Translating a Qt application, can be a daunting task. This is an overview from Qt 5 to Qt 6 and what new functionality Qt 6.7 brings.

Continue reading Translating Qt Applications at basysKom GmbH.

After having participated to both Qt Contributor Summit and Akademy, I ended up going to a few more conferences in September.

Nextcloud Conference

I went to Nextcloud Conference just after going back from Akademy. Unfortunately I was quite tired from Akademy and Qt Contributor Summit and I only stayed Saturday morning. Still it was great to meet some old colleagues there.

Matrix Conference

The Matrix Conference happened the weekend after the Nextcloud conference. This was the first Matrix Conference and a gathering of all types of actors involved in Matrix. From the grassroots community to companies deploying Matrix based solutions to their customers. The NeoChat team was there and we were super productive into bringing back the Android version, thanks to the help of Volker Krause. This resulted in many patches in NeoChat itself but also one patch in Kirigami.

Special mention to the food and coffee offered at the conference, which was always excellent and either vegan or vegetarian. Outside of the venue, food was also execellent with a lot of middle eastern food choice.

Here some photos of the event and the food:

Linux Days Dornbirn

It was my second time going to the Linux Days in Dornbirn and while the weather wasn’t as welcoming as last time, the local Linux community was again super welcoming!

During the event, I did a talk in German about Plasma 6. This was my first time doing a talk in German and I hope I did okay. I also hosted a KDE stand with Simon Österle, who offered his help with the stand. His help has been invaluable to me, so huge thanks to him.

Like last year, after the conference, all helpers, presenters and stand holders went to a local restaurent to enjoy Käsespätzle. It was again delicious.

Here some photos of the event and the food:

This release focuses on SiteSettings feature, so I will try to introduce it here.

Site Settings

This feature tries to enable per site configuration / settings of multiple options per website host / domain. It consist of having global / default options and site / local settings.

List of supported configuration options

• Cookies
• HTML5 permissions
  • Notifications
  • Geolocation
  • Microphone
  • Camera
  • Microphone and Camera
  • Hide mouse pointer
  • Screen capture
  • Screen capture with audio
• QtWebEngine permissions
  • Autoload Images
  • Enable Javascript
  • Javascript: Open popup windows
  • Javascript: Access clipboard
  • Javascript: Paste from clipboard
  • JavaScript: Activate windows
  • Local Storage
  • FullScreen support
  • Run insecure content
  • Automatic playing of videos
  • Allow reading from canvas (Needs to be enabled to pass CloudFlare) (Qt 6.6+)
  • Force dark mode (Qt 6.7+)

Previews

These options can be changed for the given site in the “Site Info” dialog.

The default options for HTML5 can be changed in “Preferences > Privacy”

The default QtWebEngine / site options can be changed in the Browsing tab or in place where they where configured until now.

In the preferences it is only possible to change existing modified permissions for given sites. At the moment it is not possible to manually add sites to the list, this can only be done from within “Site Info” dialog.

Missing feature

These features will be done at a later unspecified date.

• QML support
• Zoom level per domain

Short ChangeLog

• Add site permissions
• Enable WebInspector with disabled JavaScript (BUG: 462887)
• Random fixes

The Amarok Development Squad is happy to announce the immediate availability of Amarok 3.1.1, the first bugfix release for Amarok 3.1 "Tricks of the Light"!

3.1.1 features a number of small improvements and bug fixes, including miscellaneous fixes for toolbars and the return of tag dialog autocompletions, a functionality that initially got lost during the Qt5/KF5 port. However, most of the work has again happened under the hood to improve the codebase's Qt6/KF6 compatibility. For the 3.2 version coming up later this year, the KDE frameworks dependency will be raised to 5.108. This should allow replacing the remaining deprecated KF5 functionalities; one of the final barriers preventing Qt6/KF6 based builds from succeeding.

Changes since 3.1.0

CHANGES:

• Most of the context view QML items ported from QtControls 1 to QtControls 2
• Default to no fadeout on pause and stop (BR 491603)

BUGFIXES:

• Actually show the file browser panel toolbar
• Fix track editor autocompletions (BR 491520)
• Ensure home icon is shown in browser breadcrumb widgets (BR 491354)

Getting Amarok

In addition to source code, Amarok is available for installation from many distributions' package repositories, which are likely to get updated to 3.1.1 soon, as well as the flatpak available on flathub.

Packager section

You can find the tarball package on download.kde.org and it has been signed with Tuomas Nurmi's GPG key.

Three weeks ago, I attended KDE Akademy 2024 in Würzburg, Germany. It was pretty exciting to meet my KDE friends after one year since last Akademy 2023!

Travel drama

Ideally whole trip should’ve taken just ~18 hours door-to-door but thanks to Lufthansa whole travel turned out to be of 48 hours in total including layovers. Flight cancellation and rebooking caused by travel to start way earlier than planned (Thursday 5:00 AM instead of planned 07:00 PM) and had to spend insane amount of time in layover.

This year Akademy was in Würzburg (shock! horror!). I think its not too far fetched to say that we pulled it successfully.

How it came to be

During last years Akademy in Thessaloniki the idea came up given the high density of KDE people in the area to hold Akademy in Würzburg. On top we had the perfect venue in mind: two lecture halls for talks, BoF rooms and a ample common area for people to hack and socialize. I had such thoughts in the back of my mind for a while but did not share or go through with them.

However what Akademy does is it makes you talk to people and Tobias convinced it me that we should do it and more people even agreed that Akademy in Würzburg would be a good idea! (Of course some of these encouragers this does not mean work organizing Akademy like it would mean for us…) So on the second-to-last day of Akademy I sat down and wrote an email to my former university professor to enquire about the possibility of doing Akademy in the building that we envisioned.

And just like that, after some informal talks during Akademy and a meeting at the University and sending in a proposal after the Call for Hosts later you end up having weekly meetings to talk about and plan the next installment of Akademy.

How it did go

There were some problems but I think all in all this year Akademy went very well. I heard so much praise and positive feedback it felt a bit surreal at first (as did Sunday evening when all the talks were done). The most stressful situation for me happened on Sunday afternoon when I retrieved my charging phone from the team room to discover that the social event could not go ahead as planned and trying to manage that with the rest of the team. I think the resulting evening was very nice and chill and you could feel my relieve. I heard there was even an afterparty afterwards at the bar where we had held the welcome event.

Of course during the event there are always minor issues that need dealing with and looking out for those, dealing with them and trying to make sure everything is running smoothly (and the stress coming these things) meant that I couldn’t (and was not in the right state of mind) to focus much on the talks. When the BoF days started this was bit better but only on Thursday after the day trip I felt in a ‘conference mood’ and was able to focus fully on the BoFs that I was attending and sit down and hack a bit. If you want to learn more about the actual conference many people have blogged about it on the planet or read the report on the Akademy website.

In the end I think it’s fair to say that Akademy was a success. Made possible by KDE e.V. (go donate!), the sponsors, all the people of the Akademy team local and non-local, all the Volunteers on short and on long notice an last but not least all the awesome attendees - there would be no Akademy without any people. Thank you to you all! I am excited to learn about where next years Akademy will be (you can do it as well - it’s not hard and you get an awesome award on top) and looking forward to attending it as ‘normal Attendee’ and meeting everyone again there (if not earlier).

Future 聊天室

功能

账号管理

• 实现登录、注册、注销
• 实现找回密码（提高）

好友管理

• 实现好友的添加、删除、查询操作
• 实现显示好友在线状态
• 禁止不存在好友关系的用户间的私聊
• 实现屏蔽好友消息
• 实现好友间聊天

群管理

• 实现群组的创建、解散
• 实现用户申请加入群组
• 实现用户查看已加入的群组
• 实现群组成员退出已加入的群组
• 实现群组成员查看群组成员列表
• 实现群主对群组管理员的添加和删除
• 实现群组管理员批准用户加入群组
• 实现群组管理员/群主从群组中移除用户
• 实现群组内聊天功能

聊天功能

• 实现查看历史消息记录
• 实现用户间在线聊天
• 实现在线用户对离线用户发送消息，离线用户上线后获得通知
• 实现在线发送文件
• 实现在线用户对离线用户发送文件，离线用户上线后获得通知/接收
• 实现后台发送文件
• 实现用户在线时,消息的实时通知
  • 收到好友请求
  • 收到私聊
  • 收到加群申请

其他

• 使用 C++编程语言
• 使用 I/O 多路复用完成本项目
  • C++：Epoll ET 模式
• 使用数据库完成数据存储
  • Redis 和 mysql
  • 历史消息采用redis做告诉缓存，mysql来存储大量历史消息
• 数据库中数据的存储和取用使用序列化和反序列化完成(Json)
• 支持大量客户端同时访问
• 实现服务器日志，记录服务器的状态信息
• C/S 双端均支持在 CLI/Web 自行指定 IP:Port
• 实现具有高稳定性的客户端和服务器，防止在用户非法输入时崩溃或异常
  • 实现 TCP 心跳检测

遇到的问题

• 在客户端因某些原因异常退出时，服务端将无法正常处理其他请求.

  • 开始时服务端没有将新连接的描述符设置为非阻塞模式，导致客户端异常退出时服务端的接收recv一直在阻塞着读取，且无法处理其他请求

• 如何往线程池中传入类的成员函数.

  • auto task = [](){     类的成员函数 } m_pool.submit(task);
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    
    * `Tcp`传输为字节流传输，采用在每条消息前面加上`长度`来正确接收每条请求.
    * 在代码中往`redis`数据库中添加好友申请数据时，没有正确插入.
      * 由于好友申请当中包含时间，姓名等信息，中间含有**空格**，在redis的哈希表中无法插入.
      * 经过查阅在redis哈希表中，**空格**可以用`+`代替，在遇到`+`时会被转义为**空格**，或者存储为**十六进制**，但是这种方法在终端中的**空格**为灰色.
    
    * 在聊天界面如果输入带有`%`，服务器直接挂掉.
    
      * ```c++
        int redisAsyncContext::Lpush(const std::string &key, const std::string &value)
        {
            //std::string cmd = "lpush " + key + " " + value;
            this->m_reply = (redisReply *)redisCommand(this->m_connettion, "LPUSH %s %s", key.c_str(), value.c_str());
             // 检查 m_reply 是否为 NULL
            if (this->m_reply == NULL) {
                std::cerr << "Error: redisCommand returned NULL" << std::endl;
                return -1; // 或其他合适的错误值
            }
        
            // 检查 m_reply 类型
            if (this->m_reply->type != REDIS_REPLY_INTEGER) {
                std::cerr << "Error: Expected integer reply" << std::endl;
                freeReplyObject(this->m_reply);
                return -1; // 或其他合适的错误值
            }
            int num  = this->m_reply->integer;
            freeReplyObject(this->m_reply);
            std::cout << "G" << std::endl;
            return num;
        }
    

  • 在执行下面两句是，%会被替换为cmd.c_str(),导致无法将消息插入历史记录表，导致出现错误.

    1 2	std::string cmd = "lpush " + key + " " + value; this->m_reply = (redisReply *)redisCommand(this->m_connettion, cmd.c_str());

  • 只要更改为下面即没有问题

    1	this->m_reply = (redisReply *)redisCommand(this->m_connettion, "LPUSH %s %s", key.c_str(), value.c_str());

• 在某次测试时，新注册账号id为0614897828,导致与该账号聊天的账号进入聊天界面时，0614897828发送的消息会在他人界面显示为通知消息.

  • 由于与人聊天时会在数据库中创建有排序集合来记录某人正在聊天的人的id.运行时通过查看发现，其余账号与0614897828聊天时，数据库中记录账号为614897828.
  • 更换为首位非0的id就不会出现该问题.
  • redis会将有序集合中的score字段字符串中的0去除.将从字符串的首位非0开始存储.

• 在进入好友私聊界面时，客户端新建了来接收消息，同时主线程发消息，主线程通过判断用户是否键入Esc来退出聊天界面，在输入Esc时，接收消息线程无法正确回收，无法退出聊天界面.

  • 在接收消息线程中来判断标志位来结束该线程，主线程在键入Esc时，将标志位设置为false,但由于客户端的recv为阻塞，导致无法及时获取到标志位的更改.
  • 在键入Esc时，服务器向客户端发送退出信号，这样就可以正确及时的获取到标志位的更改，从而正确退出.

• 在进行发送文件时，服务器会先将文件存储在本地，但是服务器存储的文件会多写入一些信息，导致接收文件大小偏大.

  • 由于在用户登陆进入之后，会有一个线程每5秒向服务器送送刷新请求，导致服务器会将刷新请求当作文件内容写入文件，导致接收文件不一致
  • 在进入文件收发菜单后，关闭实时刷新，在文件结束后，再将实时刷新打开.

• 实现后台发送文件，由于会有实时刷新的存在，会导致文件发送不准确.

  • 在发送文件时，重新创建一个socket连接到服务器，在将发送这个文件交给另外一个线程
  • 初始时在用户选择发送文件时开始线程，但会导致主线程与发送线程会同时运行菜单.主线程继续循环菜单，而发送线程运行获取发送文件的信息。
    • 更改线程开始时间，在用户选择发送文件时，获取到发送文件信息后，在启动线程.
    • 新连接的socket发送文件后，服务器不用手动断开连接，服务器有心跳检测，会在一段时间后断开.

eventfd

详解

是一个Linux系统调用，也是一种进程间通信(IPC)机制，主要通过使用文件描述符生成和使用事件通知.

提供了一种在不同进程之间或同一进程内的线程之间的同步事件的方法.

异常处理

异常是程序在执行期间产生的问题。c++异常是指在程序运行时发生的特殊情况.

异常提供了一种转移程序控制权的方式。C++ 异常处理涉及到三个关键字：try、catch、throw

关键字：try、catch、throw。

• throw: 当问题出现时，程序会抛出一个异常。这是通过使用 throw 关键字来完成的。

• catch: 在您想要处理问题的地方，通过异常处理程序捕获异常。catch 关键字用于捕获异常

• try: try 块中的代码标识将被激活的特定异常。它后面通常跟着一个或多个 catch 块

1
2
3
4
5
6
7
8
9
10
11
12
13

try
{
   // 保护代码
}catch( ExceptionName e1 )
{
   // catch 块
}catch( ExceptionName e2 )
{
   // catch 块
}catch( ExceptionName eN )
{
   // catch 块
}

nlohmann::json

链接

SIGPIPE

SIGPIPE 是一种信号，当一个进程尝试向一个已经关闭的或不可写的管道或套接字写数据时，会触发这个信号。默认情况下，接收到 SIGPIPE 信号的进程会终止。这在网络编程中会导致一些问题，因为如果客户端断开连接，服务器进程在写入数据时会因为这个信号而意外退出。

在网络编程中，特别是使用套接字进行通信时，忽略 SIGPIPE 信号是一个常见的做法。这样可以防止进程因为 SIGPIPE 信号而意外终止。相反，程序可以通过检测 send 或 write 操作的返回值来处理错误，从而使程序更加健壮。

后续问题

1. 初始客户端构思方面的缺陷，导致实时消息没有线程及时接收。

   当前处理方式为服务端将通知消息放入数据库当中，客户端在登陆之后，增加一个线程来定时执行刷新函数，刷新数据库中的通知消息

   可以优化为在客户端登陆之后，采用多线程的方式来处理相关操作.

2. 目前只有在历史消息这一操作涉及到redis+mysql的处理方式.

   可以将一些重要信息也采用redis+mysql的处理方式(涉及到redis的存储方式，redis存储于内存当中，会造成数据丢失的情况)

   可以考虑将redis全部做为缓存的形式，将重要信息与历史消息类似，达到一定情况下放入mysql,使数据更加的持久化.

后续学习

1. 继续学习epoll的相关内容.

2. 了解其余网络框架，使得该项目的服务端更加的健壮.

3. 了解消息队列的信息同步的问题.

4. 熟悉零拷贝的过程，以及零拷贝的具体实现.

5. 序列化的相关协议，json与其他序列化的区别、json的优点，以及为什么不用其他的序列化

6. 数据库的深入学习，了解redis的缓存穿透、缓存雪崩、缓存击穿。加强对mysql数据库的学习.

7. 加强对网络协议相关知识的学习.

强制类型转换

C++提供了四个强制类型转换的关键字：

• static_cast
• const_cast
• reinterpret_cast
• ``dynamic_cast`

static_cast

1

static_cast<目标类型>(表达式)

1
2

int num = 2;
double result =static_cast<double>(num);

该运算符将表达式转换为目标类型。但没有进行运行时类型检查来保证转换的安全性。

主要用法

1. 用于类层次结构中父类和子类之间指针或引用的转换.进行上行转换是安全的（即将子类的指针或引用转换成父类是正确的）；进行下行转换的时候，由于没有动态类型检查，所以是不安全的。继承必须为public
2. 用于基本类型之间的转换，如int与char，安全性也需要程序员来保证
3. 把空指针转换为目标类型的空指针

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

class Person
{
public:
    void  print()
    {
        cout << "Person " << endl;
    }
};

class Son : public Person
{
public:
    void print()
    {
        cout << "Son " << endl;
    }
};

void print1(Person *p)
{
    p->print();
}

int main()
{
    Son s;
    print1(static_cast<Person *>(&s));
    return 0;
}

const_cast

const_cast是c++中专用于处理与const相关的强制类型转换的关键字

其功能为：为一个变量重新设定其const描述.

即：const_cast可以为一个变量强行增加或删除其const限定.

需要明确的是，即使用户通过const_cast强行去除了const属性，也不代表当前变量从不可变变为了可变。const_cast只是使得用户接管了编译器对于const限定的管理权，故用户必须遵守“不修改变量”的承诺。如果违反此承诺，编译器也不会因此而引发编译时错误，但可能引发运行时错误。

1. const_cast可用于更改const成员函数内的非const类成员。
2. const_cast可用于将const数据传递给不接收const的函数。
3. const_cast<>里边的内容必须是引用或者指针。
4. const_cast也可以用来抛弃volatile和__unaligned属性。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

class Student
{
private:
int roll;
public:
Student(int r) :roll(r) {}
void fun() const
{
(const_cast<Student*> (this))->roll = 5;
}
int getRoll() { return roll; }
};

int main() {
    Student student(3);
    std::cout << "Old roll number: " << student.getRoll() << std::endl;
    student.fun();
    std::cout << "New roll number: " << student.getRoll() << std::endl;

    // const_cast只能调节类型限定符，不能更改基础类型
    int a1 = 40;
    //const int* b1 = &a1;
    //char* c1 = const_cast <char*> (b1); // 编译程序时出错

    const volatile int* d1 = &a1;
    std::cout << "typeid of d1 " << typeid(d1).name() << '\n'; // int const volatile *
    int* e1 = const_cast <int*> (d1);
    std::cout << "typeid of e1 " << typeid(e1).name() << '\n'; // int *
    
    return 0;
}

在const成员函数fun()中，编译器将“this”视为“ const student const this”，即“this”是指向常量对象的常量指针，因此编译器不允许通过以下方式更改数据成员“这个”指针。const_cast将“this”指针的类型更改为“student const this”。

const_cast比简单类型转换更安全。从某种意义上讲，如果强制类型与原始对象不相同，则强制转换不会发生，这是比较安全的。

1
2
3

int a=20;
const int *p=&a;
char *c1=const_cast<char*> (p);//编译时程序出错

reinterpret_cast

reinterpret,即重新解释.

该强制类型转换的作用是提供某个变量在底层数据上的重新解释.

当我们对一个变量使用reinterpret_cast后，编译器将无视任何不合理行为，强行将被转换变量的内存数据重解释为某个新的类型。用于进行各种不同类型的指针之间、不同类型的引用之间以及指针和能容纳指针的整数类型之间的转换。转换时，执行的是逐个比特复制的操作。 它不检查指针类型和指针所指向的数据是否相同。

需要注意的是，reinterpret_cast要求转换的两个数据所占用的内存大小一致，否则会引发编译时错误.

1

data_type *var_name = reinterpret_cast <data_type *>(pointer_variable);

使用 reinterpret_cast 的目的：

1. reinterpret_cast是一种非常特殊且危险的类型转换操作符。并且建议使用适当的数据类型使用它，即（指针数据类型应与原始数据类型相同）。
2. 它可以将任何指针类型转换为任何其他数据类型。
3. 当我们要使用位时使用它。
4. 它仅用于将任何指针转换为原始类型。
5. 布尔值将转换为整数值，即0表示false，1表示true。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

class A {
public:
    int a;
    A(int i) :a(i) {}
    void fun_a()
    {
        std::cout << "In class A\n";
    }
};

class B {
public:
    int b;
    B(int i) :b(i) {}
    void fun_b()
    {
        std::cout << "In class B\n";
    }
};

void testReinterpretCast() {
    B *x = new B(5);
    A* y = reinterpret_cast<A*>(x);
    y->fun_a();                      // In class A
    std::cout << y->a << std::endl;  // 5
}

dynamic_cast

dynamic用于在运行时实现向下类型转换。

1

dynamic_cast <type-id> (expression)

将expression转换为type-id类型,type-id必须是类的指针，类的引用或者是void,

如果type-id是一个指针，那么expression也是一个指针，是引用的话同为引用

特点如下：

1. 它是在运行是进行处理的，其余三个都是在编译时完成. 运行时进行类型检查
2. 不能用于内置的基本数据类型之间的强制转换
3. dynamic_cast 要求 <> 内所描述的目标类型必须为指针或引用。dynamic_cast 转换如果成功的话返回的是指向类的指针或引用，转换失败的话则会返回 nullptr。
4. 在类的转换时，在类层次上进行向上转换（子类指针指向父类指针），与static_cast的效果是一样的。在进行父类指针向子类指针的转换时，dynamic_cast具有类型检查的功能，比static_cast更安全。
5. 向下转换的成功与否还与将要转换的类型有关，即要转换的指针指向的对象的实际类型与转换以后的对象类型一定要相同，否则转换失败。在C++中，编译期的类型转换有可能会在运行时出现错误，特别是涉及到类对象的指针或引用操作时，更容易产生错误。dynamic_cast操作符则可以在运行期对可能产生问题的类型转换进行测试。
6. 使用 dynamic_cast 进行转换的，基类中一定要有虚函数，否则编译不通过（类中存在虚函数，就说明它有想要让基类指针或引用指向派生类对象的情况，此时转换才有意义）。这是由于运行时类型检查需要运行时类型信息，而这个信息存储在类的虚函数表中，只有定义了虚函数的类才有虚函数表。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53

class AA {
public:
    virtual void print() {
        cout << "in class AA" << endl;
    };
};

class BB :public AA {
public:
    void print() {
        cout << "in class BB" << endl;
    };
};

void testDynamicCast() {
    AA* a1 = new BB; // a1是A类型的指针指向一个B类型的对象
    AA* a2 = new AA; // a2是A类型的指针指向一个A类型的对象

    BB* b1, * b2, * b3, * b4;

    b1 = dynamic_cast<BB*>(a1);// not null，向下转换成功，a1 之前指向的就是 B 类型的对象，所以可以转换成 B 类型的指针。
    if (b1 == nullptr) 
        cout << "b1 is null" << endl;
    else               
        cout << "b1 is not null" << endl;

    b2 = dynamic_cast<BB*>(a2);// null，向下转换失败
    if (b2 == nullptr) 
        cout << "b2 is null" << endl;
    else               
        cout << "b2 is not null" << endl;

    // 用 static_cast，Resharper C++ 会提示修改为 dynamic_cast
    b3 = static_cast<BB*>(a1);// not null
    if (b3 == nullptr) 
        cout << "b3 is null" << endl;
    else               
        cout << "b3 is not null" << endl;

    b4 = static_cast<BB*>(a2);// not null
    if (b4 == nullptr) 
        cout << "b4 is null" << endl;
    else               
        cout << "b4 is not null" << endl;

    a1->print();// in class BB
    a2->print();// in class AA

    b1->print();// in class BB
    //b2->print();    // null 引发异常
    b3->print();// in class BB
    b4->print();// in class AA
}

详细