Netty分布式行解码器逻辑源码解析

//数据包的最大长度, 超过该长度会进行丢弃模式
private final int maxLength;
//超出最大长度是否要抛出异常
private final boolean failFast;
//最终解析的数据包是否带有换行符
private final boolean stripDelimiter;
//为true说明当前解码过程为丢弃模式
private boolean discarding;
//丢弃了多少字节
private int discardedBytes;

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 {
    //找这行的结尾
    final int eol = findEndOfLine(buffer);
    if (!discarding) {
        if (eol >= 0) {
            final ByteBuf frame;
            //计算从换行符到可读字节之间的长度
            final int length = eol - buffer.readerIndex();
            //拿到分隔符长度, 如果是\r\n结尾, 分隔符长度为2
            final int delimLength = buffer.getByte(eol) == '\r'? 2 : 1;
            //如果长度大于最大长度
            if (length > maxLength) {
                //指向换行符之后的可读字节(这段数据完全丢弃)
                buffer.readerIndex(eol + delimLength);
                //传播异常事件
                fail(ctx, length);
                return null;
            }
            //如果这次解析的数据是有效的
            //分隔符是否算在完整数据包里
            //true为丢弃分隔符
            if (stripDelimiter) {
                //截取有效长度
                frame = buffer.readRetainedSlice(length);
                //跳过分隔符的字节
                buffer.skipBytes(delimLength);
            } else {
                //包含分隔符
                frame = buffer.readRetainedSlice(length + delimLength);
            }

            return frame;
        } else {
            //如果没找到分隔符(非丢弃模式)
            //可读字节长度
            final int length = buffer.readableBytes();
            //如果朝超过能解析的最大长度
            if (length > maxLength) {
                //将当前长度标记为可丢弃的
                discardedBytes = length;
                //直接将读指针移动到写指针
                buffer.readerIndex(buffer.writerIndex());
                //标记为丢弃模式
                discarding = true;
                //超过最大长度抛出异常
                if (failFast) {
                    fail(ctx, "over " + discardedBytes);
                }
            }
            //没有超过, 则直接返回
            return null;
        }
    } else {
        //丢弃模式
        if (eol >= 0) {
            //找到分隔符
            //当前丢弃的字节(前面已经丢弃的+现在丢弃的位置-写指针)
            final int length = discardedBytes + eol - buffer.readerIndex();
            //当前换行符长度为多少
            final int delimLength = buffer.getByte(eol) == '\r'? 2 : 1;
            //读指针直接移到换行符+换行符的长度
            buffer.readerIndex(eol + delimLength);
            //当前丢弃的字节为0
            discardedBytes = 0;
            //设置为未丢弃模式
            discarding = false;
            //丢弃完字节之后触发异常
            if (!failFast) {
                fail(ctx, length);
            }
        } else {
            //累计已丢弃的字节个数+当前可读的长度
            discardedBytes += buffer.readableBytes();
            //移动
            buffer.readerIndex(buffer.writerIndex());
        }
        return null;
    }
}

private static int findEndOfLine(final ByteBuf buffer) {
    //找到/n这个字节
    int i = buffer.forEachByte(ByteProcessor.FIND_LF);
    //如果找到了, 并且前面的字符是-r, 则指向/r字节
    if (i > 0 && buffer.getByte(i - 1) == '\r') {
        i--;
    }
    return i;
}

final ByteBuf frame; 
final int length = eol - buffer.readerIndex();
final int delimLength = buffer.getByte(eol) == '\r'? 2 : 1; 
if (length > maxLength) {
    buffer.readerIndex(eol + delimLength);
    fail(ctx, length);
    return null;
} 
if (stripDelimiter) { 
    frame = buffer.readRetainedSlice(length); 
    buffer.skipBytes(delimLength);
} else { 
    frame = buffer.readRetainedSlice(length + delimLength);
}
return frame;

final int length = buffer.readableBytes();
if (length > maxLength) { 
    discardedBytes = length; 
    buffer.readerIndex(buffer.writerIndex());
    discarding = true; 
    if (failFast) {
        fail(ctx, "over " + discardedBytes);
    }
} 
return null;

final int length = discardedBytes + eol - buffer.readerIndex();
final int delimLength = buffer.getByte(eol) == '\r'? 2 : 1;
buffer.readerIndex(eol + delimLength);
discardedBytes = 0;
discarding = false;
if (!failFast) {
    fail(ctx, length);
}

discardedBytes += buffer.readableBytes();
buffer.readerIndex(buffer.writerIndex());