Server-Sent Events

http4k provides SSE (Server-Sent Events) support using a simple, consistent, typesafe, and testable API on supported server backends.

Sse communication consists of a few main concepts:


As per the http4k ethos, an immutable message object to be pushed from the server to the connected client. There are 2 types of SseMessage - Events (for sending known constructs), and Data (for sending byte streams). Lenses can be used to provide typesafe object marshalling with SseMessages.


interface Sse {
    val connectRequest: Request
    fun send(message: SseMessage)
    fun close()
    fun onClose(fn: () -> Unit)

An interface representing the available server callback API to the Server-Sent Event channel. Sse objects can send() SseMessages to the client, or close() the connection. The Sse has a reference to the incoming HTTP Request which was used during connection.


typealias SseConsumer = (Sse) -> Unit

The primary callback received when an Sse server is connected to a client. API user behaviour is configured here.


typelias SseHandler = (Request) -> SseResponse

Provides the route mapping of an HTTP Request to a particular SseResponse (which contains a SseConsumer).


fun interface SseFilter : (SseConsumer) -> SseConsumer

Applies decoration to a matched SseConsumer before it is invoked. SseFilters can be used to apply tangental effects to the matched SseConsumer such as logging/security, or to modify the incoming HTTP Request.


interface SseRouter {
    fun match(request: Request): SseRouterMatch
    fun withBasePath(new: String): SseRouter
    fun withFilter(new: SseFilter): SseRouter

Applies the route matching functionality when requests for Sse connections are received by the server.