Handle file download from ajax post

Question

I have a javascript app that sends ajax POST requests to a certain URL. Response might be a JSON string or it might be a file (as an attachment). I can easily detect Content

Answer 1

Below is my solution for downloading multiple files depending on some list which consists of some ids and looking up in database, files will be determined and ready for download - if those exist. I am calling C# MVC action for each file using Ajax.

And Yes, like others said, it is possible to do it in jQuery Ajax. I did it with Ajax success and I am always sending response 200.

So, this is the key:

  success: function (data, textStatus, xhr) {

And this is my code:

var i = 0;
var max = 0;
function DownloadMultipleFiles() {
            if ($(".dataTables_scrollBody>tr.selected").length > 0) {
                var list = [];
                showPreloader();
                $(".dataTables_scrollBody>tr.selected").each(function (e) {
                    var element = $(this);
                    var orderid = element.data("orderid");
                    var iscustom = element.data("iscustom");
                    var orderlineid = element.data("orderlineid");
                    var folderPath = "";
                    var fileName = "";

                    list.push({ orderId: orderid, isCustomOrderLine: iscustom, orderLineId: orderlineid, folderPath: folderPath, fileName: fileName });
                });
                i = 0;
                max = list.length;
                DownloadFile(list);
            }
        }

Then calling:

function DownloadFile(list) {
        $.ajax({
            url: '@Url.Action("OpenFile","OrderLines")',
            type: "post",
            data: list[i],
            xhrFields: {
                responseType: 'blob'
            },
            beforeSend: function (xhr) {
                xhr.setRequestHeader("RequestVerificationToken",
                    $('input:hidden[name="__RequestVerificationToken"]').val());

            },
            success: function (data, textStatus, xhr) {
                // check for a filename
                var filename = "";
                var disposition = xhr.getResponseHeader('Content-Disposition');
                if (disposition && disposition.indexOf('attachment') !== -1) {
                    var filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/;
                    var matches = filenameRegex.exec(disposition);
                    if (matches != null && matches[1]) filename = matches[1].replace(/['"]/g, '');
                    var a = document.createElement('a');
                    var url = window.URL.createObjectURL(data);
                    a.href = url;
                    a.download = filename;
                    document.body.append(a);
                    a.click();
                    a.remove();
                    window.URL.revokeObjectURL(url);
                }
                else {
                    getErrorToastMessage("Production file for order line " + list[i].orderLineId + " does not exist");
                }
                i = i + 1;
                if (i < max) {
                    DownloadFile(list);
                }
            },
            error: function (XMLHttpRequest, textStatus, errorThrown) {

            },
            complete: function () {
                if(i===max)
                hidePreloader();
            }
        });
    }

C# MVC:

 [HttpPost]
 [ValidateAntiForgeryToken]
public IActionResult OpenFile(OrderLineSimpleModel model)
        {
            byte[] file = null;

            try
            {
                if (model != null)
                {
                    //code for getting file from api - part is missing here as not important for this example
                    file = apiHandler.Get(downloadApiUrl, token);

                    var contentDispositionHeader = new System.Net.Mime.ContentDisposition
                    {
                        Inline = true,
                        FileName = fileName
                    };
                    //    Response.Headers.Add("Content-Disposition", contentDispositionHeader.ToString() + "; attachment");
                    Response.Headers.Add("Content-Type", "application/pdf");
                    Response.Headers.Add("Content-Disposition", "attachment; filename=" + fileName);
                    Response.Headers.Add("Content-Transfer-Encoding", "binary");
                    Response.Headers.Add("Content-Length", file.Length.ToString());

                }
            }
            catch (Exception ex)
            {
                this.logger.LogError(ex, "Error getting pdf", null);
                return Ok();
            }

            return File(file, System.Net.Mime.MediaTypeNames.Application.Pdf);
        }

As long as you return response 200, success in Ajax can work with it, you can check if file actually exist or not as the line below in this case would be false and you can inform user about that:

 if (disposition && disposition.indexOf('attachment') !== -1) {