c# - 网络核心 : how to make the browser show file as being downloaded before it's sent

Question

我有以下生成文件的操作:

public async Task<IActionResult> GetFile()
{
    //some long running action to actually generate the content 
    //(e.g. getting data from DB for reporting)
    await Task.Delay(10000); 

    return File(new byte[]{}, "application/octet-stream");
}

问题在于，当用户点击该链接时，从点击操作到浏览器显示正在下载的文件之间存在很长的延迟。

我真正想要的是让 ASP.Net 发送带有文件名的 header (以便浏览器向用户显示文件已开始下载)并在生成文件内容时延迟发送正文。可以这样做吗？

我尝试了以下方法:

public async Task GetFile()
{
    HttpResponse response = this.HttpContext.Response;
    response.ContentType = "application/octet-stream";
    response.Headers["Content-Disposition"] = "inline; filename=\"Report.txt\"";

    //without writing the first 8 bytes 
    //Chrome doesn't display the file as being downloaded 
    //(or ASP.Net doesn't actually send the headers). 
    //The problem is, I don't know the first 8 bytes of the file :)            
    await response.WriteAsync(string.Concat(Enumerable.Repeat("1", 8)));

    await response.Body.FlushAsync();

    await Task.Delay(10000);
    await response.WriteAsync("1234567890");
}

上面的代码有效，如果我不必response.WriteAsync前 8 个字节用于发送 header ，我会很高兴。

还有其他方法可以克服吗？

Answer 1

实际上，有问题的代码可以正常工作。问题是，Chrome doesn't show file as being downloaded until 8 bytes are sent

但是，如果您想写类似的东西，请考虑阅读 Stephen Cleary's post一些有用的抽象。