/// <summary>
/// Retrive the chosen DNS response endPoint.
/// </summary>
/// <param name="service">Dns service to call.</param>
/// <exception cref="ArgumentNullException">Thrown when service is null.</exception>
/// <exception cref="Exception">Thrown when service is different to the last service call.</exception>
/// <returns>the DnsEndpoint response or null if no endPoint found.</returns>
public async Task <DnsEndPoint> SelectHostAsync(DnsSrvServiceDescription service)
{
await SemaphoreKey.WaitAsync();
try
{
CheckService(service);
if (ShouldRetrieveResult)
{
await RetrieveQueryResultFromDnsAsync(service);
}
DnsSrvResultEntry entryFound = QueryResult?.DnsEntries?.FirstOrDefault(entry => entry.IsAvailable);
if (entryFound != null)
{
Logger?.LogDebug("Entry found {entryFound}", entryFound);
return(entryFound.DnsEndPoint);
}
QueryResult?.ReduceLifeTime(ServerRecoveryUnavailableTime);
Logger?.LogDebug("No entry found : 0 / {entryCount}", QueryResult?.DnsEntries?.Count ?? 0);
Logger?.LogDebug("The DNS server will be recall at: {QueryResultTtlEndTime}", QueryResult?.TtlEndTime);
}
finally
{
SemaphoreKey.Release();
}
return(null);
}
/// <summary>
/// Extract the IDnsQueryResponse to build a List of DnsSrvResultEntry.
/// </summary>
/// <param name="result">Query response.</param>
/// <returns>Entities List.</returns>
protected List <DnsSrvResultEntry> ResolveServiceProcessResult(IDnsQueryResponse result)
{
// https://github.com/MichaCo/DnsClient.NET/blob/dev/src/DnsClient/DnsQueryExtensions.cs/#L628
var hosts = new List <DnsSrvResultEntry>();
if (result == null || result.HasError)
{
var errorMessage = result == null ? "Dns request return a null response" : result.ErrorMessage;
Logger?.LogWarning("Dns Request fail: {errorMessage} returning empty hosts list", errorMessage);
return(hosts);
}
foreach (var entry in result.Answers.SrvRecords())
{
var timeToLive = entry.TimeToLive;
var hostName = result.Additionals
.OfType <CNameRecord>()
.Where(p => p.DomainName.Equals(entry.Target))
.Select(p => p.CanonicalName).FirstOrDefault()
?? entry.Target;
var dnsEntry = new DnsSrvResultEntry(hostName, entry.Port, entry.Priority, entry.Weight, timeToLive);
Logger?.LogDebug("Dns Entry create : {dnsEntry}", dnsEntry.ToString("f"));
hosts.Add(dnsEntry);
}
return(hosts);
}
