diff --git a/akka-actor/src/main/scala/akka/util/ByteString.scala b/akka-actor/src/main/scala/akka/util/ByteString.scala
index 1e782f3c09..cb1dd3aef2 100644
--- a/akka-actor/src/main/scala/akka/util/ByteString.scala
+++ b/akka-actor/src/main/scala/akka/util/ByteString.scala
@@ -382,7 +382,7 @@ object ByteString {
       } else throw new IndexOutOfBoundsException(idx.toString)
     }
 
-    // Avoid `iterator` in performance sensitive code, call ops directly on ByteString instead
+    /** Avoid `iterator` in performance sensitive code, call ops directly on ByteString instead */
     override def iterator: ByteIterator.MultiByteArrayIterator =
       ByteIterator.MultiByteArrayIterator(bytestrings.toStream map { _.iterator })
 
diff --git a/akka-actor/src/main/scala/akka/util/OptionVal.scala b/akka-actor/src/main/scala/akka/util/OptionVal.scala
new file mode 100644
index 0000000000..7238c54233
--- /dev/null
+++ b/akka-actor/src/main/scala/akka/util/OptionVal.scala
@@ -0,0 +1,69 @@
+/**
+ * Copyright (C) 2016 Lightbend Inc. <http://www.lightbend.com>
+ */
+package akka.util
+
+/**
+ * INTERNAL API
+ */
+private[akka] object OptionVal {
+
+  def apply[A >: Null](x: A): OptionVal[A] = new OptionVal(x)
+
+  object Some {
+    def apply[A >: Null](x: A): OptionVal[A] = new OptionVal(x)
+    def unapply[A >: Null](x: OptionVal[A]): OptionVal[A] = x
+  }
+
+  /**
+   * Represents non-existent values, `null` values.
+   */
+  val None = new OptionVal[Null](null)
+}
+
+/**
+ * INTERNAL API
+ * Represents optional values similar to `scala.Option`, but
+ * as a value class to avoid allocations.
+ *
+ * Note that it can be used in pattern matching without allocations
+ * because it has name based extractor using methods `isEmpty` and `get`.
+ * See http://hseeberger.github.io/blog/2013/10/04/name-based-extractors-in-scala-2-dot-11/
+ */
+private[akka] final class OptionVal[+A >: Null](val x: A) extends AnyVal {
+
+  /**
+   * Returns true if the option is `OptionVal.None`, false otherwise.
+   */
+  def isEmpty: Boolean =
+    x == null
+
+  /**
+   * Returns true if the option is `OptionVal.None`, false otherwise.
+   */
+  def isDefined: Boolean = !isEmpty
+
+  /**
+   * Returns the option's value if the option is nonempty, otherwise
+   * return `default`.
+   */
+  def getOrElse[B >: A](default: B): B =
+    if (x == null) default else x
+
+  /**
+   *  Returns the option's value if it is nonempty, or `null` if it is empty.
+   */
+  def orNull[A1 >: A](implicit ev: Null <:< A1): A1 = this getOrElse ev(null)
+
+  /**
+   * Returns the option's value.
+   * @note The option must be nonEmpty.
+   * @throws java.util.NoSuchElementException if the option is empty.
+   */
+  def get: A =
+    if (x == null) throw new NoSuchElementException("OptionVal.None.get")
+    else x
+
+  override def toString: String =
+    if (x == null) "None" else s"Some($x)"
+}
diff --git a/akka-bench-jmh/src/main/scala/akka/http/HttpBlueprintBenchmark.scala b/akka-bench-jmh/src/main/scala/akka/http/HttpBlueprintBenchmark.scala
index c254ea5692..d9925b8a82 100644
--- a/akka-bench-jmh/src/main/scala/akka/http/HttpBlueprintBenchmark.scala
+++ b/akka-bench-jmh/src/main/scala/akka/http/HttpBlueprintBenchmark.scala
@@ -110,30 +110,13 @@ class HttpBlueprintBenchmark {
     Flow.fromSinkAndSource(Sink.cancelled, Source.empty)
 
   @Benchmark
-  @OperationsPerInvocation(100 * 1000)
-  def run_10000_reqs(blackhole: Blackhole) = {
-    val n = 100 * 1000
+  @OperationsPerInvocation(100000)
+  def run_10000_reqs() = {
+    val n = 100000
     val latch = new CountDownLatch(n)
 
     val replyCountdown = reply map { x =>
       latch.countDown()
-      blackhole.consume(x)
-      x
-    }
-    server(n).joinMat(replyCountdown)(Keep.right).run()(materializer)
-
-    latch.await()
-  }
-
-  @Benchmark
-  @OperationsPerInvocation(10 * 1000)
-  def run_1000_reqs(blackhole: Blackhole) = {
-    val n = 10 * 1000
-    val latch = new CountDownLatch(n)
-
-    val replyCountdown = reply map { x =>
-      latch.countDown()
-      blackhole.consume(x)
       x
     }
     server(n).joinMat(replyCountdown)(Keep.right).run()(materializer)
@@ -142,3 +125,4 @@ class HttpBlueprintBenchmark {
   }
 
 }
+
diff --git a/akka-bench-jmh/src/main/scala/akka/http/HttpRequestParsingBenchmark.scala b/akka-bench-jmh/src/main/scala/akka/http/HttpRequestParsingBenchmark.scala
index d6f6eb15f8..4233a5115b 100644
--- a/akka-bench-jmh/src/main/scala/akka/http/HttpRequestParsingBenchmark.scala
+++ b/akka-bench-jmh/src/main/scala/akka/http/HttpRequestParsingBenchmark.scala
@@ -3,25 +3,24 @@
  */
 package akka.http
 
-import java.util.concurrent.{ CountDownLatch, TimeUnit }
+import java.util.concurrent.TimeUnit
 import javax.net.ssl.SSLContext
 
 import akka.Done
 import akka.actor.ActorSystem
-import akka.http.impl.engine.parsing.ParserOutput.RequestOutput
-import akka.http.impl.engine.parsing.{ HttpHeaderParser, HttpMessageParser, HttpRequestParser }
+import akka.event.NoLogging
+import akka.http.impl.engine.parsing.{ HttpHeaderParser, HttpRequestParser }
 import akka.http.scaladsl.settings.ParserSettings
 import akka.event.NoLogging
+import akka.stream.ActorMaterializer
 import akka.stream.TLSProtocol.SessionBytes
-import akka.stream.scaladsl.RunnableGraph
-import akka.stream.{ ActorMaterializer, Attributes }
-import akka.stream.scaladsl.{ Flow, Keep, Sink, Source }
+import akka.stream.scaladsl._
 import akka.util.ByteString
 import org.openjdk.jmh.annotations.{ OperationsPerInvocation, _ }
 import org.openjdk.jmh.infra.Blackhole
 
-import scala.concurrent.{ Await, Future }
 import scala.concurrent.duration._
+import scala.concurrent.{ Await, Future }
 
 @State(Scope.Benchmark)
 @OutputTimeUnit(TimeUnit.SECONDS)
@@ -29,48 +28,70 @@ import scala.concurrent.duration._
 class HttpRequestParsingBenchmark {
 
   implicit val system: ActorSystem = ActorSystem("HttpRequestParsingBenchmark")
-  implicit val materializer = ActorMaterializer()
+  implicit val materializer = ActorMaterializer()(system)
   val parserSettings = ParserSettings(system)
   val parser = new HttpRequestParser(parserSettings, false, HttpHeaderParser(parserSettings, NoLogging)())
   val dummySession = SSLContext.getDefault.createSSLEngine.getSession
-  val requestBytes = SessionBytes(
+
+  @Param(Array("small", "large"))
+  var req: String = ""
+
+  def request = req match {
+    case "small" => requestBytesSmall
+    case "large" => requestBytesLarge
+  }
+
+  val requestBytesSmall: SessionBytes = SessionBytes(
     dummySession,
     ByteString(
-      "GET / HTTP/1.1\r\n" +
-        "Accept: */*\r\n" +
-        "Accept-Encoding: gzip, deflate\r\n" +
-        "Connection: keep-alive\r\n" +
-        "Host: example.com\r\n" +
-        "User-Agent: HTTPie/0.9.3\r\n" +
-        "\r\n"
+      """|GET / HTTP/1.1
+         |Accept: */*
+         |Accept-Encoding: gzip, deflate
+         |Connection: keep-alive
+         |Host: example.com
+         |User-Agent: HTTPie/0.9.3
+         |
+         |""".stripMargin.replaceAll("\n", "\r\n")
     )
   )
 
+  val requestBytesLarge: SessionBytes = SessionBytes(
+    dummySession,
+    ByteString(
+      """|GET /json HTTP/1.1
+         |Host: server
+         |User-Agent: Mozilla/5.0 (X11; Linux x86_64) Gecko/20130501 Firefox/30.0 AppleWebKit/600.00 Chrome/30.0.0000.0 Trident/10.0 Safari/600.00
+         |Cookie: uid=12345678901234567890; __utma=1.1234567890.1234567890.1234567890.1234567890.12; wd=2560x1600
+         |Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
+         |Accept-Language: en-US,en;q=0.5
+         |Connection: keep-alive
+         |
+         |""".stripMargin.replaceAll("\n", "\r\n")
+    )
+  )
+
+  /*
+  // before:
+  [info] Benchmark                                                 (req)   Mode  Cnt            Score       Error  Units
+  [info] HttpRequestParsingBenchmark.parse_10000_requests          small  thrpt   20      358 982.157 ± 93745.863  ops/s
+  [info] HttpRequestParsingBenchmark.parse_10000_requests          large  thrpt   20      388 335.666 ± 16990.715  ops/s
+  
+  // after:
+  [info] HttpRequestParsingBenchmark.parse_10000_requests_val      small  thrpt   20      623 975.879 ± 6191.897  ops/s
+  [info] HttpRequestParsingBenchmark.parse_10000_requests_val      large  thrpt   20      507 460.283 ± 4735.843  ops/s
+  */
+
   val httpMessageParser = Flow.fromGraph(parser)
 
-  def flow(n: Int): RunnableGraph[Future[Done]] =
-    Source.repeat(requestBytes).take(n)
+  def flow(bytes: SessionBytes, n: Int): RunnableGraph[Future[Done]] =
+    Source.repeat(request).take(n)
       .via(httpMessageParser)
       .toMat(Sink.ignore)(Keep.right)
 
   @Benchmark
   @OperationsPerInvocation(10000)
-  def parse_10000_single_requests(blackhole: Blackhole): Unit = {
-    val done = flow(10000).run()
-    Await.ready(done, 32.days)
-  }
-
-  @Benchmark
-  @OperationsPerInvocation(1000)
-  def parse_1000_single_requests(blackhole: Blackhole): Unit = {
-    val done = flow(1000).run()
-    Await.ready(done, 32.days)
-  }
-
-  @Benchmark
-  @OperationsPerInvocation(100)
-  def parse_100_single_requests(blackhole: Blackhole): Unit = {
-    val done = flow(100).run()
+  def parse_10000_requests_val(blackhole: Blackhole): Unit = {
+    val done = flow(requestBytesSmall, 10000).run()
     Await.ready(done, 32.days)
   }
 
diff --git a/akka-bench-jmh/src/main/scala/akka/http/HttpResponseRenderingBenchmark.scala b/akka-bench-jmh/src/main/scala/akka/http/HttpResponseRenderingBenchmark.scala
new file mode 100644
index 0000000000..8e5aa5c10a
--- /dev/null
+++ b/akka-bench-jmh/src/main/scala/akka/http/HttpResponseRenderingBenchmark.scala
@@ -0,0 +1,250 @@
+/**
+ * Copyright (C) 2015-2016 Lightbend Inc. <http://www.lightbend.com>
+ */
+
+package akka.http
+
+import java.util.concurrent.{ CountDownLatch, TimeUnit }
+
+import akka.NotUsed
+import akka.actor.ActorSystem
+import akka.event.NoLogging
+import akka.http.impl.engine.rendering.ResponseRenderingOutput.HttpData
+import akka.http.impl.engine.rendering.{ HttpResponseRendererFactory, ResponseRenderingContext, ResponseRenderingOutput }
+import akka.http.scaladsl.Http
+import akka.http.scaladsl.model._
+import akka.http.scaladsl.model.headers.Server
+import akka.http.scaladsl.unmarshalling.Unmarshal
+import akka.stream._
+import akka.stream.scaladsl._
+import akka.stream.stage.{ GraphStageLogic, GraphStageWithMaterializedValue, InHandler }
+import akka.util.ByteString
+import com.typesafe.config.ConfigFactory
+import org.openjdk.jmh.annotations._
+import org.openjdk.jmh.infra.Blackhole
+
+import scala.concurrent.duration._
+import scala.concurrent.{ Await, Future }
+import scala.util.Try
+
+@State(Scope.Benchmark)
+@OutputTimeUnit(TimeUnit.SECONDS)
+@BenchmarkMode(Array(Mode.Throughput))
+class HttpResponseRenderingBenchmark extends HttpResponseRendererFactory(
+  serverHeader = Some(Server("Akka HTTP 2.4.x")),
+  responseHeaderSizeHint = 64,
+  log = NoLogging
+) {
+
+  val config = ConfigFactory.parseString(
+    """
+      akka {
+        loglevel = "ERROR"
+      }""".stripMargin
+  ).withFallback(ConfigFactory.load())
+
+  implicit val system = ActorSystem("HttpResponseRenderingBenchmark", config)
+  implicit val materializer = ActorMaterializer()
+
+  import system.dispatcher
+
+  val requestRendered = ByteString(
+    "GET / HTTP/1.1\r\n" +
+      "Accept: */*\r\n" +
+      "Accept-Encoding: gzip, deflate\r\n" +
+      "Connection: keep-alive\r\n" +
+      "Host: example.com\r\n" +
+      "User-Agent: HTTPie/0.9.3\r\n" +
+      "\r\n"
+  )
+
+  def TCPPlacebo(requests: Int): Flow[ByteString, ByteString, NotUsed] =
+    Flow.fromSinkAndSource(
+      Flow[ByteString].takeWhile(it => !(it.utf8String contains "Connection: close")) to Sink.ignore,
+      Source.repeat(requestRendered).take(requests)
+    )
+
+  def TlsPlacebo = TLSPlacebo()
+
+  val requestRendering: Flow[HttpRequest, String, NotUsed] =
+    Http()
+      .clientLayer(headers.Host("blah.com"))
+      .atop(TlsPlacebo)
+      .join {
+        Flow[ByteString].map { x ⇒
+          val response = s"HTTP/1.1 200 OK\r\nContent-Length: ${x.size}\r\n\r\n"
+          ByteString(response) ++ x
+        }
+      }
+      .mapAsync(1)(response => Unmarshal(response).to[String])
+
+  def renderResponse: Future[String] = Source.single(HttpRequest(uri = "/foo"))
+    .via(requestRendering)
+    .runWith(Sink.head)
+
+  var request: HttpRequest = _
+  var pool: Flow[(HttpRequest, Int), (Try[HttpResponse], Int), _] = _
+
+  @TearDown
+  def shutdown(): Unit = {
+    Await.ready(Http().shutdownAllConnectionPools(), 1.second)
+    Await.result(system.terminate(), 5.seconds)
+  }
+
+  /*
+  [info] Benchmark                                               Mode  Cnt              Score              Error  Units
+  [info] HttpResponseRenderingBenchmark.header_date_val         thrpt   20  2 704 169 260 029.906 ± 234456086114.237  ops/s
+  
+  // def, normal time
+  [info] HttpResponseRenderingBenchmark.header_date_def             thrpt   20    178 297 625 609.638 ± 7429280865.659  ops/s
+  [info] HttpResponseRenderingBenchmark.response_ok_simple_val      thrpt   20          1 258 119.673 ± 58399.454  ops/s
+  [info] HttpResponseRenderingBenchmark.response_ok_simple_def      thrpt   20            687 576.928 ± 94813.618  ops/s
+  
+  // clock nanos
+  [info] HttpResponseRenderingBenchmark.response_ok_simple_clock    thrpt   20          1 676 438.649 ± 33976.590  ops/s
+  [info] HttpResponseRenderingBenchmark.response_ok_simple_clock    thrpt   40          1 199 462.263 ± 222226.304  ops/s
+  
+  // ------
+  
+  // before optimisig collectFirst
+  [info] HttpResponseRenderingBenchmark.json_response        thrpt   20  1 782 572.845 ± 16572.625  ops/s
+  [info] HttpResponseRenderingBenchmark.simple_response      thrpt   20  1 611 802.216 ± 19557.151  ops/s
+  
+  // after removing collectFirst and Option from renderHeaders
+  // not much of a difference, but hey, less Option allocs
+  [info] HttpResponseRenderingBenchmark.json_response        thrpt   20  1 785 152.896 ± 15210.299  ops/s
+  [info] HttpResponseRenderingBenchmark.simple_response      thrpt   20  1 783 800.184 ± 14938.415  ops/s
+  
+  // -----
+
+  // baseline for this optimisation is the above results (after collectFirst).
+  
+  // after introducing pre-rendered ContentType headers:
+  
+  normal clock
+  [info] HttpResponseRenderingBenchmark.json_long_raw_response  thrpt   20  1738558.895 ± 159612.661  ops/s
+  [info] HttpResponseRenderingBenchmark.json_response           thrpt   20  1714176.824 ± 100011.642  ops/s
+
+  "fast clock"
+  [info] HttpResponseRenderingBenchmark.json_long_raw_response  thrpt   20  1 528 632.480 ± 44934.827  ops/s
+  [info] HttpResponseRenderingBenchmark.json_response           thrpt   20  1 517 383.792 ± 28256.716  ops/s
+  
+   */
+
+  /**
+   * HTTP/1.1 200 OK
+   * Server: Akka HTTP 2.4.x
+   * Date: Tue, 26 Jul 2016 15:26:53 GMT
+   * Content-Type: text/plain; charset=UTF-8
+   * Content-Length: 6
+   *
+   * ENTITY
+   */
+  val simpleResponse =
+    ResponseRenderingContext(
+      response = HttpResponse(
+        200,
+        headers = Nil,
+        entity = HttpEntity("ENTITY")
+      ),
+      requestMethod = HttpMethods.GET
+    )
+
+  /**
+   * HTTP/1.1 200 OK
+   * Server: Akka HTTP 2.4.x
+   * Date: Tue, 26 Jul 2016 15:26:53 GMT
+   * Content-Type: application/json
+   * Content-Length: 27
+   *
+   * {"message":"Hello, World!"}
+   */
+  val jsonResponse =
+    ResponseRenderingContext(
+      response = HttpResponse(
+        200,
+        headers = Nil,
+        entity = HttpEntity(ContentTypes.`application/json`, """{"message":"Hello, World!"}""")
+      ),
+      requestMethod = HttpMethods.GET
+    )
+
+  /**
+   * HTTP/1.1 200 OK
+   * Server: Akka HTTP 2.4.x
+   * Date: Tue, 26 Jul 2016 15:26:53 GMT
+   * Content-Type: application/json
+   * Content-Length: 315
+   *
+   * [{"id":4174,"randomNumber":331},{"id":51,"randomNumber":6544},{"id":4462,"randomNumber":952},{"id":2221,"randomNumber":532},{"id":9276,"randomNumber":3097},{"id":3056,"randomNumber":7293},{"id":6964,"randomNumber":620},{"id":675,"randomNumber":6601},{"id":8414,"randomNumber":6569},{"id":2753,"randomNumber":4065}]
+   */
+  val jsonLongRawResponse =
+    ResponseRenderingContext(
+      response = HttpResponse(
+        200,
+        headers = Nil,
+        entity = HttpEntity(ContentTypes.`application/json`, """[{"id":4174,"randomNumber":331},{"id":51,"randomNumber":6544},{"id":4462,"randomNumber":952},{"id":2221,"randomNumber":532},{"id":9276,"randomNumber":3097},{"id":3056,"randomNumber":7293},{"id":6964,"randomNumber":620},{"id":675,"randomNumber":6601},{"id":8414,"randomNumber":6569},{"id":2753,"randomNumber":4065}]""")
+      ),
+      requestMethod = HttpMethods.GET
+    )
+
+  @Benchmark
+  @Threads(8)
+  @OperationsPerInvocation(100 * 1000)
+  def simple_response(blackhole: Blackhole): Unit =
+    renderToImpl(simpleResponse, blackhole, n = 100 * 1000).await()
+
+  @Benchmark
+  @OperationsPerInvocation(100 * 1000)
+  def json_response(blackhole: Blackhole): Unit =
+    renderToImpl(jsonResponse, blackhole, n = 100 * 1000).await()
+
+  /*
+  Difference between 27 and 315 bytes long JSON is:
+  
+  [info] Benchmark                                                   Mode  Cnt        Score       Error  Units
+  [info] HttpResponseRenderingBenchmark.json_long_raw_response      thrpt   20  1 932 331.049 ± 64125.621  ops/s
+  [info] HttpResponseRenderingBenchmark.json_response               thrpt   20  1 973 232.941 ± 18568.314  ops/s
+   */
+  @Benchmark
+  @OperationsPerInvocation(100 * 1000)
+  def json_long_raw_response(blackhole: Blackhole): Unit =
+    renderToImpl(jsonLongRawResponse, blackhole, n = 100 * 1000).await()
+
+  class JitSafeLatch[A](blackhole: Blackhole, n: Int) extends GraphStageWithMaterializedValue[SinkShape[A], CountDownLatch] {
+    val in = Inlet[A]("JitSafeLatch.in")
+    override val shape = SinkShape(in)
+
+    override def createLogicAndMaterializedValue(inheritedAttributes: Attributes): (GraphStageLogic, CountDownLatch) = {
+      val latch = new CountDownLatch(n)
+      val logic = new GraphStageLogic(shape) with InHandler {
+
+        override def preStart(): Unit = pull(in)
+        override def onPush(): Unit = {
+          if (blackhole ne null) blackhole.consume(grab(in))
+          latch.countDown()
+          pull(in)
+        }
+
+        setHandler(in, this)
+      }
+
+      (logic, latch)
+    }
+  }
+
+  def renderToImpl(ctx: ResponseRenderingContext, blackhole: Blackhole, n: Int)(implicit mat: Materializer): CountDownLatch = {
+    val latch =
+      (Source.repeat(ctx).take(n) ++ Source.maybe[ResponseRenderingContext]) // never send upstream completion
+        .via(renderer.named("renderer"))
+        .runWith(new JitSafeLatch[ResponseRenderingOutput](blackhole, n))
+
+    latch
+  }
+
+  // TODO benchmark with stable override
+  override def currentTimeMillis(): Long = System.currentTimeMillis()
+  //  override def currentTimeMillis(): Long = System.currentTimeMillis() // DateTime(2011, 8, 25, 9, 10, 29).clicks // provide a stable date for testing
+
+}
+
diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpRequestParser.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpRequestParser.scala
index 182bea75f1..c41fe5db1e 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpRequestParser.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/parsing/HttpRequestParser.scala
@@ -8,7 +8,7 @@ import java.lang.{ StringBuilder ⇒ JStringBuilder }
 
 import scala.annotation.{ switch, tailrec }
 import akka.http.scaladsl.settings.ParserSettings
-import akka.util.ByteString
+import akka.util.{ ByteString, OptionVal }
 import akka.http.impl.engine.ws.Handshake
 import akka.http.impl.model.parser.CharacterClasses
 import akka.http.scaladsl.model._
@@ -160,8 +160,8 @@ private[http] final class HttpRequestParser(
           val allHeaders =
             if (method == HttpMethods.GET) {
               Handshake.Server.websocketUpgrade(headers, hostHeaderPresent) match {
-                case Some(upgrade) ⇒ upgrade :: allHeaders0
-                case None          ⇒ allHeaders0
+                case OptionVal.Some(upgrade) ⇒ upgrade :: allHeaders0
+                case OptionVal.None          ⇒ allHeaders0
               }
             } else allHeaders0
 
diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/HttpResponseRendererFactory.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/HttpResponseRendererFactory.scala
index 8a7ca48e72..3967ac5597 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/HttpResponseRendererFactory.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/HttpResponseRendererFactory.scala
@@ -7,11 +7,11 @@ package akka.http.impl.engine.rendering
 import akka.NotUsed
 import akka.http.impl.engine.ws.{ FrameEvent, UpgradeToWebSocketResponseHeader }
 import akka.http.scaladsl.model.ws.Message
-import akka.stream.{ Outlet, Inlet, Attributes, FlowShape, Graph }
+import akka.stream.{ Attributes, FlowShape, Graph, Inlet, Outlet }
 
 import scala.annotation.tailrec
 import akka.event.LoggingAdapter
-import akka.util.ByteString
+import akka.util.{ ByteString, OptionVal }
 import akka.stream.scaladsl.{ Flow, Source }
 import akka.stream.stage._
 import akka.http.scaladsl.model._
@@ -20,6 +20,8 @@ import RenderSupport._
 import HttpProtocols._
 import headers._
 
+import scala.concurrent.duration._
+
 /**
  * INTERNAL API
  */
@@ -129,9 +131,17 @@ private[http] class HttpResponseRendererFactory(
 
           @tailrec def renderHeaders(remaining: List[HttpHeader], alwaysClose: Boolean = false,
                                      connHeader: Connection = null, serverSeen: Boolean = false,
-                                     transferEncodingSeen: Boolean = false, dateSeen: Boolean = false): Unit =
+                                     transferEncodingSeen: Boolean = false, dateSeen: Boolean = false): Unit = {
             remaining match {
               case head :: tail ⇒ head match {
+                case x: Server ⇒
+                  render(x)
+                  renderHeaders(tail, alwaysClose, connHeader, serverSeen = true, transferEncodingSeen, dateSeen)
+
+                case x: Date ⇒
+                  render(x)
+                  renderHeaders(tail, alwaysClose, connHeader, serverSeen, transferEncodingSeen, dateSeen = true)
+
                 case x: `Content-Length` ⇒
                   suppressionWarning(log, x, "explicit `Content-Length` header is not allowed. Use the appropriate HttpEntity subtype.")
                   renderHeaders(tail, alwaysClose, connHeader, serverSeen, transferEncodingSeen, dateSeen)
@@ -140,10 +150,6 @@ private[http] class HttpResponseRendererFactory(
                   suppressionWarning(log, x, "explicit `Content-Type` header is not allowed. Set `HttpResponse.entity.contentType` instead.")
                   renderHeaders(tail, alwaysClose, connHeader, serverSeen, transferEncodingSeen, dateSeen)
 
-                case x: Date ⇒
-                  render(x)
-                  renderHeaders(tail, alwaysClose, connHeader, serverSeen, transferEncodingSeen, dateSeen = true)
-
                 case x: `Transfer-Encoding` ⇒
                   x.withChunkedPeeled match {
                     case None ⇒
@@ -159,10 +165,6 @@ private[http] class HttpResponseRendererFactory(
                   val connectionHeader = if (connHeader eq null) x else Connection(x.tokens ++ connHeader.tokens)
                   renderHeaders(tail, alwaysClose, connectionHeader, serverSeen, transferEncodingSeen, dateSeen)
 
-                case x: Server ⇒
-                  render(x)
-                  renderHeaders(tail, alwaysClose, connHeader, serverSeen = true, transferEncodingSeen, dateSeen)
-
                 case x: CustomHeader ⇒
                   if (x.renderInResponses) render(x)
                   renderHeaders(tail, alwaysClose, connHeader, serverSeen, transferEncodingSeen, dateSeen)
@@ -205,13 +207,15 @@ private[http] class HttpResponseRendererFactory(
                   r ~~ Connection ~~ (if (close) CloseBytes else KeepAliveBytes) ~~ CrLf
                 else if (connHeader != null && connHeader.hasUpgrade) {
                   r ~~ connHeader ~~ CrLf
-                  headers
-                    .collectFirst { case u: UpgradeToWebSocketResponseHeader ⇒ u }
-                    .foreach { header ⇒ closeMode = SwitchToWebSocket(header.handler) }
+                  HttpHeader.fastFind(classOf[UpgradeToWebSocketResponseHeader], headers) match {
+                    case OptionVal.Some(header) ⇒ closeMode = SwitchToWebSocket(header.handler)
+                    case _                      ⇒ // nothing to do here...
+                  }
                 }
                 if (mustRenderTransferEncodingChunkedHeader && !transferEncodingSeen)
                   r ~~ `Transfer-Encoding` ~~ ChunkedBytes ~~ CrLf
             }
+          }
 
           def renderContentLengthHeader(contentLength: Long) =
             if (status.allowsEntity) r ~~ `Content-Length` ~~ contentLength ~~ CrLf else r
@@ -219,7 +223,7 @@ private[http] class HttpResponseRendererFactory(
           def byteStrings(entityBytes: ⇒ Source[ByteString, Any]): Source[ResponseRenderingOutput, Any] =
             renderByteStrings(r, entityBytes, skipEntity = noEntity).map(ResponseRenderingOutput.HttpData(_))
 
-          def completeResponseRendering(entity: ResponseEntity): StrictOrStreamed =
+          @tailrec def completeResponseRendering(entity: ResponseEntity): StrictOrStreamed =
             entity match {
               case HttpEntity.Strict(_, data) ⇒
                 renderHeaders(headers.toList)
diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/RenderSupport.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/RenderSupport.scala
index ca4a3ef0a2..0c2ddc5643 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/RenderSupport.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/rendering/RenderSupport.scala
@@ -28,6 +28,20 @@ private object RenderSupport {
   val KeepAliveBytes = "Keep-Alive".asciiBytes
   val CloseBytes = "close".asciiBytes
 
+  private[this] final val PreRenderedContentTypes = {
+    val m = new java.util.HashMap[ContentType, Array[Byte]](16)
+    def preRenderContentType(ct: ContentType) =
+      m.put(ct, (new ByteArrayRendering(32) ~~ headers.`Content-Type` ~~ ct ~~ CrLf).get)
+
+    import ContentTypes._
+    preRenderContentType(`application/json`)
+    preRenderContentType(`text/plain(UTF-8)`)
+    preRenderContentType(`text/xml(UTF-8)`)
+    preRenderContentType(`text/html(UTF-8)`)
+    preRenderContentType(`text/csv(UTF-8)`)
+    m
+  }
+
   def CrLf = Rendering.CrLf
 
   implicit val trailerRenderer = Renderer.genericSeqRenderer[Renderable, HttpHeader](CrLf, Rendering.Empty)
@@ -42,9 +56,14 @@ private object RenderSupport {
     })
   }
 
-  def renderEntityContentType(r: Rendering, entity: HttpEntity) =
-    if (entity.contentType != ContentTypes.NoContentType) r ~~ headers.`Content-Type` ~~ entity.contentType ~~ CrLf
-    else r
+  def renderEntityContentType(r: Rendering, entity: HttpEntity) = {
+    val ct = entity.contentType
+    if (ct != ContentTypes.NoContentType) {
+      val preRendered = PreRenderedContentTypes.get(ct)
+      if (preRendered ne null) r ~~ preRendered // re-use pre-rendered
+      else r ~~ headers.`Content-Type` ~~ ct ~~ CrLf // render ad-hoc
+    } else r // don't render
+  }
 
   def renderByteStrings(r: ByteStringRendering, entityBytes: ⇒ Source[ByteString, Any],
                         skipEntity: Boolean = false): Source[ByteString, Any] = {
diff --git a/akka-http-core/src/main/scala/akka/http/impl/engine/ws/Handshake.scala b/akka-http-core/src/main/scala/akka/http/impl/engine/ws/Handshake.scala
index c207b7c27e..dd704f7d2c 100644
--- a/akka-http-core/src/main/scala/akka/http/impl/engine/ws/Handshake.scala
+++ b/akka-http-core/src/main/scala/akka/http/impl/engine/ws/Handshake.scala
@@ -5,6 +5,7 @@
 package akka.http.impl.engine.ws
 
 import java.util.Random
+
 import scala.collection.immutable
 import scala.collection.immutable.Seq
 import scala.reflect.ClassTag
@@ -12,7 +13,8 @@ import akka.http.impl.util._
 import akka.http.scaladsl.model.headers._
 import akka.http.scaladsl.model.ws.{ Message, UpgradeToWebSocket }
 import akka.http.scaladsl.model._
-import akka.stream.{ Graph, FlowShape }
+import akka.stream.{ FlowShape, Graph }
+import akka.util.OptionVal
 
 /**
  * Server-side implementation of the WebSocket handshake
@@ -62,50 +64,63 @@ private[http] object Handshake {
      *        to speak.  The interpretation of this header field is discussed
      *        in Section 9.1.
      */
-    def websocketUpgrade(headers: List[HttpHeader], hostHeaderPresent: Boolean): Option[UpgradeToWebSocket] = {
-      def find[T <: HttpHeader: ClassTag]: Option[T] =
-        headers.collectFirst {
-          case t: T ⇒ t
+    def websocketUpgrade(headers: List[HttpHeader], hostHeaderPresent: Boolean): OptionVal[UpgradeToWebSocket] = {
+
+      // notes on Headers that re REQUIRE to be present here:
+      // - Host header is validated in general HTTP logic
+      // - Origin header is optional and, if required, should be validated
+      //   on higher levels (routing, application logic)
+      // 
+      // TODO See #18709 Extension support is optional in WS and currently unsupported.
+      // 
+      // these are not needed directly, we verify their presence and correctness only:
+      // - Upgrade
+      // - Connection
+      // - `Sec-WebSocket-Version`
+      def hasAllRequiredWebsocketUpgradeHeaders: Boolean = {
+        // single-pass through the headers list while collecting all needed requirements
+        // this way we avoid scanning the requirements list 3 times (as we would with collect/find)
+        val it = headers.iterator
+        var requirementsMet = 0
+        val targetRequirements = 3
+        while (it.hasNext && (requirementsMet != targetRequirements)) it.next() match {
+          case u: Upgrade                 ⇒ if (u.hasWebSocket) requirementsMet += 1
+          case c: Connection              ⇒ if (c.hasUpgrade) requirementsMet += 1
+          case v: `Sec-WebSocket-Version` ⇒ if (v.hasVersion(CurrentWebSocketVersion)) requirementsMet += 1
+          case _                          ⇒ // continue...
         }
+        requirementsMet == targetRequirements
+      }
 
-      // Host header is validated in general HTTP logic
-      // val host = find[Host]
-      val upgrade = find[Upgrade]
-      val connection = find[Connection]
-      val key = find[`Sec-WebSocket-Key`]
-      val version = find[`Sec-WebSocket-Version`]
-      // Origin header is optional and, if required, should be validated
-      // on higher levels (routing, application logic)
-      // val origin = find[Origin]
-      val protocol = find[`Sec-WebSocket-Protocol`]
-      val clientSupportedSubprotocols = protocol.toList.flatMap(_.protocols)
-      // Extension support is optional in WS and currently unsupported.
-      // TODO See #18709
-      // val extensions = find[`Sec-WebSocket-Extensions`]
+      if (hasAllRequiredWebsocketUpgradeHeaders) {
+        val key = HttpHeader.fastFind(classOf[`Sec-WebSocket-Key`], headers)
+        if (key.isDefined && key.get.isValid) {
+          val protocol = HttpHeader.fastFind(classOf[`Sec-WebSocket-Protocol`], headers)
 
-      if (upgrade.exists(_.hasWebSocket) &&
-        connection.exists(_.hasUpgrade) &&
-        version.exists(_.hasVersion(CurrentWebSocketVersion)) &&
-        key.exists(k ⇒ k.isValid)) {
-
-        val header = new UpgradeToWebSocketLowLevel {
-          def requestedProtocols: Seq[String] = clientSupportedSubprotocols
-
-          def handle(handler: Either[Graph[FlowShape[FrameEvent, FrameEvent], Any], Graph[FlowShape[Message, Message], Any]], subprotocol: Option[String]): HttpResponse = {
-            require(
-              subprotocol.forall(chosen ⇒ clientSupportedSubprotocols.contains(chosen)),
-              s"Tried to choose invalid subprotocol '$subprotocol' which wasn't offered by the client: [${requestedProtocols.mkString(", ")}]")
-            buildResponse(key.get, handler, subprotocol)
+          val clientSupportedSubprotocols = protocol match {
+            case OptionVal.Some(p) ⇒ p.protocols
+            case _                 ⇒ Nil
           }
 
-          def handleFrames(handlerFlow: Graph[FlowShape[FrameEvent, FrameEvent], Any], subprotocol: Option[String]): HttpResponse =
-            handle(Left(handlerFlow), subprotocol)
+          val header = new UpgradeToWebSocketLowLevel {
+            def requestedProtocols: Seq[String] = clientSupportedSubprotocols
 
-          override def handleMessages(handlerFlow: Graph[FlowShape[Message, Message], Any], subprotocol: Option[String] = None): HttpResponse =
-            handle(Right(handlerFlow), subprotocol)
-        }
-        Some(header)
-      } else None
+            def handle(handler: Either[Graph[FlowShape[FrameEvent, FrameEvent], Any], Graph[FlowShape[Message, Message], Any]], subprotocol: Option[String]): HttpResponse = {
+              require(
+                subprotocol.forall(chosen ⇒ clientSupportedSubprotocols.contains(chosen)),
+                s"Tried to choose invalid subprotocol '$subprotocol' which wasn't offered by the client: [${requestedProtocols.mkString(", ")}]")
+              buildResponse(key.get, handler, subprotocol)
+            }
+
+            def handleFrames(handlerFlow: Graph[FlowShape[FrameEvent, FrameEvent], Any], subprotocol: Option[String]): HttpResponse =
+              handle(Left(handlerFlow), subprotocol)
+
+            override def handleMessages(handlerFlow: Graph[FlowShape[Message, Message], Any], subprotocol: Option[String] = None): HttpResponse =
+              handle(Right(handlerFlow), subprotocol)
+          }
+          OptionVal.Some(header)
+        } else OptionVal.None
+      } else OptionVal.None
     }
 
     /*
diff --git a/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpHeader.scala b/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpHeader.scala
index 0896fec5c2..ecd3c5341a 100644
--- a/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpHeader.scala
+++ b/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpHeader.scala
@@ -4,14 +4,19 @@
 
 package akka.http.scaladsl.model
 
-import akka.http.scaladsl.settings.ParserSettings
+import java.nio.charset.StandardCharsets
 
-import scala.util.{ Success, Failure }
-import akka.parboiled2.ParseError
+import scala.util.{ Failure, Success }
+import akka.parboiled2.{ ParseError, ParserInput }
 import akka.http.impl.util.ToStringRenderable
 import akka.http.impl.model.parser.{ CharacterClasses, HeaderParser }
 import akka.http.javadsl.{ model ⇒ jm }
 import akka.http.scaladsl.model.headers._
+import akka.parboiled2.ParserInput.DefaultParserInput
+import akka.util.{ ByteString, OptionVal }
+
+import scala.annotation.tailrec
+import scala.collection.immutable
 
 /**
  * The model of an HTTP header. In its most basic form headers are simple name-value pairs. Header names
@@ -80,6 +85,16 @@ object HttpHeader {
       }
     } else ParsingResult.Error(ErrorInfo(s"Illegal HTTP header name", name))
 
+  /** INTERNAL API */
+  private[akka] def fastFind[T >: Null <: jm.HttpHeader](clazz: Class[T], headers: immutable.Seq[HttpHeader]): OptionVal[T] = {
+    val it = headers.iterator
+    while (it.hasNext) it.next() match {
+      case h if clazz.isInstance(h) ⇒ return OptionVal.Some[T](h.asInstanceOf[T])
+      case _                        ⇒ // continue ...
+    }
+    OptionVal.None.asInstanceOf[OptionVal[T]]
+  }
+
   sealed trait ParsingResult {
     def errors: List[ErrorInfo]
   }
diff --git a/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpMessage.scala b/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpMessage.scala
index ddc732305a..24601d1487 100644
--- a/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpMessage.scala
+++ b/akka-http-core/src/main/scala/akka/http/scaladsl/model/HttpMessage.scala
@@ -19,7 +19,7 @@ import scala.reflect.{ ClassTag, classTag }
 import akka.Done
 import akka.parboiled2.CharUtils
 import akka.stream.Materializer
-import akka.util.{ ByteString, HashCode }
+import akka.util.{ ByteString, HashCode, OptionVal }
 import akka.http.impl.util._
 import akka.http.javadsl.{ model ⇒ jm }
 import akka.http.scaladsl.util.FastFuture._
@@ -102,14 +102,13 @@ sealed trait HttpMessage extends jm.HttpMessage {
   }
 
   /** Returns the first header of the given type if there is one */
-  def header[T <: jm.HttpHeader: ClassTag]: Option[T] = {
-    val erasure = classTag[T].runtimeClass
-    headers.find(erasure.isInstance).asInstanceOf[Option[T]] match {
-      case header: Some[T]                         ⇒ header
-      case _ if erasure == classOf[`Content-Type`] ⇒ Some(entity.contentType).asInstanceOf[Option[T]]
-      case _                                       ⇒ None
+  def header[T >: Null <: jm.HttpHeader: ClassTag]: Option[T] = {
+    val clazz = classTag[T].runtimeClass.asInstanceOf[Class[T]]
+    HttpHeader.fastFind[T](clazz, headers) match {
+      case OptionVal.Some(h)                     ⇒ Some(h)
+      case _ if clazz == classOf[`Content-Type`] ⇒ Some(entity.contentType).asInstanceOf[Option[T]]
+      case _                                     ⇒ None
     }
-
   }
 
   /**
@@ -145,7 +144,11 @@ sealed trait HttpMessage extends jm.HttpMessage {
   /** Java API */
   def getHeaders: JIterable[jm.HttpHeader] = (headers: immutable.Seq[jm.HttpHeader]).asJava
   /** Java API */
-  def getHeader[T <: jm.HttpHeader](headerClass: Class[T]): Optional[T] = header(ClassTag(headerClass)).asJava
+  def getHeader[T <: jm.HttpHeader](headerClass: Class[T]): Optional[T] =
+    HttpHeader.fastFind[jm.HttpHeader](headerClass.asInstanceOf[Class[jm.HttpHeader]], headers) match {
+      case OptionVal.Some(h) ⇒ Optional.of(h.asInstanceOf[T])
+      case _                 ⇒ Optional.empty()
+    }
   /** Java API */
   def getHeader(headerName: String): Optional[jm.HttpHeader] = {
     val lowerCased = headerName.toRootLowerCase
@@ -322,14 +325,22 @@ object HttpRequest {
    * include a valid [[akka.http.scaladsl.model.headers.Host]] header or if URI authority and [[akka.http.scaladsl.model.headers.Host]] header don't match.
    */
   def effectiveUri(uri: Uri, headers: immutable.Seq[HttpHeader], securedConnection: Boolean, defaultHostHeader: Host): Uri = {
-    val hostHeader = headers.collectFirst { case x: Host ⇒ x }
+    def findHost(headers: immutable.Seq[HttpHeader]): OptionVal[Host] = {
+      val it = headers.iterator
+      while (it.hasNext) it.next() match {
+        case h: Host ⇒ return OptionVal.Some(h)
+        case _       ⇒ // continue ...
+      }
+      OptionVal.None
+    }
+    val hostHeader: OptionVal[Host] = findHost(headers)
     if (uri.isRelative) {
       def fail(detail: String) =
         throw IllegalUriException(s"Cannot establish effective URI of request to `$uri`, request has a relative URI and $detail")
       val Host(host, port) = hostHeader match {
-        case None                 ⇒ if (defaultHostHeader.isEmpty) fail("is missing a `Host` header") else defaultHostHeader
-        case Some(x) if x.isEmpty ⇒ if (defaultHostHeader.isEmpty) fail("an empty `Host` header") else defaultHostHeader
-        case Some(x)              ⇒ x
+        case OptionVal.None                 ⇒ if (defaultHostHeader.isEmpty) fail("is missing a `Host` header") else defaultHostHeader
+        case OptionVal.Some(x) if x.isEmpty ⇒ if (defaultHostHeader.isEmpty) fail("an empty `Host` header") else defaultHostHeader
+        case OptionVal.Some(x)              ⇒ x
       }
       uri.toEffectiveHttpRequestUri(host, port, securedConnection)
     } else // http://tools.ietf.org/html/rfc7230#section-5.4
diff --git a/akka-http-core/src/test/scala/akka/http/impl/engine/ws/WebSocketIntegrationSpec.scala b/akka-http-core/src/test/scala/akka/http/impl/engine/ws/WebSocketIntegrationSpec.scala
index 3c7c646b32..10241c6a11 100644
--- a/akka-http-core/src/test/scala/akka/http/impl/engine/ws/WebSocketIntegrationSpec.scala
+++ b/akka-http-core/src/test/scala/akka/http/impl/engine/ws/WebSocketIntegrationSpec.scala
@@ -3,7 +3,7 @@
  */
 package akka.http.impl.engine.ws
 
-import scala.concurrent.{ Await, Promise }
+import scala.concurrent.{ Await, Future, Promise }
 import scala.concurrent.duration.DurationInt
 import org.scalactic.ConversionCheckedTripleEquals
 import org.scalatest.concurrent.ScalaFutures
diff --git a/akka-http-testkit/src/main/scala/akka/http/javadsl/testkit/TestRouteResult.scala b/akka-http-testkit/src/main/scala/akka/http/javadsl/testkit/TestRouteResult.scala
index 91edde58ac..1f27424f61 100644
--- a/akka-http-testkit/src/main/scala/akka/http/javadsl/testkit/TestRouteResult.scala
+++ b/akka-http-testkit/src/main/scala/akka/http/javadsl/testkit/TestRouteResult.scala
@@ -103,7 +103,7 @@ abstract class TestRouteResult(_result: RouteResult, awaitAtMost: FiniteDuration
   /**
    * Returns the first header of the response which is of the given class.
    */
-  def header[T <: HttpHeader](clazz: Class[T]): T =
+  def header[T >: Null <: HttpHeader](clazz: Class[T]): T =
     response.header(ClassTag(clazz))
       .getOrElse(doFail(s"Expected header of type ${clazz.getSimpleName} but wasn't found."))
 
diff --git a/akka-http-testkit/src/main/scala/akka/http/scaladsl/testkit/RouteTest.scala b/akka-http-testkit/src/main/scala/akka/http/scaladsl/testkit/RouteTest.scala
index 2c71fc3538..b7e1c15a36 100644
--- a/akka-http-testkit/src/main/scala/akka/http/scaladsl/testkit/RouteTest.scala
+++ b/akka-http-testkit/src/main/scala/akka/http/scaladsl/testkit/RouteTest.scala
@@ -75,7 +75,7 @@ trait RouteTest extends RequestBuilding with WSTestRequestBuilding with RouteTes
   def charsetOption: Option[HttpCharset] = contentType.charsetOption
   def charset: HttpCharset = charsetOption getOrElse sys.error("Binary entity does not have charset")
   def headers: immutable.Seq[HttpHeader] = response.headers
-  def header[T <: HttpHeader: ClassTag]: Option[T] = response.header[T]
+  def header[T >: Null <: HttpHeader: ClassTag]: Option[T] = response.header[T](implicitly[ClassTag[T]])
   def header(name: String): Option[HttpHeader] = response.headers.find(_.is(name.toLowerCase))
   def status: StatusCode = response.status
 
diff --git a/akka-parsing/src/main/scala/akka/parboiled2/ParserInput.scala b/akka-parsing/src/main/scala/akka/parboiled2/ParserInput.scala
index 82f2b73250..445f5c0f67 100644
--- a/akka-parsing/src/main/scala/akka/parboiled2/ParserInput.scala
+++ b/akka-parsing/src/main/scala/akka/parboiled2/ParserInput.scala
@@ -18,6 +18,9 @@ package akka.parboiled2
 
 import scala.annotation.tailrec
 import java.nio.ByteBuffer
+import java.nio.charset.StandardCharsets
+
+import akka.parboiled2.ParserInput.DefaultParserInput
 
 trait ParserInput {
   /**
@@ -109,4 +112,4 @@ object ParserInput {
     def sliceString(start: Int, end: Int) = new String(chars, start, end - start)
     def sliceCharArray(start: Int, end: Int) = java.util.Arrays.copyOfRange(chars, start, end)
   }
-}
\ No newline at end of file
+}