warp: Send Connection: close when closing the conn

warp/Network/Wai/Handler/Warp/Response.hs

@@ -121,7 +121,7 @@ sendResponse
     -> IO Bool
     -- ^ Returing True if the connection is persistent.
 sendResponse settings conn ii th req reqidxhdr src response = do
-    hs <- addAltSvc settings <$> addServerAndDate hs0
+    hs <- addConnection . addAltSvc settings <$> addServerAndDate hs0
     if hasBody s
         then do
             -- The response to HEAD does not have body.
@@ -149,6 +149,9 @@ sendResponse settings conn ii th req reqidxhdr src response = do
     s = responseStatus response
     hs0 = sanitizeHeaders $ responseHeaders response
     rspidxhdr = indexResponseHeader hs0
+    addConnection hs = if (hasBody s && not ret) || (not (hasBody s) && not isPersist)
+                       then (H.hConnection, "close") : hs
+                       else hs
     getdate = getDate ii
     addServerAndDate = addDate getdate rspidxhdr . addServer defServer rspidxhdr
     (isPersist, isChunked0) = infoFromRequest req reqidxhdr