openapi-generator-original/samples/client/petstore/kotlin-default-values-jvm-volley/README.md

org.openapitools.client - Kotlin client library for Demo

A kotlin client for Android using the currently recommended http client, Volley. See https://developer.android.com/training/volley

• Currently sends GsonRequests
• Currently only supports Gson as a serializer - will throw an exception if a different serializer is chosen
• Defaults the source location to src/main/java as per standard Android builds

Design

Volley is a queue/request based layer on top of http url stack specific to Android. Android favours dependency injection and a layered architecture, and IO performed off the main thread to maintain UI responsiveness, with a preferred technique of kotlin co-routines. The code gen library reflects these factors.

• Api calls use co-routines, and execute them using volley callbacks to avoid tying up a thread.

• Facilitate dependency injection, with default implementations available.

• Generate a requestFactory that can be overridden

• Allow the passing of the RequestFactory per tag (api client) or per operation (an extra parameter is created on operations with non-global security), with per operation auth overriding global security.

• DI scoping of the Request Factory and pre-generated auth header factories allow for thread safe and secure setting of credentials.

• Lazy header factories allow for refreshing tokens etc

• Factoring of header factories to the Request Factory allow ambient provision of credentials. Code gen library is credential storage agnostic.

• Header factories allow the merging of generated headers from open api spec with dynamically added headers

• Injection of http url stack to allow custom http stacks. Default implementation is best practice singleton

• Data classes used for serialisation to reflect volley's preference - an immutable request that once queued can't be tampered with.

• Reuse model class and other jvm common infrastructure

• Optional generation of room database models, and transform methods to these from open api models

• Room and api models can be extended with additional extension properties.

Future improvements

• Option to generate image requests on certain conditionals e.g content-type gif etc
• Support for kotlin serialization.
• Multi part form parameters and support for file inputs

Usage

Hilt Dependency injection example - with default values for parameters overridden.

 @Provides
    internal fun provideSomeApi(
        context: Context,
        restService: IRestService,
        configurationService: IConfigurationService,
        sessionService: ISessionService
    ): SomeApi {
        return SomeApi(
            context = context,
            requestQueue = restService.getRequestQueue(),
            requestFactory = RequestFactory(listOf(createSessionHeaderFactory(sessionService), createTraceHeaderFactory()),
                postProcessors = listOf(retryPolicySetter)),
            basePath = configurationService.getBaseUrl()
        )
    }

Here is the constructor so you can see the defaults

val context: Context,
val requestQueue: Lazy<RequestQueue> = lazy(initializer = {
    Volley.newRequestQueue(context.applicationContext)
    }),
    val requestFactory: IRequestFactory = RequestFactory(),
    val basePath: String = "https://yourbasepath.from_input_parameter.com/api",
    private val postProcessors :List <(Request<*>) -> Unit> = listOf()) {

Overriding defaults

The above constructor for each api allows the following to be customized

• A custom context, so either a singleton request queue or different scope can be created - see https://developer.android.com/training/volley/requestqueue#singleton
• An overridable request queue - which in turn can have a custom http url stack passed to it
• An overridable request factory constructor call, or a request factory that can be overridden by a custom template, with custom header factory, request post processors and custom gson adapters injected.

Overriding request generation

Request generation can be overridden by

• Overriding the entire request factory template
• Supplying custom header factories - methods that take any possible parameters but return a map of headers
• Supplying custom request post processors - methods that take and return the request object

Header factory examples can be found in the auth section, as these are implemented as header factories. eg

val basicAuthHeaderFactoryBuilder = { username: String?, password: String? ->
{ mapOf("Authorization" to "Basic " + Base64.encodeToString("${username ?: ""}:${password ?: ""}".toByteArray(), Base64.DEFAULT))}
}

In this case it's a lambda function (a factory method) that takes an username and password, and returns a map of headers. Other generated code will supply the username and password. In this case it results in a map of just one key/value pair, but it could be multiple. The important part is it's returning a map - and that the surrounding code will can bind the inputs to it at some point.

Here is a different example that supplies tracing header values

/**
 * Create a lambda of tracing headers to be injected into an API's [RequestFactory].
 */
private fun createTraceHeaderFactory(): () -> Map<String, String> = {
    mapOf(
        HttpHeaderType.b3_traceId.rawValue to UUIDExtensions.asTraceId(UUID.randomUUID()),
        HttpHeaderType.b3_spanId.rawValue to UUIDExtensions.asSpanId(UUID.randomUUID()),
        HttpHeaderType.b3_sampled.rawValue to "1"
    )
}

Finally a post processor example

 /**
     * Configure a [DefaultRetryPolicy] to be injected into the [RequestFactory] with a maximum number of retries of zero.
     */
    private val retryPolicySetter = { request: Request<*> ->
        Unit.apply {
            request.setRetryPolicy(
                DefaultRetryPolicy(
                    RestService.DEFAULT_TIMEOUT_MS,
                    0,
                    DefaultRetryPolicy.DEFAULT_BACKOFF_MULT
                )
            )
        }
    }

Serialization

Gson and Polymorphic types

The GsonRequest object can be passed custom type adapters

class GsonRequest<T>(
    method: Int,
    url: String,
    private val body: Any?,
    private val headers: Map<String, String>?,
    private val params: MutableMap<String, String>?,
    private val contentTypeForBody: String?,
    private val encodingForParams: String?,
    private val gsonAdapters: Map<Type, Object>?,
    private val type: Type,
    private val listener: Response.Listener<T>,
    errorListener: Response.ErrorListener
) : Request<T>(method, url, errorListener) {

    val gsonBuilder: GsonBuilder = GsonBuilder()
        .registerTypeAdapter(OffsetDateTime::class.java, OffsetDateTimeAdapter())
        .registerTypeAdapter(LocalDateTime::class.java, LocalDateTimeAdapter())
        .registerTypeAdapter(LocalDate::class.java, LocalDateAdapter())
        .registerTypeAdapter(ByteArray::class.java, ByteArrayAdapter())

Requires

• Kotlin 1.4.30
• Gradle 6.8.3

Build

First, create the gradle wrapper script:

gradle wrapper

Then, run:

./gradlew check assemble

This runs all tests and packages the library.

Documentation for API Endpoints

All URIs are relative to http://localhost

Class	Method	HTTP request	Description
DefaultApi	test	POST /test	Tests default values

Documentation for Models

• org.openapitools.client.models.Apa

Documentation for Authorization

Endpoints do not require authorization.