+htc migrate pipelining-limit server config setting from spray

akka-http-core/src/main/resources/reference.conf

@@ -29,6 +29,18 @@ akka.http {
     # deliver an unlimited backpressured stream of incoming connections.
     max-connections = 1024
 
+    # The maximum number of requests that are accepted (and dispatched to
+    # the application) on one single connection before the first request
+    # has to be completed.
+    # Incoming requests that would cause the pipelining limit to be exceeded
+    # are not read from the connections socket so as to build up "back-pressure"
+    # to the client via TCP flow control.
+    # A setting of 1 disables HTTP pipelining, since only one request per
+    # connection can be "open" (i.e. being processed by the application) at any
+    # time. Set to higher values to enable HTTP pipelining.
+    # This value must be > 0 and <= 1024.
+    pipelining-limit = 16
+
     # Enables/disables the addition of a `Remote-Address` header
     # holding the clients (remote) IP address.
     remote-address-header = off

akka-http-core/src/main/scala/akka/http/ServerSettings.scala

@@ -26,6 +26,7 @@ final case class ServerSettings(
   serverHeader: Option[Server],
   timeouts: ServerSettings.Timeouts,
   maxConnections: Int,
+  pipeliningLimit: Int,
   remoteAddressHeader: Boolean,
   rawRequestUriHeader: Boolean,
   transparentHeadRequests: Boolean,
@@ -38,6 +39,7 @@ final case class ServerSettings(
   parserSettings: ParserSettings) {
 
   require(0 < maxConnections, "max-connections must be > 0")
+  require(0 < pipeliningLimit && pipeliningLimit <= 1024, "pipelining-limit must be > 0 and <= 1024")
   require(0 < responseHeaderSizeHint, "response-size-hint must be > 0")
   require(0 < backlog, "backlog must be > 0")
 }
@@ -55,6 +57,7 @@ object ServerSettings extends SettingsCompanion[ServerSettings]("akka.http.serve
       c getPotentiallyInfiniteDuration "idle-timeout",
       c getFiniteDuration "bind-timeout"),
     c getInt "max-connections",
+    c getInt "pipelining-limit",
     c getBoolean "remote-address-header",
     c getBoolean "raw-request-uri-header",
     c getBoolean "transparent-head-requests",

akka-http-core/src/main/scala/akka/http/impl/engine/server/HttpServerBluePrint.scala

@@ -127,7 +127,7 @@ private[http] object HttpServerBluePrint {
         csRequestPrepOut ~> requestPrep
 
         // One2OneBidi
-        val one2one = b.add(new One2OneBidi[HttpRequest, HttpResponse](16)) // TODO: replace hard-coded value by reintroducing `pipeline-limit` setting from spray
+        val one2one = b.add(new One2OneBidi[HttpRequest, HttpResponse](settings.pipeliningLimit))
         requestPrep.outlet ~> one2one.in1
         one2one.out2 ~> csHttpResponseIn