An Alternative .NET Configuration Handler
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README.md

Cfg-NET

Build status NuGet

An open source configuration handler for .NET licensed under Apache 2.

Cfg-NET Configurations:

  • are editable by end-users
  • reduce the need to re-compile
  • co-exist with other configurations

Cfg-NET:

  • is easy to use
  • supports collections
  • validates and reports errors and warnings
  • offers protection from null
  • allows you to store your configuration where you want (e.g. web, file, string)
  • is extensible
  • is composable
  • is small (~68 KB)
  • has zero dependencies
  • is portable (.NETStandard1.0 with PCL compatibility)
  • is available on Nuget

Configuration

Out of the box, Cfg-NET supports XML and JSON configurations.

An XML example:

<cfg>
    <fruit>
        <add name="apple">
            <colors>
                <add name="red" />
                <add name="yellow" />
                <add name="green" />
            </colors>
        </add>
        <add name="banana">
            <colors>
                <add name="yellow" />
            </colors>
        </add>
    </fruit>
</cfg>

Or, if you prefer JSON:

{
    "fruit": [
        { 
            "name":"apple",
            "colors": [
                {"name":"red"},
                {"name":"yellow"},
                {"name":"green"}
            ]
        },
        {
            "name":"banana",
            "colors": [
                {"name":"yellow"}
            ]
        }
    ]
}

Code

In code, you want to deal with a corresponding C# model like this:

using System.Collections.Generic;

class Cfg {
    public List<Fruit> Fruit { get; set; }
}

class Fruit {
    public string Name { get; set; }
    public List<Color> Colors {get; set;}
}

class Color {
    public string Name {get; set;}
}

To make the above model work with Cfg-NET, have each class inherit CfgNode and decorate the properties with the Cfg custom attribute:

using System.Collections.Generic;
using Cfg.Net;

class Cfg : CfgNode {
    [Cfg]
    public List<Fruit> Fruit { get; set; }
}

class Fruit : CfgNode {
    [Cfg]
    public string Name { get; set; }
    [Cfg]
    public List<Color> Colors {get; set;}
}

class Color : CfgNode {
    [Cfg]
    public string Name {get; set;}
}

Design the Configuration

Inheriting from CfgNode provides:

  • a constructor allowing for dependency injection
  • a Load() method for processing an external configuration
  • a Check() method for processing an model you created in code
  • a Sequence property indicating the order your configuration was processed
  • an Errors() method to get errors in your configuration (after Load, or Check called)
  • an Warnings() method to get warnings in your configuration (after Load, or Check called)
  • a Serialize() method to get your model out as a string (xml, json, etc.)

The Cfg attributes add validation and modification instructions. An attribute has these built-in options:

  • value, as in default value
  • toLower or toUpper
  • trim, trimStart, or trimEnd
  • required
  • unique
  • domain with delimiter and ignoreCase options
  • minLength and/or maxLength
  • minValue and/or maxValue
  • regex with ignoreCase option

If we want to make sure some fruit is defined in our configuration, we would add required=true to the fruit list like this:

class Cfg : CfgNode {
    [Cfg(required=true)] // THERE MUST BE SOME FRUIT!
    public List<Fruit> Fruit { get; set; }
}

If we want to make sure the fruit names are unique, we could add unique=true to the fruit name attribute like this:

class Fruit : CfgNode {
    [Cfg(unique=true)] // THE FRUIT MUST BE UNIQUE!
    public string Name { get; set; }
    [Cfg]
    public List<Color> Colors {get; set;}
}

If we want to control what colors are used, we could add domain="red,green,etc" to the color name attribute like this:

class Color : CfgNode {
    [Cfg(domain="red,yellow,green,blue,purple,orange")]
    public string Name {get; set;}
}

Load the Configuration

Now that we have a model and our choice of JSON or XML configurations, we may load the configuration into the model like this:

// let xml be your configuration
var cfg = new Cfg();
cfg.Load(xml);

Examine for Errors and/or Warnings

When you load a configuration, Cfg-NET doesn't throw exceptions. Instead, it collects errors and/or warnings.

After loading, always examine your model for any issues using the Errors() and Warnings() methods:

//LOAD CONFIGURATION
var cfg = new Cfg();
cfg.Load(xml);

/* CHECK FOR WARNINGS */
Assert.AreEqual(0, cfg.Warnings().Length);

/* CHECK FOR ERRORS */
Assert.AreEqual(0, cfg.Errors().Length);

/* EVERYTHING IS AWESOME!!! */

By convention, an error means the configuration is invalid. A warning is something you ought to address, but the program should still work.

Errors and warnings should be reported to the end-user so they can fix them. Here are some example errors:

Remove the required fruit and...

fruit must be populated in cfg.

Add another apple and...

Duplicate name value apple in fruit.

Add the color pink...

An invalid value of pink is in name. The valid domain is: red, yellow, green, purple, blue, orange.

If Cfg-NET doesn't report issues, your configuration is valid. You can loop through your fruits and their colors without a care in the world:

var cfg = new Cfg();
cfg.Load(xml);
    
foreach (var fruit in cfg.Fruit) {
    foreach (var color in fruit.Colors) {
        /* use fruit.Name and color.Name... */  
    }
}

You never have to worry about a Cfg decorated list being null because they are initialized as the configuration loads. Moreover, if you set default values (e.g. [Cfg(value="default")]), a property is never null.

Play with the apples and bananas on .NET Fiddle.

Customization

The Cfg attribute's optional properties offer simple validation. If it's not enough, you have ways to extend:

  1. Overriding PreValidate()
  2. Overriding Validate()
  3. Overriding PostValidate()

PreValidate()

If you want to modify the configuration before validation, override PreValidate() like this:

protected override void PreValidate() {
    if (Provider == "Bad Words") {
        Provider = "Good Words. Ha!";
        Warn("Please watch your language.");
    }
}

Validate()

To perform validation involving more than one property, override Validate() like this:

public class Connection : CfgNode {
    [Cfg(required = true, domain = "file,folder,other")]
    public string Provider { get; set; }
    
    [Cfg()]
    public string File { get; set; }
    
    [Cfg()]
    public string Folder { get; set; }
    
    /* CUSTOM VALIDATION */
    protected override void Validate() {
        if (Provider == "file" && string.IsNullOrEmpty(File)) {
            Error("file provider needs file attribute.");
        } else if (Provider == "folder" && string.IsNullOrEmpty(Folder)) {
            Error("folder provider needs folder attribute.");
        }
    }
}

When you override Validate, add issues using the Error() and Warn() methods.

PostValidate()

Overriding PostValidate gives you an opportunity to run code after validation. You may check Errors() and/or Warnings() and make further preparations.

protected override void PostValidate() {
    if (Errors().Length == 0) {
        /* make further preparations... */
    }
}

Customization

If the attributes and methods aren't enough, you may inject customizers (e.g. things implementing ICustomizer) into your model's contructor.

Serialize

After your configuration is loaded into code, you can serialize it back to a string with Serialize().

// load
var cfg = new Cfg();
cfg.Load(xml);

// modify
cfg.Fruit.RemoveAll(f => f.Name == "apple");
cfg.Fruit.Add(new Fruit {
    Name = "plum",
    Colors = new List<Color> {
        new Color { Name = "purple" }
    }
});

// serialize
var result = cfg.Serialize();

This produces a result of:

<cfg>
    <fruit>
        <add name="banana">
            <colors>
                <add name="yellow" />
            </colors>
        </add>
        <add name="plum">
            <colors>
                <add name="purple" />
            </colors>
        </add>
    </fruit>
</cfg>

Configure with Code and Check

Loading configurations is great. However, sometimes you need to write a configuration in code and still be able to check it for errors and/or warnings. To do this, just create your model however you like, and the run the Check method.

var cfg = new Cfg {
    Fruit = new List<Fruit> {
        new Fruit {
            Name = "Apple",
            Colors = new List<Color> {
                new Color {Name = "red"},
                new Color {Name = "aqua"}
            }
        }
    }
};

// Instead of using Load(), use Check()
cfg.Check();

// I put an error in there on purpose (hint: aqua is invalid)
Assert.AreEqual(1, cfg.Errors().Length);

Conclusion

So, if you need really great configurations for your programs, give Cfg-NET a try. I use it in just about all the programs I write, and I am very happy with it. Thank you for taking the time to read this. I appreciate the stars and feedback.

Credits

  • a modified version of NanoXmlParser found here.
  • a modified version of fastJSON found here
  • .NET Source of WebUtility.HtmlDecode found here, used as reference.

Further Reading