finagle-http: Remove Use of request.response from ExceptionFilter

Problem / Solution

Use of 'request.response' within Finagle is an anti-pattern. Let's
remove its use from finagle-http's `ExceptionFilter`.

JIRA Issues: CSL-8391

Differential Revision: https://phabricator.twitter.biz/D333509

CHANGELOG.rst

@@ -13,6 +13,10 @@ Runtime Behavior Changes
 * finagle-http: `c.t.f.http.Cors` has been changed to no longer use the `c.t.f.http.Response`
   associated with the passed in `c.t.f.http.Request`. ``PHAB_ID=D332765``
 
+* finagle-http: `c.t.f.http.filter.ExceptionFilter` has been changed to no longer
+  use the `c.t.f.http.Response` associated with the passed in `c.t.f.http.Request`.
+  ``PHAB_ID=D333509``
+
 Breaking API Changes
 ~~~~~~~~~~~~~~~~~~~~
 

finagle-http/src/main/scala/com/twitter/finagle/http/filter/ExceptionFilter.scala

@@ -30,11 +30,11 @@ class ExceptionFilter[REQUEST <: Request] extends SimpleFilter[REQUEST, Response
     case e: CancelledRequestException =>
       // This only happens when ChannelService cancels a reply.
       log.warning("cancelled request: uri:%s", request.uri)
-      respond(request, ClientClosedRequestStatus)
+      respond(ClientClosedRequestStatus)
     case e: Throwable =>
       try {
         log.warning(e, "exception: uri:%s exception:%s", request.uri, e)
-        respond(request, Status.InternalServerError)
+        respond(Status.InternalServerError)
       } catch {
         // logging or internals are broken.  Write static string to console -
         // don't attempt to include request or exception.
@@ -44,13 +44,8 @@ class ExceptionFilter[REQUEST <: Request] extends SimpleFilter[REQUEST, Response
       }
   }
 
-  private def respond(request: REQUEST, responseStatus: Status): Future[Response] = {
-    val response = request.response
-    response.status = responseStatus
-    response.clearContent()
-    response.contentLength = 0
-    Future.value(response)
-  }
+  private def respond(responseStatus: Status): Future[Response] =
+    Future.value(Response(responseStatus))
 }
 
 object ExceptionFilter extends ExceptionFilter[Request] {

finagle-http/src/test/scala/com/twitter/finagle/http/filter/ExceptionFilterTest.scala

@@ -41,7 +41,7 @@ class ExceptionFilterTest extends FunSuite {
 
     assert(response.status == Status.InternalServerError)
     assert(response.contentString == "")
-    assert(response.contentLength == Some(0))
+    assert(response.contentLength == None)
   }
 
   test("handle throw") {
@@ -50,7 +50,7 @@ class ExceptionFilterTest extends FunSuite {
 
     assert(response.status == Status.InternalServerError)
     assert(response.contentString == "")
-    assert(response.contentLength == Some(0))
+    assert(response.contentLength == None)
   }
 
   test("handle cancel") {
@@ -59,6 +59,6 @@ class ExceptionFilterTest extends FunSuite {
 
     assert(response.statusCode == 499)
     assert(response.contentString == "")
-    assert(response.contentLength == Some(0))
+    assert(response.contentLength == None)
   }
 }