fix: Ensure AddPolicyName without adding a Provider does not get stuck in infinite loop

[kylejuliandev]

This PR

Updates the code such that it does not rely on any previous registration of a IFeatureClient. If you fail to specify a Provider and instruct the FeatureBuilder to introduce a policy for determining which provider to use, the code will get stuck infinitely trying to resolve IFeatureClient. For example:

var builder = WebApplication.CreateSlimBuilder(args);

builder.Services.AddOpenFeature(featureBuilder =>
{
    featureBuilder
        .AddPolicyName(policy =>
        {
            policy.DefaultNameSelector = provider =>
            {
                return null;
            };
        });
});

var app = builder.Build();

app.MapGet("/welcome", async ([FromServices] IFeatureClient featureClient) =>
{
    var welcomeMessageEnabled = await featureClient.GetBooleanValueAsync("welcome-message", false);

    if (welcomeMessageEnabled)
    {
        return TypedResults.Ok("Hello world! The welcome-message feature flag was enabled!");
    }

    return TypedResults.Ok("Hello world!");
});

app.Run();

Related Issues

Fixes #543

Notes

Follow-up Tasks

How to test

[gemini-code-assist]

Summary of Changes

Hello @kylejuliandev, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical issue in the OpenFeature .NET SDK where applications could get stuck in an infinite loop if AddPolicyName was used without a pre-registered feature provider. The fix refactors the IFeatureClient resolution logic to directly interact with the OpenFeature API, ensuring that clients are correctly obtained regardless of explicit provider registration, thereby preventing application startup failures and improving the stability of policy-based client configurations.

Highlights

• Infinite Loop Fix: Addresses a critical bug where configuring policy-based client selection using AddPolicyName without explicitly registering an IFeatureClient provider would cause an infinite loop during service resolution.
• Refactored Client Resolution: Introduces a new private helper method, ResolveFeatureClient, to centralize and correctly handle the resolution of IFeatureClient instances, whether default or named, directly from the OpenFeature API.
• Improved Dependency Robustness: Enhances the robustness of the OpenFeatureBuilder by no longer relying on the prior registration of IFeatureClient instances through the service provider, preventing potential dependency resolution failures.

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[gemini-code-assist]

Code Review

This pull request correctly addresses a critical issue that could lead to an infinite loop when resolving IFeatureClient without a registered provider. The introduction of the ResolveFeatureClient method effectively breaks the circular dependency. I've included a couple of suggestions to further simplify the new code by reducing redundancy, which will improve its maintainability. Overall, this is a solid fix.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.88%. Comparing base (29e1657) to head (774be8e).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #606      +/-   ##
==========================================
+ Coverage   89.76%   89.88%   +0.11%     
==========================================
  Files          77       77              
  Lines        3166     3172       +6     
  Branches      364      364              
==========================================
+ Hits         2842     2851       +9     
+ Misses        253      251       -2     
+ Partials       71       70       -1     

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