Nett分布式分隔符解码器逻辑源码剖析

protected final void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
    Object decoded = decode(ctx, in);
    if (decoded != null) {
        out.add(decoded);
    }
}

protected Object decode(ChannelHandlerContext ctx, ByteBuf buffer) throws Exception {
    //行处理器(1)
    if (lineBasedDecoder != null) { 
        return lineBasedDecoder.decode(ctx, buffer);
    }
    int minFrameLength = Integer.MAX_VALUE;
    ByteBuf minDelim = null; 
    //找到最小长度的分隔符(2)
    for (ByteBuf delim: delimiters) {
        //每个分隔符分隔的数据包长度
        int frameLength = indexOf(buffer, delim);
        if (frameLength >= 0 && frameLength < minFrameLength) {
            minFrameLength = frameLength;
            minDelim = delim;
        }
    }
    //解码(3)
    //已经找到分隔符
    if (minDelim != null) {
        int minDelimLength = minDelim.capacity();
        ByteBuf frame;
        //当前分隔符否处于丢弃模式
        if (discardingTooLongFrame) { 
            //首先设置为非丢弃模式
            discardingTooLongFrame = false;
            //丢弃
            buffer.skipBytes(minFrameLength + minDelimLength);

            int tooLongFrameLength = this.tooLongFrameLength;
            this.tooLongFrameLength = 0;
            if (!failFast) {
                fail(tooLongFrameLength);
            }
            return null;
        }
        //处于非丢弃模式
        //当前找到的数据包, 大于允许的数据包
        if (minFrameLength > maxFrameLength) {
            //当前数据包+最小分隔符长度 全部丢弃
            buffer.skipBytes(minFrameLength + minDelimLength);
            //传递异常事件
            fail(minFrameLength);
            return null;
        }
        //如果是正常的长度
        //解析出来的数据包是否忽略分隔符
        if (stripDelimiter) {
            //如果不包含分隔符
            //截取
            frame = buffer.readRetainedSlice(minFrameLength);
            //跳过分隔符
            buffer.skipBytes(minDelimLength);
        } else {
            //截取包含分隔符的长度
            frame = buffer.readRetainedSlice(minFrameLength + minDelimLength);
        }
        return frame;
    } else {
        //如果没有找到分隔符
        //非丢弃模式
        if (!discardingTooLongFrame) {
            //可读字节大于允许的解析出来的长度
            if (buffer.readableBytes() > maxFrameLength) {
                //将这个长度记录下
                tooLongFrameLength = buffer.readableBytes();
                //跳过这段长度
                buffer.skipBytes(buffer.readableBytes());
                //标记当前处于丢弃状态
                discardingTooLongFrame = true;
                if (failFast) {
                    fail(tooLongFrameLength);
                }
            }
        } else {
            tooLongFrameLength += buffer.readableBytes();
            buffer.skipBytes(buffer.readableBytes());
        }
        return null;
    }
}

public DelimiterBasedFrameDecoder(
        int maxFrameLength, boolean stripDelimiter, boolean failFast, ByteBuf... delimiters) {
    //代码省略
    //如果是基于行的分隔
    if (isLineBased(delimiters) && !isSubclass()) {
        //初始化行处理器
        lineBasedDecoder = new LineBasedFrameDecoder(maxFrameLength, stripDelimiter, failFast);
        this.delimiters = null;
    } else {
        //代码省略
    }
    //代码省略
}

private static boolean isLineBased(final ByteBuf[] delimiters) {
    //分隔符长度不为2
    if (delimiters.length != 2) {
        return false;
    }
    //拿到第一个分隔符
    ByteBuf a = delimiters[0];
    //拿到第二个分隔符
    ByteBuf b = delimiters[1];
    if (a.capacity() < b.capacity()) {
        a = delimiters[1];
        b = delimiters[0];
    }
    //确保a是/r/n分隔符, 确保b是/n分隔符
    return a.capacity() == 2 && b.capacity() == 1
            && a.getByte(0) == '\r' && a.getByte(1) == '\n'
            && b.getByte(0) == '\n';
}

for (ByteBuf delim: delimiters) {
    //每个分隔符分隔的数据包长度
    int frameLength = indexOf(buffer, delim);
    if (frameLength >= 0 && frameLength < minFrameLength) {
        minFrameLength = frameLength;
        minDelim = delim;
    }
}

int minDelimLength = minDelim.capacity();
ByteBuf frame; 
if (discardingTooLongFrame) { 
    discardingTooLongFrame = false; 
    buffer.skipBytes(minFrameLength + minDelimLength); 
    int tooLongFrameLength = this.tooLongFrameLength;
    this.tooLongFrameLength = 0;
    if (!failFast) {
        fail(tooLongFrameLength);
    }
    return null;
} 
if (minFrameLength > maxFrameLength) { 
    buffer.skipBytes(minFrameLength + minDelimLength); 
    fail(minFrameLength);
    return null;
} 
if (stripDelimiter) { 
    frame = buffer.readRetainedSlice(minFrameLength); 
    buffer.skipBytes(minDelimLength);
} else { 
    frame = buffer.readRetainedSlice(minFrameLength + minDelimLength);
}
return frame;

if (!discardingTooLongFrame) { 
    if (buffer.readableBytes() > maxFrameLength) { 
        tooLongFrameLength = buffer.readableBytes();
        buffer.skipBytes(buffer.readableBytes());
        discardingTooLongFrame = true;
        if (failFast) {
            fail(tooLongFrameLength);
        }
    }
} else {
    tooLongFrameLength += buffer.readableBytes();
    buffer.skipBytes(buffer.readableBytes());
}
return null;