The Ktor OpenAPI Generator is a library to automatically generate the descriptor as you route your ktor application.

This version by LukasForst was migrated to Ktor 2.0.0 and is hosted on Maven Central.

dependencies {
    implementation("dev.forst:ktor-openapi-generator:0.6.1")
}

See MinimalExample.kt for minimal example app and then MinimalExampleTest.kt that it actually works.

/**
 * Minimal example of OpenAPI plugin for Ktor.
 */
fun Application.minimalExample() {
    // install OpenAPI plugin
    install(OpenAPIGen) {
        // this servers OpenAPI definition on /openapi.json
        serveOpenApiJson = true
        // this servers Swagger UI on /swagger-ui/index.html
        serveSwaggerUi = true
        info {
            title = "Minimal Example API"
        }
    }
    // install JSON support
    install(ContentNegotiation) {
        jackson()
    }
    // and now example routing
    apiRouting {
        route("/example/{name}") {
            // SomeParams are parameters (query or path), SomeResponse is what the backend returns and SomeRequest
            // is what was passed in the body of the request
            post<SomeParams, SomeResponse, SomeRequest> { params, someRequest ->
                respond(SomeResponse(bar = "Hello ${params.name}! From body: ${someRequest.foo}."))
            }
        }
    }
}

data class SomeParams(@PathParam("who to say hello") val name: String)
data class SomeRequest(val foo: String)
data class SomeResponse(val bar: String)

Ktor OpenAPI Generator is:

• Modular
• Strongly typed
• Explicit

Currently Supported:

• Authentication interoperability with strongly typed Principal (OAuth only, see TestServer in tests)
• Content Negotiation interoperability (see TestServer in tests)
• Custom response codes (as parameter in @Response)
• Automatic and custom content Type routing and parsing (see com.papsign.ktor.openapigen.content.type, Binary Parser and default JSON parser (that uses the ktor implicit parsing/serializing))
• Exception handling (use .throws(ex) {} in the routes with an APIException object) with Status pages interop (with .withAPI in the StatusPages configuration)
• tags (.tag(tag) {} in route with a tag object, currently must be an enum, but may be subject to change)
• Spec compliant Parameter Parsing (see basic example)
• Legacy Polymorphism with use of @DiscriminatorAnnotation() attribute and sealed classes

Extra Features:

• Includes Swagger-UI (enabled by default, can be managed in the install(OpenAPIGen) { ... } section)

Take a look at a few examples