protected override async Task ResolveAsync(CancellationToken cancellationToken)
{
try
{
var elapsedTimeSinceLastRefresh = SystemClock.UtcNow - _lastResolveStart;
if (elapsedTimeSinceLastRefresh < MinimumDnsResolutionRate)
{
var delay = MinimumDnsResolutionRate - elapsedTimeSinceLastRefresh;
DnsResolverLog.StartingRateLimitDelay(_logger, delay, MinimumDnsResolutionRate);
await Task.Delay(delay, cancellationToken).ConfigureAwait(false);
}
var lastResolveStart = SystemClock.UtcNow;
if (string.IsNullOrEmpty(_dnsAddress))
{
throw new InvalidOperationException($"Resolver address '{_originalAddress}' is not valid. Please use dns:/// for DNS provider.");
}
DnsResolverLog.StartingDnsQuery(_logger, _dnsAddress);
var addresses =
#if NET6_0_OR_GREATER
await Dns.GetHostAddressesAsync(_dnsAddress, cancellationToken).ConfigureAwait(false);
#else
await Dns.GetHostAddressesAsync(_dnsAddress).ConfigureAwait(false);
#endif
DnsResolverLog.ReceivedDnsResults(_logger, addresses.Length, _dnsAddress, addresses);
var endpoints = addresses.Select(a => new BalancerAddress(a.ToString(), _port)).ToArray();
var resolverResult = ResolverResult.ForResult(endpoints);
Listener(resolverResult);
// Only update last resolve start if successful. Backoff will handle limiting resolves on failure.
_lastResolveStart = lastResolveStart;
}
catch (Exception ex)
{
var message = $"Error getting DNS hosts for address '{_dnsAddress}'.";
DnsResolverLog.ErrorQueryingDns(_logger, _dnsAddress, ex);
Listener(ResolverResult.ForFailure(GrpcProtocolHelpers.CreateStatusFromException(message, ex, StatusCode.Unavailable)));
}
}
private async Task ResolveNowAsync(CancellationToken cancellationToken)
{
try
{
await ResolveAsync(cancellationToken).ConfigureAwait(false);
}
catch (OperationCanceledException) when(cancellationToken.IsCancellationRequested)
{
// Ignore cancellation.
}
catch (Exception ex)
{
Log.ResolverRefreshError(_logger, ex);
var status = GrpcProtocolHelpers.CreateStatusFromException("Error refreshing resolver.", ex);
Listener(ResolverResult.ForFailure(status));
}
}
public override void Start(Action <ResolverResult> listener)
{
// Send addresses to listener once. They will never change.
listener(ResolverResult.ForResult(_addresses, serviceConfig: null, serviceConfigStatus: null));
}
private async Task ResolveNowAsync(CancellationToken cancellationToken)
{
// Reset resolve success to false. Will be set to true when an OK result is sent to listener.
_resolveSuccessful = false;
try
{
var backoffPolicy = _backoffPolicyFactory?.Create();
for (var attempt = 0; ; attempt++)
{
try
{
await ResolveAsync(cancellationToken).ConfigureAwait(false);
// ResolveAsync may report a failure but not throw. Check to see whether an OK result
// has been reported. If not then start retry loop.
if (_resolveSuccessful)
{
return;
}
}
catch (OperationCanceledException) when(cancellationToken.IsCancellationRequested)
{
// Ignore cancellation.
break;
}
catch (Exception ex)
{
Log.ResolveError(_logger, GetType(), ex);
var status = GrpcProtocolHelpers.CreateStatusFromException("Error refreshing resolver.", ex);
Listener(ResolverResult.ForFailure(status));
}
// No backoff policy specified. Exit immediately.
if (backoffPolicy == null)
{
break;
}
var backoffTicks = backoffPolicy.NextBackoff().Ticks;
// Task.Delay supports up to Int32.MaxValue milliseconds.
// Note that even if the maximum backoff is configured to this maximum, the jitter could push it over the limit.
// Force an upper bound here to ensure an unsupported backoff is never used.
backoffTicks = Math.Min(backoffTicks, TimeSpan.TicksPerMillisecond * int.MaxValue);
var backkoff = TimeSpan.FromTicks(backoffTicks);
Log.StartingResolveBackoff(_logger, GetType(), backkoff);
await Task.Delay(backkoff, cancellationToken).ConfigureAwait(false);
}
}
catch (OperationCanceledException) when(cancellationToken.IsCancellationRequested)
{
// Ignore cancellation.
}
catch (Exception ex)
{
Log.ErrorRetryingResolve(_logger, GetType(), ex);
}
}
protected override void OnStarted()
{
// Send addresses to listener once. They will never change.
Listener(ResolverResult.ForResult(_addresses, serviceConfig: null, serviceConfigStatus: null));
}