Writing data on closed socket causes unnecessary exception in Netty

[kornefalk]

public class DefaultSmppSession ...

public void sendResponsePdu(PduResponse pdu) throws RecoverablePduException, UnrecoverablePduException, SmppChannelException, InterruptedException {
...
        // write the pdu out & wait timeout amount of time
        ChannelFuture channelFuture = this.channel.writeAndFlush(buffer);
        if(configuration.getWriteTimeout() > 0){
            channelFuture.await(configuration.getWriteTimeout());
        } else {
            channelFuture.await();
        }

Line 518-523 in master branch at October 4, 2017

By adding a simple test before writing to the socket, the long exception will be avoided
For example add the following code just before:

        if (!this.channel.isOpen()) {
            logger.info("Channel closed.");
            return;
        }

Exception

2017-10-03 12:52:49.809 ERROR 16945 --- [cation.SMPP.csn] c.c.smpp.impl.DefaultSmppSession         : Unable to cleanly return response PDU: {}

com.cloudhopper.smpp.type.SmppChannelException: null
	at com.cloudhopper.smpp.impl.DefaultSmppSession.sendResponsePdu(DefaultSmppSession.java:573) ~[ch-smpp-6.0.0-netty4-beta-3.jar!/:6.0.0-netty4-beta-3]
	at com.cloudhopper.smpp.impl.DefaultSmppSession.firePduReceived(DefaultSmppSession.java:606) ~[ch-smpp-6.0.0-netty4-beta-3.jar!/:6.0.0-netty4-beta-3]
	at com.cloudhopper.smpp.channel.SmppSessionWrapper.channelRead0(SmppSessionWrapper.java:48) [ch-smpp-6.0.0-netty4-beta-3.jar!/:6.0.0-netty4-beta-3]
	at com.cloudhopper.smpp.channel.SmppSessionWrapper.channelRead0(SmppSessionWrapper.java:36) [ch-smpp-6.0.0-netty4-beta-3.jar!/:6.0.0-netty4-beta-3]
	at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:349) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:341) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:293) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:267) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:349) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:341) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at com.cloudhopper.smpp.channel.SmppSessionLogger.channelRead(SmppSessionLogger.java:104) [ch-smpp-6.0.0-netty4-beta-3.jar!/:6.0.0-netty4-beta-3]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:349) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:341) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at com.cloudhopper.smpp.channel.SmppSessionThreadRenamer.channelRead(SmppSessionThreadRenamer.java:89) [ch-smpp-6.0.0-netty4-beta-3.jar!/:6.0.0-netty4-beta-3]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:349) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:341) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at com.cloudhopper.smpp.channel.LoggingChannelInboundHandlerAdapter.channelRead(LoggingChannelInboundHandlerAdapter.java:94) [ch-smpp-6.0.0-netty4-beta-3.jar!/:6.0.0-netty4-beta-3]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:349) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:341) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1334) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:363) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:349) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:926) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:129) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:642) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.nio.NioEventLoop.processSelectedKeysPlain(NioEventLoop.java:527) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:481) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:441) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144) [netty-all-4.1.7.Final.jar!/:4.1.7.Final]
	at java.lang.Thread.run(java.base@9-internal/Thread.java:804) [na:na]
Caused by: java.nio.channels.ClosedChannelException: null
	at io.netty.channel.AbstractChannel$AbstractUnsafe.write(...)(Unknown Source) ~[netty-all-4.1.7.Final.jar!/:4.1.7.Final]