Json errror in watch

[zhiweiv]

The kubernetes API server closes watch connection after 30~60 minutes if nothing returned, in this case the client gets json deserialize error.

I am wondering if we can change the line https://github.com/kubernetes-client/csharp/blob/master/src/KubernetesClient/Watcher.cs#L182 from line == null to string.IsNullOrEmpty(line) to fix this.

The full exception stack here:

Microsoft.Rest.SerializationException: Unable to deserialize the response.
 ---> System.Text.Json.JsonException: The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. Path: $ | LineNumber: 0 | BytePositionInLine: 0.
 ---> System.Text.Json.JsonReaderException: The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. LineNumber: 0 | BytePositionInLine: 0.
   at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes)
   at System.Text.Json.Utf8JsonReader.Read()
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, JsonReaderException ex)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.JsonSerializer.ReadCore[TValue](JsonReaderState& readerState, Boolean isFinalBlock, ReadOnlySpan`1 buffer, JsonSerializerOptions options, ReadStack& state, JsonConverter converterBase)
   at System.Text.Json.JsonSerializer.ContinueDeserialize[TValue](ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack, JsonConverter converter, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializer.ReadAll[TValue](Stream utf8Json, JsonTypeInfo jsonTypeInfo)
   at k8s.Kubernetes.CreateResultAsync[T](HttpRequestMessage httpRequest, HttpResponseMessage httpResponse, Nullable`1 watch, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at k8s.Kubernetes.CreateResultAsync[T](HttpRequestMessage httpRequest, HttpResponseMessage httpResponse, Nullable`1 watch, CancellationToken cancellationToken)
   at k8s.Kubernetes.ListPodForAllNamespacesWithHttpMessagesAsync(Nullable`1 allowWatchBookmarks, String continueParameter, String fieldSelector, String labelSelector, Nullable`1 limit, Nullable`1 pretty, String resourceVersion, String resourceVersionMatch, Nullable`1 timeoutSeconds, Nullable`1 watch, IDictionary`2 customHeaders, CancellationToken cancellationToken)
   at k8s.WatcherExt.<>c__DisplayClass1_0`2.<<MakeStreamReaderCreator>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at k8s.Watcher`1.<>c.<CreateWatchEventEnumerator>b__21_1[TR](Task`1 t)
   at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location ---
   at k8s.Watcher`1.CreateWatchEventEnumerator(Func`1 streamReaderCreator, Action`1 onError, CancellationToken cancellationToken)+MoveNext()
   at k8s.Watcher`1.CreateWatchEventEnumerator(Func`1 streamReaderCreator, Action`1 onError, CancellationToken cancellationToken)+System.Threading.Tasks.Sources.IValueTaskSource<System.Boolean>.GetResult()
   at k8s.Watcher`1.WatcherLoop(CancellationToken cancellationToken)
   at k8s.Watcher`1.WatcherLoop(CancellationToken cancellationToken)

[tg123]

did you catch what returned from server side?

[zhiweiv]

There is no chance to get it, the exception was thrown in internal code here https://github.com/kubernetes-client/csharp/blob/master/src/KubernetesClient/Watcher.cs#L191, so I guess it maybe an empty string.

[tg123]

i believe it is something else like <html>, we'd better to throw the ex with original content.

[zhiweiv]

After further check the exception stack, the exception is thrown here: https://github.com/kubernetes-client/csharp/blob/master/src/KubernetesClient/Kubernetes.cs#L89, before the previous location.

The exception only occur when nothing returned at all since watch request started.

[tg123]

lets try to do wireshark or tcpdump to see if it is server side err

[zhiweiv]

I will do more tests soon.

[zhiweiv]

I figured out the problem, for the code

csharp/src/KubernetesClient/Kubernetes.cs

Lines 86 to 90 in 8cfe60b

	using (Stream stream = await httpResponse.Content.ReadAsStreamAsync().ConfigureAwait(false))
	#endif
	{
	result.Body = KubernetesJson.Deserialize<T>(stream);
	}

When watch without any result, the request hang here util the api server close the connection, the json deserialize from empty stream will throw exception.

Since the result.Body is not used in watch case, I think we can change to code to following to fix this issue

if (!watch.GetValueOrDefault())
{
    result.Body = KubernetesJson.Deserialize<T>(stream);
}

I have verified in local the watch works without json exception anymore.

Another way to fix is change stream to string before json deserialize

var content = await httpResponse.Content.ReadAsStringAsync().ConfigureAwait(false);
if (content != null)
{
    result.Body = KubernetesJson.Deserialize<T>(content);
}

[tg123]

the internal stream is replaced by LineSeparatedHttpContent and content should returned from PeekFirstLine

checked code here

csharp/src/KubernetesClient/LineSeparatedHttpContent.cs

Line 172 in 8cfe60b

return _inner.ReadLineAsync();

should throw EOF if null

[zhiweiv]

In the later code after the change I made, it gets string first before json deserialize, and return if string null, so the watch can finish without exception in watch no result case.

csharp/src/KubernetesClient/Watcher.cs

Lines 178 to 185 in 8cfe60b

	var line = await AttachCancellationToken(streamReader.ReadLineAsync()).ConfigureAwait(false);
	cancellationToken.ThrowIfCancellationRequested();
	if (line == null)
	{
	yield break;
	}

[tg123]

please drop a PR

[zhiweiv]

I will create PR soon after I figure out another problem(watch hang in version 7.1+, 7.0.15 is ok).

[zhiweiv]

There are two way to avoid json deserialize error in following code while watch no result

csharp/src/KubernetesClient/Kubernetes.cs

Lines 83 to 90 in 199ec8b

	#if NET5_0_OR_GREATER
	using (Stream stream = await httpResponse.Content.ReadAsStreamAsync(cancellationToken).ConfigureAwait(false))
	#else
	using (Stream stream = await httpResponse.Content.ReadAsStreamAsync().ConfigureAwait(false))
	#endif
	{
	result.Body = KubernetesJson.Deserialize<T>(stream);
	}

1. Skip body in watch as it is not used in watch case, but this will introduce breaking change, for example client.ListNode(watch: true) will return null

if (!watch)
{
    result.Body = KubernetesJson.Deserialize<T>(stream);
}

2. Use string instead of stream, I am not sure if it is performance consideration to use stream.

var content = await httpResponse.Content.ReadAsStringAsync().ConfigureAwait(false);
if (content != null)
{
    result.Body = KubernetesJson.Deserialize<T>(content);
}

@tg123
Which way you prefer to fix this problem?

[tg123]

maybe to throw en eof exception

at

csharp/src/KubernetesClient/LineSeparatedHttpContent.cs

Line 177 in 8cfe60b

var line = await ReadLineAsync().ConfigureAwait(false);

when peekline === null, which means it is eof and nothing returned from server in the first line

[zhiweiv]

If throw EOFException in LineSeparatedHttpContent, do you mean we catch EOFException like following

try
{
    using (Stream stream = await httpResponse.Content.ReadAsStreamAsync().ConfigureAwait(false))
    {
        result.Body = KubernetesJson.Deserialize<T>(stream);
    }
}
catch (JsonException)
{
    httpRequest.Dispose();
    httpResponse.Dispose();
    throw;
}
catch (EofException) //catch eof 
{
    httpRequest.Dispose();
    httpResponse.Dispose();
}
return result;

[tg123]

I think throw the exception, because the read does not finish