forceTextStrict.scala

  implicit class flowTweaks[M](val wsInput: Source[Message, M]) {
    def forceTextStrict: Source[Strict, M] = wsInput
      .collect {
        case TextMessage.Strict(text)             ⇒ Future.successful(text)
        case TextMessage.Streamed(textStream)     ⇒ textStream.runFold("")(_ + _)
        case BinaryMessage.Strict(binary)         ⇒ Skip
        case BinaryMessage.Streamed(binaryStream) ⇒ binaryStream.runWith(Sink.ignore); Skip
      }
      .filterNot(_ == Skip)
      .mapAsync(1)(ConstantFun.scalaIdentityFunction)
      .map(TextMessage.Strict)
    }