fix: Fatal error when requesting limit=0 and db-max-rows is set (#2560)

CHANGELOG.md

@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
  - #2548, Fix regression when embedding views with partial references to multi column FKs - @wolfgangwalther
+ - #2558, Fix regression when requesting limit=0 and `db-max-row` is set - @laurenceisla
 
 ## [10.1.0] - 2022-10-28
 

src/PostgREST/ApiRequest.hs

@@ -59,8 +59,8 @@ import PostgREST.MediaType               (MTPlanAttrs (..),
                                           MTPlanFormat (..),
                                           MediaType (..))
 import PostgREST.RangeQuery              (NonnegRange, allRange,
+                                          convertToLimitZeroRange,
                                           hasLimitZero,
-                                          limitZeroRange,
                                           rangeRequested)
 import PostgREST.SchemaCache             (SchemaCache (..))
 import PostgREST.SchemaCache.Identifiers (FieldName,
@@ -354,7 +354,7 @@ apiRequest conf sCache req reqBody queryparams@QueryParams{..} PathInfo{pathName
 
   -- Bypass all the ranges and send only the limit zero range (0 <= x <= -1) if
   -- limit=0 is present in the query params (not allowed for the Range header)
-  ranges = HM.insert "limit" (if hasLimitZero limitRange then limitZeroRange else headerAndLimitRange) qsRanges
+  ranges = HM.insert "limit" (convertToLimitZeroRange limitRange headerAndLimitRange) qsRanges
   -- The only emptyRange allowed is the limit zero range
   isInvalidRange = topLevelRange == emptyRange && not (hasLimitZero limitRange)
 

src/PostgREST/Plan.hs

@@ -40,6 +40,7 @@ import PostgREST.Config                   (AppConfig (..))
 import PostgREST.Error                    (Error (..))
 import PostgREST.Query.SqlFragment        (sourceCTEName)
 import PostgREST.RangeQuery               (NonnegRange, allRange,
+                                           convertToLimitZeroRange,
                                            restrictRange)
 import PostgREST.SchemaCache              (SchemaCache (..))
 import PostgREST.SchemaCache.Identifiers  (FieldName,
@@ -123,7 +124,7 @@ treeRestrictRange _ (ActionMutate _) request = Right request
 treeRestrictRange maxRows _ request = pure $ nodeRestrictRange maxRows <$> request
   where
     nodeRestrictRange :: Maybe Integer -> ReadPlan -> ReadPlan
-    nodeRestrictRange m q@ReadPlan{range_=r} = q{range_=restrictRange m r }
+    nodeRestrictRange m q@ReadPlan{range_=r} = q{range_= convertToLimitZeroRange r (restrictRange m r) }
 
 -- add relationships to the nodes of the tree by traversing the forest while keeping track of the parentNode(https://stackoverflow.com/questions/22721064/get-the-parent-of-a-node-in-data-tree-haskell#comment34627048_22721064)
 -- also adds aliasing

src/PostgREST/RangeQuery.hs

@@ -12,6 +12,7 @@ module PostgREST.RangeQuery (
 , allRange
 , limitZeroRange
 , hasLimitZero
+, convertToLimitZeroRange
 , NonnegRange
 , rangeStatusHeader
 , contentRangeH
@@ -86,6 +87,12 @@ limitZeroRange = Range (BoundaryBelow 0) (BoundaryAbove (-1))
 hasLimitZero :: Range Integer -> Bool
 hasLimitZero r = rangeUpper r == rangeUpper limitZeroRange
 
+-- Used to convert a range into a special limitZeroRange if it has a
+-- limit=0 in order to bypass validations for empty ranges.
+convertToLimitZeroRange :: Range Integer -> Range Integer -> Range Integer
+convertToLimitZeroRange range fallbackRange =
+  if hasLimitZero range then limitZeroRange else fallbackRange
+
 rangeStatusHeader :: NonnegRange -> Int64 -> Maybe Int64 -> (Status, Header)
 rangeStatusHeader topLevelRange queryTotal tableTotal =
   let lower = rangeOffset topLevelRange

test/spec/Feature/Query/QueryLimitedSpec.hs

@@ -114,3 +114,10 @@ spec =
               { "first_name": "Daniel B.", "last_name": "Lyon" },
               { "first_name": "Edwin S.", "last_name": "Smith" } ]|]
             { matchStatus  = 200 }
+
+    context "max-rows is set and limits are requested" $ do
+      it "should work with limit 0" $
+        get "/items?limit=0"
+          `shouldRespondWith`
+            [json| [] |]
+            { matchHeaders = ["Content-Range" <:> "*/*"] }