Question

I’m returning some Json via a C# MVC Controller. Other browsers work fine, but Internet Explorer (IE9) tries to Save the returned Json data as a Text file. Any ideas how to keep this from happening?

//MVC Controller Code...
return Json(new { redirectToUrl = Url.Action("Create", "Album",
                  new { url = url, isLocalFile = isLocalFile})});

//Clientside Javascript Code
$("#uploadImageForm").ajaxForm({
  beforeSubmit: function () {

  },
  success: function (data, textStatus, xhr) {
          window.location.href = data.redirectToUrl;
  },
  error: function (data, textStatus, xhr) {
  } 
});

I’ve tried adding “text/plain” and “text/json” to the second argument of the return Json method, it doesn’t work.

Many thanks!

Answer 1

Quote from the documentation of the jquery.form plugin:

Browsers that support the XMLHttpRequest Level 2 will be able to
upload files seamlessly and even get progress updates as the upload
proceeds. For older browsers, a fallback technology is used which
involves iframes since it is not possible to upload files using the
level 1 implmenentation of the XMLHttpRequest object. This is a common
fallback technique, but it has inherent limitations. The iframe
element is used as the target of the form’s submit operation which
means that the server response is written to the iframe. This is fine
if the response type is HTML or XML, but doesn’t work as well if the
response type is script or JSON, both of which often contain
characters that need to be repesented using entity references when
found in HTML markup.

To account for the challenges of script and JSON responses when using
the iframe mode, the Form Plugin allows these responses to be embedded
in a textarea element and it is recommended that you do so for these
response types when used in conjuction with file uploads and older
browsers. Please note, however, that if there is no file input in the
form then the request uses normal XHR to submit the form (not an
iframe). This puts the burden on your server code to know when to use
a textarea and when not to.

This means that if your form contains file input fields and you are submitting this form to a controller action that returns JSON, you must wrap this JSON in a <textarea> tags.

So your response should not look like this:

{ "redirectToUrl":"some url" }

it should look like this:

<textarea>{ "redirectToUrl":"some url" }</textarea>

In order to achieve that you could use a custom action result that will wrap the response with those tags:

public class TextareaJsonResult : JsonResult
{
    public TextareaJsonResult(object data)
    {
        this.Data = data;
    }

    public override void ExecuteResult(ControllerContext context)
    {
        var response = context.HttpContext.Response;
        bool shouldWrap = !context.HttpContext.Request.IsAjaxRequest();
        if (shouldWrap)
        {
            response.Write("<textarea>");
        }

        base.ExecuteResult(context);

        if (shouldWrap)
        {
            response.ContentType = "text/html";
            response.Write("</textarea>");
        }
    }
}

and then have your controller action return this custom result:

[HttpPost]
public ActionResult Upload(HttpPostedFileBase file)
{
    // ... some processing

    var redirectToUrl = Url.Action(
        "Create", 
        "Album",
        new { url = url, isLocalFile = isLocalFile }
    );
    return new TextareaJsonResult(new { redirectToUrl = redirectToUrl });
}

Now obviously in your AJAX success callback you also need to account for this difference by testing the typeof result and in the case of a legacy browser (such as Internet Explorer) manually parse the response. You may take a look at the source code of the page I have linked to.

But this being said, I can see that in your success callback you are redirecting to a controller action contained in the JSON response returned by the server. Here comes my question: What’s the point of using AJAX in the first place if you are going to redirect? Why don’t you use a standard form post to the controller action and have the controller action directly perform the redirect? AJAX should be used when you want to stay on the same page.