Setting ApplicationName to random value when using CreateDefaultBuilder fails in Development

[AndreyTretyak]

If you are using Host.CreateDefaultBuilder(args) to create HostBuilder, set environment to Development and set application name to a value other then assembly names used in this project following code path will fail with FileNotFoundException:

if (env.IsDevelopment() && !string.IsNullOrEmpty(env.ApplicationName))
{
    var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));

To me, it looks like it should not fail the whole host while trying to load dev secrets based on application name or if it's intended behavior then limitations in application name values should be specified clearly.

Code to reproduce

static async Task Main(string[] args)
{
	Environment.SetEnvironmentVariable("DOTNET_APPLICATIONNAME", "DummyName2");

	await Host.CreateDefaultBuilder(args)
		.UseEnvironment(Environments.Development)
		.Build()
		.RunAsync();
}

Or

static async Task Main(string[] args)
{
	await Host.CreateDefaultBuilder(args)
		.UseEnvironment(Environments.Development)
		.UseApplicationName("DummyName1")
		.Build()
		.RunAsync();
}

internal static IHostBuilder UseApplicationName(this IHostBuilder builder, string applicationName) =>
	builder.ConfigureHostConfiguration(configuration =>
	{
		configuration.AddInMemoryCollection(new[]
		{
			new KeyValuePair<string, string>(
				HostDefaults.ApplicationKey,
				applicationName)
		});
	});

Exception Information

Message:

System.IO.FileNotFoundException: 'Could not load file or assembly 'DummyName1, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.'

StackTrace:

at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, RuntimeAssembly assemblyContext, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, AssemblyLoadContext assemblyLoadContext)
at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext) in /_/src/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs:line 345
at System.Reflection.Assembly.Load(AssemblyName assemblyRef, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext) in /_/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs:line 73
at System.Reflection.Assembly.Load(AssemblyName assemblyRef) in /_/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs:line 55
at Microsoft.Extensions.Hosting.Host.<>c__DisplayClass1_0.<CreateDefaultBuilder>b__1(HostBuilderContext hostingContext, IConfigurationBuilder config) in /_/src/libraries/Microsoft.Extensions.Hosting/src/Host.cs:line 81
at Microsoft.Extensions.Hosting.HostBuilder.BuildAppConfiguration() in /_/src/libraries/Microsoft.Extensions.Hosting/src/HostBuilder.cs:line 196
at Microsoft.Extensions.Hosting.HostBuilder.Build() in /_/src/libraries/Microsoft.Extensions.Hosting/src/HostBuilder.cs:line 131
at ConsoleApp1.Program.<Main>d__0.MoveNext() in D:\Projects\WebApplication4\ConsoleApp1\Program.cs:line 12
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() in /_/src/System.Private.CoreLib/shared/System/Runtime/ExceptionServices/ExceptionDispatchInfo.cs:line 63
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) in /_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs:line 180
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) in /_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs:line 151
at System.Runtime.CompilerServices.TaskAwaiter.GetResult() in /_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs:line 107
at ConsoleApp1.Program.<Main>(String[] args)

[sakno]

You should not use ApplicationName property to define the app name. Here is the comment from David Fowler. The value of this property is reserved by DI internals. Check this line of code for more details.

Related issues and PRs:

• Using a custom "ApplicationName" and UseStartup<Startup>() doesn't work aspnet/Hosting#1179
• Decouple ApplicationName from any assembly names aspnet/Hosting#1180

[AndreyTretyak]

Thank you for the details @sakno, if it required to be an executing assembly name (I'm not sure is it the case for Asp Net Core or for all application using GenericHost but looks like all of them need it) then maybe it should in fail in all cases not only with some special preconditions like using dev environment, also using other assembly names (ex, Newtonsoft.Json) would work fine :)

Maybe it should fail during HostBuilder.Build with a more meaningful error? What do you think?

Also @sakno in your comment "Check this line of code for more details."
you are pointing to the same line I was referencing in the issue is it the correct link?

[sakno]

Oops, sorry for my inattention. Yes, it's the same line of code. I also tried to use this property for app name but without luck. There are many places especially in ASP.NET Core MVC utilizing its special meaning.

[ghost]

Tagging subscribers to this area: @eerhardt, @maryamariyan
See info in area-owners.md if you want to be subscribed.

---

Issue meta data

Issue content:

If you are using `Host.CreateDefaultBuilder(args)` to create `HostBuilder`, set environment to `Development` and set application name to a value other then assembly names used in this project [following code path](https://github.com/dotnet/runtime/blob/6a5a78bec9a6e14b4aa52cd5ac558f6cf5c6a211/src/libraries/Microsoft.Extensions.Hosting/src/Host.cs#L81) will fail with `FileNotFoundException`: ```CSharp if (env.IsDevelopment() && !string.IsNullOrEmpty(env.ApplicationName)) { var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName)); ``` To me, it looks like it should not fail the whole host while trying to load dev secrets based on application name or if it's intended behavior then limitations in application name values should be specified clearly. Code to reproduce static async Task Main(string[] args) { Environment.SetEnvironmentVariable("DOTNET_APPLICATIONNAME", "DummyName2"); await Host.CreateDefaultBuilder(args) .UseEnvironment(Environments.Development) .Build() .RunAsync(); } Or static async Task Main(string[] args) { await Host.CreateDefaultBuilder(args) .UseEnvironment(Environments.Development) .UseApplicationName("DummyName1") .Build() .RunAsync(); } internal static IHostBuilder UseApplicationName(this IHostBuilder builder, string applicationName) => builder.ConfigureHostConfiguration(configuration => { configuration.AddInMemoryCollection(new[] { new KeyValuePair<string, string>( HostDefaults.ApplicationKey, applicationName) }); }); Exception Information Message: System.IO.FileNotFoundException: 'Could not load file or assembly 'DummyName1, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.' StackTrace: at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, RuntimeAssembly assemblyContext, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, AssemblyLoadContext assemblyLoadContext) at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext) in /_/src/System.Private.CoreLib/src/System/Reflection/RuntimeAssembly.cs:line 345 at System.Reflection.Assembly.Load(AssemblyName assemblyRef, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext) in /_/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs:line 73 at System.Reflection.Assembly.Load(AssemblyName assemblyRef) in /_/src/System.Private.CoreLib/src/System/Reflection/Assembly.CoreCLR.cs:line 55 at Microsoft.Extensions.Hosting.Host.<>c__DisplayClass1_0.<CreateDefaultBuilder>b__1(HostBuilderContext hostingContext, IConfigurationBuilder config) in /_/src/libraries/Microsoft.Extensions.Hosting/src/Host.cs:line 81 at Microsoft.Extensions.Hosting.HostBuilder.BuildAppConfiguration() in /_/src/libraries/Microsoft.Extensions.Hosting/src/HostBuilder.cs:line 196 at Microsoft.Extensions.Hosting.HostBuilder.Build() in /_/src/libraries/Microsoft.Extensions.Hosting/src/HostBuilder.cs:line 131 at ConsoleApp1.Program.<Main>d__0.MoveNext() in D:\Projects\WebApplication4\ConsoleApp1\Program.cs:line 12 at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() in /_/src/System.Private.CoreLib/shared/System/Runtime/ExceptionServices/ExceptionDispatchInfo.cs:line 63 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) in /_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs:line 180 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) in /_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs:line 151 at System.Runtime.CompilerServices.TaskAwaiter.GetResult() in /_/src/System.Private.CoreLib/shared/System/Runtime/CompilerServices/TaskAwaiter.cs:line 107 at ConsoleApp1.Program.<Main>(String[] args) ```</td> </tr> <tr> <td>Issue author:</td> <td>AndreyTretyak</td> </tr> <tr> <td>Assignees:</td> <td>-</td> </tr> <tr> <td>Milestone:</td> <td>-</td> </tr> </table> </details>

[maryamariyan]

You should not use ApplicationName property to define the app name. Here is the comment from David Fowler. The value of this property is reserved by DI internals. Check this line of code for more details.

Closing issue as by design

[AndreyTretyak]

@maryamariyan should not docs and error message be more explicit about this problem?