How to return a Task<T> in an async method

Question

I have this method in my Windows Phone 8 app where I get some data from a url

   public async static Task<byte[]> getData(string url)
    {
    HttpClient client = null;
    HttpResponseMessage response = null;
    Stream stream = null;
    byte[] dataBytes = null;
    bool error = false;

    try
    {
        Uri uri = new Uri(url);

        client = new HttpClient();
        response = await client.GetAsync(uri);
        response.EnsureSuccessStatusCode();

        stream = await response.Content.ReadAsStreamAsync();
        dataBytes = getDataBytes(stream); 

        if (dataBytes == null)
        {
            error = true;
        }
        else if (dataBytes.Length == 0)
        {
            error = true;
        }
    }
    catch (HttpRequestException )
    {
    }

    if (error)
    {
        return getData(url); // this is where the issue is
    }

    return dataBytes;
    }

But since the method is an async one, the return type cannot be a Task, like I have done on the line return getData(url); since getData(string) returns Task. Any ideas on how I can rewrite this to make it work?

Answer 1

Awaiting the result of getData may do the trick. Still, I strongly recommand you to rewrite your method with a loop, rather than recursively call the method again. It makes it hard to read, and may lead to unforeseen issues.

public async static Task<byte[]> getData(string url)
{
    bool success = false;

    byte[] dataBytes = null;

    while (!success)
    {               
        try
        {
            Uri uri = new Uri(url);

            var client = new HttpClient();
            var response = await client.GetAsync(uri);
            response.EnsureSuccessStatusCode();

            var stream = await response.Content.ReadAsStreamAsync();
            dataBytes = getDataBytes(stream); 

            success = dataBytes != null && dataBytes.Length > 0;
        }
        catch (HttpRequestException)
        {
        }
    }

    return dataBytes;
}

Answer 2

you can get around the compile error by adding changing the return to the following :

if (error)
{
return await getData(url); // this is where the issue is
}

I hope you do realize that this code will keep on looping as long as no data is returned? having many clients like this could easily overload your server.