使用MessageToByteEncoder作为最后一个出站处理程序不会返回任何内容

Question

I have a pipeline as follows:

Preprocessor -> Decoder -> Encoder -> Processor

Preprocessor , Decoder and Processor are all ChannelInboundHandlerAdapter . Encoder is a MessageToByteEncoder<CommandResponse> .

When my request (sent as UDP datagram) is received by the pipeline, it is parsed as String by the Preprocessor , and the String is passed to the Decoder . The Decoder parses the String to create a Command object, and passes the resulting object to the Processor . The Processor processes the Command and generates a CommandResponse object which is passed to the Encoder by calling ctx.writeAndFlush(commandResponse); . The Encoder encodes the command to a byte array and then to a ByteBuf as follows:

@Override
protected void encode(ChannelHandlerContext ctx, CommandResponse msg, ByteBuf out) throws Exception {
    //Encode the response
    String responseString;
    .....

    //Convert resulting string to bytes using specified charset
    byte[] bytes = responseString.getBytes(charset);

    //Send bytes
    out.writeBytes(bytes);
}

However, nothing is received on the sending side.

I precise I use an NioDatagramChannel for the channel and Netty version 4.0.x.

Thanks, Mickael

Answer 1

I guess the ChannelFuture which was returned by the write call was failed. Check this. Also as you use a NioDatagramChannel you most likely want to convert from CommandResponse to a DatagramPacket. Use a MessageToMessageEncoder for that.