Silverlight download JSON from API fails

Question

I cant seem to download the JSON for the questions on SO, I cant get the HTML and JSON from other addresses, but the SO API always returns jibberish.

Here is my code:

public void BeginGetAllRecentQuestions()
    {
        WebClient client = new WebClient();
        client.Headers = new WebHeaderCollection();
        client.DownloadStringCompleted += DownloadRecentQuestionsStringCompleted;
        client.DownloadStringAsync(new Uri("http://api.stackoverflow.com/1.0/questions?key=MYKEYHERE", UriKind.Absolute));
    }

private void DownloadRecentQuestionsStringCompleted(object sender, DownloadStringCompletedEventArgs e)
    {
        var resultsString = e.Result;
        Console.WriteLine(resultsString);
    }

I just want basic JSON text returned, but all I ever get is, what looks like, strangley encoded text, which is not right.

I have tried other JSON URL's and they work fine. Its just this URL that fails.

Can someone please try out this code and help me out?

Answer 1

Update

Ok, I see from comments that you are using phone7 - the story is slightly different than mainstream silverlight as there is ONLY ClientHttp stack and you will need to manually decompress, as you have found out.

I use Silverlight.SharpZipLib for this purpose.

Good luck.

Here is a method that will work in Silverlight and Phone 7. You can use it for API calls as well as others as it will check for gzip and respond accordingly.

private static string GetResponseText(WebResponse response)
{
    string responseText;
    using (Stream stream = response.GetResponseStream())
    {
        if (stream == null)
        {
            throw new Exception("response stream null");
        }

        byte[] data;

        var buffer = new byte[32768];

        using (var ms = new MemoryStream())
        {
            int read;
            while ((read = stream.Read(buffer, 0, buffer.Length)) > 0)
            {
                ms.Write(buffer, 0, read);

            }
            data = ms.ToArray();
        }

        // check for magic numbers
        if (data.Length > 2 && (data[0] == 31 && data[1] == 139))
        {
            using (var ms = new MemoryStream(data))
            using (var gzip = new GZipInputStream(ms))
            using (var reader = new StreamReader(gzip))
            {
                responseText = reader.ReadToEnd();
            }
        }
        else
        {
            responseText = Encoding.UTF8.GetString(data, 0, data.Length);
        }

    }
    return responseText;
}

---

Previous answer

ALL output from the API is gzipped.

There are two stacks available in silverlight:

• BrowserHttp - supports transparent gzip - see Soapi.CS source code for a working example, but I will try to provide an isolated spike below.

• ClientHttp - does not support gzip - you will need determine if the content is gzipped and decompress manually - using perhaps Silverlight.SharpZipLib. But really there are other issues that surface when trying to use the ClientHttp stack so I do not recommend this approach.

So, if you have a line of code in your app resembling

WebRequest.RegisterPrefix("http"..., ClientHttp....

remove it and you should get better results.

Answer 2

Random thing to try, but I wonder if this is a compression issue? i.e. WebClient (on silverlight) is failing to decode GZIP of DEFLATE encoded data. What http headers do you send/receive? (via a network trace)