Question

我正在Scala中构建一个Play Framework应用程序，我希望将一个字节数组流式传输到S3。我正在使用Play-S3库来执行此操作。＆＃34; Multipart文件上传＆＃34;文档部分的相关内容如下：

// Retrieve an upload ticket
val result:Future[BucketFileUploadTicket] =
  bucket initiateMultipartUpload BucketFile(fileName, mimeType)

// Upload the parts and save the tickets
val result:Future[BucketFilePartUploadTicket] =
  bucket uploadPart (uploadTicket, BucketFilePart(partNumber, content))

// Complete the upload using both the upload ticket and the part upload tickets
val result:Future[Unit] =
  bucket completeMultipartUpload (uploadTicket, partUploadTickets)

我正在尝试在我的应用程序中执行相同的操作但使用Iteratee和Enumerator s。

流和异步性使事情变得有点复杂，但这是我到目前为止（注意uploadTicket在代码的前面定义）：

val partNumberStream = Stream.iterate(1)(_ + 1).iterator
val partUploadTicketsIteratee = Iteratee.fold[Array[Byte], Future[Vector[BucketFilePartUploadTicket]]](Future.successful(Vector.empty[BucketFilePartUploadTicket])) { (partUploadTickets, bytes) =>
  bucket.uploadPart(uploadTicket, BucketFilePart(partNumberStream.next(), bytes)).flatMap(partUploadTicket => partUploadTickets.map( _ :+ partUploadTicket))
}
(body |>>> partUploadTicketsIteratee).andThen {
  case result =>
    result.map(_.map(partUploadTickets => bucket.completeMultipartUpload(uploadTicket, partUploadTickets))) match {
      case Success(x) => x.map(d => println("Success"))
      case Failure(t) => throw t
    }
}

所有内容都会编译并运行而不会发生任何事故。事实上，"Success"会被打印出来，但S3上没有任何文件显示出来。

Answer 1

您的代码可能存在多个问题。由map方法调用引起的有点不可读。您的未来构图可能有问题。另一个问题可能是由于所有块（除了最后一块）至少应为5MB这一事实。

以下代码尚未经过测试，但显示了不同的方法。 iteratee方法是一种可以创建小构建块并将它们组合成一个操作管道的方法。

为了使代码编译，我添加了一个特征和一些方法

trait BucketFilePartUploadTicket
val uploadPart: (Int, Array[Byte]) => Future[BucketFilePartUploadTicket] = ???
val completeUpload: Seq[BucketFilePartUploadTicket] => Future[Unit] = ???
val body: Enumerator[Array[Byte]] = ???

这里我们创建几个部分

// Create 5MB chunks
val chunked = {
  val take5MB = Traversable.takeUpTo[Array[Byte]](1024 * 1024 * 5)
  Enumeratee.grouped(take5MB transform Iteratee.consume())
}

// Add a counter, used as part number later on
val zipWithIndex = Enumeratee.scanLeft[Array[Byte]](0 -> Array.empty[Byte]) {
  case ((counter, _), bytes) => (counter + 1) -> bytes
}

// Map the (Int, Array[Byte]) tuple to a BucketFilePartUploadTicket
val uploadPartTickets = Enumeratee.mapM[(Int, Array[Byte])](uploadPart.tupled)

// Construct the pipe to connect to the enumerator
// the ><> operator is an alias for compose, it is more intuitive because of 
// it's arrow like structure
val pipe = chunked ><> zipWithIndex ><> uploadPartTickets

// Create a consumer that ends by finishing the upload
val consumeAndComplete = 
  Iteratee.getChunks[BucketFilePartUploadTicket] mapM completeUpload

只需连接部件即可完成运行

// This is the result, a Future[Unit]
val result = body through pipe run consumeAndComplete

请注意，我没有测试任何代码，可能在我的方法中犯了一些错误。然而，这显示了处理问题的不同方式，并且应该可以帮助您找到一个好的解决方案。

请注意，此方法等待一部分完成上传，然后才能进入下一部分。如果从服务器到亚马逊的连接比从浏览器到服务器的连接慢，则此机制将减慢输入。

您可以采用另一种方法，即不等待部件上传的Future完成。这将导致另一个步骤，您使用Future.sequence将上传期货序列转换为包含结果序列的单个未来。结果将是一旦有足够数据就将一部分发送到亚马逊的机制。

在Play Scala中使用Iteratees和Enumerators将数据流式传输到S3

1 个答案: