Play Framework Scala:如何流式传输请求正文

问题描述

我正在使用 Scala 使用 Play Framework 2.3.x 构建微服务(我是这两个方面的初学者)，但我无法找到一种方法来流式传输我的请求正文.

I'm building a micro-service using Play Framework 2.3.x using Scala (I'm a beginner in both) but I can't figure out a way to stream my request body.

问题来了:

我需要一个端点 /transform 在那里我可以接收一个巨大的 TSV 文件，我将解析并以另一种格式呈现:简单转换.问题是我的控制器中的每个命令都太晚了".它在启动代码之前等待接收完整文件.

I need an endpoint /transform where I can receive a huge TSV file that I will parse and render in another format: simple transformation. The problem is that every single command in my controller is ran "too late". It waits to receive the full file before starting the code.

示例:

  def transform = Action.async {
    Future {
      Logger.info("Too late")
      Ok("A response")
    }
  }

我希望能够在上传过程中逐行读取请求正文并处理请求，而不必等待文件被完全接收.

I want to be able to read line-by-line the request body during its upload and process already the request without having to wait for the file to be received completely.

欢迎提供任何提示.

推荐答案

此答案适用于 Play 2.5.x 及更高版本，因为它使用 Akka 流 API，该 API 取代了该版本中 Play 基于 Iteratee 的流.

This answer applies to Play 2.5.x and higher since it uses the Akka streams API that replaced Play's Iteratee-based streaming in that version.

基本上，您可以创建一个返回 Source[T] 的正文解析器，您可以将其传递给 Ok.chunked(...).一种方法是在正文解析器中使用 Accumulator.source[T].例如，一个刚刚逐字返回发送给它的数据的操作可能如下所示:

Basically, you can create a body parser that returns a Source[T] that you can pass to Ok.chunked(...). One way to do this is to use Accumulator.source[T] in the body parser. For example, an action that just returned data sent to it verbatim might look like this:

def verbatimBodyParser: BodyParser[Source[ByteString, _]] = BodyParser { _ =>
  // Return the source directly. We need to return
  // an Accumulator[Either[Result, T]], so if we were
  // handling any errors we could map to something like
  // a Left(BadRequest("error")). Since we're not
  // we just wrap the source in a Right(...)
  Accumulator.source[ByteString]
    .map(Right.apply)
}

def stream = Action(verbatimBodyParser) { implicit request =>
  Ok.chunked(request.body)
}

如果你想做一些像转换 TSV 文件的事情，你可以使用 Flow 来转换源，例如:

If you want to do something like transform a TSV file you can use a Flow to transform the source, e.g:

val tsvToCsv: BodyParser[Source[ByteString, _]] = BodyParser { req =>

  val transformFlow: Flow[ByteString, ByteString, NotUsed] = Flow[ByteString]
    // Chunk incoming bytes by newlines, truncating them if the lines
    // are longer than 1000 bytes...
    .via(Framing.delimiter(ByteString("
"), 1000, allowTruncation = true))
    // Replace tabs by commas. This is just a silly example and
    // you could obviously do something more clever here...
    .map(s => ByteString(s.utf8String.split('	').mkString(",") + "
"))

  Accumulator.source[ByteString]
    .map(_.via(transformFlow))
    .map(Right.apply)
}

def convert = Action(tsvToCsv) { implicit request =>
  Ok.chunked(request.body).as("text/csv")
}

Directing the Body 可能会有更多的灵感Play 文档的其他地方部分.

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