Saunter

Saunter is an AsyncAPI documentation generator for dotnet.

Getting Started

See examples/StreetlightsAPI.

1. Install the Saunter package

   dotnet add package Saunter
   

2. In the ConfigureServices method of Startup.cs, configure Saunter.

   // Add Saunter to the application services. 
   services.AddAsyncApiSchemaGeneration(options =>
   {
       // Specify example type(s) from assemblies to scan.
       options.AssemblyMarkerTypes = new[] {typeof(StreetlightMessageBus)};
   
       // Build as much (or as little) of the AsyncApi document as you like.
       // Saunter will generate Channels, Operations, Messages, etc, but you
       // may want to specify Info here.
       options.AsyncApi = new AsyncApiDocument
       {
           Info = new Info("Streetlights API", "1.0.0")
           {
               Description = "The Smartylighting Streetlights API allows you\nto remotely manage the city lights.",
               License = new License("Apache 2.0")
               {
                   Url = "https://www.apache.org/licenses/LICENSE-2.0"
               }
           },
           Servers =
           {
               { "mosquitto", new Server("test.mosquitto.org", "mqtt") }
           }
       };
   });
   

3. Add attributes to your classes which publish or subscribe to messages.

   [AsyncApi] // Tells Saunter to scan this class.
   public class StreetlightMessageBus : IStreetlightMessageBus
   {
       [Channel("publish/light/measured")] // Creates a Channel
       [PublishOperation(typeof(LightMeasuredEvent), Summary = "Inform about environmental lighting conditions for a particular streetlight.")] // A simple Publish operation.
       public void PublishLightMeasuredEvent(Streetlight streetlight, int lumens) {}
   

4. Add saunter middleware to host the AsyncApi json document. In the Configure method of Startup.cs:

   app.UseEndpoints(endpoints =>
   {
       endpoints.MapAsyncApiDocuments();
   });
   

5. Use the published AsyncApi document:

   // HTTP GET /asyncapi/asyncapi.json
   {
       // Properties from Startup.cs
       "asyncapi": "2.0.0",
       "info": {
           "title": "Streetlights API",
           "version": "1.0.0",
           "description": "The Smartylighting Streetlights API allows you\nto remotely manage the city lights.",
          // ...
       },
       // Properties generated from Attributes
       "channels": {
           "light/measured": {
           "publish": {
               "operationId": "PublishLightMeasuredEvent",
               "summary": "Inform about environmental lighting conditions for a particular streetlight.",
           //...
   }
   

Bindings

Bindings are used to describe protocol specific information. These can be added by creating a Filter which will be applied to each operation during the AsyncAPI document generation.

To use a filter, create a class which implements IOperationFilter and register it in Startup.cs

In the filter you can set custom binding information.

public class MyCustomOperationFilter : IOperationFilter
{
    public void Apply(Operation operation, OperationFilterContext context)
    {
        // Here you have access to the generated Operation which you can modify.
        // You are also provided with the Context which contains things like the MethodInfo and Attribute
        // used to generate the Operation.
        
        operation.Bindings = new OperationBindings
        {
            Http = // set http binding info
            Kafka = // set kafka binding info
            // etc
        }
    }
}

services.AddAsyncApiSchemaGeneration(options =>
{
    options.OperationFilters.Add(new MyCustomOperationFilter());
});

Once these steps are complete, when you generate your documentation any class with a [PublishOperation] or [SubscribeOperation] attributes will have the binding information added to the documentation.

Http Bindings

Example HTTP binding operation filter

public class HttpOperationFilter : IOperationFilter
{
    public void Apply(Operation operation, OperationFilterContext context)
    {
        operation.Bindings = new OperationBindings
        {
            Http = new HttpOperationBinding
            {
                Type = "request",
                Method = "GET",
                Query = new HttpOperationBindingQuery
                {
                    Type = "object",
                    Required = new string[] { "companyId" },
                    Properties = new
                    {
                        CompanyId = new
                        {
                            Type = "number",
                            Minimum = 1,
                            Desciption = "The Id of the company."
                        }
                    },
                    AdditionalProperties = false
                },
                BindingVersion = "0.1.0"
            }
        };
    }
}

Kafka Bindings

Example Kafka binding operation filter

public class KafkaOperationFilter : IOperationFilter
{
    public void Apply(Operation operation, OperationFilterContext context)
    {
        operation.Bindings = new OperationBindings
        {
            Kafka = new KafkaOperationBinding
            {          
                GroupId = new KafkaOperationBindingGroupId
                {
                    Type = "string",
                    Enum = new string[] { "myGroupId" }     
                },
                ClientId = new KafkaOperationBindingClientId
                {
                    Type = "string",
                    Enum = new string[] { "myClientId" }
                },
                BindingVersion = "0.1.0"
            }
        };
    }
}

Contributing

See our contributing guide.

Feel free to get involved in the project by opening issues, or submitting pull requests.

Thanks

• This project is heavily inspired by Swashbuckle.
• We use Namotion.Reflection for pulling xml documentation.