[Bug] Serilog Sinks Cannot Be Configured From Microsoft.AspNetCore.Mvc.Testing

[EmperorArthur]

Issue

It is impossible to configure Serilog Sinks from the command line Microsoft.AspNetCore.Mvc.Testing, or when certain command line arguments are set.

Expected Behavior

Logs are written to console in the requested form.

Actual Behavior

No logs are written!

How To Reproduce

1. Create a new project using dotnet new web
2. Set the Program.cs to below

string[] sargs = [
    "--Serilog=",
    "--Serilog:WriteTo=",
    "--Serilog:WriteTo:0=",
    "--Serilog:WriteTo:0:Name=Console"
    ]
var builder = WebApplication.CreateBuilder
builder.Host.UseSerilog((host, services, configuration) =>
{
    configuration.ReadFrom.Services(services);
    configuration.ReadFrom.Configuration(host.Configuration);
});
var app = builder.Build();
app.Logger.LogInformation("test");

2. Ensure there is no "Serilog" section in appsettings.json and appsettings..json
3. Run the site via dotnet run.

System / Version Information

• .NET SDK 8.0.415
• Windows 10 LTSC

Other Information

Using the simplified form, without setting the output template works as expected.

--Serilog:WriteTo:0=Console

Cause & Suggested Fix

ConfigurationReader.GetMethodCalls checks if the list contains strings or objects using Value!=null and Value==null checks.

This makes the assumption that any section with a value cannot be an object. However, that is incorrect. When entering setting values via Microsoft.AspNetCore.Mvc.Testing, all sections have a value set to "" instead of null.

Tabular representation of the difference:

Section	Value (Testing)	Value (JSON)
Serilog	""	null
Serilog:WriteTo	""	null
Serilog:WriteTo:0	""	null
Serilog:WriteTo:0:Name	"Console"	"Console"

Suggested Fix

Replace the null checks with string.IsNullOrEmpty

Edit: Adjusted root cause, and reproducible example.

[nblumhardt]

Thanks for the report and investigation, @EmperorArthur! Microsoft.Extensions.Configuration is certainly full of surprises :-/

It'd be nice to support this; care would be taken not to regress cases where a string argument is explicitly given the value "", but at first skim it seems doable. If anyone's interested in sending a minimal PR with a fix and some test cases the help would be appreciated.

[EmperorArthur]

After more investigation it appears Microsoft.AspNetCore.Mvc.Testing deliberately adds the argument "--Serilog:WriteTo:0=" which is an empty string.

Because, of course, dotnet allows configurations that cannot be represented by JSON, and doesn't document that.

[nblumhardt]

Ah, interesting - thanks for the follow-up! Weird thing for it to add, any ideas why that is?

[EmperorArthur]

No clue. The dotnet devs also seem to think that it's obvious an IConfigurationSection can have a value and children. Thus cannot be represented as JSON..

I'm using the pattern to create a custom WebApplicationFactory<Program> based on AspNetCore Samples.

public class MyWebApplicationFactory : WebApplicationFactory<Program>
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.UseSetting("Serilog:MinimumLevel:Default", "Information");
        // Broken
        builder.UseSetting("Serilog:WriteTo:0:Name", "Console");
        builder.UseSetting("Serilog:WriteTo:0:Args:outputTemplate", "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] <{SourceContext}> {Message:lj} - {NewLine}{Exception}");
    }
}