Uploading and downloading files with ASP.NET WEB API

public HttpResponseMessage Get(string filename) {
    var path = Path.Combine(ROOT, filename);
    // ROOT would be in our case equal to HttpContext.Current.Server.MapPath("~/App_Data");
    if (!File.Exists(path))
    throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.NotFound));
    // The above line will not work with my setup
    // When I change it to 
    // throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.NotFound, "Not found"));
    // It will compile but the Exception handling will not be elegant

    var result = new HttpResponseMessage(HttpStatusCode.OK);
    var stream = new FileStream(path, FileMode.Open);
    result.Content = new StreamContent(stream);
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    // There are different options and different outcomes based on how you set up the ContentType
    // and ContentDisposition headers
    // One example:
    // result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") { FileName = name };
    return result;
}

public HttpResponseMessage Get(string filename) {
    var data = GetFromSomewhere(filename);
    if (data = null)
    throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.NotFound));

    var result = new HttpResponseMessage(HttpStatusCode.OK);
    result.Content = new ByteArrayContent(data);
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    return result;
}

public HttpResponseMessage Get(string file1, string file2) {
    var fileA = new StreamContent(new FileStream(Path.Combine(ROOT, file1), FileMode.Open));
    filaA.Headers.ContentType = new MediaTypeHeaderValue("image/jpeg");

    var fileB = new StreamContent(new FileStream(Path.Combine(ROOT, file2), FileMode.Open));
    filaB.Headers.ContentType = new MediaTypeHeaderValue("image/jpeg");

    var result = new HttpResponseMessage(HttpStatusCode.OK);
    result.Content = new MultipartContent();
    result.Content.Add(fileA);
    result.Content.Add(fileB);

    return result;
}