/// <summary>
/// Constructor.
/// </summary>
/// <param name="request">The DNS request.</param>
/// <param name="nameServers">The name server IP addresses.</param>
/// <param name="maxSendCount">
/// The number of times a request should be sent to a
/// particular name server.
/// </param>
/// <param name="timeout">The timeout to use for each request retry.</param>
/// <param name="callback">The deleate to be called when the operation completes (or <c>null</c>).</param>
/// <param name="state">The application defined state (or <c>null</c>).</param>
/// <remarks>
/// <para>
/// Note that a random name server endpoint from the list will be
/// selected and moved to the head of the list.
/// </para>
/// <para>
/// This initializes <see cref="SendCount" /> to 1 under the assumption
/// that the first request will be sent out immediately.
/// </para>
/// </remarks>
public DnsRetryAsyncResult(DnsRequest request, IPAddress[] nameServers, int maxSendCount, TimeSpan timeout,
AsyncCallback callback, object state)
: base(null, callback, state)
{
this.NameServers = new List <IPAddress>(nameServers.Length);
for (int i = 0; i < nameServers.Length; i++)
{
this.NameServers.Add(nameServers[i]);
}
this.Request = request;
this.Response = null;
this.MaxSendCount = maxSendCount;
this.SendCount = 1;
this.Timeout = timeout;
RandomizeNameServers();
}
/// <summary>
/// Initiates an asynchronous DNS request to a name server.
/// </summary>
/// <param name="nameServer">IP address of the name server.</param>
/// <param name="request">The DNS request.</param>
/// <param name="timeout">The maximum time to wait for a response.</param>
/// <param name="callback">The delegate to be called when the operation completes (or <c>null</c>).</param>
/// <param name="state">Application state to be passed to the callback (or <c>null</c>).</param>
/// <returns>The IAsyncResult object to be used to track the operation.</returns>
/// <remarks>
/// <note>
/// This DNS resolver does not implement any local caching of DNS
/// responses.
/// </note>
/// <para>
/// This method in combination with <see cref="EndQuery" /> does not perform any
/// iterative processing on the request or implement any retry behavior. It simply
/// sends a DNS message to the name server and returns the response message or throws a
/// <see cref="TimeoutException" />.
/// </para>
/// <note>
/// The method will initialize the request's <see cref="DnsMessage.QID" />
/// property with a unique 16-bit query ID.
/// </note>
/// </remarks>
public static IAsyncResult BeginQuery(IPAddress nameServer, DnsRequest request, TimeSpan timeout,
AsyncCallback callback, object state)
{
DnsAsyncResult arDns;
byte[] packet;
int cbPacket;
lock (syncLock)
{
arDns = PrepareQuery(request, timeout, callback, state);
packet = request.FormatPacket(out cbPacket);
arDns.TimerStart = HiResTimer.Count;
request.Trace(TraceSubSystem, 0, nameServer, null);
arDns.DnsSocket.Socket.SendTo(packet, 0, cbPacket, SocketFlags.None, new IPEndPoint(nameServer, NetworkPort.DNS));
arDns.Started();
}
return(arDns);
}
/// <summary>
/// Constructor.
/// </summary>
/// <param name="remoteEP">The <see cref="IPEndPoint" /> of the DNS resolver making the request.</param>
/// <param name="request">The received <see cref="DnsRequest" />.</param>
internal DnsServerEventArgs(IPEndPoint remoteEP, DnsRequest request)
{
this.RemoteEP = remoteEP;
this.Request = request;
this.Response = null;
}
/// <summary>
/// Handles received packets.
/// </summary>
/// <param name="ar">The <see cref="IAsyncResult" /> instance.</param>
private void OnReceive(IAsyncResult ar)
{
DnsRequest request = null;
int cbRecv;
IPEndPoint ep;
try
{
cbRecv = ((EnhancedSocket)ar.AsyncState).EndReceiveFrom(ar, ref remoteEP);
}
catch
{
cbRecv = 0;
}
if (sock == null)
{
return; // The server has stopped
}
if (cbRecv != 0)
{
// Parse the request packet
try
{
request = new DnsRequest();
request.ParsePacket(recvBuf, cbRecv);
}
catch (Exception e)
{
SysLog.LogException(e);
}
}
// Save the remote EP and then initiate another async
// packet receive.
ep = (IPEndPoint)remoteEP;
remoteEP = new IPEndPoint(IPAddress.Any, 0);
sock.BeginReceiveFrom(recvBuf, 0, recvBuf.Length, SocketFlags.None, ref remoteEP, onReceive, sock);
// Process the request and transmit the response (if there is one).
if (request != null && RequestEvent != null)
{
var args = new DnsServerEventArgs(ep, request);
RequestEvent(this, args);
if (args.Response != null)
{
byte[] sendBuf;
int cbSend;
// $todo(jeff.lill):
//
// Remove this exception code after figuring out why the
// response's QName field is sometimes NULL.
try
{
sendBuf = args.Response.FormatPacket(out cbSend);
}
catch
{
SysLog.LogError("DNS Formatting Error:\r\n\r\n" +
args.Request.GetTraceDetails(ep.Address) +
"\r\n" +
args.Response.GetTraceDetails(ep.Address));
throw;
}
lock (syncLock)
{
if (sock != null)
{
sock.SendTo(sendBuf, cbSend, SocketFlags.None, args.RemoteEP);
}
}
}
}
}
/// <summary>
/// Performs a more advanced query that load balances against a set of
/// DNS server endpoints and also implements retry behaviors.
/// </summary>
/// <param name="nameServers">The set of name server IP addresses.</param>
/// <param name="request">The DNS request.</param>
/// <param name="timeout">The timeout to use for the initial request as well as the retries.</param>
/// <param name="maxSendCount">The maximum number of requests to send to any single name server.</param>
/// <returns>The received DNS response message.</returns>
/// <remarks>
/// <note>
/// This DNS resolver does not implement any local caching of DNS
/// responses.
/// </note>
/// </remarks>
public static DnsResponse QueryWithRetry(IPAddress[] nameServers, DnsRequest request, TimeSpan timeout, int maxSendCount)
{
var ar = BeginQueryWithRetry(nameServers, request, timeout, maxSendCount, null, null);
return(EndQueryWithRetry(ar));
}
/// <summary>
/// Transmits a DNS request to a name server and then waits for and
/// then returns the response.
/// </summary>
/// <param name="nameServer">IP address of the name server.</param>
/// <param name="request">The DNS request.</param>
/// <param name="timeout">The maximum time to wait for a response.</param>
/// <returns>The query response.</returns>
/// <remarks>
/// <note>
/// This DNS resolver does not implement any local caching of DNS
/// responses.
/// </note>
/// <para>
/// This method does not perform any iterative processing on the request
/// or implement any retry behavior. It simply sends a DNS message to the
/// name server and returns the response message or throws a
/// <see cref="TimeoutException" />.
/// </para>
/// <note>
/// The method will initialize the request's <see cref="DnsMessage.QID" />
/// property with a unique 16-bit query ID.
/// </note>
/// <note>
/// This method performs no checks to verify that the
/// response returned actually answers the question posed in the
/// request. The only validation performed is to verify that the
/// message is a valid response and that its QID matches that
/// of the request.
/// </note>
/// </remarks>
public static DnsResponse Query(IPAddress nameServer, DnsRequest request, TimeSpan timeout)
{
var arDns = BeginQuery(nameServer, request, timeout, null, null);
return(EndQuery(arDns));
}
