/// <summary>
/// Construct the question reading from a DNS Server response. Consult RFC1035 4.1.2
/// for byte-wise details of this structure in byte array form
/// </summary>
/// <param name="pointer">a logical pointer to the Question in byte array form</param>
internal Question(Pointer pointer)
{
// extract from the message
_domain = pointer.ReadDomain();
_dnsType = (DnsType)pointer.ReadShort();
_dnsClass = (DnsClass)pointer.ReadShort();
}
/// <summary>
/// Construct a resource record from a pointer to a byte array
/// </summary>
/// <param name="pointer">the position in the byte array of the record</param>
internal ResourceRecord(Pointer pointer)
{
// extract the domain, question type, question class and Ttl
_domain = pointer.ReadDomain();
_dnsType = (DnsType)pointer.ReadShort();
_dnsClass = (DnsClass)pointer.ReadShort();
_Ttl = pointer.ReadInt();
// the next short is the record length, we only use it for unrecognised record types
int recordLength = pointer.ReadShort();
// and create the appropriate RDATA record based on the dnsType
switch (_dnsType)
{
case DnsType.NS: _record = new NSRecord(pointer); break;
case DnsType.MX: _record = new MXRecord(pointer); break;
case DnsType.ANAME: _record = new ANameRecord(pointer); break;
case DnsType.SOA: _record = new SoaRecord(pointer); break;
default:
{
// move the pointer over this unrecognised record
pointer += recordLength;
break;
}
}
}
/// <summary>
/// Constructs an ANAME record by reading bytes from a return message
/// </summary>
/// <param name="pointer">A logical pointer to the bytes holding the record</param>
internal ANameRecord(Pointer pointer)
{
byte b1 = pointer.ReadByte();
byte b2 = pointer.ReadByte();
byte b3 = pointer.ReadByte();
byte b4 = pointer.ReadByte();
// this next line's not brilliant - couldn't find a better way though
_ipAddress = IPAddress.Parse(string.Format("{0}.{1}.{2}.{3}", b1, b2, b3, b4));
}
/// <summary>
/// Construct a Response object from the supplied byte array
/// </summary>
/// <param name="message">a byte array returned from a DNS server query</param>
internal Response(byte[] message)
{
// the bit flags are in bytes 2 and 3
byte flags1 = message[2];
byte flags2 = message[3];
// get return code from lowest 4 bits of byte 3
int returnCode = flags2 & 15;
// if its in the reserved section, set to other
if (returnCode > 6) returnCode = 6;
_returnCode = (ReturnCode)returnCode;
// other bit flags
_authoritativeAnswer = ((flags1 & 4) != 0);
_recursionAvailable = ((flags2 & 128) != 0);
_truncated = ((flags1 & 2) != 0);
// create the arrays of response objects
_questions = new Question[GetShort(message, 4)];
_answers = new Answer[GetShort(message, 6)];
_nameServers = new NameServer[GetShort(message, 8)];
_additionalRecords = new AdditionalRecord[GetShort(message, 10)];
// need a pointer to do this, position just after the header
Pointer pointer = new Pointer(message, 12);
// and now populate them, they always follow this order
for (int index = 0; index < _questions.Length; index++)
{
try
{
// try to build a quesion from the response
_questions[index] = new Question(pointer);
}
catch (Exception ex)
{
// something grim has happened, we can't continue
throw new InvalidResponseException(ex);
}
}
for (int index = 0; index < _answers.Length; index++)
{
_answers[index] = new Answer(pointer);
}
for (int index = 0; index < _nameServers.Length; index++)
{
_nameServers[index] = new NameServer(pointer);
}
for (int index = 0; index < _additionalRecords.Length; index++)
{
_additionalRecords[index] = new AdditionalRecord(pointer);
}
}
internal AdditionalRecord(Pointer pointer) : base(pointer) {}
internal NameServer(Pointer pointer) : base(pointer) {}
internal Answer(Pointer pointer) : base(pointer) {}
/// <summary>
/// Constructs an MX record by reading bytes from a return message
/// </summary>
/// <param name="pointer">A logical pointer to the bytes holding the record</param>
internal MXRecord(Pointer pointer)
{
_preference = pointer.ReadShort();
_domainName = pointer.ReadDomain();
}