using System;
using System.IO;
using System.Collections.Generic;
using System.Net;
using System.Text;
namespace Heijden.DNS
{
#region RFC specification
/*
4.1.1. Header section format
The header contains the following fields:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode |AA|TC|RD|RA| Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ANCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NSCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
where:
ID A 16 bit identifier assigned by the program that
generates any kind of query. This identifier is copied
the corresponding reply and can be used by the requester
to match up replies to outstanding queries.
QR A one bit field that specifies whether this message is a
query (0), or a response (1).
OPCODE A four bit field that specifies kind of query in this
message. This value is set by the originator of a query
and copied into the response. The values are:
0 a standard query (QUERY)
1 an inverse query (IQUERY)
2 a server status request (STATUS)
3-15 reserved for future use
AA Authoritative Answer - this bit is valid in responses,
and specifies that the responding name server is an
authority for the domain name in question section.
Note that the contents of the answer section may have
multiple owner names because of aliases. The AA bit
corresponds to the name which matches the query name, or
the first owner name in the answer section.
TC TrunCation - specifies that this message was truncated
due to length greater than that permitted on the
transmission channel.
RD Recursion Desired - this bit may be set in a query and
is copied into the response. If RD is set, it directs
the name server to pursue the query recursively.
Recursive query support is optional.
RA Recursion Available - this be is set or cleared in a
response, and denotes whether recursive query support is
available in the name server.
Z Reserved for future use. Must be zero in all queries
and responses.
RCODE Response code - this 4 bit field is set as part of
responses. The values have the following
interpretation:
0 No error condition
1 Format error - The name server was
unable to interpret the query.
2 Server failure - The name server was
unable to process this query due to a
problem with the name server.
3 Name Error - Meaningful only for
responses from an authoritative name
server, this code signifies that the
domain name referenced in the query does
not exist.
4 Not Implemented - The name server does
not support the requested kind of query.
5 Refused - The name server refuses to
perform the specified operation for
policy reasons. For example, a name
server may not wish to provide the
information to the particular requester,
or a name server may not wish to perform
a particular operation (e.g., zone
transfer) for particular data.
6-15 Reserved for future use.
QDCOUNT an unsigned 16 bit integer specifying the number of
entries in the question section.
ANCOUNT an unsigned 16 bit integer specifying the number of
resource records in the answer section.
NSCOUNT an unsigned 16 bit integer specifying the number of name
server resource records in the authority records
section.
ARCOUNT an unsigned 16 bit integer specifying the number of
resource records in the additional records section.
*/
#endregion
public class Header
{
/// <summary>
/// An identifier assigned by the program
/// </summary>
public ushort ID;
// internal flag
private ushort Flags;
/// <summary>
/// the number of entries in the question section
/// </summary>
public ushort QDCOUNT;
/// <summary>
/// the number of resource records in the answer section
/// </summary>
public ushort ANCOUNT;
/// <summary>
/// the number of name server resource records in the authority records section
/// </summary>
public ushort NSCOUNT;
/// <summary>
/// the number of resource records in the additional records section
/// </summary>
public ushort ARCOUNT;
public Header()
{
}
public Header(RecordReader rr)
{
ID = rr.ReadUInt16();
Flags = rr.ReadUInt16();
QDCOUNT = rr.ReadUInt16();
ANCOUNT = rr.ReadUInt16();
NSCOUNT = rr.ReadUInt16();
ARCOUNT = rr.ReadUInt16();
}
private ushort SetBits(ushort oldValue, int position, int length, bool blnValue)
{
return SetBits(oldValue, position, length, blnValue ? (ushort)1 : (ushort)0);
}
private ushort SetBits(ushort oldValue, int position, int length, ushort newValue)
{
// sanity check
if (length <= 0 || position >= 16)
return oldValue;
// get some mask to put on
int mask = (2 << (length - 1)) - 1;
// clear out value
oldValue &= (ushort)~(mask << position);
// set new value
oldValue |= (ushort)((newValue & mask) << position);
return oldValue;
}
private ushort GetBits(ushort oldValue, int position, int length)
{
// sanity check
if (length <= 0 || position >= 16)
return 0;
// get some mask to put on
int mask = (2 << (length - 1)) - 1;
// shift down to get some value and mask it
return (ushort)((oldValue >> position) & mask);
}
/// <summary>
/// Represents the header as a byte array
/// </summary>
public byte[] Data
{
get
{
List<byte> data = new List<byte>();
data.AddRange(WriteShort(ID));
data.AddRange(WriteShort(Flags));
data.AddRange(WriteShort(QDCOUNT));
data.AddRange(WriteShort(ANCOUNT));
data.AddRange(WriteShort(NSCOUNT));
data.AddRange(WriteShort(ARCOUNT));
return data.ToArray();
}
}
private byte[] WriteShort(ushort sValue)
{
return BitConverter.GetBytes(IPAddress.HostToNetworkOrder((short)sValue));
}
/// <summary>
/// query (false), or a response (true)
/// </summary>
public bool QR
{
get
{
return GetBits(Flags, 15, 1) == 1;
}
set
{
Flags = SetBits(Flags, 15, 1, value);
}
}
/// <summary>
/// Specifies kind of query
/// </summary>
public OPCode OPCODE
{
get
{
return (OPCode)GetBits(Flags, 11, 4);
}
set
{
Flags = SetBits(Flags, 11, 4, (ushort)value);
}
}
/// <summary>
/// Authoritative Answer
/// </summary>
public bool AA
{
get
{
return GetBits(Flags, 10, 1) == 1;
}
set
{
Flags = SetBits(Flags, 10, 1, value);
}
}
/// <summary>
/// TrunCation
/// </summary>
public bool TC
{
get
{
return GetBits(Flags, 9, 1) == 1;
}
set
{
Flags = SetBits(Flags, 9, 1, value);
}
}
/// <summary>
/// Recursion Desired
/// </summary>
public bool RD
{
get
{
return GetBits(Flags, 8, 1) == 1;
}
set
{
Flags = SetBits(Flags, 8, 1, value);
}
}
/// <summary>
/// Recursion Available
/// </summary>
public bool RA
{
get
{
return GetBits(Flags, 7, 1) == 1;
}
set
{
Flags = SetBits(Flags, 7, 1, value);
}
}
/// <summary>
/// Reserved for future use
/// </summary>
public ushort Z
{
get
{
return GetBits(Flags, 4, 3);
}
set
{
Flags = SetBits(Flags, 4, 3, value);
}
}
/// <summary>
/// Response code
/// </summary>
public RCode RCODE
{
get
{
return (RCode)GetBits(Flags, 0, 4);
}
set
{
Flags = SetBits(Flags, 0, 4, (ushort)value);
}
}
}
}
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