HttpServer - autoclose HttpResponse OutputStream on onRequest exit

[DartBot]

This issue was originally filed by Fir...@gmail.com

---

What steps will reproduce the problem?
void onRequestHandler( HttpRequest httpRequest, HttpResponse httpResponse ) {
  httpResponse.writeString("test");
  httpResponse.outputStream.close();
  print("test");
}
The code above blocks HttpServer response and because of that the browser too.

void onRequestHandler( HttpRequest httpRequest, HttpResponse httpResponse ) {
  httpResponse.writeString("test");
  httpResponse.outputStream.close();
  print("test");
}
Closing the outputstream fixes the problem.

What is the expected output? What do you see instead?
Shouldn't outputstream be closed by HttpServer after exit the onRequest method?

What version of the product are you using? On what operating system?
dart-sdk revision 4978
Mint KDE 12

Please provide any additional information below.

[DartBot]

This comment was originally written by ladicek@gmail.com

---

Shouldn't outputstream be closed by HttpServer after exit the onRequest method?

Most certainly not. This is a little confusing (I think that something like httpResponse.done() would be more instructive and easily discoverable), but the output stream really can't be closed automatically when the onRequest callback finishes. The reason is -- there might be (and probably will be) async operations still running when the callback returns, and they will want to write to the stream. Consider something like this:

httpServer.onRequest = (req, resp) {
  var in = new File("/path/to/very/big/file").openInputStream();
  in.pipe(resp.outputStream);
};

Here, the onRequest callback most probably ends a lot sooner than the whole response is written (streaming a big file to the client), so the HttpServer really can't close the output stream automatically. (As a side note: InputStream.pipe closes the given OutputStream automatically after everything is written, and closing an "exhausted" InputStream isn't necessary. So streaming a file really is this simple, except of error handling -- kudos to the dart:io team!)

[DartBot]

This comment was originally written by Firen2k5...@gmail.com

---

Yes, adding httpResponse.writeDone() method was my second thought.
Any second thoughts about it?

[DartBot]

This comment was originally written by ladicek@gmail.com

---

Actually, something like httpResponse.writeDone() used to be there, but it's long gone. I hope it's coming back in some form, having it in the HttpResponse interface is much more instructive than having a mention about closing the output stream in the documentation comment.

[madsager]

Added Area-IO, Triaged labels.

[madsager]

We cannot automatically close the response at the end of onRequest. For simple examples it would work. However, as Ladislav points out, as soon as you start performing async IO operations to get parts of you response it would break.

Consider:

server.onRequest = (request, response) {
  var f = new File(request.path);
  f.exists((res) {
    if (exists) {
      response.outputStream.writeString("hello");
    } else {
      ...
    }
  });
}

Since the exists call is asynchronous we will exit onRequest immediately without having written anything to response. Therefore, we cannot close it at that point.

Regarding adding shortcuts to HttpResponse itself that will forward to the outputStream. That would be very simple. I personally like the current way with no shortcuts. It is clear what you are doing. You are operating on an output stream.

---

Added AsDesigned label.

[kevmoo]

Removed Area-IO label.
Added Area-Library, Library-IO labels.