/// <summary>
/// Adds a question to the request to be sent to the DNS server.
/// </summary>
/// <param name="question">The question to add to the request</param>
public void AddQuestion(Question question)
{
// abandon if null
if (question == null) throw new ArgumentNullException("question");
// add this question to our collection
_questions.Add(question);
}
/// <summary>
/// Do an QClass=IN Query on specified DNS servers
/// </summary>
/// <param name="name">Name to query</param>
/// <param name="qtype">Question type</param>
/// <returns>Response of the query</returns>
public Response Query(string name, QType qtype)
{
var question = new Question(name, qtype, QClass.IN);
var response = SearchInCache(question);
if (response != null)
return response;
var request = new Request();
request.AddQuestion(question);
return GetResponse(request);
}
private Response SearchInCache(Question question)
{
if (!_mUseCache)
return null;
var strKey = question.QClass + "-" + question.QType + "-" + question.QName;
Response response;
lock (_mResponseCache)
{
if (!_mResponseCache.ContainsKey(strKey))
return null;
response = _mResponseCache[strKey];
}
var timeLived = (int) ((DateTime.Now.Ticks - response.TimeStamp.Ticks)/TimeSpan.TicksPerSecond);
foreach (var rr in response.RecordsRR)
{
rr.TimeLived = timeLived;
// The TTL property calculates its actual time to live
if (rr.TTL == 0)
return null; // out of date
}
return response;
}
/// <summary>
/// Construct a Response object from the supplied byte array
/// </summary>
/// <param name="message">a byte array returned from a DNS server query</param>
internal Response(byte[] message)
{
// the bit flags are in bytes 2 and 3
var flags1 = message[2];
var flags2 = message[3];
// get return code from lowest 4 bits of byte 3
var returnCode = flags2 & 15;
// if its in the reserved section, set to other
if (returnCode > 6) returnCode = 6;
_returnCode = (ReturnCode)returnCode;
// other bit flags
_authoritativeAnswer = ((flags1 & 4) != 0);
_recursionAvailable = ((flags2 & 128) != 0);
_truncated = ((flags1 & 2) != 0);
// create the arrays of response objects
_questions = new Question[GetShort(message, 4)];
_answers = new Answer[GetShort(message, 6)];
_nameServers = new NameServer[GetShort(message, 8)];
_additionalRecords = new AdditionalRecord[GetShort(message, 10)];
// need a pointer to do this, position just after the header
var pointer = new Pointer(message, 12);
// and now populate them, they always follow this order
for (var index = 0; index < _questions.Length; index++)
{
try
{
// try to build a quesion from the response
_questions[index] = new Question(pointer);
}
catch (Exception ex)
{
// something grim has happened, we can't continue
throw new InvalidResponseException(ex);
}
}
for (var index = 0; index < _answers.Length; index++)
{
_answers[index] = new Answer(pointer);
}
for (var index = 0; index < _nameServers.Length; index++)
{
_nameServers[index] = new NameServer(pointer);
}
for (var index = 0; index < _additionalRecords.Length; index++)
{
_additionalRecords[index] = new AdditionalRecord(pointer);
}
}
