extractOfferedWsProtocols

def extractOfferedWsProtocols: Directive1[immutable.Seq[String]]

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 ExpectedWebSocketRequestRejectionExpectedWebSocketRequestRejection, otherwise.

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

Example

Scala

def echoService: Flow[Message, Message, Any] =
  Flow[Message]
    // needed because a noop flow hasn't any buffer that would start processing in tests
    .buffer(1, OverflowStrategy.backpressure)

def route =
  path("services") {
    extractOfferedWsProtocols { protocols =>
      handleWebSocketMessagesForOptionalProtocol(echoService, protocols.headOption)
    }
  }

// tests:
val wsClient = WSProbe()

// WS creates a WebSocket request for testing
WS("/services", wsClient.flow, List("echo", "alfa", "kilo")) ~> route ~> check {
  expectWebSocketUpgradeWithProtocol { protocol =>
    protocol shouldEqual "echo"
    wsClient.sendMessage("ping")
    wsClient.expectMessage("ping")
    wsClient.sendCompletion()
    wsClient.expectCompletion()
  }
}

Java

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();