Summary

I am developing a WAV file format reader under WinRT, and for this I need to read random amounts of structs consisting of fundamental types such as int, uint, float and so on.

Back in desktop development one would rely on BinaryReader, now in WinRT it has been replaced by DataReader which works asynchronously.

Problem

I cannot grasp how to use this new class since now, an intermediate buffer must be filled using LoadAsync(), prior calling reading methods such as ReadInt32().

In contrast, with the old BinaryReader there was no notion of having to fill an intermediate buffer prior reading primitives from the source.

Every example I have seen on the web are 'naive' in the sense that they entirely read the source stream in memory, but in my case a WAV file is in the range of hundred megabytes and possibly gigabytes.

I have sketched the following helper methods which pre-fills the intermediate buffer with only what's needed and basically frees me from systematically calling LoadAsync every time before reading something from the stream:

internal static class DataReaderExtensions
{
    public static async Task<string> ReadStringAsync(this DataReader reader, uint length)
    {
        await LoadAsync(reader, length);
        return reader.ReadString(length);
    }

    private static async Task LoadAsync(DataReader reader, uint length)
    {
        var u = await reader.LoadAsync(length);
        if (u < length) throw new InvalidOperationException();
    }
}

But I'm not entirely sure whether it is the way to go when using DataReader.

Question

How is one supposed to pre-fill the intermediate buffer in my case ?

• should one load only the needed amount as shown above ?
• or should one load a constant size (e.g. 65536 bytes), keep track of reading position then possibly pre-fetch more on larger requests ? (basically wrapping a DataReader in a helper class)