add: add "Vary" header to responses

Author: develop7

CHANGELOG.md

@@ -10,6 +10,7 @@ All notable changes to this project will be documented in this file. From versio
 - Add a `HINT` when the LISTEN channel stops working due to a PostgreSQL bug by @laurenceisla in #4581
 - Add string slicing operator for `jwt-role-claim-key` by @taimoorzaeem in #4599
 - Log host, port and pg version of listener database connection by @mkleczek in #4617 #4618
+- Add `Vary` header to responses by @develop7 in #4609
 
 ### Fixed
 

src/PostgREST/App.hs

@@ -178,7 +178,14 @@ postgrestResponse appState conf@AppConfig{..} maybeSchemaCache authResult@AuthRe
 
   where
     toWaiResponse :: ServerTiming -> Response.PgrstResponse -> Wai.Response
-    toWaiResponse timing (Response.PgrstResponse st hdrs bod) = Wai.responseLBS st (hdrs ++ ([serverTimingHeader timing | configServerTimingEnabled])) bod
+    toWaiResponse timing (Response.PgrstResponse st hdrs bod) =
+      Wai.responseLBS st (hdrs ++ serverTimingHeaders timing ++ [varyHeader]) bod
+
+    varyHeader :: HTTP.Header
+    varyHeader = ("Vary", "Accept-Encoding, Accept, Prefer, Range")
+
+    serverTimingHeaders :: ServerTiming -> [HTTP.Header]
+    serverTimingHeaders timing = [serverTimingHeader timing | configServerTimingEnabled]
 
     withTiming :: Handler IO a -> Handler IO (Maybe Double, a)
     withTiming f = if configServerTimingEnabled