by Andrew Lock

posted on: April 19, 2022

In this post I describe how you can use the JavaScriptEngineSwitcher NuGet package to run JavaScript inside a .NET application…

by Gérald Barré

posted on: April 18, 2022

When your ASP.NET Core application is big enough, you may want to have a comprehensive view of all routes. There are multiple ways to declare routes. You can use Minimal API, Controllers, Razor Pages, gRPC, Health checks, etc. But all of them use the same routing system under the hood.The collectio

by Steve Gordon

posted on: April 13, 2022

In this post, I demonstrate how to analyse a .NET solution using the Roslyn APIs and aMsBuildWorkspace.

by Andrew Lock

posted on: April 12, 2022

In this post I describe some of the sources I use to learn about new features and APIs when a new version of .NET is released…

by Vladimir Khorikov

posted on: April 11, 2022

My new online training course about Encapsulating EF Core Usage went live.

by Oren Eini

posted on: April 11, 2022

Last week I did a webinar about Clean Architecture, and it run about twice as long as I expected it to be. Mostly because I got some really interesting questions and I think we had a great discussion.You can watch all of it here, as usual, comments are very welcome:

by Gérald Barré

posted on: April 11, 2022

Blazor provides a component to upload files. You can use the <InputFile> component and its OnChange event to get the selected files. It works well for single-file uploads. But, if the user selects new files while the first files are still uploading, you may get an error. You can reproduce thi

by Oren Eini

posted on: April 08, 2022

We run into a really interesting bug. For some reason, the system was behaving in a totally unexpected manner for some parts of the data. For pretty much the same input, we would get the wrong result, and we couldn’t figure out why. Here is our source data: This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters { "Server": "PRD-392", "CpuLoad": { "2": "94%", "1": "49%", "0": "32%", "3": "10%" } } view raw metrics.json hosted with ❤ by GitHub This is some metrics data about servers, and you’ll note that we report the CPU load for each core on the instance and that the results are sorted based on the actual load. Here is what this looks like, the image on the left is wrong while the image on the right is right (pun intended). Why do we have this behavior? Well, let’s look at the actual data, shall we? They are… the same. Exactly the same, in fact. We can throw that into diff engine and they will tell me that they are identical (except for the document id). What is going on here? Well, here is the issue, what you see is not what you get. Look at the JSON text that I have above, and compare that to the documents we see in the images. RavenDB shows the documents in a nicely formatted manner, and along the way, it messed up something pretty important. In our case, we used an object to hold the various details about the instances. And we relied that the insertion sort order for the properties would stay the same when reading the document. That is actually the case, and RavenDB goes to great lengths to ensure that this is the case. However… In order to prettify the document, we call to JSON.parse() and JSON.stringify() (on the client side), which give us nicely formatted output. Along the way, however, we run into JavaScript and its “ideas” about how things should work. In particular, JavaScript threats properties whose key is a number in a different way than other values. All the numeric properties will be sorted according to their integer value, while non numeric values will be sorted using insertion order. That only applies to documents that were modified in the studio, however. The RavenDB server and client API are keeping the properties in insertion order. Only if you modified the document using the Studio will you get this. But because we always show the documents in the same manner, it was invisible to us for a long while. For that matter, it took an embarrassingly long time of debugging this problem, because (naturally) whenever we viewed the data, we did that with formatting, which meant that we never actually saw the differences between the raw versions of the documents.

by Oren Eini

posted on: April 07, 2022

I asked why this code is broken, and now is the time to dig into this. The issue is in this block of code. Take a look at that for a moment, if you please: This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters tasks.Add(Task.Factory.StartNew(async () => { using var data = File.OpenRead(file); var url = "/file?=" + Uri.EscapeDataString(Path.GetFileName(file)); await httpClient.PostAsync(url, new StreamContent(data)); })); view raw problem.cs hosted with ❤ by GitHub The code is trying to gather the async upload of all the files, and then it will await them. This code compile and runs successfully, but it will not do what you expect it to do. Let’s break it up a bit to understand what is going on: This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters var task = Task.Factory.StartNew(async () => { // redacted }) tasks.Add(task); view raw one.cs hosted with ❤ by GitHub We are passing the variable task to the list of tasks we have. We just extract a variable, nothing much going on here. Let’s explore further, what is the type of task? We know it must be a subtype of Task, since that is what the tasks collection will take. It turns out that this isn’t that simple: This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters Task<Task> task = Task.Factory.StartNew(async () => { // redacted }) tasks.Add(task); view raw two.cs hosted with ❤ by GitHub What is that, Task<Task> thingie? Well, let’s look at the signature of Task.Factory.StartNew(), shall we? public Task<TResult> StartNew<TResult>(Func<TResult> function); Just from the signature, we can tell what is going on. StartNew() accepts a function that returns a value and will then return a task for the eventual result of this function. However, the function we are actually passing to the StartNew() doesn’t produce a value. Except that it does… Let’s explore that thing for a bit: var func = async () => { }; What is the type of func in this case? Func<Task> func = async() => {}; The idea is that when the compiler sees the async keyword, it transforms the function to one that returns a Task. Combining both those features together means that our original code actually registers the start of the asynchronous process to happen and will return as soon as it got started. Basically, we’ll only wait for the actual opening of the file, not for the actual network work that has to happen here. The right way to express what we want here is: Task.Run(async () => {}); The signature for this is: public static Task Run<TResult>(Func<Task> function); You can see here that we get a function that returns a task, but we aren’t actually wrapping that in another Task instance. The task that will be returned will be completed once the full work has been completed. It is an interesting pitfall in the API, and can be quite hard to figure out exactly what is going on. Mostly because there are several different things happening all at once.

by Oren Eini

posted on: April 06, 2022

The following code looks straightforward, but it has a really subtle issue. This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters public async Task SendFiles(params string[] files) { var httpClient = new HttpClient { BaseAddress = new Uri("https://my.backup.server") }; var tasks = new List<Task>(); foreach (var f in files) { var file = f; tasks.Add(Task.Factory.StartNew(async () => { using var data = File.OpenRead(file); var url = "/file?=" + Uri.EscapeDataString(Path.GetFileName(file)); await httpClient.PostAsync(url, new StreamContent(data)); })); } await Task.WhenAll(tasks); Console.WriteLine("All you data has been backed up!"); } view raw subtle.cs hosted with ❤ by GitHub Can you spot what is going on?You can ignore the error handling here, by the way, the issue isn’t related to handling unexpected errors.