How do I download a file from a Byte[] array in a Web Api2 method that returns IHttpActionResult? - download

Question

Below is the method I've got in my ApiController class.
The _fileContents dictionary is populated in another WebApi2 method BuildContent(params).
When the user makes an ajax call to the BuildContent(params) method, the method builds
the string end of the dictionary, which contains full HTML content including a table tag and passes back a the Guid, end of the dictionary. The javascript in turn does the following:
window.location = 'api/MyController/DownloadFile/' + guid;
ApiController static:
private static Dictionary<Guid, String> _fileContents = new Dictionary<Guid, String>();
ApiController method:
public IHttpActionResult DownloadFile(Guid guid)
{
try
{
if (_fileContents.ContainsKey(guid))
{
HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
var content = Encoding.ASCII.GetBytes(_fileContents[guid]);
using (var stream = new MemoryStream(content))
{
result.Content = new StreamContent(stream);
result.Content.Headers.ContentType =
new MediaTypeHeaderValue("application/octet-stream");
result.Content.Headers.ContentDisposition =
new ContentDispositionHeaderValue("attachment");
result.Content.Headers.ContentDisposition.FileName = "MyFile.bin";
}
return Ok(result);
}
else
{
return NotFound();
}
}
catch (Exception ex)
{
return InternalServerError(ex);
}
return BadRequest();
}
The calling sequence works perfectly but the DownloadFile() method throws the following exception:
<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'.
</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace/>
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>
Type 'System.Net.Http.StreamContent' cannot be serialized. Consider marking it with the DataContractAttribute attribute, and marking all of its members you want serialized with the DataMemberAttribute attribute. If the type is a collection, consider marking it with the CollectionDataContractAttribute. See the Microsoft .NET Framework documentation for other supported types.
</ExceptionMessage>
<ExceptionType>
System.Runtime.Serialization.InvalidDataContractException
</ExceptionType>
Can anyone tell me what is going on and how to accomplish my goal of downloading a simple html file?