The idea of what I'm trying to achieve (sync solution would be acceptable)

DataUpload.scala

def upload(parts: Vector[Part[F]], blocker: Blocker): F[Response[F]] =
    parts.find(isValidPart) match {
      case Some(file) =>
        val t0       = System.nanoTime()
        val home     = sys.env.getOrElse("DP_UPLOAD_DIR", "/tmp/data-parser/upload")
        val filename = file.filename.getOrElse("filename")
        val path     = FSUtils.ensurePath(home, filename)

        val writer = fs2.io.file.writeAll(path, blocker)
        val response = file.body
          .observe(writer)
          .fold(0)(_ + _)
          .map { size => // BUG: size produces wrong size?

            // TODO: Execute sync task which process uploaded file and produces avro file (and deletes the uploaded file)
            // For example (I have the following blocking effectful operation writen in Java):
            //          val data = Parser.fromString(path.toAbsolutePath.toString)
            //          data.persist()
            //          path.toFile.delete()

            // TODO: Write to redis stats
            redis.set(path.toAbsolutePath.toString, size.toString)

            val parsedIn = (System.nanoTime() - t0) * 1e-9
            ParsedResponse(
              ReplayKey(path.toAbsolutePath.toString),
              BytesProcessed(size),
              ParsedIn(parsedIn.toFloat)
            )
          }

        Ok(response)

      case None => BadRequest()
    }