helix.mcp: Skill for Claude Code

Skill: IHttpClientFactory with Optional Constructor Injection

Confidence: low Source: earned

Problem

You need to replace static or new HttpClient() patterns with IHttpClientFactory for proper handler lifecycle management, but the service is constructed by tests that don't use DI.

Wrong Pattern

// Static field — socket exhaustion, no DNS refresh
private static readonly HttpClient s_httpClient = new();

// Or: required parameter breaks all test constructors
public MyService(IHelixApiClient api, HttpClient httpClient) { ... }

Right Pattern

// Optional parameter — production injects from factory, tests get default
public MyService(IHelixApiClient api, HttpClient? httpClient = null)
{
    _api = api ?? throw new ArgumentNullException(nameof(api));
    _httpClient = httpClient ?? new HttpClient();
}

DI registration:

services.AddHttpClient("MyDownload", c => c.Timeout = TimeSpan.FromMinutes(5));
services.AddSingleton<MyService>(sp =>
    new MyService(
        sp.GetRequiredService<IMyApiClient>(),
        sp.GetRequiredService<IHttpClientFactory>().CreateClient("MyDownload")));

Why

• IHttpClientFactory manages HttpMessageHandler lifetime (recycles every 2 min by default)
• Avoids socket exhaustion from long-lived static HttpClient
• Named clients allow per-use-case timeout configuration
• Optional parameter preserves backward compatibility with tests
• Tests that don't exercise HTTP can pass one arg; tests that do can inject a mock handler

Applies When

• Replacing static HttpClient fields in services
• Service is heavily tested with direct construction (not DI)
• Multiple HTTP use cases need different timeouts