feat: Add explicit headers-only POST request using Prefer header

Allows using header "Prefer=headers-only" explicitly to get a response with only a Location header.

BREAKING CHANGE: Change default for POST request from headers-only to minimal

Resolves #1656

src/PostgREST/Request/ApiRequest.hs

@@ -334,11 +334,10 @@ userApiRequest confSchemas rootSpec dbStructure req reqBody
         split :: BS.ByteString -> [Text]
         split = map T.strip . T.split (==',') . toS
   representation
-    | hasPrefer (show Full) = Full
-    | hasPrefer (show None) = None
-    | otherwise             = if action == ActionCreate
-                                then HeadersOnly -- Assume the user wants the Location header(for POST) by default
-                                else None
+    | hasPrefer (show Full)        = Full
+    | hasPrefer (show None)        = None
+    | hasPrefer (show HeadersOnly) = HeadersOnly
+    | otherwise                    = None
   auth = fromMaybe "" $ lookupHeader hAuthorization
   tokenStr = case T.split (== ' ') (toS auth) of
     ("Bearer" : t : _) -> t

src/PostgREST/Request/Preferences.hs

@@ -22,7 +22,7 @@ data PreferRepresentation
 instance Show PreferRepresentation where
   show Full        = "return=representation"
   show None        = "return=minimal"
-  show HeadersOnly = mempty
+  show HeadersOnly = "return=headers-only"
 
 data PreferParameters
   = SingleObject    -- ^ Pass all parameters as a single json object to a stored procedure