Dart ServerSocket Connection reset by peer

[azproduction]

I just created simple Dart http server and stat to ab it. ab often
ends with "apr_socket_recv: Connection reset by peer (54)" What is
wrong?
https://gist.github.com/1292557

[Florin Malita]

    void onConnect() {
        List<int> receiveBuffer = new List();

        Socket receiveSocket = serverSocket.accept();
        InputStream inputStream = receiveSocket.inputStream;
        OutputStream outputStream = receiveSocket.outputStream;

        inputStream.readUntil(receiveBuffer, bufferReady);
        outputStream.write(output, 0, output.length, onSend);

        receiveSocket.close();
    }

The main problem is that you're performing I/O and closing the socket in your onConnect() handler. The current Dart socket API is non-blocking => your read there is most likely not getting any data, and you're closing the connection before the peer has had a chance to send anything.

You should be waiting for receiveSocket events and perform the I/O only when notified. Also keep in mind that reads and writes can always transfer fewer bytes than requested. Try something like this:

    void onConnect() {

        void onWrite(Socket sock, int offset) {

            int written = sock.writeList(output, offset, output.length - offset);

            if (written > 0 && written < output.length - offset)

                sock.setWriteHandler(() => onWrite(sock, offset + written));

            else

                sock.close();

        }

        void onData(Socket sock) {

            List<int> buf = new List<int>(1024);

            // this is incomplete - should keep reading until a full HTTP request is received

            sock.readList(buf, 0, buf.length);

            sock.setWriteHandler(() => onWrite(sock, 0));

        }

        void onClose(Socket sock) {

            sock.close();

        }

        Socket receiveSocket = serverSocket.accept();

        receiveSocket.setCloseHandler(() => onClose(receiveSocket));

        receiveSocket.setDataHandler(() => onData(receiveSocket));

        

        return;

    }

[azproduction]

I updated my script, but the problem is still there.

https://github.com/azproduction/dart-http/blob/master/HttpServer.dart#L190-199

On 18 окт, 00:26, Florin Malita <fmal...@google.com> wrote:

[Florin Malita]

On Thu, Oct 20, 2011 at 5:01 AM, azproduction <azazel....@gmail.com> wrote:

I updated my script, but the problem is still there.

https://github.com/azproduction/dart-http/blob/master/HttpServer.dart#L190-199

What level of concurrency are you using with AB (-c) and what OS are you running on?

I was able to consistently complete 100K runs @ 100 concurrent requests with the following tweaks:

* removed the onClose() handler - apparently the socket is cleaned up automatically; calling close explicitly in the handler is race-prone and can end up throwing an invalid socket exception

* increased listen backlog - this must be able to buffer the number of concurrent connections that AB throws at it before they're accepted.

FWIW, I could trigger the same AB errors running against Apache when I lowered its ListenBacklog setting to something like 10. It also seems to be a poor error message choice (connection reset by peer) because a packet capture showed it was really AB resetting the connection (while trying to close it after a connect timeout), and not its peer.

Try the patch below and let me know whether it stabilizes your runs - it did for me.

--

Florin

--- HttpServer.dart.orig 2011-10-20 10:17:27.359189967 -0400

+++ HttpServer.dart 2011-10-20 13:40:43.637947155 -0400

@@ -166,7 +166,7 @@

 

     HttpServer listen(cb(HttpRequest request, HttpResponse response)) {

         // initialize the server

-        serverSocket = new ServerSocket(host, port, 5);

+        serverSocket = new ServerSocket(host, port, 100);

         if (serverSocket == null) {

             throw "can't get server socket";

         }

@@ -198,13 +198,8 @@

         }

     }

 

-    void _onClose(Socket sock) {

-        sock.close();

-    }

-

     void _onConnect() {

         Socket receiveSocket = serverSocket.accept();

-        receiveSocket.setCloseHandler(() => this._onClose(receiveSocket));

         receiveSocket.setDataHandler(() => this._onData(receiveSocket));

         return;

     }