Play Framework/Scala example source code file (HeadAction.scala)

This example Play Framework source code file (HeadAction.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Play Framework (and Scala) source code examples by using tags.

All credit for the original source code belongs to Play Framework; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Play Framework tags/keywords

api, boolean, concurrent, core, defaultwriteables, done, hascontentlength, http_1_1, iteratee, mvc, option, play, play framework, requestheader, result, usestransferencoding

The HeadAction.scala Play Framework example source code

/*
 * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
 */

package play.core.actions

import play.api.mvc._
import play.api.libs.iteratee._
import play.api.http.{ HttpProtocol, HeaderNames, DefaultWriteables }
import play.api.mvc.Result
import scala.concurrent.Future

import HeaderNames._

/**
 * RFC2616-compatible HEAD implementation: provides a full header set and empty body for a given GET resource
 *
 * @param handler Action for the relevant GET path.
 */
class HeadAction(handler: Handler) extends EssentialAction with DefaultWriteables with HttpProtocol {
  def apply(requestHeader: RequestHeader): Iteratee[Array[Byte], Result] = {
    def bodyIterator: Iteratee[Array[Byte], Result] = handler.asInstanceOf[EssentialAction](requestHeader)

    def createHeadResult(result: Result): Future[Result] = result match {
      // Respond immediately for bodies which have finished evaluating
      case UsesTransferEncoding() | HasContentLength() =>
        val newResult = Result(result.header, Enumerator(Array.emptyByteArray), result.connection)
        Future.successful(newResult)
      // We need to evaluate the body further to determine appropriate headers (Content-Length or Transfer-Encoding)
      case _ =>
        result.body |>>> singleChunkIteratee(result, requestHeader.version)
    }

    import play.core.Execution.Implicits.internalContext

    bodyIterator.mapM(result =>
      createHeadResult(result)
    )
  }

  /**
   * Creates an Iteratee that will evaluate at most one chunk of a given resource
   * @param result Contains initial result information
   * @param httpVersion HTTP Version from the RequestHeader to ensure proper response headers
   * @return
   */
  def singleChunkIteratee(result: Result, httpVersion: String): Iteratee[Array[Byte], Result] = {
    lazy val resultWithEmptyBody = Result(result.header, Enumerator(Array.emptyByteArray), result.connection)

    def takeUpToOneChunk(chunk: Option[Array[Byte]]): Iteratee[Array[Byte], Either[Array[Byte], Option[Array[Byte]]]] = Cont {
      // We have a second chunk, fail with left
      case in @ Input.El(data) if chunk.isDefined => Done(Left(chunk.get), in)
      // This is the first chunk
      case Input.El(data) => takeUpToOneChunk(Some(data))
      case Input.Empty => takeUpToOneChunk(chunk)
      // We reached EOF, which means we either have one or zero chunks
      case Input.EOF => Done(Right(chunk))
    }

    import play.api.libs.iteratee.Execution.Implicits.trampoline

    takeUpToOneChunk(None).flatMap {
      // Single chunk response
      case Right(chunk) =>
        val contentLength = chunk.map(_.length).getOrElse(0)
        val newResult = resultWithEmptyBody.withHeaders(
          CONTENT_LENGTH -> contentLength.toString
        )

        Done[Array[Byte], Result](newResult)

      case Left(chunk) =>
        // The body is in multiple chunks.
        val newResult = httpVersion match {
          // HTTP 1.0 doesn't support chunked transfer
          case HTTP_1_0 =>
            resultWithEmptyBody
          case HTTP_1_1 =>
            resultWithEmptyBody.withHeaders(
              TRANSFER_ENCODING -> CHUNKED
            )
        }

        Done[Array[Byte], Result](newResult)
    }
  }
}

/**
 * Extractor object that determines whether the result uses a transfer encoding
 */
object UsesTransferEncoding {
  def unapply(result: Result): Boolean = result.header.headers.contains(TRANSFER_ENCODING)
}

/**
 * Extractor that determines whether a content-length has been set on a result
 */
object HasContentLength {
  def unapply(result: Result): Boolean = result.header.headers.contains(CONTENT_LENGTH)
}