/// <summary>
/// Constructs an SOA record by reading bytes from a return message
/// </summary>
/// <param name="pointer">A logical pointer to the bytes holding the record</param>
internal SoaRecord(Pointer pointer)
{
// read all fields RFC1035 3.3.13
_primaryNameServer = pointer.ReadDomain();
_responsibleMailAddress = pointer.ReadDomain();
_serial = pointer.ReadInt();
_refresh = pointer.ReadInt();
_retry = pointer.ReadInt();
_expire = pointer.ReadInt();
_defaultTtl = pointer.ReadInt();
}
/// <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>
/// Reads a domain name from the byte array. The method by which this works is described
/// in RFC1035 - 4.1.4. Essentially to minimise the size of the message, if part of a domain
/// name already been seen in the message, rather than repeating it, a pointer to the existing
/// definition is used. Each word in a domain name is a label, and is preceded by its length
///
/// eg. bigdevelopments.co.uk
///
/// is [15] (size of bigdevelopments) + "bigdevelopments"
/// [2] "co"
/// [2] "uk"
/// [1] 0 (NULL)
/// </summary>
/// <returns>the byte at the pointer</returns>
public string ReadDomain()
{
StringBuilder domain = new StringBuilder();
int length = 0;
// get the length of the first label
while ((length = ReadByte()) != 0)
{
// top 2 bits set denotes domain name compression and to reference elsewhere
if ((length & 0xc0) == 0xc0)
{
// work out the existing domain name, copy this pointer
Pointer newPointer = Copy();
// and move it to where specified here
newPointer.SetPosition((length & 0x3f) << 8 | ReadByte());
// repeat call recursively
domain.Append(newPointer.ReadDomain());
return(domain.ToString());
}
// if not using compression, copy a char at a time to the domain name
while (length > 0)
{
domain.Append(ReadChar());
length--;
}
// if size of next label isn't null (end of domain name) add a period ready for next label
if (Peek() != 0)
{
domain.Append('.');
}
}
// and return
return(domain.ToString());
}
/// <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();
}
/// <summary>
/// Constructs a NS record by reading bytes from a return message
/// </summary>
/// <param name="pointer">A logical pointer to the bytes holding the record</param>
internal NSRecord(Pointer pointer)
{
_domainName = pointer.ReadDomain();
}
