/// <summary>
/// Creates a new instance of <see cref="LookupClient"/> with one or more <see cref="IPAddress"/> and port combination
/// stored in <see cref="IPEndPoint"/>(s).
/// </summary>
/// <param name="nameServers">The <see cref="IPEndPoint"/>(s) to be used by this <see cref="LookupClient"/> instance.</param>
/// <example>
/// In this example, we instantiate a new <see cref="IPEndPoint"/> using an <see cref="IPAddress"/> and custom port which is different than the default port <c>53</c>.
/// <code>
/// <![CDATA[
/// // Using localhost and port 8600 to connect to a Consul agent.
/// var endpoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 8600);
/// var client = new LookupClient(endpoint);
/// ]]>
/// </code>
/// <para>
/// The <see cref="NameServer"/> class also contains pre defined <see cref="IPEndPoint"/>s for the public google DNS servers, which can be used as follows:
/// <code>
/// <![CDATA[
/// var client = new LookupClient(NameServer.GooglePublicDns, NameServer.GooglePublicDnsIPv6);
/// ]]>
/// </code>
/// </para>
/// </example>
public LookupClient(params IPEndPoint[] nameServers)
{
if (nameServers == null || nameServers.Length == 0)
{
throw new ArgumentException("At least one name server must be configured.", nameof(nameServers));
}
// TODO validate ip endpoints
NameServers = nameServers.Select(p => new NameServer(p)).ToArray();
_endpoints = new ConcurrentQueue <NameServer>(NameServers);
_messageHandler = new DnsUdpMessageHandler(true);
_tcpFallbackHandler = new DnsTcpMessageHandler();
}
private async Task <IDnsQueryResponse> ResolveQueryAsync(DnsMessageHandler handler, DnsRequestMessage request, CancellationToken cancellationToken, Audit continueAudit = null)
{
if (request == null)
{
throw new ArgumentNullException(nameof(request));
}
var audit = continueAudit ?? new Audit();
var servers = GetNextServers();
foreach (var serverInfo in servers)
{
var tries = 0;
do
{
tries++;
try
{
cancellationToken.ThrowIfCancellationRequested();
if (EnableAuditTrail)
{
audit.StartTimer();
}
DnsResponseMessage response;
Action onCancel = () => { };
Task <DnsResponseMessage> resultTask = handler.QueryAsync(serverInfo.Endpoint, request, cancellationToken, (cancel) =>
{
onCancel = cancel;
});
if (Timeout != s_infiniteTimeout || (cancellationToken != CancellationToken.None && cancellationToken.CanBeCanceled))
{
var cts = new CancellationTokenSource(Timeout);
CancellationTokenSource linkedCts = null;
if (cancellationToken != CancellationToken.None)
{
linkedCts = CancellationTokenSource.CreateLinkedTokenSource(cts.Token, cancellationToken);
}
using (cts)
using (linkedCts)
{
response = await resultTask.WithCancellation((linkedCts ?? cts).Token, onCancel).ConfigureAwait(false);
}
}
else
{
response = await resultTask.ConfigureAwait(false);
}
if (response.Header.ResultTruncated && UseTcpFallback && !handler.GetType().Equals(typeof(DnsTcpMessageHandler)))
{
if (EnableAuditTrail)
{
audit.AuditTruncatedRetryTcp();
}
return(await ResolveQueryAsync(_tcpFallbackHandler, request, cancellationToken, audit).ConfigureAwait(false));
}
if (EnableAuditTrail)
{
audit.AuditResolveServers(_endpoints.Count);
audit.AuditResponseHeader(response.Header);
}
if (response.Header.ResponseCode != DnsResponseCode.NoError)
{
if (EnableAuditTrail)
{
audit.AuditResponseError(response.Header.ResponseCode);
}
if (ThrowDnsErrors)
{
throw new DnsResponseException(response.Header.ResponseCode);
}
}
HandleOptRecords(audit, serverInfo, response);
DnsQueryResponse queryResponse = response.AsQueryResponse(serverInfo.Clone());
if (EnableAuditTrail)
{
audit.AuditResponse(queryResponse);
audit.AuditEnd(queryResponse);
queryResponse.AuditTrail = audit.Build();
}
Interlocked.Increment(ref StaticLog.ResolveQueryCount);
Interlocked.Add(ref StaticLog.ResolveQueryTries, tries);
return(queryResponse);
}
catch (DnsResponseException ex)
{
audit.AuditException(ex);
ex.AuditTrail = audit.Build();
throw;
}
catch (SocketException ex) when(ex.SocketErrorCode == SocketError.AddressFamilyNotSupported)
{
// this socket error might indicate the server endpoint is actually bad and should be ignored in future queries.
DisableServer(serverInfo);
break;
}
catch (Exception ex) when(ex is TimeoutException || handler.IsTransientException(ex))
{
// our timeout got eventually triggered by the a task cancelation token, throw OCE instead...
if (cancellationToken.IsCancellationRequested)
{
throw new OperationCanceledException(cancellationToken);
}
DisableServer(serverInfo);
}
catch (Exception ex)
{
DisableServer(serverInfo);
var handleEx = ex;
var agg = ex as AggregateException;
if (agg != null)
{
if (agg.InnerExceptions.Any(e => e is TimeoutException || handler.IsTransientException(e)))
{
continue;
}
handleEx = agg.InnerException;
}
if (handleEx is OperationCanceledException || handleEx is TaskCanceledException)
{
if (cancellationToken.IsCancellationRequested)
{
throw new OperationCanceledException(cancellationToken);
}
continue;
}
audit.AuditException(ex);
throw new DnsResponseException("Unhandled exception", ex)
{
AuditTrail = audit.Build()
};
}
} while (tries <= Retries && !cancellationToken.IsCancellationRequested && serverInfo.Enabled);
}
throw new DnsResponseException(
DnsResponseCode.ConnectionTimeout,
$"No connection could be established to any of the following name servers: {string.Join(", ", NameServers)}.")
{
AuditTrail = audit.Build()
};
}
private IDnsQueryResponse ResolveQuery(DnsMessageHandler handler, DnsRequestMessage request, Audit continueAudit = null)
{
if (request == null)
{
throw new ArgumentNullException(nameof(request));
}
var audit = continueAudit ?? new Audit();
var servers = GetNextServers();
foreach (var serverInfo in servers)
{
var tries = 0;
do
{
tries++;
try
{
if (EnableAuditTrail)
{
audit.StartTimer();
}
DnsResponseMessage response = handler.Query(serverInfo.Endpoint, request, Timeout);
if (response.Header.ResultTruncated && UseTcpFallback && !handler.GetType().Equals(typeof(DnsTcpMessageHandler)))
{
if (EnableAuditTrail)
{
audit.AuditTruncatedRetryTcp();
}
return(ResolveQuery(_tcpFallbackHandler, request, audit));
}
if (EnableAuditTrail)
{
audit.AuditResolveServers(_endpoints.Count);
audit.AuditResponseHeader(response.Header);
}
if (response.Header.ResponseCode != DnsResponseCode.NoError)
{
if (EnableAuditTrail)
{
audit.AuditResponseError(response.Header.ResponseCode);
}
if (ThrowDnsErrors)
{
throw new DnsResponseException(response.Header.ResponseCode);
}
}
HandleOptRecords(audit, serverInfo, response);
DnsQueryResponse queryResponse = response.AsQueryResponse(serverInfo.Clone());
if (EnableAuditTrail)
{
audit.AuditResponse(queryResponse);
audit.AuditEnd(queryResponse);
queryResponse.AuditTrail = audit.Build();
}
Interlocked.Increment(ref StaticLog.ResolveQueryCount);
Interlocked.Add(ref StaticLog.ResolveQueryTries, tries);
return(queryResponse);
}
catch (DnsResponseException ex)
{
audit.AuditException(ex);
ex.AuditTrail = audit.Build();
throw;
}
catch (SocketException ex) when(ex.SocketErrorCode == SocketError.AddressFamilyNotSupported)
{
// this socket error might indicate the server endpoint is actually bad and should be ignored in future queries.
DisableServer(serverInfo);
break;
}
catch (Exception ex) when(ex is TimeoutException || handler.IsTransientException(ex))
{
DisableServer(serverInfo);
}
catch (Exception ex)
{
DisableServer(serverInfo);
if (ex is OperationCanceledException || ex is TaskCanceledException)
{
// timeout
continue;
}
audit.AuditException(ex);
throw new DnsResponseException(DnsResponseCode.Unassigned, "Unhandled exception", ex)
{
AuditTrail = audit.Build()
};
}
} while (tries <= Retries && serverInfo.Enabled);
}
throw new DnsResponseException(DnsResponseCode.ConnectionTimeout, $"No connection could be established to any of the following name servers: {string.Join(", ", NameServers)}.")
{
AuditTrail = audit.Build()
};
}
