How to run possibly synchronous or possibly asynchronous code?

IObservable<byte[]> readFromNetwork()
{
    var ret = new AsyncSubject();
    // Here's a traditional async function that you provide a callback to
    asyncReaderFunc(theFile, buffer => {
        ret.OnNext(buffer);
        ret.OnCompleted();
    });

    return ret;
}

// Make it into a sync function
byte[] results = readFromNetwork().First();

// Keep reading blocks one at a time until we run out
readFromNetwork().Repeat().TakeUntil(x => x == null || x.Length == 0).Subscribe(bytes => {
    Console.WriteLine("Read {0} bytes in chunk", bytes.Length);
})

// Read the entire stream and get notified when the whole deal is finished
readFromNetwork()
    .Repeat().TakeUntil(x => x == null || x.Length == 0)
    .Aggregate(new MemoryStream(), (ms, bytes) => ms.Write(bytes))
    .Subscribe(ms => {
        Console.WriteLine("Got {0} bytes in total", ms.ToArray().Length);
    });

// Or just get the entire thing as a MemoryStream and wait for it
var memoryStream = readFromNetwork()
    .Repeat().TakeUntil(x => x == null || x.Length == 0)
    .Aggregate(new MemoryStream(), (ms, bytes) => ms.Write(bytes))
    .First();