BREAKING: HttpClientEngine no longer implements Closeable

[lucix-aws]

The upcoming AWS SDK for Kotlin release, 0.20.0-beta on Jan. 26, 2023, introduces a breaking change to the API definition of HttpClientEngine by removing the Closeable supertype from the interface.

Background
The AWS SDK for Kotlin defines the Closeable interface as

/**
 * A resource than can be closed. The [close] method is invoked to release resources
 * an object is holding (e.g. such as open files)
 */
public expect interface Closeable {
    /**
     * Release any resources held by this object
     */
    public fun close()
}

In the past, the HttpClientEngine interface implemented Closeable as a supertype. This detail has been internalized within the SDK and now only applies to SDK-provided HTTP clients, as only internally-managed HttpClientEngines are closed by the SDK.

Breaking changes
The interface definition for HttpClientEngine is now

/**
 * Functionality a real HTTP client must provide.
 */
public interface HttpClientEngine : CoroutineScope {
    /**
     * Execute a single HTTP request and return the response.
     * Consumers *MUST* call `HttpCall.complete()` when finished processing the response
     */
    public suspend fun roundTrip(context: ExecutionContext, request: HttpRequest): HttpCall
}

In practice, this now means external implementations are not required to implement cleanup logic via the Closeable interface.

How to migrate
If your project implements its own HttpClientEngine, you will need to remove the override keyword from its close() declaration, as the function no longer overrides anything. You are free to leave the method as-is or move resource cleanup elsewhere within your codebase.

Alternatively, you can change your implementation's supertype to CloseableHttpClientEngine, which is a new interface included in this release that SDK-provided clients implement. As always, the SDK will NOT call close() or manage the lifecycle of any resources passed explicitly to an SDK client's config by the caller.

If you have any questions or concerns regarding this change, please don't hesitate to engage with us in this discussion thread.