`DescribeTopicsAsync` hangs forever when targeting Event Hub

[logicaloud]

A call to DescribeTopicsAsync for an existing topic with otherwise working connection parameters for Event Hub never returns.

Example code:

using Confluent.Kafka;

const string BootstrapServers = "********.servicebus.windows.net:9093";
const string TopicName = "ExistingTopic";
const string Username = "$ConnectionString";
const string Password = "Endpoint=sb://****************";

var config = new Confluent.Kafka.AdminClientConfig
{
    BootstrapServers = BootstrapServers,
    SecurityProtocol = Confluent.Kafka.SecurityProtocol.SaslSsl,
    SaslMechanism = Confluent.Kafka.SaslMechanism.Plain,
    SaslUsername = Username,
    SaslPassword = Password
};

try
{
    using (var adminClient = new AdminClientBuilder(config).Build())
    {
        var topicCollection = TopicCollection.OfTopicNames(new List<string> { TopicName });
        var options = new Confluent.Kafka.Admin.DescribeTopicsOptions() { RequestTimeout = TimeSpan.FromSeconds(10) };
        Console.WriteLine($"BEGIN Describing topics");
        var describeTopicsResult = await adminClient.DescribeTopicsAsync(topicCollection, options).ConfigureAwait(false);
        Console.WriteLine($"END Describing topics");
    }
}
catch (Exception ex)
{
    Console.WriteLine($"Error: {ex.Message}");
}

The END Describing topics console output is never printed.

An ArgumentNullException can be caught by enabling Common Language Runtime Exceptions in Exception Settings in Visual Studio but the exception never reaches the DescribeTopicsAsync caller. Stack trace is:

>	System.Private.CoreLib.dll!System.ArgumentNullException.Throw(string paramName) Line 71	C#
 	System.Private.CoreLib.dll!System.Runtime.InteropServices.Marshal.CopyToManaged<nint>(nint source, nint[] destination, int startIndex, int length) Line 925	C#
 	Confluent.Kafka.dll!Confluent.Kafka.AdminClient.extractNodeList(nint nodesPtr, int nodesCount)	Unknown
 	Confluent.Kafka.dll!Confluent.Kafka.AdminClient.extractTopicPartitionInfo.AnonymousMethod__20_0(nint topicPartitionInfoPtr)	Unknown
 	System.Linq.dll!System.Linq.Enumerable.SelectArrayIterator<nint, Confluent.Kafka.TopicPartitionInfo>.Fill(System.ReadOnlySpan<nint> source, System.Span<Confluent.Kafka.TopicPartitionInfo> destination, System.Func<nint, Confluent.Kafka.TopicPartitionInfo> func)	Unknown
 	System.Linq.dll!System.Linq.Enumerable.SelectArrayIterator<nint, Confluent.Kafka.TopicPartitionInfo>.ToList()	Unknown
 	Confluent.Kafka.dll!Confluent.Kafka.AdminClient.extractTopicPartitionInfo(nint topicPartitionInfosPtr, int topicPartitionInfosCount)	Unknown
 	Confluent.Kafka.dll!Confluent.Kafka.AdminClient.extractDescribeTopicsResults.AnonymousMethod__21_0(nint topicPtr)	Unknown
 	System.Linq.dll!System.Linq.Enumerable.SelectArrayIterator<nint, Confluent.Kafka.Admin.TopicDescription>.Fill(System.ReadOnlySpan<nint> source, System.Span<Confluent.Kafka.Admin.TopicDescription> destination, System.Func<nint, Confluent.Kafka.Admin.TopicDescription> func)	Unknown
 	System.Linq.dll!System.Linq.Enumerable.SelectArrayIterator<nint, Confluent.Kafka.Admin.TopicDescription>.ToList()	Unknown
 	Confluent.Kafka.dll!Confluent.Kafka.AdminClient.extractDescribeTopicsResults(nint resultPtr)	Unknown
 	Confluent.Kafka.dll!Confluent.Kafka.AdminClient.StartPollTask.AnonymousMethod__0()	Unknown
 	System.Private.CoreLib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) Line 138	C#
 	System.Private.CoreLib.dll!System.Threading.Tasks.Task.ExecuteWithThreadLocal(ref System.Threading.Tasks.Task currentTaskSlot, System.Threading.Thread threadPoolThread) Line 2190	C#