/// <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>
protected ResourceRecord(Pointer pointer)
{
// 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)pointer.ReadShort())
{
case DnsType.NS:
this._record = new NSRecord(pointer);
break;
case DnsType.MX:
this._record = new MXRecord(pointer);
break;
case DnsType.ANAME:
this._record = new ANameRecord(pointer);
break;
case DnsType.SOA:
this._record = new SoaRecord(pointer);
break;
default:
{
// move the pointer over this unrecognised record
pointer += recordLength;
break;
}
}
}
/// <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>
public Question(Pointer pointer)
{
// extract from the message
this._domain = pointer.ReadDomain();
this._dnsType = (DnsType) pointer.ReadShort();
this._dnsClass = (DnsClass) pointer.ReadShort();
}
// expose this IP address r/o to the world
/// <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>
public 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
this.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>
public Response(byte[] message)
{
// create the arrays of response objects
this.questions = new Question[GetShort(message, 4)];
this.answers = new Answer[GetShort(message, 6)];
this.nameServers = new NameServer[GetShort(message, 8)];
this.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 < this.questions.Length; index++)
{
try
{
// try to build a quesion from the response
this.questions[index] = new Question(pointer);
}
catch (Exception ex)
{
Log.Error("A DNS response question failure occured.", ex);
// something grim has happened, we can't continue
throw new InvalidResponseException(ex);
}
}
for (int index = 0; index < this.answers.Length; index++)
{
this.answers[index] = new Answer(pointer);
}
for (int index = 0; index < this.nameServers.Length; index++)
{
this.nameServers[index] = new NameServer(pointer);
}
for (int index = 0; index < this.additionalRecords.Length; index++)
{
this.additionalRecords[index] = new AdditionalRecord(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>
public MXRecord(Pointer pointer)
{
this._preference = pointer.ReadShort();
this._domainName = pointer.ReadDomain();
}
public NameServer(Pointer pointer) : base(pointer)
{
}
public Answer(Pointer pointer) : base(pointer)
{
}
public AdditionalRecord(Pointer pointer) : base(pointer)
{
}