Category: Code

CMake Multi-Project Template With Library, App, Tests

Robert LohrLeave a comment

CMake is a powerful tool but can also be very complicated and daunting when starting out. Much of my C++ career took place in Microsoft’s Visual Studio on Windows, so I am mainly used to the IDE maintaining the build system and relying on a graphical interface to configure dependencies. I started my WorkTracker utility this way – Visual Studio in combination with the Qt plugin.

Eventually, I migrated to Qt’s build system, qmake, and after that, to CMake. This is how I managed to build WorkTracker on macOS. If I am honest, though, I took a minimalist approach and learned only as much as was necessary to get it working. I like building an application, not knowing about build tools.

As a result, the resulting build script was mostly a hodgepodge of somewhat modern and outdated CMake. My lack of more profound knowledge – which I still do not claim to have – and the convoluted CMakeLists file of WorkTracker somehow presented a mental obstacle for me to start improving it or build other C++ tools.

To remedy this situation, I started looking at the bare minimum modern CMake. I set up a template repository containing a library, an application based on that library, and a Googletest-based testing application. This should provide a good starting point for new projects and give me enough knowledge to slowly start dissecting parts out of WorkTracker and create one or more libraries from it.

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Connect Spring Cloud Stream With Kafka Binder to Azure Event Hub

Robert Lohr2 Comments

In two previous blog posts, I explained how to create a Kafka consumer and producer with the Spring Cloud Stream framework. In the Famous Last Words section of the producer, I already hinted at the notion of utilizing this technology for connecting to Azure Event Hub. While doing so, I discovered an error in one of Microsoft’s examples that has cost me about two days of work. I show you how to avoid the dreaded “Node -1 disconnected” error.

In this tutorial, I explain how to use the exact same code to connect to Azure Event Hub using a Shared Access Signature Token (connection string) and a Service Principal.

I have good news and bad news. Which one first? The bad? Okay, here we go:

There will not be any code in this tutorial, only YAML configuration.

Now to the good part:

There will not be any code in this tutorial, only YAML configuration.

This is the beauty of Spring Cloud Stream. Granted, I am not even swapping the binder for an Azure-native variant. So why would there be any code changes? But let me say this: I briefly plugged in the Event Hub Binder without changing the code in my research on getting this to work. Even the updates to the config were minimal. A few Event Hub-specific settings, especially the Storage Account for checkpoints, and that was it.

Enough foreplay; let me explain what you likely came here for.

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Produce Messages With Spring Cloud Stream Kafka

Robert Lohr2 Comments

Update:

In a recent post, I explained how to create a Kafka Consumer application with Spring Boot using Spring Cloud Stream with the Kafka Binder. In this installment, I explain how to build the other side of the Kafka connection: the producer.

The main concepts are the same. The most significant change is that instead of a Consumer<T>, you implement a Supplier<T>.

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Package Qt6 macOS App Bundle With Translation Files In CMake

Robert LohrLeave a comment

Recently, I wrote about how you can create a macOS app bundle with CMake for a Qt6 application. I omitted the inclusion of translation files, which also required code changes. Well, I figured it out and will briefly explain what I had to do.

In my WorkTracker application, I store the language files in a folder called “l10n” at the project’s root. The first thing to do is instruct CMake to copy the *.qm files to the app bundle’s “Resource” folder. I have done that before for the app icon, and the process is similar for this kind of file.

set(l10n_files
    "${CMAKE_SOURCE_DIR}/l10n/qt_de_DE.qm"
    "${CMAKE_SOURCE_DIR}/l10n/de_DE.qm"
    "${CMAKE_SOURCE_DIR}/l10n/en_US.qm"
)

set_source_files_properties(${l10n_files} PROPERTIES 
    MACOSX_PACKAGE_LOCATION "Resources/l10n")

qt_add_executable(WorkTracker MACOSX_BUNDLE 
    ${worktracker_src} 
    ${app_icon_macos} 
    ${l10n_files})
  1. Define a variable l10n_files that contains all the files.
  2. Tell CMake that these files shall end up in the app bundle, in the “Resources/l10n” folder, to be precise.
  3. Include the files in the call to the qt_add_executable function.
A macOS Finder window showing the contents of the "Resources/l10n" folder in an app bundle.

Now that the translations are part of the bundle, a minor modification to the code tells the application where to find them. The Qt documentation contains a section about using macOS APIs to determine the bundle location. That is not necessary, though. Qt also has a helpful method to achieve the same goal, QApplication::applicationDirPath().

#if defined(Q_OS_LINUX)
    // On Linux the translations can be found in /usr/share/worktracker/l10n.
    auto l10nPath = "/../share/worktracker/l10n/";
#elif defined (Q_OS_WIN)
    // On Windows the translations are in the l10n folder in the exe dir.
    auto l10nPath = "/l10n/";
#elif defined (Q_OS_MAC)
    // On OS X the data is somewhere in the bundle.
    auto l10nPath = "/../Resources/l10n/";
#endif

auto appDir = QApplication::applicationDirPath() + l10nPath;

This method returns the absolute path to the “MacOS” folder inside of the bundle, the folder where the application’s binary is located. Appending /../Resources/l10n/ first navigates up to the “Content” folder (via /..), which is more or less the bundle’s “root” directory, and from there, goes to “Resources/l10n”. Finally, the language files are loaded like on Windows, and the translation works as expected.

I hope this was helpful because I could not find much information on this specific topic.

Thank you for reading.

Package Qt6 App as macOS App Bundle With CMake

Robert Lohr1 Comment

The Qt documentation contains all the necessary pieces to create a macOS app bundle. Some steps require CMake configuration, while others require manual labor, i.e., terminal commands. Ideally, you, the developer, want to automate the whole thing and not enter the commands every time you build a release.

You can do that with CMake, and this How-To will show you what to do. I am taking my WorkTracker application as an example since it isn’t just a little toy with an executable binary. It is a fully functional application I use daily at work (albeit on Windows) with icon resources, language files, and several Qt libraries and plugins.

Note: I will not elaborate on the language file topic, as it requires code changes to find the translations in the bundle file. This post focuses on automating the app-bundle creation and setting an application icon.

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Consume Messages With Spring Cloud Stream Kafka

Robert Lohr2 Comments

Update:

Spring Cloud Stream is a very complex topic and a remarkable piece of technology. It builds on other intricate Spring technologies like Spring Integration and Spring Cloud Function, and when you add Apache Kafka to the mix, you have a steep learning curve on your hands.

There is a lot of documentation to read and comprehend, and I do not think it helps that your first interaction with the technology is by showing off. Here is the sample in the “Introducing Spring Cloud Stream” section.

@SpringBootApplication
public class SampleApplication {
    public static void main(String[] args) {
        SpringApplication.run(SampleApplication.class, args);
    }
    @Bean
    public Function<String, String> uppercase() {
        return value -> value.toUpperCase();
    }
}

That supposedly is a fully functioning application. The uppercase() method consumes and produces simultaneously, essentially turning it into a way software can pleasure itself. To understand this example, you must know about all the Spring Boot auto-configuration magic happening in the background. Otherwise, it is an opaque magical, and indecipherable showpiece.

This post will show a practical example of a simple consumer application receiving messages from a Kafka cluster. This was my use case, and while the documentation contains a ton of helpful information, it only succeeded in confusing me at first, coming to the technology with fresh eyes. As a result, it took me a long time to put together all the pieces before I understood what was going on.

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AD Workload Identity for AKS Pod-Assigned Managed Identity (Cross-Post)

Robert LohrLeave a comment

Managing credentials and other types of access tokens is a hassle. In Microsoft’s Azure Cloud, you can take advantage of Service Principals and RBAC. But even then, a Service Principal requires a password. There is a better solution in Azure called Managed Identity. But how can you employ this feature when your workload runs in AKS? There is a solution, and I’ve explained all you need to know in an article on my employer’s developer blog.

There was this thing called Pod-Managed Identities, but that was pretty elaborate in its setup. Azure Workload Identity is much leaner, making the configuration and usage more straightforward. Managing credentials and connection strings in Kubernetes microservices is a hassle I have disliked from the start. Assigning a Managed Identity to an AKS pod or even a Service Principal and then relying on Azure RBAC can make your life as a developer or IT ops engineer so much more enjoyable.

Visit the blog linked earlier to read the full version. It’ll contain my usual bad jokes and is not censored in any way. I’d post the same article 1:1 on this blog if I had not researched the topic on company time.

I hope it can help you, and thank you for reading.

Spring Boot Push Micrometer Metrics to Prometheus Pushgateway

Robert LohrLeave a comment

Prometheus, as a metrics solution, gets its data by actively reading it from designated services – a process known as scraping. This approach might not work if your workload contains short-lived tasks, as your task may not fall within the scraping time window.

Luckily, Prometheus has a solution for this: the Pushgateway.

It presents a push-based target for your metrics that itself is scraped by Prometheus. But how do you configure this in a Spring Boot application? Let me show you.

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Spring Boot Custom Field Error Messages in Class-Based Custom Bean ConstraintValidator

Robert LohrLeave a comment

This short guide will focus on a single specific aspect of custom bean validation. If you need to catch up on how to write a custom bean validator, check out the tutorial on reflectoring.io. What is usually missing from these how-tos is the handling of validators for an entire class instead of just a field and how to set custom errors for specific field errors in a class.

Why would you want to write a validator for an entire class?

You may run into a situation where the value of one field of a class depends on the value of another field. For example, the field “type” value impacts which values are valid for the field “content”.

But when you define a custom validator, the validation annotation @interface only represents a single error message. The result is that any field error would result in the same error message. In a web service, this is not very helpful for users of your API.

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I Bestow Upon Thee “HotkeyAutoExecute”, My Game Screenshot Automator

Robert LohrLeave a comment

HotkeyAutoExecute is a simple single-window tool that lets you manage a list of frequently used hotkeys, of which one is repeatedly executed in configurable intervals.

That was the TLDR blurp, and now let’s get into the details. This tool scratches an itch I had in 2020 when I wanted to simplify the process of taking game screenshots for my reviews. During intense gameplay moments, it is difficult to focus on the game and press a keyboard shortcut to take an image of on-screen action. Therefore, I hacked something that would do the job but was not quite baked to be open-sourced as an application. I have changed that now, and boy, was it more complicated than I would have liked.

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Convert QKeySequence of QKeySequenceEdit to Native Windows Virtual Key Codes VK_*

Robert Lohr1 Comment

In a blog post in 2020, I described how to utilize the WinAPI SendInput() function to emulate hotkey presses to automatically take game screenshots for my video game reviews. While I intended to create a simple GUI application to do the task, I ended up with only a hack because of a massive boulder that Windows threw in my way. Or after me, chasing me down a narrow path.

Forget the boulder.

(Although it would be a fitting metaphor to describe Windows: tall, fat, and destructive to user privacy.)

I wanted a simple input field where the user can press a key sequence that will be executed repeatedly at an interval. Qt conveniently provides QKeySequenceEdit for this purpose, and when I tried to insert the Xbox Game Bar hotkey, it did not register. Well, it did, in that Windows took a screenshot. But it was not recorded by the widget. Windows seems to intercept and eat the key presses. That was when I decided to just hard-code my needs and call it a day.

Two years later, I figured that it was about damn time to fix this, and this is where I ran into issues with the translation of key codes from QKeySequenceEdit and QKeySequence to native Windows virtual key codes.

This is where our adventure begins.

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Spring Boot @RestController Action Returning java.util.Optional

Robert LohrLeave a comment

Recently, I wondered what would happen if a Spring Boot RestController returned a java.util.Optional instead of a regular POJO.

I invested 30 minutes of my life to find out, and created an over-engineered example on GitHub.

Here is the controller.

@Slf4j
@RestController
@RequiredArgsConstructor
public class MusicController {

    private final MusicService musicService;

    @GetMapping(path = "/value")
    Album getValue(@RequestParam("isNull") boolean isNull) {
        log.info("Request album value (is null: {})", isNull);
        return musicService.getAlbumAsValue(isNull);
    }

    @GetMapping(path = "/optional")
    Optional<Album> getOptional(@RequestParam("isNull") boolean isNull) {
        log.info("Request album optional (is null: {})", isNull);
        return musicService.getAlbumAsOptional(isNull);
    }
}

The first question I had was if Spring Boot would even start up. You never know. It does, and with this hurdle out of the way, here’s the output of a couple of curl commands.

~ % curl -i 'http://localhost:8080/value?isNull=false'   
HTTP/1.1 200 
Content-Type: application/json
Transfer-Encoding: chunked
Date: Sun, 24 Jul 2022 08:24:50 GMT

{"artist":"Insomnium","title":"Winter's Gate","genre":"Melodic Death Metal","year":2016} 

~ % curl -i 'http://localhost:8080/value?isNull=true'    
HTTP/1.1 200 
Content-Length: 0
Date: Sun, 24 Jul 2022 08:24:55 GMT
 
~ % curl -i 'http://localhost:8080/optional?isNull=false'
HTTP/1.1 200 
Content-Type: application/json
Transfer-Encoding: chunked
Date: Sun, 24 Jul 2022 08:25:00 GMT

{"artist":"Insomnium","title":"Winter's Gate","genre":"Melodic Death Metal","year":2016} 

~ % curl -i 'http://localhost:8080/optional?isNull=true' 
HTTP/1.1 200 
Content-Type: application/json
Transfer-Encoding: chunked
Date: Sun, 24 Jul 2022 08:25:06 GMT

null

Everything works as expected except for the null-case with the Optional. It returns the string “null” instead of nothing.

The moral of the story: Do not return java.util.Optional from a @RestController, or you need to do more work to unpack it.

Thank you for reading.

Simplify Spring Boot Access to Kubernetes Secrets Using Environment Variables

Robert Lohr1 Comment

This blog post is a follow-up to a previous blog post titled “Simplify Spring Boot Access to Secrets Using Spring Cloud Kubernetes“. Despite the downsides I mentioned, I already hinted at a more straightforward solution that utilizes environment variables. The plan is to get everything into the Pod with as little configuration effort as possible.

So, I promised a twist, and here it is, thanks to one of my colleagues who pushed me in this direction. Kubernetes gives you yet another tool to handle Secrets in environment variables. This time, it is more convenient since you only point it to the complete Secret, not just a single value. Kubernetes will then make all key-value pairs available as individual environment variables.

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Simplify Spring Boot Access to Secrets Using Spring Cloud Kubernetes

Robert Lohr1 Comment

This topic has its origin in how we manage Kubernetes Secrets at my workplace. We use Helm for deployments, and we must support several environments with their connection strings, passwords, and other settings. As a result, some things are a bit more complicated, and one of them is the access to Kubernetes Secrets from a Spring Boot application running in a Pod.

This blog post covers the following:

  1. How do you generally get Secrets into a Pod?
  2. How do we currently do it using Helm?
  3. How can it be improved with less configuration?
  4. Any gotchas? Of course, it is software.

I will explain a lot of rationales, so expect a substantial amount of prose between the (code) snippets.

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Apache Commons CLI Handling of –help

Robert LohrLeave a comment

An odd thing about Commons CLI is that it has no built-in concept of a “–help” option. Other libraries, like JCommander do (which had other problems, or I would not have bothered with Commons CLI). As a result, you have to build it on your own. It is not enough to include it with all the other application options, especially if you use required arguments. Then it is impossible to only set the Help option.

You must implement a two-step process. See this demo application on GitHub that I created for another blog post. It shows this in action.

First, only parse for the Help option, and if it is present, print the help text and exit the application. To print the complete help text, you must add the other parameters first, though. Otherwise there would be only “–help”.

final var applicationOptions = example_2_Options();

final var options = example_2_Help();
final var cli = parser.parse(options, args, true);

if (cli.hasOption(help)) {
    // Append the actual options for printing to the command-line.
    applicationOptions.getOptions().forEach(options::addOption);
    new HelpFormatter().printHelp("external-config-commons-cli", options);
    return;
}

Second, if no help is requested, parse for the application options.

final var cli = parser.parse(applicationOptions, args, true);

applicationOptions.getOptions().forEach(opt -> {
    if (cli.hasOption(opt)) {
        System.out.printf("Found option %s with value %s%n",
                opt.getOpt(), cli.getOptionValue(opt));
    }
});

Thank you very much for reading. I hope this was helpful.