Kompendium

What is Kompendium

Kompendium is intended to be a minimally invasive OpenApi Specification generator for Ktor. Minimally invasive meaning that users will use only Ktor native functions when implementing their API, and will supplement with Kompendium code in order to generate the appropriate spec.

How to install

Kompendium uses GitHub packages as its repository. Installing with Gradle is pretty painless. In your build.gradle.kts add the following

// 1 Setup a helper function to import any Github Repository Package
// This step is optional but I have a bunch of stuff stored on github so I find it useful 😄
fun RepositoryHandler.github(packageUrl: String) = maven { 
    name = "GithubPackages"
    url = uri(packageUrl)
    credentials { // TODO Not sure this is necessary for public repositories?
      username = java.lang.System.getenv("GITHUB_USER")
      password = java.lang.System.getenv("GITHUB_TOKEN")
    } 
}

// 2 Add the repo in question (in this case Kompendium)
repositories {
    github("https://maven.pkg.github.com/lg-backbone/kompendium")
}

// 3 Add the package like any normal dependency
dependencies { 
    implementation("org.leafygreens:kompendium-core:0.1.0-SNAPSHOT")
}

In depth

Warning 🚨

Kompendium is still under active development ⚠️ There are a number of yet-to-be-implemented features, including

Multiple Responses 📜
Sealed Class / Polymorphic Support 😬
Validation / Enforcement (❓👀❓)

If you have a feature that is not listed here, please open an issue!

Notarized Routes

Kompendium introduces the concept of notarized HTTP methods. That is, for all your GET, POST, PUT, and DELETE operations, there is a corresponding notarized method. These operations are strongly typed, and use reification for a lot of the class based reflection that powers Kompendium. Generally speaking the three types that a notarized method will consume are

TParam: Held for future implementations, will allow Kompendium to register information on path and query parameters
TReq: Used to build the object schema for a request body
TResp: Used to build the object schema for a response body

GET and DELETE take TParam and TResp while PUT and POST take all three.

In keeping with minimal invasion, these extension methods all consume the same code block as a standard Ktor route method, meaning that swapping in a default Ktor route and a Kompendium notarized route is as simple as a single method change.

Supplemental Annotations

In general, Kompendium tries to limit the number of annotations that developers need to use in order to get an app integrated.

Currently, the annotations used by Kompendium are as follows

KompendiumField
PathParam
QueryParam
HeaderParam
CookieParam

The intended purpose of KompendiumField is to offer field level overrides such as naming conventions (ie snake instead of camel).

The 4 "param" annotations are to offer supplemental information in data classes that describe the set of parameters types that a notarized route needs to analyze.

Examples

The full source code can be found in the kompendium-playground module. Here we show just the adjustments needed to a standard Ktor server to get up and running in Kompendium.

// Minimal API Example
fun main() {
  embeddedServer(
    Netty,
    port = 8081,
    module = Application::mainModule
  ).start(wait = true)
}

fun Application.mainModule() {
  install(ContentNegotiation) {
    jackson {
      enable(SerializationFeature.INDENT_OUTPUT)
      setSerializationInclusion(JsonInclude.Include.NON_NULL)
    }
  }
  routing {
    openApi()
    redoc()
    route("/test") {
      route("/{id}") {
        notarizedGet<ExampleParams, ExampleResponse>(testIdGetInfo) {
          call.respondText("get by id")
        }
      }
      route("/single") {
        notarizedGet<ExampleParams, ExampleResponse>(testSingleGetInfo) {
          call.respondText("get single")
        }
        notarizedPost<Unit, ExampleRequest, ExampleCreatedResponse>(testSinglePostInfo) {
          call.respondText("test post")
        }
        notarizedPut<ExampleParams, ExampleRequest, ExampleCreatedResponse>(testSinglePutInfo) {
          call.respondText { "hey" }
        }
        notarizedDelete<Unit, Unit>(testSingleDeleteInfo) {
          call.respondText { "heya" }
        }
      }
    }
  }
}

When run in the playground, this would output the following at /openapi.json

https://gist.github.com/rgbrizzlehizzle/b9544922f2e99a2815177f8bdbf80668

Kompendium Auth and security schemes

There is a seperate library to handle security schemes: kompendium-auth. This needs to be added to your project as dependency.

At the moment, the basic and jwt authentication is only supported.

A minimal example would be:

  install(Authentication) {
    notarizedBasic("basic") {
      realm = "Ktor realm 1"
      // configure basic authentication provider..
    }
    notarizedJwt("jwt") {
      realm = "Ktor realm 2"
      // configure jwt authentication provider...
    }
  }
  routing {
    authenticate("basic") {
      route("/basic_auth") {
        notarizedGet<TestParams, TestResponse>(
          MethodInfo(
            // securitySchemes needs to be set
            "Another get test", "testing more", testGetResponse, securitySchemes = setOf("basic")
          )
        ) {
          call.respondText { "basic auth" }
        }
      }
    }
    authenticate("jwt") {
      route("/jwt") {
        notarizedGet<TestParams, TestResponse>(
          MethodInfo(
            // securitySchemes needs to be set
            "Another get test", "testing more", testGetResponse, securitySchemes = setOf("jwt")
          )
        ) {
          call.respondText { "jwt" }
        }
      }
    }
  }

Enabling Swagger ui

To enable Swagger UI, kompendium-swagger-ui needs to be added. This will also add the ktor webjars feature to your classpath as it is required for swagger ui. Minimal Example:

  install(Webjars)
  routing {
    openApi()
    swaggerUI()
  }

Limitations

Kompendium as a singleton

Currently, Kompendium exists as a Kotlin object. This comes with a couple perks, but a couple downsides. Primarily, it offers a seriously clean UX where the implementer doesn't need to worry about what instance to send data to. The main drawback, however, is that you are limited to a single API per classpath.

If this is a blocker, please open a GitHub issue, and we can start to think out solutions!

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