When is java.io.IOException: Connection reset by peer thrown with Netty?

Question

When I send a request to a webserver using netty. I get the following exception. What can cause this exception ?

java.io.IOException: Connection reset by peer
        at sun.nio.ch.FileDispatcherImpl.read0(Native Method) ~[na:1.7.0_25]
        at sun.nio.ch.SocketDispatcher.read(Unknown Source) ~[na:1.7.0_25]
        at sun.nio.ch.IOUtil.readIntoNativeBuffer(Unknown Source) ~[na:1.7.0_25]
        at sun.nio.ch.IOUtil.read(Unknown Source) ~[na:1.7.0_25]
        at sun.nio.ch.SocketChannelImpl.read(Unknown Source) ~[na:1.7.0_25]
        at io.netty.buffer.UnpooledHeapByteBuf.setBytes(UnpooledHeapByteBuf.java:237) ~[netty-all-4.0.6.Final.jar:na]
        at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:867) ~[netty-all-4.0.6.Final.jar:na]
        at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:227) ~[netty-all-4.0.6.Final.jar:na]
        at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:87) ~[netty-all-4.0.6.Final.jar:na]
        at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:497) ~[netty-all-4.0.6.Final.jar:na]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:465) ~[netty-all-4.0.6.Final.jar:na]
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:359) ~[netty-all-4.0.6.Final.jar:na]
        at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) ~[netty-all-4.0.6.Final.jar:na]
        at java.lang.Thread.run(Unknown Source) ~[na:1.7.0_25]

Answer 1

The usual cause of this error is that you have written to a connection which had already been closed by the other end. In other words, an application protocol error. There are other causes, but this is the most common.

NB Netty has nothing to do with it.