java - Netty4 可读字节太小

Question

使用 Netty4 解码时出现异常。消息长度只有640，但可读字节数不够。

 06-19 21:45:13.150 4192-4233/com.seewo.remote V/RemoteMassageDecoder: Decoder messageType == 1, messageLength: 640
 06-19 21:45:13.152 4192-4233/com.seewo.remote E/exceptionCaught: io.netty.handler.codec.DecoderException: java.lang.Exception: readableBytes is too small

1、首先在ChannelInitializer中添加解码器

private static final int MAX_FRAME_LENGTH = 1024 * 1024;
private static final int LENGTH_FIELD_LENGTH = 4;
private static final int LENGTH_FIELD_OFFSET = 1;
private static final int LENGTH_ADJUSTMENT = 2;
private static final int INITIAL_BYTES_TO_STRIP = 0;
channelPipeline.addLast("decoder", new RemoteMassageDecoder(MAX_FRAME_LENGTH,
                LENGTH_FIELD_LENGTH, LENGTH_FIELD_OFFSET, LENGTH_ADJUSTMENT, INITIAL_BYTES_TO_STRIP));
channelPipeline.addLast("encoder", new RemoteMessageEncoder());

2、第二步，解码来自服务器的字节

@Override
protected Object decode(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
    byte startCharacter = in.readByte();
    int messageLength = in.readInt();
    byte messageType = in.readByte();
    in.readByte();
    Log.v("RemoteMassageDecoder", "startCharacter == " + (startCharacter & 0xff));
    Log.v("RemoteMassageDecoder", "Decoder messageType == " + messageType + ", messageLength: " + messageLength);
    if (messageLength < 0) {
        throw new Exception("messageLength < 0");
    }
    if (messageLength == 0 || messageType == 0) {
        in.readByte();
        return null;
    }
    if (in.readableBytes() < messageLength) {
        throw new Exception("readableBytes is too small");
    }
    byte[] content = new byte[messageLength];
    in.readBytes(content);
    byte stopCharacter = in.readByte();
    if (startCharacter != START_CHARACTER || stopCharacter != STOP_CHARACTER) {
        return null;
    }
    return ProtocolPack.parseFrom(AESHelper.decryptContent(content));
}

Answer 1

这个问题的原因很简单:你不能期望 TCP 流总是同时返回足够的数据。

解决方案也很简单:您的 ChannelHandler 可以扩展 ReplyingDecoder，它可以帮助您正确处理底层流。