def completeMultipartUpload()

in app/services/FileMove/ImprovedLargeFileCopier.scala [457:499]
41 lines of code
7 McCabe index (conditional complexity)

  def completeMultipartUpload(region:Regions, credentialsProvider:Option[AwsCredentialsProvider], destBucket:String, destKey:String, uploadId:String, parts:Seq[UploadedPart])
                             (implicit poolClientFlow:HostConnectionPool[Any]) = {
    val xmlContent = <CompleteMultipartUpload xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
      {
      parts.sortBy(_.partNumber).map(_.toXml) //must put the parts into ascending order
      }
    </CompleteMultipartUpload>

    val req = createRequest(HttpMethods.POST, region, destBucket, destKey, None) { partialReq=>
      partialReq
        .withUri(partialReq.uri.withRawQueryString(s"uploadId=$uploadId"))
        .withEntity(HttpEntity(xmlContent.toString()))
    }

    Source
      .single(req)
      .mapAsync(1)(reqparts=>doRequestSigning(reqparts._1, region, credentialsProvider).map(rq=>(rq, ())))
      .via(poolClientFlow)
      .runWith(Sink.head)
      .flatMap({
        case (Success(response), _)=>
          loadResponseBody(response).map(content=>{
            (response.status: @switch) match {
              case StatusCodes.OK=>
                CompletedUpload.fromXMLString(content) match {
                  case Success(completedUpload)=>
                    logger.info(s"Copy to s3://$destBucket/$destKey completed with eTag ${completedUpload.eTag}")
                    completedUpload
                  case Failure(err)=>
                    logger.error(s"Copy to s3://$destBucket/$destKey completed but could not parse the response: ${err.getMessage}")
                    logger.error(s"s3://$destBucket/$destKey raw response was $content")
                    throw new RuntimeException("Could not parse completed-upload response")
                }
              case _=>
                logger.error(s"Copy to s3://$destBucket/$destKey failed with error ${response.status}: $content")
                throw new RuntimeException(s"Server error ${response.status}")
            }
          })
        case (Failure(err), _)=>
          logger.error(s"Could not complete copy to s3://$destBucket/$destKey: ${err.getMessage}", err)
          Future.failed(err)
      })
  }