Download a file in FORM POST request C#

Question

I am using C# ASP.NET code and trying to download file on the post request of a form. here is my sample code.

    [HttpPost]
    public ActionResult PostMethodName(PostModel inputModel)
    {
        if (ModelState.IsValid)
        {
//other code is removed.
 //Writing this for the test 
            //Download Method call
            DownloadCertificate("This is the test file to download.");

            var statusHtml = RenderViewToString("Status",
            new ErrorMsgModel
            {                    
                IsSuccess = true,
                ErrorDesc = "desc"
            });

            return Json(new { IsSuccess = true, ErrorDescription = 
statusHtml}, JsonRequestBehavior.AllowGet);
        }
        var statusHtml1 = RenderViewToString("Status",
            new ErrorMsgModel
            {
                IsSuccess = false,
                ErrorDesc = "desc"
            });
        statusHtml1 = statusHtml1.Replace("'", "\\'");
        statusHtml1 = statusHtml1.Replace(Environment.NewLine, "");
        return Json(new { IsSuccess = false, ErrorDescription = statusHtml1 
}, JsonRequestBehavior.AllowGet);
    }

Download method which is called from this method.

public ActionResult DownloadCertificate(string content)
    {
        //Certificate Download
        const string fileType = "application/pkcs10";
        string fileName = "Certificate" + DateTime.Today.ToString(@"yyyy-MM-dd") + ".csr";
        var fileContent = String.IsNullOrEmpty(contrnt) ? "" : contrnt;
        byte[] fileContents = Encoding.UTF8.GetBytes(fileContent);
        var result = new FileContentResult(fileContents, fileType) { FileDownloadName = fileName };
        return result;
    }

file download is not working, post functionality is working as desired.

Answer 1

Your DownloadCertificate method returns a value, but you never use the return value in your PostMethodName method.

Given that you are returning json from that method I would suggest that you return a direct link to the file result in the response. The consuming client can then initiate the download. Something like:

return Json(new { IsSuccess = true, Location = Url.Action("DownloadContent")});

Alternatively you could consider a more restful approach and return a 302 response from the post action:

if (ModelState.IsValid)
{
    // you code here
    return RedirectToAction("Controller", "DownloadContent", new {content = "myContent"});
}

This may well proceed with the download transparently depending on your client whilst keeping to the Post-Redirect-Get pattern

Answer 2

[HttpPost]
public ActionResult DownloadCertificate(PostModel inputModel, string content)
{
    if(!ModelState.IsValid){return Json(new {Success=false,//error descr})}
    //Certificate Download
    const string fileType = "application/pkcs10";
    string fileName = "Certificate" + DateTime.Today.ToString(@"yyyy-MM-dd") + ".csr";
    var fileContent = String.IsNullOrEmpty(contrnt) ? "" : contrnt;
    byte[] fileContents = Encoding.UTF8.GetBytes(fileContent);
    var result = new FileContentResult(fileContents, fileType) { FileDownloadName = fileName };
    return result;
}

In your previous code you don`t use DownloadCertificate result, you simly execute it.