The previous part is here.

And finally, we are in the most important part which explains what works differently between the .NET Framework and .NET 6. Just in case I will talk about behavioral changes and about obvious parts like some methods that do not exist in .NET 6 but I will

1. The .NET Framework will suppress all exceptions when it releases a reference to a COM object but .NET 6 will crash. One example of such a problem is when some object is freed despite having a reference count of more than zero. It is a bug and needs to be fixed. I just was surprised by how often it happened in our application.
2. Accessing .NET from DllMain will lead to deadlocks. We had these in the .NET Framework, but they happened much more often in the .NET 6. And obviously, it needs to be fixed. It will take some time because it works most of the time and deadlock happens quite seldom.
3. string.GetHashCode will return different values every time you start the application. Basically during startup runtime will generate a random seed and add it to the hash code. If you want hash code to persist then write a function that hashes string differently.
4. When the application converts a floating point number to a string, the result will be slightly different. Here blog post that explains the changes. For example, when the .NET Framework outputs 3.1415, .NET may output as 3.141500001 or 3.141499999.
5. Encoding.Default will be always UTF8 in .NET 6. If you want to return old behavior then you need to create Encoding from the current Windows code page.
6. System.Diagnostics.ProcessStartInfo.UseShellExecute is true for .NET Framework but false for .NET As a result, previously it was possible to open the http link without changing properties but now UseShellExecute must be set specifically to true.
7. Previously it was possible to bind to read-only property in WPF. Now it throws an exception and you need to add “, Mode=OneWay”.
8. SHA512.Create("System.Security.Cryptography.SHA512CryptoServiceProvider") will return null. We replaced it with new SHA512CryptoServiceProvider().
9. There is no SHA512Cng class. We replaced it with SHA512CryptoServiceProvider class that uses SHA512Cng internally when the application is running for Windows.
10. Setting SecurityProtocolType.Ssl3 will throw an exception.
11. Some controls were removed from WinForms. For example ContextMenu. They were replaced with a set of different controls quite some time ago but our code used an old version for some reason.
12. In the .NET Framework, your application can load assembly A 2.0.0.0 from the application directory. Later it can load assembly K located in a different directory and assembly K can load assembly A version 1.0.0.0 from the same directory that contains assembly K and it will work. This will fail in the .NET 6 because another version with a higher version is already loaded. To fix this you will need to use AssemblyLoadContext.
13. If you are using different assembly versions in WPF then it will work properly. You will have to rename assemblies to include the version in the assembly name. I spent quite a bit of time on this and I didn’t find any better way.
14. If you are enumerating over HashSet sometimes it will contain elements in a different order in .NET 6. We found that during tests. But HashSet does not guarantee the order so it was an issue on our side.
15. string.Compare("C-O", "CA") will return 1 for the .NET Framework and -1 for .NET 6. It is because Microsoft changed how comparing works to have the same result for all platforms. Previously it used Windows API for this.

[...Read More]

And just for perspective, we have 824 C# projects and when someone thinks about converting, they may believe that they need to convert all these projects to support .NET X (where X >= 5), change the build system, etc.

It turns out that there is an easy way to do and it allows us to do proof of concept very quickly and then test compatibility. And to do this you need to do nothing. Yep, you heard me right. Our application is a native application that loads .NET Framework runtime and then loads .NET Framework assemblies.

It turns out that all we need to do is to change the .NET Framework loader to load .NET 6 runtime. It is described [...Read More]

Previous part is here. This post will explain, how to restart your web site at specific intervals without returning errors to clients. You can scroll to solution, if you are no interested in my thoughts and to see what I try.

Thoughts and research

As I mentioned in this post, I decided to restart my web site periodically to avoid out of memory issue. And I would like to mention that it wasn’t easy to do. Obviously, restarting web site is super simple and all you need is to restart its service. But that means that your web site will be unavailable for some time. Depending on size of the web site, we are talking about seconds or [...Read More]

Some time ago, I wrote series of posts on how to run .NET Core app on AWS Lightsail Linux instance. Everything worked nice but sometimes, about once per month my web site stopped responding. And I cannot connect to my instance at all to diagnose that issue. All I can do is just restart my AWS instance. At the beginning I thought it could be AWS issue, or perhaps some issues in .NET. I updated everything I can, but problem persists. And when it happened last time, I decided to check kernel logs and I found this:

Feb 10 07:31:18 ip-1-2-3-4 kernel: [1512878.216567] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/system.slice/www.example.com.service,task=dotnet,pid=511,uid=1001
Feb 10 07:31:18 ip-1-2-3-4 kernel: [1512878.216597] Out of memory: Killed process 511 (dotnet) total-vm:3007440kB, anon-rss:105260kB, file-rss:0kB, shmem-rss:0kB, UID:1001 pgtables:712kB oom_score_adj:0
Feb 10 07:31:18 ip-1-2-3-4 kernel: [1512878.241642] oom_reaper: reaped process 511 (dotnet), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB

[...Read More]

Recently I was asked to check why one of our applications crashes when it calls CreateNamedPipe function. Everything works fine in the x64 version, but the x86 version crashes. There are no differences in the code between x86 and x64 and they compiled the same.

Let’s see how CreateNamedPipe defined in our code:

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
static extern SafePipeHandle CreateNamedPipe(string lpName, uint dwOpenMode,
    uint dwPipeMode, uint nMaxInstances, uint nOutBufferSize, uint nInBufferSize,
    uint nDefaultTimeOut, SECURITY_ATTRIBUTES securityAttributes);

and here is how it called:

SafePipeHandle safeHandle = CreateNamedPipe(
                $@"\\.\pipe\{pipeName}",
                cPipeAccessDuplex |
                cFileFlagOverlapped,
                cPipeTypeMessage |
                cPipeWait,
                cPipeUnlimitedInstances,
                nOutBufferSize: 0,
                nInBufferSize: 0,
                cWaitForever,
                securityAttr);

Everything looks correct. I checked flags, compared them with [...Read More]

Previous part is here.

I found that I was missed one critical part that I did in my application but forgot to explain here. Let me explain little bit. Effectively secure communication via HTTPS protocol happens between browser and nginx that is web server. Nginx communicates with .NET application via HTTP protocol. And effectively .NET application believes that it is communicating via HTTP. It called SSL termination.

And as result .NET application can return something that is not compatible with HTTPS protocol. In my case it returns link to profile from Gravatar service via HTTP. This in turn leads to complain from web browser that there is mixed content: HTTP and HTTPS. And that one only minor problem but [...Read More]

This is continuation of Running .NET Core app on AWS Lightsail Linux instance.

By this moment everything is working exactly as I want. But I have 2 things that really annoys me: backup and updating web site. Because I revoked access to web site directory for every account except www.example.com I have to run a lot of commands from sudo user to backup and update my web site. I would like to automate these steps.

Backup

I have 2 things to backup: web site itself and its data. I separate them because they have different update schedule. For example, I can update web site few times per day and then did not update it for weeks. Obviously, I [...Read More]

This is continuation of Running .NET Core app on AWS Lightsail Linux instance.

One of the useful features I always use for .NET and .NET Core application in IIS is special file app_offline.htm. If this found exist in application’s directory, then .NET module for IIS will return contents of that file for every request. Usually, it used for maintenance. For example, I put some text that web site is under maintenance and that it will be finished in few minutes. Then I am updating all necessary files that are impossible to update while web site is running. When I finished, I will rename it to app_offline.hml_ until next maintenance.

I found like to implement something [...Read More]

Previous part is here.

DNS

Firstly, you need domain name. “You can purchase a domain name from Namecheap, get one for free with Freenom, or use the domain registrar of your choice”. Then follow instructions on how to setup A record. Because you have static IP it will be really easy to do. For example from Namecheap instructions are here.

Keep in mind that it could take up to 24 hours to propagate changes. But if you never accessed your domain before, then it should work in few minutes. Remove your changes from hosts file on your computer and when changes are propagated, you should be able to refresh your browser and see your site with [...Read More]