Web Api returns garbage for text files unless run

Question

I am writing a file service using Asp.Net’s Web Api. The service retrieves files (Css, Excel, Csv, etc.) from SQL Server and serves them up in response to Get requests.

My first test case is for Css files. The issue is that, while I can see the correct data on the server side, when the browser retrieves/decodes it, the results are mangled. The issue appears to be related to the encodings.

Here are the request/response headers in FireFox:

When I click on the response tab in FireBug, here’s what it looks like:

The results look like ascii being displayed as utf8. This is the html view in FireBug:

The above example is an iFrame inside a Facebook application which is running ssl.

If I take the url and open it directly in the browser, it works and correctly displays my Css:

In summary, when I retrieve my Css file from a tag inside my Facebook app, I get garbage (encoding issue?). If I retrieve it straight from the browser, it works.

My CssFormatter MediaTypeFormatter code:

    public override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
    {

        var taskSource = new TaskCompletionSource<object>(); 
        try
        {
            var incomingFile = value as FileRestService.Entity.IFile;

            var ms = new MemoryStream(incomingFile.DataBuffer);

            ms.CopyTo(writeStream);
            ms.Flush();

            taskSource.SetResult(writeStream);

        }
        catch (Exception e) 
        { 
            taskSource.SetException(e); 
        } 
        return taskSource.Task; 

    }

Am I creating the response stream incorrectly? I noticed that the response headers do not specify the encoding. Is this an issue?

Answer 1

I find the easiest way to handle this is to write something along the lines of (here's the important details):

public class Formatter : MediaTypeFormatter {
    // TODO override the constructor to add some mappings or some other way for this formatter to be picked up

    // TODO override CanReadType and CanWriteType according to your rules

    public override void SetDefaultContentHeaders(Type t, HttpContentHeaders headers, string mediaType) {
        base.SetDefaultContentHeaders(t, headers, mediaType);
        headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") {
            FileName = "SomeName.ext"
        };
    }

    public override Task WriteToStreamAsync(Type t, object value, Stream s, HttpContentHeaders headers, TransportContext context) {
        return Task.Factory.StartNew(() => {
            // TODO code to write to the output stream, flush it but don't explicitly close it
        });
    }
}