internal static ResourceRecord ReadFrom(PacketReader reader)
{
string name = reader.ReadName();
RecordType type = (RecordType)reader.ReadUShort();
RecordClass rClass = (RecordClass)reader.ReadUShort();
DateTime expiry = DateTime.UtcNow + TimeSpan.FromSeconds(reader.ReadInt());
switch (type)
{
case RecordType.Pointer:
return new PointerRecord(name, type, rClass, expiry, reader);
case RecordType.CanonicalName:
return new CanonicalNameRecord(name, type, rClass, expiry, reader);
case RecordType.Address:
return new IP4AddressRecord(name, type, rClass, expiry, reader);
case RecordType.Text:
return new TextRecord(name, type, rClass, expiry, reader);
case RecordType.Service:
return new ServiceRecord(name, type, rClass, expiry, reader);
default:
int len = reader.ReadUShort();
reader.Position += len;
return new ResourceRecord(name, type, rClass, expiry);
}
}
public static Message Read(PacketReader reader)
{
Message result = new Message();
result.TransactionId = reader.ReadUShort();
result.Flags = new MessageFlags(reader.ReadUShort());
ushort questions = reader.ReadUShort();
ushort answers = reader.ReadUShort();
ushort authorityRecords = reader.ReadUShort();
ushort additionalRecords = reader.ReadUShort();
for (int i = 0; i < questions; ++i)
{
result.Questions.Add(Question.ReadFrom(reader));
}
for (int i = 0; i < answers; ++i)
{
result.Answers.Add(ResourceRecord.ReadFrom(reader));
}
for (int i = 0; i < authorityRecords; ++i)
{
result.AuthorityRecords.Add(ResourceRecord.ReadFrom(reader));
}
for (int i = 0; i < additionalRecords; ++i)
{
result.AdditionalRecords.Add(ResourceRecord.ReadFrom(reader));
}
return result;
}
internal PointerRecord(string name, RecordType type, RecordClass rClass, DateTime expiry, PacketReader reader)
: base(name, type, rClass, expiry)
{
ushort dataLen = reader.ReadUShort();
int pos = reader.Position;
_targetName = reader.ReadName();
reader.Position = pos + dataLen;
}
internal IP4AddressRecord(string name, RecordType type, RecordClass rClass, DateTime expiry, PacketReader reader)
: base(name, type, rClass, expiry)
{
ushort dataLen = reader.ReadUShort();
int pos = reader.Position;
_address = new IPAddress(reader.ReadBytes(dataLen));
reader.Position = pos + dataLen;
}
internal ServiceRecord(string name, RecordType type, RecordClass rClass, DateTime expiry, PacketReader reader)
: base(name, type, rClass, expiry)
{
ushort dataLen = reader.ReadUShort();
int pos = reader.Position;
_priority = reader.ReadUShort();
_weight = reader.ReadUShort();
_port = reader.ReadUShort();
_target = reader.ReadName();
reader.Position = pos + dataLen;
}
internal TextRecord(string name, RecordType type, RecordClass rClass, DateTime expiry, PacketReader reader)
: base(name, type, rClass, expiry)
{
_values = new Dictionary<string, byte[]>();
ushort dataLen = reader.ReadUShort();
int pos = reader.Position;
while (reader.Position < pos + dataLen)
{
int valueLen = reader.ReadByte();
byte[] valueBinary = reader.ReadBytes(valueLen);
StoreValue(valueBinary);
}
}
private void ReceiveCallback(IAsyncResult ar)
{
try
{
IPEndPoint sender = null;
byte[] packetBytes;
lock (_udpClient)
{
packetBytes = _udpClient.EndReceive(ar, ref sender);
}
PacketReader reader = new PacketReader(packetBytes);
Message msg = Message.Read(reader);
lock (_transactions)
{
Transaction transaction;
_transactions.TryGetValue(msg.TransactionId, out transaction);
foreach (var answer in msg.AdditionalRecords)
{
AddRecord(_cache, answer);
}
foreach (var answer in msg.Answers)
{
if (transaction != null)
{
transaction.Answers.Add(answer);
}
AddRecord(_cache, answer);
}
}
}
finally
{
lock (_udpClient)
{
_udpClient.BeginReceive(ReceiveCallback, null);
}
}
}
/// <summary>
/// Looks up a record in DNS.
/// </summary>
/// <param name="name">The name to lookup</param>
/// <param name="type">The type of record requested</param>
/// <returns>The records returned by the DNS server, if any</returns>
public override ResourceRecord[] Lookup(string name, RecordType type)
{
ushort transactionId = _nextTransId++;
string normName = NormalizeDomainName(name);
using (UdpClient udpClient = new UdpClient(0))
{
IAsyncResult result = udpClient.BeginReceive(null, null);
PacketWriter writer = new PacketWriter(1800);
Message msg = new Message();
msg.TransactionId = transactionId;
msg.Flags = new MessageFlags(false, OpCode.Query, false, false, false, false, ResponseCode.Success);
msg.Questions.Add(new Question() { Name = normName, Type = type, Class = RecordClass.Internet });
msg.WriteTo(writer);
byte[] msgBytes = writer.GetBytes();
foreach (var server in _servers)
{
udpClient.Send(msgBytes, msgBytes.Length, server);
}
for (int i = 0; i < maxRetries; ++i)
{
DateTime now = DateTime.UtcNow;
while (result.AsyncWaitHandle.WaitOne(Math.Max(responseTimeout - (DateTime.UtcNow - now).Milliseconds, 0)))
{
try
{
IPEndPoint sourceEndPoint = null;
byte[] packetBytes = udpClient.EndReceive(result, ref sourceEndPoint);
PacketReader reader = new PacketReader(packetBytes);
Message response = Message.Read(reader);
if (response.TransactionId == transactionId)
{
return response.Answers.ToArray();
}
}
catch
{
// Do nothing - bad packet (probably...)
}
}
}
}
return null;
}