte1 >> 2) & 1);
dnsMessageHeader.IsTruncated = 1 == ((queryHeaderByte1 >> 1) & 1);
dnsMessageHeader.RecursionDesired = 1 == ((queryHeaderByte1 >> 0) & 1);
dnsMessageHeader.RecursionSupported = 1 == ((queryHeaderByte2 >> 7) & 1);
// 2 bytes - QDCOUNT
dnsMessageHeader.QuestionCount = DnsEncoder.ParseUint16(array, offset);
// 4 bytes, skip
offset += 6;
// 2 bytes - Additional questions
dnsMessageHeader.AdditionalQuestionCount = DnsEncoder.ParseUint16(array, offset);
// TODO: what to do if number of questions is 0?
// TODO: what to do if number of questions does not match
return(dnsMessageHeader);
}
/// <summary>
/// Get the response data
/// </summary>
/// <returns>The response.</returns>
public int GetData(byte[] responseBuffer)
{
// Create and write the response header
var dnsMessageHeader = new DnsMessageHeader(this.Query.Header.MessageId)
{
StatusCode = DnsQueryStatusCode.OK,
AdditionalAnswerCount = this.AdditionalAnswerCount,
NameServerAnswerCount = this.NameServerAnswerCount,
NormalAnswerCount = this.NormalAnswerCount,
QuestionCount = (uint)this.Query.Questions.Count,
IsAuthorativeMessage = true,
IsResponse = true,
IsTruncated = false,
RecursionDesired = false,
RecursionSupported = false
};
dnsMessageHeader.WriteHeader(responseBuffer, 0);
// After the header, copy the original request
Buffer.BlockCopy(
src: this.Query.OriginalQuestionData,
srcOffset: DnsMessageHeader.SizeInBytes,
dst: responseBuffer,
dstOffset: DnsMessageHeader.SizeInBytes,
count: this.Query.OriginalQuestionData.Length - DnsMessageHeader.SizeInBytes);
// Now write the response
var byteIndex = this.Query.OriginalQuestionData.Length;
foreach (var answer in this.Answers)
{
byteIndex += answer.WriteAnswer(responseBuffer, byteIndex);
}
// Return the number of bytes written
return(byteIndex);
}
/// <summary>
/// Parse the DnsQuery from the given UdpReceiveResult
/// </summary>
/// <param name="data"></param>
/// <returns></returns>
public static DnsQuery Parse(byte[] buffer, IPAddress remoteEndpoint)
{
// Create the query
var query = new DnsQuery();
query.Status = DnsQueryStatus.OK;
query.ClientIPAddress = remoteEndpoint;
// Parse the dns request header
query.Header = DnsMessageHeader.Parse(buffer, 0);
// DNS QUESTIONS:
int offset = 12;
for (int i = 0; i < query.Header.QuestionCount; i++)
{
try
{
// Save the question
DnsQuestion question;
offset += DnsQuestion.Parse(out question, buffer, offset);
if (question != null)
{
query.Questions.Add(question);
}
}
catch (Exception e) {
Console.WriteLine(e.Message);
Console.WriteLine(e.StackTrace);
query.Status = DnsQueryStatus.ParsingError;
break;
}
}
// Save the original question data to include it in the answer
query.OriginalQuestionData = new byte[offset];
Buffer.BlockCopy(buffer, 0, query.OriginalQuestionData, 0, offset);
// Parse the additional EDNS question
// For now, we only support a single additional question
if (query.Header.AdditionalQuestionCount > 0)
{
//Console.WriteLine("Reading OPT");
try
{
int bytesProcessed = 0;
query.EdnsQuestion = EdnsQuestion.Parse(buffer, offset, ref bytesProcessed);
offset += bytesProcessed;
// If the question was validely parsed, try using the subnet to assign the IP based on the user's location instead of the
// dns proxy server
if (query.EdnsQuestion != null)
{
var clientSubnetOption = (EdnsClientSubnetOption)query.EdnsQuestion.GetOption(EdnsOptionCode.ClientSubnet);
if (clientSubnetOption != null)
{
query.ClientIPAddress = clientSubnetOption.IPAddress;
}
}
}
catch (Exception e) {
Console.WriteLine(e.Message);
Console.WriteLine(e.StackTrace);
// If this fails, we still try to proceed normally
// TODO: log
}
}
return(query);
}
/// <summary>
/// Parse a DnsMessageHeader object from the given array
/// </summary>
/// <param name="array">Array.</param>
public static DnsMessageHeader Parse(byte[] array, int offset)
{
// TODO: check length
// HEADER: A total of 12 bytes
// 2 bytes - Message ID
byte[] messageId = new byte[2];
messageId[0] = array[offset++];
messageId[1] = array[offset++];
var dnsMessageHeader = new DnsMessageHeader (messageId);
// 1 bit - QR query response, should be set to 0
var queryHeaderByte1 = array[offset++];
var queryHeaderByte2 = array[offset++];
var isQuestion = ((queryHeaderByte1 >> 7) & 1) == 0;
if (!isQuestion) {
// INVALID DNS query
return null;
}
// 4 bits - Request type
dnsMessageHeader.RequestType = (DnsQueryRequestType)DnsEncoder.Parse4BitNumeric(queryHeaderByte1, 1);
// 1 bit - authorative answer
dnsMessageHeader.IsAuthorativeMessage = 1 == ((queryHeaderByte1 >> 2) & 1);
dnsMessageHeader.IsTruncated = 1 == ((queryHeaderByte1 >> 1) & 1);
dnsMessageHeader.RecursionDesired = 1 == ((queryHeaderByte1 >> 0) & 1);
dnsMessageHeader.RecursionSupported = 1 == ((queryHeaderByte2 >> 7) & 1);
// 2 bytes - QDCOUNT
dnsMessageHeader.QuestionCount = DnsEncoder.ParseUint16(array, offset);
// 4 bytes, skip
offset += 6;
// 2 bytes - Additional questions
dnsMessageHeader.AdditionalQuestionCount = DnsEncoder.ParseUint16(array, offset);
// TODO: what to do if number of questions is 0?
// TODO: what to do if number of questions does not match
return dnsMessageHeader;
}
