HostDefaults overridden by `HttpApplicationHost.CreateBuilder()`

[EmperorArthur]

What I am trying to accomplish

I should be able to set "IHostEnvironment.Environment" and other build-time variables for HttpApplicationHost before the configuration files, like "appsettings..json" are read. Ideally, this would be done by passing in a HostApplicationBuilderSettings object. However, HttpApplicationHost.CreateBuilder() takes no arguments.

However, there are other ways to set the Environment which should work, but do not.

BUG: Failing methods to set "IHostEnvironment.Environment" or any variable based on Microsoft.Extensions.Hosting.HostDefaults

• Setting a value to be used by ConfigurationManager
• Setting the "DOTNET_environment" environment variable
• Adding command line configuration variables

Root Cause

HttpApplicationHost.CreateBuilder() internally creates a HostApplicationBuilderSettings and populates it.

This prevents other methods from working, since "HostApplicationBuilderSettings override all other config sources." 1

Proposed Solutions

I suggest both be implemented.

• Switch to using HostDefaults that can be overridden.
• Allow the user to pass an optional HostApplicationBuilderSettings to HttpApplicationHost.CreateBuilder().

Faulty Code

public static HttpApplicationHostBuilder CreateBuilder()
{
var config = new ConfigurationManager();
config.AddConfigurationManager();
var builder = new HostApplicationBuilder(new HostApplicationBuilderSettings()
{
    Configuration = config,
    ApplicationName = HostingEnvironment.SiteName,
    ContentRootPath = HostingEnvironment.ApplicationPhysicalPath,
    EnvironmentName = HostingEnvironment.IsDevelopmentEnvironment || IsIISExpress() ? Environments.Development : Environments.Production
});
...

Proposed Code

Based on 1

private static void UseHostingEnvironmentFallback(ConfigurationManager configuration)
{
    List<KeyValuePair<string, string?>>? optionList = null;
    if (configuration[HostDefaults.ApplicationKey] is null)
    {
        optionList ??= new List<KeyValuePair<string, string?>>();
        optionList.Add(new KeyValuePair<string, string?>(HostDefaults.ApplicationKey, HostingEnvironment.SiteName));
    }
    if (configuration[HostDefaults.EnvironmentKey] is null)
    {
        optionList ??= new List<KeyValuePair<string, string?>>();
        optionList.Add(new KeyValuePair<string, string?>(HostDefaults.EnvironmentKey, HostingEnvironment.IsDevelopmentEnvironment || IsIISExpress() ? Environments.Development : Environments.Production));
    }
    if (configuration[HostDefaults.ContentRootKey] is null)
    {
        optionList ??= new List<KeyValuePair<string, string?>>();
        optionList.Add(new KeyValuePair<string, string?>(HostDefaults.ContentRootKey, HostingEnvironment.ApplicationPhysicalPath));
    }
    if (optionList is not null)
    {
        configuration.AddInMemoryCollection(optionList);
    }
        static bool IsIISExpress()
        {
            using var currentProcess = Process.GetCurrentProcess();

            return string.Equals(currentProcess.ProcessName, "iisexpress", StringComparison.Ordinal);
        }
}

public static HttpApplicationHostBuilder CreateBuilder(HostApplicationBuilderSettings? settings = null)
{
settings ??= new HostApplicationBuilderSettings();
settings.Configuration ??= new ConfigurationManager();
settings.Configuration.AddConfigurationManager();

UseHostingEnvironmentFallback(settings.Configuration);

var builder = new HostApplicationBuilder(settings);
...

To Reproduce

Attempt to set environment prior to configuration loading, when using HttpApplicationHost.CreateBuilder()

Further technical details

ASP.NET Framework Application: 4.8
Microsoft.AspNetCore.SystemWebAdapters.FrameworkServices 2.3.0
Microsoft.AspNetCore.Hosting 2.3.0
Microsoft.Extensions.Hosting 9.0.5

[twsouthwick]

I'm not opposed to the idea, but I'm a little confused by what you're proposing as it is written. Am I understanding you right that these are the two asks:

Switch to using HostDefaults that can be overridden

Not sure what you mean by "Switch". It appears that you're asking for a new feature that these values can be auto-populated by existing configuration values.

Allow the user to pass an optional HostApplicationBuilderSettings to HttpApplicationHost.CreateBuilder()

Makes sense to me.

AFAICT, by adding the HostApplicationBuilderSettings overload should enable the other (the host defaults are not being set currently because the values have been explicitly set).

Other open questions:

• Currently, the configuration manager adds a source to read from AppSettings/ConnextionStrings. Should that still be done with a custom settings? I think so, but open

Feel free to create a PR to enable this.

[EmperorArthur]

Appreciate the feedback and you being open to this.

It started as a bug because I had previously assumed the host would set the environment the same as other aspnetcore builders. However, as I tracked down the root cause, I realized by assumption was incorrect.

I will submit a PR.

[EmperorArthur]

Opened #667 with the commit message matching same format you used for b7a60a8.

[twsouthwick]

Fixes by #667