Netty connect to unix domain socket failed

Question

I am writing a small Java program that using Netty to connect to a unix domain socket to retrieve some information. I am using Netty 4.0.32.Final and using native epoll package. Here is the bootstrap code I wrote:

final Bootstrap bootstrap = new Bootstrap();
bootstrap
    .group(new EpollEventLoopGroup())
    .channel(EpollDomainSocketChannel.class)
    .handler(
        new ChannelInitializer<DomainSocketChannel>() {
            @Override
            protected void initChannel(
                final DomainSocketChannel channel) throws Exception {
                channel.pipeline().addLast(
                    new ChannelInboundHandlerAdapter() {
                        @Override
                        public void channelRead(
                            final ChannelHandlerContext ctx,
                            final Object msg) throws Exception {
                            final ByteBuf buff = (ByteBuf) msg;
                            try {
                                buff.readBytes(
                                    DomainSocket.this.out,
                                    buff.readableBytes()
                                );
                            } finally {
                                buff.release();
                            }
                        }
                        @Override
                        public void exceptionCaught(
                            final ChannelHandlerContext ctx,
                            final Throwable cause) throws Exception {
                            Logger.error(
                                "Error occur when reading from Unix domain socket: %s",
                                cause.getMessage()
                            );
                            ctx.close();
                        }
                    }
                );
            }
        }
    );

It looks fine to me but when I run

bootstrap.connect(new DomainSocketAddress("/tmp/test.sock"));

It always complains with the following errors:

java.net.ConnectException: connect() failed: Connection refused: /tmp/test.sock
  at io.netty.channel.epoll.Native.newConnectException(Native.java:504)
  at io.netty.channel.epoll.Native.connect(Native.java:481)
  at io.netty.channel.epoll.AbstractEpollStreamChannel.doConnect(AbstractEpollStreamChannel.java:567)
  at io.netty.channel.epoll.EpollDomainSocketChannel.doConnect(EpollDomainSocketChannel.java:81)
  at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.connect(AbstractEpollStreamChannel.java:627)
  at io.netty.channel.DefaultChannelPipeline$HeadContext.connect(DefaultChannelPipeline.java:1097)

May I know is there anything wrong with the bootstrap setup? Thanks.

Update I wrote a simple server to test the code above in a unit test. Here are the server codes:

final ServerBootstrap bootstrap = new ServerBootstrap();
    bootstrap
        .group(new EpollEventLoopGroup(), new EpollEventLoopGroup())
        .channel(EpollServerDomainSocketChannel.class)
        .childHandler(
            new ChannelInitializer<ServerDomainSocketChannel>() {
                @Override
                protected void initChannel(
                    final ServerDomainSocketChannel channel)
                    throws Exception {
                    channel.pipeline().addLast(
                        new ChannelInboundHandlerAdapter() {
                            @Override
                            public void channelActive(
                                final ChannelHandlerContext ctx)
                                throws Exception {
                                final ByteBuf buff = ctx.alloc().buffer();
                                buff.writeBytes("This is a test".getBytes());
                                ctx.writeAndFlush(buff)
                                    .addListener(
                                        ChannelFutureListener.CLOSE
                                    );
                            }
                        }
                    );
                }
            }
        );
final ChannelFuture future =
    bootstrap.bind(new DomainSocketAddress(input)).sync();
future.channel().closeFuture().sync();

I started this server code in a separate thread using ExecutorService. Thanks.

Zbynek Vyskovsky - kvr000 · Accepted Answer · 2015-10-23 14:35:19Z

1

It looks like nothing is listening on that socket. Did you run any server listening there? Can you check:

netstat -na | grep /tmp/test.sock

answered Oct 23, 2015 at 14:35

Zbynek Vyskovsky - kvr000

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3 Comments

Jason Wong Over a year ago

Thanks for your reply. I did write a server to listen to the file above. I updated my question above with server codes, which is still using Netty. Thanks.

Zbynek Vyskovsky - kvr000 Over a year ago

Looks correct at the first sight. I assume input is equal to "/tmp/test.sock" . Can you check the output of the netstat I wrote earlier?

Jason Wong Over a year ago

Thanks Zbynek. I found out that it was a synchronisation problem making the client connect to the socket earlier than the server starts up. I used some latches to synchronise them and it works now. Thanks for your tips to verify the socket. Also, I need to change the ChannelInitializer to be with type of UnixChannel to make it works as it had ClassCastException upon client connection.

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