void OnReceive(byte[] data, int length)
{
    // 把收到的数据追加到缓存末尾
    Array.Copy(data, 0, cacheBuffer, cacheCount, length);
    cacheCount += length;

    // 循环处理缓存中的完整消息
    while (true)
    {
        // 不足4字节，说明长度头还没收全
        if (cacheCount < 4)
            break;

        // 取出前4字节的消息长度
        int msgLength = BitConverter.ToInt32(cacheBuffer, 0);

        // 检查是否收全整个消息
        if (cacheCount - 4 < msgLength)
            break;

        // 提取消息体
        byte[] msgBody = new byte[msgLength];
        Array.Copy(cacheBuffer, 4, msgBody, 0, msgLength);

        // ---- 处理消息 ----
        ProcessMessage(msgBody);

        // 将剩余数据前移
        int remain = cacheCount - 4 - msgLength;
        Array.Copy(cacheBuffer, 4 + msgLength, cacheBuffer, 0, remain);
        cacheCount = remain;
    }
}