Help!!!1.19.4 About the issue of channel packet string

Please Help!!!!

public static void encode(MessageFromClient msg, FriendlyByteBuf buf) {
//        buf.writeString(msg.message);
        LOGGER.info("here:"+msg.message);
        buf.writeUtf(msg.message);
//        try {
//            buf.writeBytes(msg.message.getBytes("utf-8"));
//        } catch (UnsupportedEncodingException e) {
//            e.printStackTrace();
//        }
    }

I use this method to send string data to the server,this is correct for client side printing

{"id":"Manager","formPlug":"Manager","toPlug":"Trmenu","type":3,"playerName":"mohuangNPC","uuid":"85bfd415-4262-352e-ab70-e0f08c077db1","msg":"trmenu open Main"}

But what the server receives is:

SOH{"id":"Manager","formPlug":"Manager","toPlug":"Trmenu","type":3,"playerName":"mohuangNPC","uuid":"85bfd415-4262-352e-ab70-e0f08c077db1","msg":"trmenu open Main"

The prefix is SOH,I searched for information and found that it belongs to ascii,and the symbol is missing at the end "}"

This is the server receiving code:

 public void onPluginMessageReceived(String channel, Player player, byte[] message) {
        ByteArrayDataInput in = ByteStreams.newDataInput(message);
        String subchannel = in.readUTF();
        Logger.debug(subchannel);
        String[] split = subchannel.split("\001", -1);
        if(split.length == 2){
            subchannel = split[1];
        }else{
            subchannel = split[0];
        }
        String[] split1 = subchannel.split("\u0001", -1);
        if(split1.length == 2){
            subchannel = split1[1];
        }else{
            subchannel = split1[0];
        }
        Logger.debug(subchannel);
        subchannel = subchannel + "}";
        Logger.debug(subchannel);
}

I now manually remove the prefix and add the suffix,but I want to know what is the reason for this!

If anyone knows please help me, I would be very grateful.