How to mock SelectObjectContent async call.

[nideeshmanian]

I am trying to mock the s3client.SelectObjectContentAsync. I am not able to figure out how to do that. Please help. I was able to mock the GetObjectAsync. I tried stackoverflow as well. I could not find examples for c#. I could find for java and go. I have put the code below which i have tried. Please check the method "GetSelectObjectContentResponse"

private static Mock<IAmazonS3> GetMockS3()
{
    var mockS3Client = new Mock<IAmazonS3>();
    mockS3Client.Setup(x =>
            x.GetObjectAsync(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<CancellationToken>()))
        .Returns(new Func<string, string, CancellationToken, Task<GetObjectResponse>>(GetObjectAsync));
    mockS3Client.Setup(x =>
            x.SelectObjectContentAsync(It.IsAny<SelectObjectContentRequest>(), It.IsAny<CancellationToken>()))
        .Returns(new Func<SelectObjectContentRequest, CancellationToken, Task<SelectObjectContentResponse>>(GetSelectObjectContentResponse));

    return mockS3Client;
}


private static async Task<SelectObjectContentResponse> GetSelectObjectContentResponse(SelectObjectContentRequest request,
    CancellationToken cancellationToken = default)
{
    // set json string based on request.Key
    var jsonString = "{a:1,b:1},{a:2,b:2}";
    EventStreamMessage eventStreamMessage = new EventStreamMessage(new List<IEventStreamHeader> { },
    Encoding.UTF8.GetBytes(jsonString));
    RecordsEvent recordsEvent = new RecordsEvent(eventStreamMessage);            
    SelectObjectContentEventStream s3Events = new SelectObjectContentEventStream(recordsEvent.Payload);
    var response = new SelectObjectContentResponse
    {
        Payload = s3Events
    };
    return response;
}

private static async Task<GetObjectResponse> GetObjectAsync(string bucketName, string key, CancellationToken cancellationToken = default)
{

    var streamObj = new MemoryStream();
    await ParquetSerializer.SerializeAsync(new classa{b="1"}, streamObj); 
    streamObj.Position = 0;
    return new GetObjectResponse()
    {
        ResponseStream = streamObj
    };
}

Below is the error message
System.Net.Http.HttpRequestException : InternalServerError - Internal Server Error: Amazon.S3.Model.S3EventStreamException: Error.
---> Amazon.Runtime.EventStreams.EventStreamChecksumFailureException: Message Prelude Checksum failure. Expected 2100067169 but was 1438216584
at Amazon.Runtime.EventStreams.Internal.EventStreamDecoder.ProcessPrelude(Byte[] data, Int32 offset, Int32 length)
at Amazon.Runtime.EventStreams.Internal.EventStreamDecoder.ProcessData(Byte[] data, Int32 offset, Int32 length)
at Amazon.Runtime.EventStreams.Internal.EventStream2.ReadFromStream(Byte[] buffer) at Amazon.Runtime.EventStreams.Internal.EnumerableEventStream2.GetEnumerator()+MoveNext()
--- End of inner exception stack trace ---
at Amazon.Runtime.EventStreams.Internal.EnumerableEventStream`2.GetEnumerator()+MoveNext()

[nideeshmanian]

Found the solution. Mock the interface "ISelectObjectContentEventStream" with a constructor to pass IS3Event.

internal class MockSelectObjectContentEventStream : ISelectObjectContentEventStream
{
    private readonly List<IS3Event> s3Events;
    public int BufferSize { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

    public event EventHandler<EventStreamEventReceivedArgs<IS3Event>> EventReceived;
    public event EventHandler<EventStreamExceptionReceivedArgs<S3EventStreamException>> ExceptionReceived;
    public event EventHandler<EventStreamEventReceivedArgs<RecordsEvent>> RecordsEventReceived;
    public event EventHandler<EventStreamEventReceivedArgs<StatsEvent>> StatsEventReceived;
    public event EventHandler<EventStreamEventReceivedArgs<ProgressEvent>> ProgressEventReceived;
    public event EventHandler<EventStreamEventReceivedArgs<ContinuationEvent>> ContinuationEventReceived;
    public event EventHandler<EventStreamEventReceivedArgs<EndEvent>> EndEventReceived;

    public MockSelectObjectContentEventStream(List<IS3Event> S3Events)
    {
        s3Events = S3Events;
    }
    public void Dispose()
    {
    }
    public IEnumerator<IS3Event> GetEnumerator()
    {
        return s3Events.GetEnumerator();
    }

    public void StartProcessing()
    {
    }

    public Task StartProcessingAsync()
    {
        return Task.CompletedTask;
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return s3Events.GetEnumerator();
    }
}

//Then the mock method should be as below
private static async Task<SelectObjectContentResponse> GetSelectObjectContentResponse(SelectObjectContentRequest request,
    CancellationToken cancellationToken = default)
{
    var jsonstring = "{}";
    switch (request.Key) {
        case "request1":
            jsonstring = "{a:1}";
            break;
        case "request2":
            jsonstring = "{a:1}";
            break;
    }
    var response = new SelectObjectContentResponse
    {
        Payload = new MockSelectObjectContentEventStream(
new List<IS3Event> {
    new RecordsEvent(
        new EventStreamMessage(
            new List<IEventStreamHeader> { },Encoding.UTF8.GetBytes(jsonstring)))});
    };
    return response;
}

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