Hi,
I was debugging a little and the cause might be the method processReadKey (SelectionKey key) in the class NioUdpClient.

When we get an IO exception, then the channel does not get closed.

` public void processReadyKey(SelectionKey key) {
if (!key.isReadable()) {
f.completeExceptionally(new EOFException("channel not readable"));
pendingTransactions.remove(this);
return;
}

  DatagramChannel channel = (DatagramChannel) key.channel();
  ByteBuffer buffer = ByteBuffer.allocate(max);
  int read;
  try {
    read = channel.read(buffer);
    if (read <= 0) {
      throw new EOFException();
    }
  } catch (IOException e) {
    **_// Shouldn't the channel be closed here?_**
    pendingTransactions.remove(this);
    f.completeExceptionally(e);
    return;
  }

  buffer.flip();
  byte[] data = new byte[read];
  System.arraycopy(buffer.array(), 0, data, 0, read);
  verboseLog(
      "UDP read",
      channel.socket().getLocalSocketAddress(),
      channel.socket().getRemoteSocketAddress(),
      data);
  try {
    channel.disconnect();
    channel.close();
  } catch (IOException e) {
    // ignore, we already have everything we need
  }

  f.complete(data);
  pendingTransactions.remove(this);
}

`

I think, the channel should be closed in the catch (IOException e) block.

Yes, you're probably right. I need to verify the behavior, which might take me a while.

I added some code to close the channel in the above situation and it is now working fine for me. However, I am not sure, whether this are all error conditions where you should close the datagram socket...

Verifying is pretty easy. Run in a loop DNS requests against an IP that doesn't have a DNS server installed. You will get an error and after a while, you will have plenty of open UDP datagram sockets.

If you already changed this, would you mind creating a pull request? Ideally including a unit test that verifies your fix is working.

Hi,

this is my modified version of the NioUdpClient.java based on 3.1.0 release. I have added a block to close the channels.

I was testing it by checking the list of open UDP ports using the netstat command. Don't know how you might automate that in a unit test....

NioUdpClient.java.txt