JsonTypeDefinition

An RFC 8927 compliant parser for .NET.

Json Type Definitions (JTDs) provide a human-readable, portable type description that can be consumed by any programming language.

A common use-case would be a REST API describing the form in which payloads are expected. It could publicize this form as a Json Type Definition which could subsequently be interpreted by any client independent of their technology stack.

Installation

dotnet add package JsonTypeDefinition

Usage

The JsonTypeDefinitionParser provides two methods:

var x = JsonTypeDefinitionParser.Parse(typeof(User));
var y = JsonTypeDefinitionParser.Parse<User>();

Both methods will produce the same output. Given the following types:

class User
{
    [Required]
    public string Name { get; set; }
    public Address Address { get; set; }
    public DateTimeOffset JoinedAt { get; set; }
    public double GPA { get; set; }
}

class Address 
{
    public string StreetName { get; set; }
    public int HouseNumber { get; set; }
}

The parser would produce the following Json Type Definition:

{
    "properties": {
        "Name": { "type": "string" }
    },
    "optionalProperties": {
        "Address": { "ref": "Address" },
        "JoinedAt": { "type": "timestamp" },
        "GPA": { "type": "float64" }
    },
    "definitions": {
        "Adress": {
            "optionalProperties": {
                "StreetName": { "type": "string" },
                "HouseNumber": { "type": "int32" }
            }
        }
    }
}

Do note that JsonTypeDefinitionParser.Parse returns a record of type RootSchema and has no reference to Newtonsoft.Json or System.Text.Json. Feel free to use your favorite JSON serializer to get the appropriate JSON representation! Recommended serialization settings:

// Newtonsoft.Json:
var settings = new Newtonsoft.Json.JsonSerializerSettings()
{
    NullValueHandling = Newtonsoft.Json.NullValueHandling.Ignore,
    Converters = new Newtonsoft.Json.JsonConverter[] { new Newtonsoft.Json.Converters.StringEnumConverter() }
};

// System.Text.Json:
var options = new System.Text.Json.JsonSerializerOptions { IgnoreNullValues = true };
options.Converters.Add(new System.Text.Json.Serialization.JsonStringEnumConverter());

Limitations

When defining the models it is important to design them around the limitations that come with a portable, consumer agnostic type definition.

Some commonly used .NET types are currently not supported, including System.TimeSpan. Imagine what would happen if you were to create a JTD from a time span object. RFC 8927 does not define a fitting primitive type that could be used (timestamp is more akin to System.DateTimeOffset) as there is no universally agreed upon way to describe durations. 10 minutes could be described as 00:10:00, PT10M (ISO 8601), 3600 (in seconds), etc. There would be no way for consumers of the JTD to know which notation to use. Instead you're encouraged to work around these limitations for example by replacing

public TimeSpan TimeToLive { get; set; }

with

public double TimeToLiveInSeconds { get; set; }

so that any consumer nows exactly what format you expect.

Future improvements

Contributions are welcome :)

• custom handlers for handling otherwise unsupported types
• generate .NET types from JTDs