/// <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);
}
private async Task RetrieveQueryResultFromDnsAsync(DnsSrvServiceDescription service)
{
Logger?.LogDebug("Retrieve DnsService values {service}", service);
QueryResult = await DnsQuerier.QueryServiceAsync(service);
DnsSortResult.Sort(QueryResult);
LastService = service;
}
/// <summary>
/// Create a Dns url string from the DnsSrvServiceDescription.
/// </summary>
/// <param name="service">The dns info.</param>
/// <returns>Dns url create.</returns>
protected string CreateDnsQueryString(DnsSrvServiceDescription service)
{
service = service ?? throw new ArgumentNullException(nameof(service), "The service should not be null.");
string dnsQueryString = $"_{service.ServiceName}._{service.Protocol}.{service.Domain}.";
Logger?.LogDebug("Dns query string build : {dnsQueryString}" + dnsQueryString);
return(dnsQueryString);
}
/// <summary>
/// Initializes a new instance of the <see cref="DnsServiceBalancingMessageHandler"/> class.
/// </summary>
/// <param name="serviceDescription">The server description.</param>
/// <param name="targetSelector">The api caller and selector.</param>
/// <param name="quarantinePolicy">The respose quarantine policy to blacklist an host and retrieve the request.</param>
/// <param name="logger">The logger.</param>
public DnsServiceBalancingMessageHandler(
DnsSrvServiceDescription serviceDescription,
IDnsServiceTargetSelector targetSelector,
ITargetQuarantinePolicy quarantinePolicy,
ILogger logger = null)
{
ServiceDescription = serviceDescription;
TargetSelector = targetSelector;
QuarantinePolicy = quarantinePolicy;
Logger = logger;
}
/// <summary>
/// Are this object equal to an other DnsSrvServiceDescription.
/// </summary>
/// <param name="obj">an other DnsSrvServiceDescription.</param>
/// <returns>Is equal or not.</returns>
public override bool Equals(object obj)
{
if ((obj == null) || !this.GetType().Equals(obj.GetType()))
{
return(false);
}
else
{
DnsSrvServiceDescription service = (DnsSrvServiceDescription)obj;
return(GetHashCode() == service.GetHashCode());
}
}
internal void CheckService(DnsSrvServiceDescription service)
{
if (service == null)
{
Logger?.LogError("DnsSrvServiceDescription service null found");
throw new ArgumentNullException(nameof(service));
}
if (LastService != null && !service.Equals(LastService))
{
Logger?.LogError("Cannot change the resolved service");
throw new Exception("Cannot change the resolved service");
}
}
/// <summary>
/// Reset all the DnsSrvServiceDescription values.
/// </summary>
/// <returns>The Task return.</returns>
public async Task ResetAsync()
{
await SemaphoreKey.WaitAsync();
try
{
Logger?.LogDebug("Reset of DnsServiceTargetSelectorReal");
QueryResult = null;
LastService = null;
}
finally
{
SemaphoreKey.Release();
}
}
/// <summary>
/// Ask a new srv call.
/// </summary>
/// <param name="service">Address to be call.</param>
/// <returns>Call Response with HostName, Port, Priority, Weight and Ttl.</returns>
public async Task <DnsSrvQueryResult> QueryServiceAsync(DnsSrvServiceDescription service)
{
if (service == null)
{
Logger?.LogError("DnsSrvServiceDescription cannot be null.");
throw new ArgumentNullException(nameof(service));
}
string queryString = CreateDnsQueryString(service);
var result = await LookupClient.QueryAsync(queryString, QueryType.SRV).ConfigureAwait(false);
var queryResult = ResolveServiceProcessResult(result);
return(new DnsSrvQueryResult(queryResult));
}
/// <summary>
/// Extract a service and a domain from an Uri.
/// </summary>
/// <param name="uri">Uri to be extract.</param>
/// <returns>DnsSrvServiceDescription object.</returns>
public DnsSrvServiceDescription FromUri(Uri uri)
{
uri = uri ?? throw new ArgumentNullException(nameof(uri), "The uri should not be null.");
var splitIndex = uri.DnsSafeHost.IndexOf(".");
var serviceName = uri.DnsSafeHost.Substring(0, splitIndex);
var domain = uri.DnsSafeHost.Substring(splitIndex + 1);
if ((ServiceWhiteList != null && !ServiceWhiteList.Contains(serviceName)) ||
(DomainWhiteList != null &&
((AllowSubDomains && !DomainWhiteList.Any(dom => domain.EndsWith(dom))) ||
(!AllowSubDomains && !DomainWhiteList.Contains(domain)))))
{
return(null);
}
var dnsSrvServiceDescription = new DnsSrvServiceDescription(
serviceName: serviceName,
protocol: Protocol,
domain: domain);
return(dnsSrvServiceDescription);
}
