нормик

val byteArrayOutputStream = new java.io.ByteArrayOutputStream()
file.writeTo(byteArrayOutputStream)
event.response.write(byteArrayOutputStream.toByteArray)

Не нормик
          val bufReader = new BufferedReader(new InputStreamReader(file.inputStream))

          var line: String = null
          def readString: Boolean = {
            line = bufReader.readLine()
              line != null
          }
          while (readString) {
            event.response.writeChunk(line.getBytes())
          }