如何使用ASP.NET Core进行流式处理

Question

How to properly stream response in ASP.NET Core? There is a controller like this ( UPDATED CODE ):

[HttpGet("test")]
public async Task GetTest()
{
    HttpContext.Response.ContentType = "text/plain";
    using (var writer = new StreamWriter(HttpContext.Response.Body))
        await writer.WriteLineAsync("Hello World");            
}

Firefox/Edge browsers show

Hello World

, while Chrome/Postman report an error:

The localhost page isn't working

localhost unexpectedly closed the connection.

ERR_INCOMPLETE_CHUNKED_ENCODING

PS I am about to stream a lot of content, so I cannot specify Content-Length header in advance.

Answer 1

To stream a response that should appear to the browser like a downloaded file, you should use FileStreamResult :

[HttpGet]
public FileStreamResult GetTest()
{
  var stream = new MemoryStream(Encoding.ASCII.GetBytes("Hello World"));
  return new FileStreamResult(stream, new MediaTypeHeaderValue("text/plain"))
  {
    FileDownloadName = "test.txt"
  };
}

Answer 2

It is possible to return null or EmptyResult() (which are equivalent), even when previously writing to Response.Body . It may be useful if the method returns ActionResult to be able to use all the other results aswell (eg BadQuery() ) easily.

[HttpGet("test")]
public ActionResult Test()
{
    Response.StatusCode = 200;
    Response.ContentType = "text/plain";
    using (var sw = new StreamWriter(Response.Body))
    {
        sw.Write("something");
    }
    return null;
}

Answer 3

I was wondering as well how to do this, and have found out that the original question's code actually works OK on ASP.NET Core 2.1.0-rc1-final , neither Chrome (and few other browsers) nor JavaScript application do not fail with such endpoint.

Minor things I would like to add are just set StatusCode and close the response Stream to make the response fulfilled:

[HttpGet("test")]
public void Test()
{
    Response.StatusCode = 200;
    Response.ContentType = "text/plain";
    using (Response.Body)
    {
        using (var sw = new StreamWriter(Response.Body))
        {
            sw.Write("Hi there!");
        }
    }
}

Answer 4

something like this might work:

[HttpGet]
public async Task<IActionResult> GetTest()
{
    var contentType = "text/plain";
    using (var stream = new MemoryStream(Encoding.ASCII.GetBytes("Hello World")))
    return new FileStreamResult(stream, contentType);

}