从ASP.NET Core 2控制器返回PDF

Question

I am trying to return a PDF file from my ASP.NET Core 2 controller. I have this code (mostly borrowed from this SO question ):

var net = new System.Net.WebClient();
//a random pdf file link
var fileLocation = "https://syntera.io/documents/T&C.pdf";/
var data = net.DownloadData(fileLocation);
MemoryStream content = null;
try
{
    content = new MemoryStream(data);
    return new FileStreamResult(content, "Application/octet-stream");
}
finally
{
    content?.Dispose();
}

This code above is part of a service class that my controller calls. This is the code from my controller.

public async Task<IActionResult> DownloadFile(string fileName)
{
    var result = await _downloader.DownloadFileAsync(fileName);
    return result;
}

But I keep getting ObjectDisposedException: Cannot access a closed Stream.

The try and finally block was an attempt to fix it , from another SO question .

The main question is A) Is this the right way to send a PDF file back to the browser and B) if it isn't, how can I change the code to send the pdf to the browser?

Ideally , I don't want to first save the file on the server and then return it to the controller. I'd rather return it while keeping everything in memory.

Answer 1

The finally will always get called ( even after the return ) so it will always dispose of the content stream before it can be sent to the client, hence the error.

Ideally , I don't want to first save the file on the server and then return it to the controller. I'd rather return it while keeping everything in memory.

Use a FileContentResult class to take the raw byte array data and return it directly.

FileContentResult : Represents an ActionResult that when executed will write a binary file to the response.

async Task<IActionResult> DownloadFileAsync(string fileName){
    using(var net = new System.Net.WebClient()) {
        byte[] data = await net.DownloadDataTaskAsync(fileName);
        return new FileContentResult(data, "application/pdf") {
            FileDownloadName = "file_name_here.pdf"
        };
    }
}

No need for the additional memory stream

Answer 2

You must specify :

Response.AppendHeader("content-disposition", "inline; filename=file.pdf");
return new FileStreamResult(stream, "application/pdf")

For the file to be opened directly in the browser.