Question

How can I structure the following code so that I can read all of the stream in chunks.
Currently it keeps returning the same data. Can not advance.

public static IObservable<byte[]> AsyncRead(this Stream stream, int bufferSize)
{
    var asyncRead = Observable.FromAsyncPattern<byte[], int, int, int>(stream.BeginRead, stream.EndRead);

    var buffer = new byte[bufferSize];

    return asyncRead(buffer, 0, bufferSize)
        .Select(cbRead =>
                    {
                        var dataChunk = new byte[cbRead];

                        Buffer.BlockCopy(buffer, 0, dataChunk, 0, cbRead);

                        return dataChunk;
                    })
        .Repeat()
        .TakeWhile(dataChunk => dataChunk.Length > 0);
}

Answer 1

Fell into the same trap as well. Async streams behave like a replayable one. Although it only contains that one item. To fix that, wrap it in Defer like this

Observable.Defer(() => asyncRead(buffer, 0, bufferSize))
...