/// <summary>
/// Parses a resource record from the packet passed.
/// </summary>
/// <param name="message">The message containing the record being parsed.</param>
/// <param name="packet">The raw DNS message packet.</param>
/// <param name="offset">
/// The current offset in the packet. Returns as the offset of the first byte
/// after the record.
/// </param>
/// <returns>The resource record or <c>null</c> if there was an error.</returns>
public static DnsRR Parse(DnsMessage message, byte[] packet, ref int offset)
{
string qname;
DnsRRType rrtype;
DnsRR rr;
int savePos;
// Peek the qname and record type
savePos = offset;
if (!message.ReadName(packet, ref offset, out qname))
{
return(null);
}
rrtype = (DnsRRType)Helper.ReadInt16(packet, ref offset);
offset = savePos;
switch (rrtype)
{
case DnsRRType.A:
rr = new A_RR();
break;
case DnsRRType.CNAME:
rr = new CNAME_RR();
break;
case DnsRRType.NS:
rr = new NS_RR();
break;
case DnsRRType.MX:
rr = new MX_RR();
break;
case DnsRRType.SOA:
rr = new SOA_RR();
break;
default:
rr = new DnsRR();
break;
}
if (!rr.Read(message, packet, ref offset))
{
return(null);
}
return(rr);
}
/// <summary>
/// This method parses the raw DNS message packet passed and initializes
/// the message properties.
/// </summary>
/// <param name="packet">The raw DNS packet received.</param>
/// <param name="cbPacket">Number of bytes in that packet.</param>
/// <returns>True on success.</returns>
public bool ParsePacket(byte[] packet, int cbPacket)
{
uint qdCount;
uint anCount;
uint nsCount;
uint arCount;
int pos;
// Read the message header
pos = 0;
this.qid = (ushort)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
this.flags = (DnsFlag)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
qdCount = (ushort)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
anCount = (ushort)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
nsCount = (ushort)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
arCount = (ushort)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
Assertion.Test(pos == 12);
// Check for unsupported packets
if ((this.flags & DnsFlag.TC) != 0) // truncation bit is set
{
return(false);
}
if (this.Opcode != DnsOpcode.QUERY) // only accept standard queries
{
return(false);
}
if (qdCount != 1) // only supporting one question
{
return(false);
}
// Parse the question
if (!ReadName(packet, ref pos, out this.qname))
{
return(false);
}
if (pos > cbPacket)
{
return(false);
}
this.qtype = (DnsQType)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
this.qclass = (DnsQClass)Helper.ReadInt16(packet, ref pos); if (pos > cbPacket)
{
return(false);
}
// We're only going to accept Internet queries
if (this.qclass != DnsQClass.IN)
{
return(false);
}
// Parse the answer records
for (int i = 0; i < anCount; i++)
{
var rr = DnsRR.Parse(this, packet, ref pos);
if (rr == null || pos > cbPacket)
{
return(false);
}
this.Answers.Add(rr);
}
// Parse the authority records
for (int i = 0; i < nsCount; i++)
{
var rr = DnsRR.Parse(this, packet, ref pos);
if (rr == null || pos > cbPacket)
{
return(false);
}
this.Authorities.Add(rr);
}
// Parse the additional records
for (int i = 0; i < arCount; i++)
{
var rr = DnsRR.Parse(this, packet, ref pos);
if (rr == null || pos > cbPacket)
{
return(false);
}
this.Additional.Add(rr);
}
// $todo(jeff.lill):
//
// Delete this once we've figured out why the DNS server
// sometimes get requests with NULL QNAME properties.
if (this.QName == null)
{
var packetBytes = Helper.Extract(packet, cbPacket);
var hexDump = Helper.HexDump(packetBytes, 16, HexDumpOption.ShowAll);
var diagnostics = GetTraceDetails(IPAddress.Any);
var extendedLogInfo = new StringSysLogEntryExtension(diagnostics + "\r\n\r\nPacket:\r\n\r\n" + hexDump);
SysLog.LogWarning(extendedLogInfo, "DNS Packet with QNAME=NULL");
}
return(true);
}
