Add websocket support to Ktor cio

[jaffwu]

No description provided.

[daviddenton]

Feel free to PR it! It will be interesting to see if Ktor websockets fit into how we have modelled them! 😄

[waterbang]

Hi, I had originally intended to do it this way, but I couldn't find a place to return WsResponse. Does that mean I have to choose another engine instead? (For example, Netty) .

private val engine: CIOApplicationEngine = embeddedServer(CIO, port) {
        install(createApplicationPlugin(name = "http4k") {
          onCall {
            withContext(Default) {
              if (it.request.headers[HttpHeaders.Upgrade]?.equals("websocket",true) == true) {
               val wsResponse = it.request.asHttp4k()?.let(ws)
                // I can't construct the websocket returns
              } else {
                it.response.fromHttp4K(
                  it.request.asHttp4k()?.let(http) ?: Response(
                    NOT_IMPLEMENTED
                  )
                )
              }
            }
          }
        })
      }