extractOfferedWsProtocols

Description

Extracts the list of WebSocket subprotocols as offered by the client in the Sec-WebSocket-Protocol header if this is a WebSocket request. Rejects with an ExpectedWebSocketRequestRejection, otherwise.

The extractOfferedWsProtocols directive is used as a building block for Custom Directives to provide the extracted protocols to the inner route.

Example

final Flow<Message, Message, NotUsed> echoService = Flow.of(Message.class).buffer(1, OverflowStrategy.backpressure());

final Route websocketRoute = path("services", () ->
  route(
    extractOfferedWsProtocols(protocols ->
      handleWebSocketMessagesForOptionalProtocol(echoService, protocols.stream().findFirst())
    )
  )
);

// tests:
// create a testing probe representing the client-side
final WSProbe wsClient = WSProbe.create(system(), materializer());

testRoute(websocketRoute)
  .run(WS(Uri.create("/services"), wsClient.flow(), materializer(), Arrays.asList("echo", "alfa", "kilo")))
  .assertHeaderExists(SecWebSocketProtocol.create("echo"));

wsClient.sendMessage("ping");
wsClient.expectMessage("ping");

wsClient.sendCompletion();
wsClient.expectCompletion();