Configuration.Writable

A lightweight library that allows for easy saving and referencing of settings, with extensive customization options.

Features

• Read and write user settings with type safety.
• Built-in: Atomic file writing, automatic retry, and backup creation.
• Automatic detection of external changes to configuration files and reflection of the latest settings.
• Simple API that can be easily used in applications both with and without DI.
• Extends Microsoft.Extensions.Options interfaces, so it works seamlessly with existing code using IOptions<T>, IOptionsMonitor<T>, etc.
• Supports various file formats (Json, Xml, Yaml, Encrypted, etc...) via providers.

See more...

Usage

Setup

Install Configuration.Writable from NuGet.

dotnet add package Configuration.Writable

Then, prepare a class (UserSetting) in advance that you want to read and write as settings.

public class UserSetting
{
    public string Name { get; set; } = "default name";
    public int Age { get; set; } = 20;
}

Without DI

If you are not using DI (for example, in WinForms, WPF, console apps, etc.), Use WritableConfig as the starting point for reading and writing settings.

using Configuration.Writable;

// initialize once (at application startup)
WritableConfig.Initialize<SampleSetting>();

// -------------
// get the writable config instance with the specified setting class
var options = WritableConfig.GetOptions<SampleSetting>();

// get the UserSetting instance
var sampleSetting = options.CurrentValue;
Console.WriteLine($">> Name: {sampleSetting.Name}");

// and save to storage
await options.SaveAsync(setting =>
{
    setting.Name = "new name";
});
// By default, it's saved to ./usersettings.json

With DI

If you are using DI (for example, in ASP.NET Core, Blazor, Worker Service, etc.), register IReadOnlyOptions<T> and IWritableOptions<T> in the DI container. First, call AddWritableOptions<T> to register the settings class.

// Program.cs
builder.Services.AddWritableOptions<UserSetting>();

Then, inject IReadOnlyOptions<T> or IWritableOptions<T> to read and write settings.

// read config in your class
// you can also use IOptions<T>, IOptionsMonitor<T> or IOptionsSnapshot<T>
public class ConfigReadService(IReadOnlyOptions<UserSetting> options)
{
    public void Print()
    {
        // get the UserSetting instance
        var sampleSetting = options.CurrentValue;
        Console.WriteLine($">> Name: {sampleSetting.Name}");
    }
}

// read and write config in your class
public class ConfigReadWriteService(IWritableOptions<UserSetting> options)
{
    public async Task UpdateAsync()
    {
        // get the UserSetting instance
        var sampleSetting = options.CurrentValue;
        // and save to storage
        await options.SaveAsync(setting =>
        {
            setting.Name = "new name";
        });
    }
}

Customization

Configuration Method

You can change various settings as arguments to Initialize or AddWritableOptions.

// Without DI
WritableConfig.Initialize<SampleSetting>(opt => { /* ... */ });

// With DI
builder.Services.AddWritableOptions<UserSetting>(opt => { /* ... */ });

Save Location

Default behavior is to save to {AppContext.BaseDirectory}/usersettings.json (in general, the same directory as the executable). If you want to change the save location, use opt.FilePath or opt.UseStandardSaveLocation("MyAppId").

For example:

// to save to the parent directory
opt.FilePath = "../myconfig";

// to save to child directory
opt.FilePath = "config/myconfig";

// to save to a common settings directory
//   in Windows: %APPDATA%/MyAppId
//   in macOS: $XDG_CONFIG_HOME/MyAppId or ~/Library/Application Support/MyAppId
//   in Linux: $XDG_CONFIG_HOME/MyAppId or ~/.config/MyAppId
opt.UseStandardSaveLocation("MyAppId");

If you want to toggle between development and production environments, you can use #if RELEASE pattern or builder.Environtment.IsProduction().

// those pattern are saved to
// - development: ./mysettings.json (executable directory)
// - production:  %APPDATA%/MyAppId/mysettings.json (on Windows)

// without DI
WritableConfig.Initialize<UserSetting>(opt => {
    opt.FilePath = "mysettings.json";
#if RELEASE
    opt.UseStandardSaveLocation("MyAppId");
#endif
});

// if using IHostApplicationBuilder
builder.Services.AddWritableOptions<UserSetting>(opt => {
    opt.FilePath = "mysettings.json";
    if (builder.Environment.IsProduction()) {
        opt.UseStandardSaveLocation("MyAppId");
    }
});

Provider

If you want to change the format when saving files, specify opt.Provider. Currently, the following providers are available:

Provider	Description	NuGet Package
WritableConfigJsonProvider	save in JSON format.	Built-in
WritableConfigXmlProvider	save in XML format.
WritableConfigYamlProvider	save in YAML format.
WritableConfigEncryptProvider	save in AES-256-CBC encrypted JSON format.

// use Json format with indentation
opt.Provider = new WritableConfigJsonProvider() {
    JsonSerializerOptions = { WriteIndented = true },
};

// use Yaml format
// (you need to install Configuration.Writable.Yaml package)
opt.Provider = new WritableConfigYamlProvider();

// use encrypted format
// NOTE: Be aware that this is a simple encryption.
// (you need to install Configuration.Writable.Encrypt package)
opt.Provider = new WritableConfigEncryptProvider("any-encrypt-password");

Note

To reduce dependencies and allow users to choose only the features they need, providers are offered as separate packages. That said, the JSON provider is built into the main package because since many users are likely to use the JSON format.

FileProvider

Default FileProvider (CommonFileProvider) supports the following features:

• Automatically retry when file access fails (default is max 3 times, wait 100ms each)
• Create backup files rotated by timestamp (default is disabled)
• Atomic file writing (write to a temporary file first, then rename it)
• Thread-safe: uses internal semaphore to ensure safe concurrent access

If you want to change the way files are written, create a class that implements IFileProvider and specify it in opt.FileProvider.

using Configuration.Writable.FileProvider;

opt.FileProvider = new CommonFileProvider() {
    // retry up to 5 times when file access fails
    MaxRetryCount = 5,
    // wait 100ms, 200ms, 300ms, ... before each retry
    RetryDelay = (attempt) => 100 * attempt,
    // keep 5 backup files when saving
    BackupMaxCount = 5,
};

Direct Reference Without Option Type

If you want to directly reference the settings class, specify opt.RegisterInstanceToContainer = true.

Note

The dynamic update functionality provided by IOptionsMonitor<T> will no longer be available. Be mindful of lifecycle management, as settings applied during instance creation will be reflected.

builder.Services.AddWritableOptions<UserSetting>(opt => {
    opt.RegisterInstanceToContainer = true;
});

// you can use UserSetting directly
public class MyService(UserSetting setting)
{
    public void Print()
    {
        Console.WriteLine($">> Name: {setting.Name}");
    }
}

// and you can also use IReadOnlyOptions<T> as usual
public class MyOtherService(IReadOnlyOptions<UserSetting> options)
{
    public void Print()
    {
        var setting = options.CurrentValue;
        Console.WriteLine($">> Name: {setting.Name}");
    }
}

Logging

Logging is enabled by default in DI environments.
If you are not using DI, or if you want to override the logging settings, you can enable logging by specifying opt.Logger.

// without DI
// package add Microsoft.Extensions.Logging.Console
opt.Logger = LoggerFactory
    // enable console logging 
    .Create(builder => builder.AddConsole())
    .CreateLogger("Configuration.Writable");

// with DI
// no setup required (uses the logger from DI)

When the output level is set to Information, mainly the following two logs are output.

info: Configuration.Writable[0]
      Configuration file change detected: mysettings.json (Renamed)
info: Configuration.Writable[0]
      Configuration saved successfully to mysettings.json

SectionName

When saving settings, they are written to a configuration file in a structured format. By default, settings are stored directly at the root level:

{
  // properties of UserSetting are stored directly at the root level
  "Name": "custom name",
  "Age": 30
}

To organize settings under a specific section, use opt.SectionName.

{
  // opt.SectionName = "MyAppSettings:Foo:Bar"
  "MyAppSettings": {
    "Foo": {
      "Bar": {
        // properties of UserSetting
        "Name": "custom name",
        "Age": 30
      }
    }
  }
}

InstanceName

If you want to manage multiple settings of the same type, you must specify different InstanceName for each setting.

// first setting
builder.Services.AddWritableOptions<UserSetting>(opt => {
    opt.FilePath = "firstsettings.json";
    opt.InstanceName = "First";
});
// second setting
builder.Services.AddWritableOptions<UserSetting>(opt => {
    opt.FilePath = "secondsettings.json";
    opt.InstanceName = "Second";
});

// and get each setting from DI
public class MyService(IWritableOptions<UserSetting> options)
{
    public void GetAndSave()
    {
        // cannot use .CurrentValue if multiple settings of the same type are registered
        var firstSetting = options.Get("First");
        var secondSetting = options.Get("Second");
        // and you must specify instance name when saving
        await options.SaveWithNameAsync("First", setting => {
            setting.Name = "first name";
        });
        await options.SaveWithNameAsync("Second", setting => {
            setting.Name = "second name";
        });
    }
}

Note

When not using DI (direct use of WritableConfig), managing multiple configurations is intentionally not supported. This is to avoid complicating usage.

Validation

By default, validation using DataAnnotations is enabled. If validation fails, an OptionsValidationException is thrown and the settings are not saved.

using Microsoft.Extensions.Options;

builder.Services.AddWritableOptions<UserSetting>(opt => {
    // if you want to disable validation of DataAnnotations, do the following:
    // opt.UseDataAnnotationsValidation = false;
});

var options = WritableConfig.GetOptions<UserSetting>();
try {
    await options.SaveAsync(setting => {
        setting.Name = "ab"; // too short
        setting.Age = 200;  // out of range
    });
}
catch (OptionsValidationException ex)
{
    Console.WriteLine($">> Validation failed: {ex.Message}");
    // setting is not saved if validation fails
}

internal class UserSetting
{
    [Required, MinLength(3)]
    public string Name { get; set; } = "default name";
    [Range(0, 150)]
    public int Age { get; set; } = 20;
}

To use source generators for DataAnnotations, use the following pattern.

builder.Services.AddWritableOptions<UserSetting>(opt => {
    // disable attributes-based validation
    opt.UseDataAnnotationsValidation = false;
    // enable source-generator-based validation
    opt.WithValidator<UserSettingValidator>();
});

internal class UserSetting { /* ... */ }

[OptionsValidator]
public partial class UserSettingValidator : IValidateOptions<UserSetting>;

Alternatively, you can add custom validation using WithValidatorFunction or WithValidator.

using Microsoft.Extensions.Options;

builder.Services.AddWritableOptions<UserSetting>(opt => {
    // add custom validation function
    opt.WithValidatorFunction(setting => {
        if (setting.Name.Contains("invalid"))
            return ValidateOptionsResult.Fail("Name must not contain 'invalid'.");
        return ValidateOptionsResult.Success;
    });
    // or use a custom validator class
    opt.WithValidator<MyCustomValidator>();
});

// IValidateOptions sample
internal class MyCustomValidator : IValidateOptions<UserSetting>
{
    public ValidateOptionsResult Validate(string? name, UserSetting options)
    {
        if (options.Age < 10)
            return ValidateOptionsResult.Fail("Age must be at least 10.");
        if (options.Age > 100)
            return ValidateOptionsResult.Fail("Age must be 100 or less.");
        return ValidateOptionsResult.Success;
    }
}

Note

Validation at startup is intentionally not provided. The reason is that in the case of user settings, it is preferable to prompt for correction rather than prevent startup when a validation error occurs.

Advanced Usage

Dynamic Add/Remove Options

You can dynamically add or remove writable options at runtime using IOptionsConfigRegistry. for example, in addition to common application settings, it is useful when you want to have individual settings for each document opened by the user.

// use IOptionsConfigRegistry from DI
public class DynamicOptionsService(IOptionsConfigRegistry<UserSetting> registry)
{
    public void AddNewOptions(string instanceName, string filePath)
    {
        registry.TryAdd(opt => {
            opt.InstanceName = instanceName;
            opt.FilePath = filePath;
        });
    }

    public void RemoveOptions(string instanceName)
    {
        registry.TryRemove(instanceName);
    }
}

// and you can access IOptionsMonitor<T> or IWritableOptions<T> as usual
public class MyService(IWritableOptions<UserSetting> options)
{
    public void UseOptions()
    {
        var commonSetting = options.Get("Common");
        var documentSetting = options.Get("UserDocument1");
        var name = documentSetting.Name ?? commonSetting.Name ?? "default";
        Console.WriteLine($">> Name: {name}");

        // and save to specific instance
        await options.SaveWithNameAsync("UserDocument1", setting => {
            setting.Name = "document specific name";
        }
    }
}

Multiple Settings in a Single File

Using ZipFileProvider, you can save multiple settings classes in a single configuration file. for example, to save Foo(foo.json) and Bar(bar.json) in configurations.zip:

var zipFileProvider = new ZipFileProvider { ZipFileName = "configurations.zip" };

// initialize each setting with the same file provider
builder.Services.AddWritableOptions<Foo>(opt =>
{
    opt.FilePath = "foo";
    opt.FileProvider = zipFileProvider;
});
builder.Services.AddWritableOptions<Bar>(opt =>
{
    opt.FilePath = "bar";
    opt.FileProvider = zipFileProvider;
});

Testing

If you simply want to obtain IReadOnlyOptions<T> or IWritableOptions<T>, using WritableOptionsStub is straightforward.

using Configuration.Writable.Testing;

var settingValue = new UserSetting();
var options = WritableOptionsStub.Create(settingValue);

// and use options in your test
var yourService = new YourService(options);
yourService.DoSomething();

// settingValue is updated when yourService changes it
Assert.Equal("expected name", settingValue.Name);

If you want to perform tests that actually involve writing to the file system, use WritableOptionsSimpleInstance.

var sampleFilePath = Path.GetTempFileName();
var instance = new WritableOptionsSimpleInstance<UserSetting>();
instance.Initialize(opt => {
    opt.FilePath = sampleFilePath;
});
var option = instance.GetOptions();

// and use options in your test
var yourService = new YourService(options);
yourService.DoSomething();

// sampleFilePath now contains the updated settings
var json = File.ReadAllText(sampleFilePath);
Assert.Contains("expected name", json);

Interfaces

IReadOnlyOptions

An interface for reading the settings of the registered type T.
It automatically reflects the latest settings when the underlying configuration is updated.
This interface provides functionality equivalent to IOptionsMonitor<T> from MS.E.O.

public interface IReadOnlyOptions<T> : IOptionsMonitor<T> where T : class, new()

The additional features compared to IOptionsMonitor<T> are as follows:

• The GetConfigurationOptions method to retrieve configuration options.
• In environments where file change detection is not possible, you can always get the latest settings (internal cached value is updated when SaveAsync is called).

IWritableOptions

An interface for reading and writing the settings of the registered type T. It provides the same functionality as IReadOnlyOptions<T>, with additional support for saving settings.

public interface IWritableOptions<T> : IReadOnlyOptions<T> where T : class, new()

ToDo

• Support version update migration
• Support multiple configurations merging

License

This project is licensed under the Apache-2.0 License.