dotnet-csharp-configuration

dotnet-csharp-configuration

使用 Microsoft.Extensions.Configuration 和 Microsoft.Extensions.Options 为 .NET 应用配置的模式。涵盖 Options 模式（IOptions<T>、IOptionsMonitor<T>、IOptionsSnapshot<T>）、验证、用户机密、基于环境的配置，以及使用 Microsoft.FeatureManagement 的功能标志。

交叉引用：[skill:dotnet-csharp-dependency-injection]，了解服务注册模式；[skill:dotnet-csharp-coding-standards]，了解命名约定。

---

配置源与优先级

WebApplication.CreateBuilder 中的默认配置源（后者优先）：

1. appsettings.json
2. appsettings.{Environment}.json
3. 用户机密（仅限 Development）
4. 环境变量
5. 命令行参数

var builder = WebApplication.CreateBuilder(args);
// Sources above are loaded automatically. Add custom sources:
builder.Configuration.AddJsonFile("features.json", optional: true, reloadOnChange: true);

---

Options 模式

将配置节绑定到强类型类，并通过 DI 注入。

定义 Options 类

public sealed class SmtpOptions
{
    public const string SectionName = "Smtp";

    public string Host { get; set; } = "";
    public int Port { get; set; } = 587;
    public string FromAddress { get; set; } = "";
    public bool UseSsl { get; set; } = true;
}

Options 类使用 { get; set; }（而非 init），因为配置绑定器和 PostConfigure 需要修改属性。必填字段应使用数据注释中的 [Required]。

注册

builder.Services
    .AddOptions<SmtpOptions>()
    .BindConfiguration(SmtpOptions.SectionName)
    .ValidateDataAnnotations()
    .ValidateOnStart();

appsettings.json

{
  "Smtp": {
    "Host": "smtp.example.com",
    "Port": 587,
    "FromAddress": "[email protected]",
    "UseSsl": true
  }
}

---

Options 接口

接口	生命周期	重新加载行为	用例
IOptions<T>	Singleton	启动后不会重新加载	静态配置，大多数服务
IOptionsSnapshot<T>	Scoped	每个请求/作用域重新加载	ASP.NET 中按请求提供的配置
IOptionsMonitor<T>	Singleton	实时重新加载 + 更改通知	单例、后台服务

注入示例

// Static -- most common, singleton-safe
public sealed class EmailService(IOptions<SmtpOptions> options)
{
    private readonly SmtpOptions _smtp = options.Value;

    public Task SendAsync(string to, string subject, string body,
        CancellationToken ct = default)
    {
        // Use _smtp.Host, _smtp.Port, etc.
        return Task.CompletedTask;
    }
}

// Live reload in singletons -- monitors config file changes
public sealed class FeatureService(IOptionsMonitor<FeatureOptions> monitor)
{
    public bool IsEnabled(string feature)
        => monitor.CurrentValue.EnabledFeatures.Contains(feature);
}

// Per-request in scoped services -- reads latest config each request
public sealed class PricingService(IOptionsSnapshot<PricingOptions> snapshot)
{
    public decimal GetMarkup() => snapshot.Value.MarkupPercent;
}

使用 IOptionsMonitor<T> 接收更改通知

public sealed class CacheService : IDisposable
{
    private readonly IDisposable? _changeListener;
    private CacheOptions _current;

    public CacheService(IOptionsMonitor<CacheOptions> monitor)
    {
        _current = monitor.CurrentValue;
        _changeListener = monitor.OnChange(updated =>
        {
            _current = updated;
            // React to config change -- flush cache, resize pool, etc.
        });
    }

    public void Dispose() => _changeListener?.Dispose();
}

---

Options 验证

数据注释

using System.ComponentModel.DataAnnotations;

public sealed class SmtpOptions
{
    public const string SectionName = "Smtp";

    [Required, MinLength(1)]
    public string Host { get; set; } = "";

    [Range(1, 65535)]
    public int Port { get; set; } = 587;

    [Required, EmailAddress]
    public string FromAddress { get; set; } = "";
}

builder.Services
    .AddOptions<SmtpOptions>()
    .BindConfiguration(SmtpOptions.SectionName)
    .ValidateDataAnnotations()
    .ValidateOnStart(); // Fail fast at startup, not on first use

IValidateOptions<T>（复杂验证）

当验证逻辑需要检查多个属性或使用外部依赖项时使用。

public sealed class SmtpOptionsValidator : IValidateOptions<SmtpOptions>
{
    public ValidateOptionsResult Validate(string? name, SmtpOptions options)
    {
        var failures = new List<string>();

        if (options.UseSsl && options.Port == 25)
        {
            failures.Add("Port 25 does not support SSL. Use 465 or 587.");
        }

        if (string.IsNullOrWhiteSpace(options.Host))
        {
            failures.Add("SMTP host is required.");
        }

        return failures.Count > 0
            ? ValidateOptionsResult.Fail(failures)
            : ValidateOptionsResult.Success;
    }
}

// Register the validator
builder.Services.AddSingleton<IValidateOptions<SmtpOptions>, SmtpOptionsValidator>();

ValidateOnStart（快速失败）

始终使用 .ValidateOnStart()，以便在启动时而非首次解析时发现配置错误。如果不使用它，只有首次访问 IOptions<T>.Value 时，无效配置才会引发异常。

---

用户机密（Development）

在开发期间将敏感值存储在源代码管理之外。

# Initialize (once per project)
dotnet user-secrets init

# Set values
dotnet user-secrets set "Smtp:Host" "smtp.example.com"
dotnet user-secrets set "ConnectionStrings:Default" "Server=..."

# List all secrets
dotnet user-secrets list

# Clear all
dotnet user-secrets clear

用户机密存储在 ~/.microsoft/usersecrets/<UserSecretsId>/secrets.json 中，并会在 Development 环境中覆盖 appsettings.json 中的值。

关键规则：

• 生产环境中绝不要使用用户机密——应使用环境变量、Azure Key Vault 或其他密钥保管库提供程序
• 当 ASPNETCORE_ENVIRONMENT=Development 时，会自动加载用户机密
• 对于非 Web 主机，需显式添加：builder.Configuration.AddUserSecrets<Program>()

---

基于环境的配置

环境变量

// Hierarchical keys use __ (double underscore) as separator
// Environment variable: Smtp__Host=smtp.prod.com
// Maps to: configuration["Smtp:Host"]

按环境划分的文件

appsettings.json                 # Base (all environments)
appsettings.Development.json     # Overrides for dev
appsettings.Staging.json         # Overrides for staging
appsettings.Production.json      # Overrides for prod

// Set environment via ASPNETCORE_ENVIRONMENT or DOTNET_ENVIRONMENT
// Defaults to "Production" if not set
var env = builder.Environment.EnvironmentName; // "Development", "Staging", "Production"

条件式服务注册

if (builder.Environment.IsDevelopment())
{
    builder.Services.AddSingleton<IEmailSender, ConsoleEmailSender>();
}
else
{
    builder.Services.AddSingleton<IEmailSender, SmtpEmailSender>();
}

---

使用 Microsoft.FeatureManagement 实现功能标志

Microsoft.FeatureManagement.AspNetCore 提供结构化的功能标志支持，包括筛选器、目标定位和渐进式发布。

设置

dotnet add package Microsoft.FeatureManagement.AspNetCore

builder.Services.AddFeatureManagement();

配置

{
  "FeatureManagement": {
    "NewDashboard": true,
    "BetaSearch": {
      "EnabledFor": [
        {
          "Name": "Percentage",
          "Parameters": { "Value": 50 }
        }
      ]
    },
    "DarkMode": {
      "EnabledFor": [
        {
          "Name": "Targeting",
          "Parameters": {
            "Audience": {
              "Users": [ "[email protected]" ],
              "Groups": [
                { "Name": "Beta", "RolloutPercentage": 100 }
              ],
              "DefaultRolloutPercentage": 0
            }
          }
        }
      ]
    }
  }
}

在代码中使用

// Inject IFeatureManager
public sealed class DashboardController(IFeatureManager featureManager) : ControllerBase
{
    [HttpGet]
    public async Task<IActionResult> Get(CancellationToken ct = default)
    {
        if (await featureManager.IsEnabledAsync("NewDashboard"))
        {
            return Ok(new { version = "v2", dashboard = "new" });
        }

        return Ok(new { version = "v1", dashboard = "legacy" });
    }
}

功能门控特性

// Entire endpoint gated on feature flag
[FeatureGate("BetaSearch")]
[HttpGet("search")]
public async Task<IActionResult> Search(string query, CancellationToken ct = default)
{
    var results = await _searchService.SearchAsync(query, ct);
    return Ok(results);
}

功能筛选器

筛选器	用途
Percentage	为 N% 的请求启用（随机）
TimeWindow	在开始/结束日期之间启用
Targeting	为特定用户、组或发布百分比启用
自定义	实现 IFeatureFilter 以编写特定于领域的逻辑

自定义功能筛选器

[FilterAlias("Browser")]
public sealed class BrowserFeatureFilter(IHttpContextAccessor accessor) : IFeatureFilter
{
    public Task<bool> EvaluateAsync(FeatureFilterEvaluationContext context)
    {
        var userAgent = accessor.HttpContext?.Request.Headers.UserAgent.ToString() ?? "";
        var settings = context.Parameters.Get<BrowserFilterSettings>();

        return Task.FromResult(
            settings?.AllowedBrowsers?.Any(b =>
                userAgent.Contains(b, StringComparison.OrdinalIgnoreCase)) ?? false);
    }
}

public sealed class BrowserFilterSettings
{
    public string[] AllowedBrowsers { get; init; } = [];
}

// Register
builder.Services.AddFeatureManagement()
    .AddFeatureFilter<BrowserFeatureFilter>();

---

命名 Options

当需要同一 Options 类型的多个实例时（例如，多个 API 客户端），请使用命名 Options。

// Registration with names
builder.Services
    .AddOptions<ApiClientOptions>("GitHub")
    .BindConfiguration("ApiClients:GitHub");

builder.Services
    .AddOptions<ApiClientOptions>("Jira")
    .BindConfiguration("ApiClients:Jira");

// Resolution via IOptionsSnapshot<T> or IOptionsMonitor<T>
public sealed class ApiClientFactory(IOptionsSnapshot<ApiClientOptions> snapshot)
{
    public HttpClient CreateFor(string name)
    {
        var options = snapshot.Get(name); // "GitHub" or "Jira"
        return new HttpClient { BaseAddress = new Uri(options.BaseUrl) };
    }
}

---

后期配置

在处理完所有配置源后应用默认值或覆盖值。

builder.Services.PostConfigure<SmtpOptions>(options =>
{
    // Ensure a default port if none specified
    if (options.Port == 0)
    {
        options.Port = options.UseSsl ? 465 : 25;
    }
});

---

测试配置

[Fact]
public void SmtpOptions_Validates_InvalidPort()
{
    var options = new SmtpOptions
    {
        Host = "smtp.example.com",
        FromAddress = "[email protected]",
        Port = 25,
        UseSsl = true
    };

    var validator = new SmtpOptionsValidator();
    var result = validator.Validate(null, options);

    Assert.True(result.Failed);
    Assert.Contains("Port 25 does not support SSL", result.FailureMessage);
}

[Fact]
public void Configuration_BindsCorrectly()
{
    var config = new ConfigurationBuilder()
        .AddInMemoryCollection(new Dictionary<string, string?>
        {
            ["Smtp:Host"] = "smtp.test.com",
            ["Smtp:Port"] = "465",
            ["Smtp:FromAddress"] = "[email protected]",
        })
        .Build();

    var options = new SmtpOptions();
    config.GetSection("Smtp").Bind(options);

    Assert.Equal("smtp.test.com", options.Host);
    Assert.Equal(465, options.Port);
}

---

参考资料

• .NET 中的 Options 模式
• .NET 中的配置
• 开发期间的用户机密
• .NET 中的功能管理
• IValidateOptions
• .NET Framework 设计指南