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refactor: move content negotiation logic to Negotiate.hs

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Moves the `negotiateContent` function to `Plan/Negotiate.hs`
module. This also adds comments to describe the current approach
we have for negotiation.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>
This commit is contained in:
Taimoor Zaeem
2026-01-02 06:32:17 +08:00
committed by Steve Chavez
parent 76e0e1fbff
commit 9ec5b030ce
3 changed files with 84 additions and 35 deletions
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src/PostgREST/Plan.hs
+1 -35
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@@ -43,6 +43,7 @@ import PostgREST.Error (ApiRequestError (..),
Error (..),
SchemaCacheError (..))
import PostgREST.MediaType (MediaType (..))
import PostgREST.Plan.Negotiate (negotiateContent)
import PostgREST.Query.SqlFragment (sourceCTEName)
import PostgREST.RangeQuery (NonnegRange, allRange,
convertToLimitZeroRange,
@@ -50,7 +51,6 @@ import PostgREST.RangeQuery (NonnegRange, allRange,
import PostgREST.SchemaCache (SchemaCache (..))
import PostgREST.SchemaCache.Identifiers (FieldName,
QualifiedIdentifier (..),
RelIdentifier (..),
Schema)
import PostgREST.SchemaCache.Relationship (Cardinality (..),
Junction (..),
@@ -60,8 +60,6 @@ import PostgREST.SchemaCache.Relationship (Cardinality (..),
import PostgREST.SchemaCache.Representations (DataRepresentation (..),
RepresentationsMap)
import PostgREST.SchemaCache.Routine (MediaHandler (..),
MediaHandlerMap,
ResolvedHandler,
Routine (..),
RoutineMap,
RoutineParam (..),
@@ -1116,35 +1114,3 @@ inferColsEmbedNeeds (Node ReadPlan{select} forest) pkCols
-- they are later concatenated with AND in the QueryBuilder
addFilterToLogicForest :: CoercibleFilter -> [CoercibleLogicTree] -> [CoercibleLogicTree]
addFilterToLogicForest flt lf = CoercibleStmnt flt : lf
-- | Do content negotiation. i.e. choose a media type based on the intersection of accepted/produced media types.
negotiateContent :: AppConfig -> ApiRequest -> QualifiedIdentifier -> [MediaType] -> MediaHandlerMap -> Bool -> Either ApiRequestError ResolvedHandler
negotiateContent conf ApiRequest{iAction=act, iPreferences=Preferences{preferRepresentation=rep}} identifier accepts produces defaultSelect =
case (act, firstAcceptedPick) of
(_, Nothing) -> Left . MediaTypeError $ map MediaType.toMime accepts
(ActDb (ActRelationMut _ _), Just (x, mt)) -> Right (if rep == Just Full then x else NoAgg, mt)
-- no need for an aggregate on HEAD https://github.com/PostgREST/postgrest/issues/2849
-- TODO: despite no aggregate, these are responding with a Content-Type, which is not correct.
(ActDb (ActRelationRead _ True), Just (_, mt)) -> Right (NoAgg, mt)
(ActDb (ActRoutine _ (InvRead True)), Just (_, mt)) -> Right (NoAgg, mt)
(_, Just (x, mt)) -> Right (x, mt)
where
firstAcceptedPick = listToMaybe $ mapMaybe matchMT accepts -- If there are multiple accepted media types, pick the first. This is usual in content negotiation.
matchMT mt = case mt of
-- all the vendored media types have special handling as they have media type parameters, they cannot be overridden
m@(MTVndSingularJSON strip) -> Just (BuiltinAggSingleJson strip, m)
m@MTVndArrayJSONStrip -> Just (BuiltinAggArrayJsonStrip, m)
m@(MTVndPlan (MTVndSingularJSON strip) _ _) -> mtPlanToNothing $ Just (BuiltinAggSingleJson strip, m)
m@(MTVndPlan MTVndArrayJSONStrip _ _) -> mtPlanToNothing $ Just (BuiltinAggArrayJsonStrip, m)
-- TODO the plan should have its own MediaHandler instead of relying on MediaType
m@(MTVndPlan mType _ _) -> mtPlanToNothing $ ((,) . fst <$> lookupHandler mType) <*> pure m
-- all the other media types can be overridden
x -> lookupHandler x
mtPlanToNothing x = if configDbPlanEnabled conf then x else Nothing -- don't find anything if the plan media type is not allowed
lookupHandler mt =
when' defaultSelect (HM.lookup (RelId identifier, MTAny) produces) <|> -- lookup for identifier and `*/*`
when' defaultSelect (HM.lookup (RelId identifier, mt) produces) <|> -- lookup for identifier and a particular media type
HM.lookup (RelAnyElement, mt) produces -- lookup for anyelement and a particular media type
when' :: Bool -> Maybe a -> Maybe a
when' True (Just a) = Just a
when' _ _ = Nothing