Download file from MVC 5 to Angular 2

Question

I have experience in C# backend and ASP.Net MVC. Now I am making my first attempt on Angular 2. It takes time but I like most of it. Now I am stuck on a simple file download.

I have read all examples that i found here on Stackoverflow, but I still don't get my example to work.

On server side I have this C# code:

    public ActionResult DownloadPicture(long id)
    {
        var bytes = System.IO.File.ReadAllBytes("images\dummy.jpg");
        return GetAttachement(bytes, "DummyFile.jpg");
    }

    private ActionResult GetAttachement(byte[] bytes, string fileName)
    {
        var contentType = MimeMapping.GetMimeMapping(fileName);
        var contentDisposition = new System.Net.Mime.ContentDisposition
        {
            FileName = fileName,
            Inline = true
        };
        Response.AppendHeader("Content-Disposition", contentDisposition.ToString());
        return File(bytes, contentType);
    }

On client side I have this Typescript code:

public pictureDownload(id: number): void {
    let options = new RequestOptions({ search: new URLSearchParams("id=" + id) });
    this.http.get(this.urlPictureDownload, options).subscribe((data: any) => {
                // var blob = new Blob([data._body], { type: "image/jpeg" });
                // var url = window.URL.createObjectURL(blob);
                // window.open(url);
       });
 }

The request is coming in to server side. The array is downloaded. I guess my problem lies on client side. Can anyone help me out?

Answer 1

For whatever its worth, this isn't just an issue with Angular2. This seems to be an 'issue' with the browsers(or possibly a spec). There are a few different options you have with this approach that I'm aware of.

1. Once the bytearray is returned to the browser, you could do something like this: var pom = document.createElement('a'); pom.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(data)); pom.setAttribute('download', 'PICTURENAME.jpeg'); pom.style.display = 'none'; document.body.appendChild(pom); pom.click(); document.body.removeChild(pom);

2. The other approach I'm aware of is to create the file on the server at a temp path and then return a redirect result to the user with an id identifying that file(often times a GUID) and have that route that is redirected to return your file result.

Answer 2

For all future readers I sum it all up here. By suggestion from EsDF with suggestion from peinearydevelopment I now have a working solution. Specifying the responseType as ArrayBuffer in the request was the most crucial part and the download trick was really helpful.

Alt 1: I think Casey is right. Whenever possible the easiest way is to just use a simple link tag that points to a server resource. When as in my case, that is not an option, any of the other two alternatives will be useful.

Alt 2: The method openPictureInNewWindow is the simple and straightforward approach. The downside is that it will present an odd url that looks like this: blob:http://localhost/037713d1-a8b9-4fe3-8c43-ee5998ffdc5d.

Alt 3: The other method downloadFile will go one step further and create a temporary link tag and make use of it for file download. That will for most users look like the normal approach. But it doesn't feel like an "Angular 2 approach" manipulating the DOM, but it is a more user friendly way, so for now that is the one I will use. Thanks for all good input!

public pictureDownload(id: number) {
    let options = new RequestOptions({ search: new URLSearchParams("id=" + id), responseType: ResponseContentType.ArrayBuffer });
    this.http.get(this.urlPictureDownload, options).subscribe((data: any) => {
        //this.openPictureInNewWindow(data._body, "image/jpeg");
        this.downloadFile(data._body, "Screenshot_" + id + ".jpg", "image/jpeg");
    });
}

private openPictureInNewWindow(data: ArrayBuffer, contentType: string) {
    var blob = new Blob([data], { type: contentType });
    var url = window.URL.createObjectURL(blob);
    window.open(url);
}

private downloadFile(data: ArrayBuffer, fileName: string, contentType: string) {
    var blob = new Blob([data], { type: contentType });
    var url = window.URL.createObjectURL(blob);

    var link = document.createElement("a");
    link.setAttribute("href", url);
    link.setAttribute("download", fileName);
    link.style.display = "none";
    document.body.appendChild(link);
    link.click();
    document.body.removeChild(link);
}

Answer 3

If you are seeing an image in browser for your backend url of application. Then you could directly assign it to src of img in markup of component like this:

suppose you declare a field with imgURL in component and initialize it with your backend image action method. then in markup you could do so

<img src='{{imgURL}}' alt='any message'/>