netty ByteToMessageDecoder 分析

    ByteToMessageDecoder

        1.socket 移除时触发,最后次读数据处理

        

            @Override

        public final void handlerRemoved(ChannelHandlerContext ctx) throws Exception {

            ByteBuf buf = internalBuffer();

             if (buf.isReadable()) {

                ByteBuf bytes = buf.readBytes(buf.readableBytes());

                buf.release();

                ctx.fireChannelRead(bytes);

            }

            cumulation = null;

            ctx.fireChannelReadComplete();

            handlerRemoved0(ctx);

        }

        

        2.读取数据 ByteBuf release,discardSomeReadBytes 方法后面研究

        

         public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {

            RecyclableArrayList out = RecyclableArrayList.newInstance();//创建包装过的数组

            try {

                if (msg instanceof ByteBuf) {

                    ByteBuf data = (ByteBuf) msg;

                    if (cumulation == null) { //是否继续读取数据

                        cumulation = data;

                        try {

                            callDecode(ctx, cumulation, out);

                        } finally {

                            if (cumulation != null && !cumulation.isReadable()) {

                                cumulation.release();

                                cumulation = null;

                            }

                        }

                    } else {//继续读取处理

                        try {

                            //如果剩余空间不够开创建新空间

                            if (cumulation.writerIndex() > cumulation.maxCapacity() - data.readableBytes()) {

                                ByteBuf oldCumulation = cumulation;

                                cumulation = ctx.alloc().buffer(oldCumulation.readableBytes() + data.readableBytes());

                                cumulation.writeBytes(oldCumulation);

                                oldCumulation.release();

                            }

                            cumulation.writeBytes(data);

                            callDecode(ctx, cumulation, out);

                        } finally {

                            if (cumulation != null) {

                                if (!cumulation.isReadable()) {

                                    cumulation.release();

                                    cumulation = null;

                                } else {

                                    cumulation.discardSomeReadBytes();

                                }

                            }

                            data.release();

                        }

                    }

                } else {

                    out.add(msg);

                }

            } catch (DecoderException e) {

                throw e;

            } catch (Throwable t) {

                throw new DecoderException(t);

            } finally {

                int size = out.size();

                if (size == 0) {

                    decodeWasNull = true;

                } else {

                    for (int i = 0; i < size; i ++) {

                        ctx.fireChannelRead(out.get(i));

                    }

                }

                out.recycle();

            }

        }

        

        //其实只要管核心代码 decode 调用业务处理

         protected void callDecode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) {

            try {

                //循环读取数据

                while (in.isReadable()) {

                    int outSize = out.size();

                    int oldInputLength = in.readableBytes();

                    decode(ctx, in, out);//业务扩展处理



                    // Check if this handler was removed before continuing the loop.

                    // If it was removed, it is not safe to continue to operate on the buffer.

                    //

                    // See https://github.com/netty/netty/issues/1664

                    //如果 handler 删除之前，那么不读取数据了

                    if (ctx.isRemoved()) {

                        break;

                    }

                    //下面写得很不清晰。。。。。

                    

                    if (outSize == out.size()) {

                        if (oldInputLength == in.readableBytes()) {

                            break;

                        } else {

                            continue;

                        }

                    }



                    if (oldInputLength == in.readableBytes()) {

                        throw new DecoderException(

                                StringUtil.simpleClassName(getClass()) +

                                ".decode() did not read anything but decoded a message.");

                    }



                    if (isSingleDecode()) {

                        break;

                    }

                }

            } catch (DecoderException e) {

                throw e;

            } catch (Throwable cause) {

                throw new DecoderException(cause);

            }

        }