PostgREST · taimoorzaeem · Oct 2, 2023
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -12,6 +12,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
  - #2771, Add `Server-Timing` header with JWT duration - @taimoorzaeem
  - #2698, Add config `jwt-cache-max-lifetime` and implement JWT caching - @taimoorzaeem
  - #2943, Add `handling=strict/lenient` for Prefer header - @taimoorzaeem
+ - #2777, Add config `db-exact-count-enable` to disable `Prefer: count=exact` - @taimoorzaeem
 
 ### Fixed
 

diff --git a/postgrest.cabal b/postgrest.cabal
@@ -204,6 +204,7 @@ test-suite spec
                       Feature.Query.AndOrParamsSpec
                       Feature.Query.ComputedRelsSpec
                       Feature.Query.DeleteSpec
+                      Feature.Query.DisableExactCountSpec
                       Feature.Query.EmbedDisambiguationSpec
                       Feature.Query.EmbedInnerJoinSpec
                       Feature.Query.ErrorSpec

diff --git a/src/PostgREST/ApiRequest.hs b/src/PostgREST/ApiRequest.hs
@@ -152,7 +152,7 @@ userApiRequest conf req reqBody = do
   , iRange = ranges
   , iTopLevelRange = topLevelRange
   , iPayload = payload
-  , iPreferences = Preferences.fromHeaders (configDbTxAllowOverride conf) hdrs
+  , iPreferences = Preferences.fromHeaders (configDbTxAllowOverride conf, configDbExactCountEnable conf) hdrs
   , iQueryParams = qPrms
   , iColumns = columns
   , iHeaders = iHdrs

diff --git a/src/PostgREST/ApiRequest/Preferences.hs b/src/PostgREST/ApiRequest/Preferences.hs
@@ -57,7 +57,7 @@ data Preferences
 --
 -- One header with comma-separated values can be used to set multiple preferences:
 --
--- >>> pPrint $ fromHeaders True [("Prefer", "resolution=ignore-duplicates, count=exact")]
+-- >>> pPrint $ fromHeaders (True,True) [("Prefer", "resolution=ignore-duplicates, count=exact")]
 -- Preferences
 --     { preferResolution = Just IgnoreDuplicates
 --     , preferRepresentation = Nothing
@@ -71,7 +71,7 @@ data Preferences
 --
 -- Multiple headers can also be used:
 --
--- >>> pPrint $ fromHeaders True [("Prefer", "resolution=ignore-duplicates"), ("Prefer", "count=exact"), ("Prefer", "missing=null"), ("Prefer", "handling=lenient"), ("Prefer", "invalid")]
+-- >>> pPrint $ fromHeaders (True,True) [("Prefer", "resolution=ignore-duplicates"), ("Prefer", "count=exact"), ("Prefer", "missing=null"), ("Prefer", "handling=lenient"), ("Prefer", "invalid")]
 -- Preferences
 --     { preferResolution = Just IgnoreDuplicates
 --     , preferRepresentation = Nothing
@@ -85,13 +85,13 @@ data Preferences
 --
 -- If a preference is set more than once, only the first is used:
 --
--- >>> preferTransaction $ fromHeaders True [("Prefer", "tx=commit, tx=rollback")]
+-- >>> preferTransaction $ fromHeaders (True,True) [("Prefer", "tx=commit, tx=rollback")]
 -- Just Commit
 --
 -- This is also the case across multiple headers:
 --
 -- >>> :{
---   preferResolution . fromHeaders True $
+--   preferResolution . fromHeaders (True,True) $
 --     [ ("Prefer", "resolution=ignore-duplicates")
 --     , ("Prefer", "resolution=merge-duplicates")
 --     ]
@@ -101,7 +101,7 @@ data Preferences
 --
 -- Preferences can be separated by arbitrary amounts of space, lower-case header is also recognized:
 --
--- >>> pPrint $ fromHeaders True [("prefer", "count=exact,    tx=commit   ,return=representation , missing=default, handling=strict, anything")]
+-- >>> pPrint $ fromHeaders (True,True) [("prefer", "count=exact,    tx=commit   ,return=representation , missing=default, handling=strict, anything")]
 -- Preferences
 --     { preferResolution = Nothing
 --     , preferRepresentation = Just Full
@@ -113,14 +113,18 @@ data Preferences
 --     , invalidPrefs = [ "anything" ]
 --     }
 --
-fromHeaders :: Bool -> [HTTP.Header] -> Preferences
-fromHeaders allowTxEndOverride headers =
+fromHeaders :: (Bool,Bool) -> [HTTP.Header] -> Preferences
+fromHeaders (dbAllowTxOverride,exactCountEnable) headers =
   Preferences
     { preferResolution     = parsePrefs [MergeDuplicates, IgnoreDuplicates]
     , preferRepresentation = parsePrefs [Full, None, HeadersOnly]
     , preferParameters     = parsePrefs [SingleObject]
-    , preferCount          = parsePrefs [ExactCount, PlannedCount, EstimatedCount]
-    , preferTransaction    = if allowTxEndOverride then parsePrefs [Commit, Rollback] else Nothing
+    , preferCount          = if exactCountEnable
+                                then parsePrefs [ExactCount, PlannedCount, EstimatedCount]
+                                else parsePrefs [PlannedCount, EstimatedCount]
+    , preferTransaction    = if dbAllowTxOverride
+                                then parsePrefs [Commit, Rollback]
+                                else Nothing
     , preferMissing        = parsePrefs [ApplyDefaults, ApplyNulls]
     , preferHandling       = parsePrefs [Strict, Lenient]
     , invalidPrefs         = filter (`notElem` acceptedPrefs) prefs

diff --git a/src/PostgREST/CLI.hs b/src/PostgREST/CLI.hs
@@ -141,6 +141,9 @@ exampleConfigFile =
       |## Function for in-database configuration
       |## db-pre-config = "postgrest.pre_config"
       |
+      |## Enable or Disable `Prefer: count=exact`
+      |# db-exact-count-enable = true
+      |
       |## Extra schemas to add to the search_path of every request
       |db-extra-search-path = "public"
       |

diff --git a/src/PostgREST/Config.hs b/src/PostgREST/Config.hs
@@ -73,6 +73,7 @@ data AppConfig = AppConfig
   , configDbAnonRole               :: Maybe BS.ByteString
   , configDbChannel                :: Text
   , configDbChannelEnabled         :: Bool
+  , configDbExactCountEnable       :: Bool
   , configDbExtraSearchPath        :: [Text]
   , configDbMaxRows                :: Maybe Integer
   , configDbPlanEnabled            :: Bool
@@ -142,6 +143,7 @@ toText conf =
       [("db-anon-role",              q . T.decodeUtf8 . fromMaybe "" . configDbAnonRole)
       ,("db-channel",                q . configDbChannel)
       ,("db-channel-enabled",            T.toLower . show . configDbChannelEnabled)
+      ,("db-exact-count-enable",         T.toLower . show . configDbExactCountEnable)
       ,("db-extra-search-path",      q . T.intercalate "," . configDbExtraSearchPath)
       ,("db-max-rows",                   maybe "\"\"" show . configDbMaxRows)
       ,("db-plan-enabled",               T.toLower . show . configDbPlanEnabled)
@@ -236,6 +238,7 @@ parser optPath env dbSettings roleSettings roleIsolationLvl =
     <*> (fmap encodeUtf8 <$> optString "db-anon-role")
     <*> (fromMaybe "pgrst" <$> optString "db-channel")
     <*> (fromMaybe True <$> optBool "db-channel-enabled")
+    <*> (fromMaybe True <$> optBool "db-exact-count-enable")
     <*> (maybe ["public"] splitOnCommas <$> optValue "db-extra-search-path")
     <*> optWithAlias (optInt "db-max-rows")
                      (optInt "max-rows")

diff --git a/test/io/configs/expected/aliases.config b/test/io/configs/expected/aliases.config
@@ -1,6 +1,7 @@
 db-anon-role = ""
 db-channel = "pgrst"
 db-channel-enabled = true
+db-exact-count-enable = true
 db-extra-search-path = "public"
 db-max-rows = 1000
 db-plan-enabled = false

diff --git a/test/io/configs/expected/boolean-numeric.config b/test/io/configs/expected/boolean-numeric.config
@@ -1,6 +1,7 @@
 db-anon-role = ""
 db-channel = "pgrst"
 db-channel-enabled = true
+db-exact-count-enable = true
 db-extra-search-path = "public"
 db-max-rows = ""
 db-plan-enabled = false

diff --git a/test/io/configs/expected/boolean-string.config b/test/io/configs/expected/boolean-string.config
@@ -1,6 +1,7 @@
 db-anon-role = ""
 db-channel = "pgrst"
 db-channel-enabled = true
+db-exact-count-enable = true
 db-extra-search-path = "public"
 db-max-rows = ""
 db-plan-enabled = false

diff --git a/test/io/configs/expected/defaults.config b/test/io/configs/expected/defaults.config
@@ -1,6 +1,7 @@
 db-anon-role = ""
 db-channel = "pgrst"
 db-channel-enabled = true
+db-exact-count-enable = true
 db-extra-search-path = "public"
 db-max-rows = ""
 db-plan-enabled = false

diff --git a/test/io/configs/expected/no-defaults-with-db-other-authenticator.config b/test/io/configs/expected/no-defaults-with-db-other-authenticator.config
@@ -1,6 +1,7 @@
 db-anon-role = "pre_config_role"
 db-channel = "postgrest"
 db-channel-enabled = false
+db-exact-count-enable = false
 db-extra-search-path = "public,extensions,other"
 db-max-rows = 100
 db-plan-enabled = true

diff --git a/test/io/configs/expected/no-defaults-with-db.config b/test/io/configs/expected/no-defaults-with-db.config
@@ -1,6 +1,7 @@
 db-anon-role = "anonymous"
 db-channel = "postgrest"
 db-channel-enabled = false
+db-exact-count-enable = false
 db-extra-search-path = "public,extensions,private"
 db-max-rows = 1000
 db-plan-enabled = true

diff --git a/test/io/configs/expected/no-defaults.config b/test/io/configs/expected/no-defaults.config
@@ -1,6 +1,7 @@
 db-anon-role = "root"
 db-channel = "postgrest"
 db-channel-enabled = false
+db-exact-count-enable = false
 db-extra-search-path = "public,test"
 db-max-rows = 1000
 db-plan-enabled = true

diff --git a/test/io/configs/expected/types.config b/test/io/configs/expected/types.config
@@ -1,6 +1,7 @@
 db-anon-role = ""
 db-channel = "pgrst"
 db-channel-enabled = true
+db-exact-count-enable = true
 db-extra-search-path = "public"
 db-max-rows = ""
 db-plan-enabled = false

diff --git a/test/io/configs/no-defaults-env.yaml b/test/io/configs/no-defaults-env.yaml
@@ -3,6 +3,7 @@ PGRST_APP_SETTINGS_test: test
 PGRST_DB_ANON_ROLE: root
 PGRST_DB_CHANNEL: postgrest
 PGRST_DB_CHANNEL_ENABLED: false
+PGRST_DB_EXACT_COUNT_ENABLE: false
 PGRST_DB_EXTRA_SEARCH_PATH: public, test
 PGRST_DB_MAX_ROWS: 1000
 PGRST_DB_PLAN_ENABLED: true

diff --git a/test/io/configs/no-defaults.config b/test/io/configs/no-defaults.config
@@ -1,6 +1,7 @@
 db-anon-role = "root"
 db-channel = "postgrest"
 db-channel-enabled = false
+db-exact-count-enable = false
 db-extra-search-path = "public, test"
 db-max-rows = 1000
 db-plan-enabled = true

diff --git a/test/spec/Feature/Query/DisableExactCountSpec.hs b/test/spec/Feature/Query/DisableExactCountSpec.hs
@@ -0,0 +1,27 @@
+module Feature.Query.DisableExactCountSpec where
+
+import Network.Wai (Application)
+
+import Network.HTTP.Types
+import Test.Hspec
+import Test.Hspec.Wai
+
+import Protolude  hiding (get)
+import SpecHelper
+
+spec :: SpecWith ((), Application)
+spec =
+  describe "tests for config db-exact-count-enable" $ do
+
+    context "should not return exact count" $ do
+      it "returns * in content-range instead of exact count" $ do
+        request methodHead  "/getallprojects_view"
+          [("Prefer", "count=exact")]
+          ""
+          `shouldRespondWith`
+          ""
+          { matchStatus  = 200
+          , matchHeaders = [ matchContentTypeJson
+                           , "Content-Range" <:> "0-4/*"]
+          }
+
diff --git a/test/spec/Main.hs b/test/spec/Main.hs
@@ -38,6 +38,7 @@ import qualified Feature.OptionsSpec
 import qualified Feature.Query.AndOrParamsSpec
 import qualified Feature.Query.ComputedRelsSpec
 import qualified Feature.Query.DeleteSpec
+import qualified Feature.Query.DisableExactCountSpec
 import qualified Feature.Query.EmbedDisambiguationSpec
 import qualified Feature.Query.EmbedInnerJoinSpec
 import qualified Feature.Query.ErrorSpec
@@ -112,6 +113,7 @@ main = do
       pgSafeUpdateApp      = app testPgSafeUpdateEnabledCfg
       obsApp               = app testObservabilityCfg
       serverTiming         = app testCfgServerTiming
+      exactCountEnable     = app testCfgExactCountEnable
 
       extraSearchPathApp   = appDbs testCfgExtraSearchPath
       unicodeApp           = appDbs testUnicodeCfg
@@ -252,6 +254,10 @@ main = do
     parallel $ before serverTiming $
       describe "Feature.Query.ServerTimingSpec.spec" Feature.Query.ServerTimingSpec.spec
 
+    -- this test runs with db-exact-count-enable = false
+    before exactCountEnable $
+      describe "Feature.Query.DisableExactCountSpec" Feature.Query.DisableExactCountSpec.spec
+
     -- Note: the rollback tests can not run in parallel, because they test persistance and
     -- this results in race conditions
 

diff --git a/test/spec/SpecHelper.hs b/test/spec/SpecHelper.hs
@@ -96,6 +96,7 @@ baseCfg = let secret = Just $ encodeUtf8 "reallyreallyreallyreallyverysafe" in
   , configDbAnonRole            = Just "postgrest_test_anonymous"
   , configDbChannel             = mempty
   , configDbChannelEnabled      = True
+  , configDbExactCountEnable    = True
   , configDbExtraSearchPath     = []
   , configDbMaxRows             = Nothing
   , configDbPlanEnabled         = False
@@ -236,6 +237,9 @@ testObservabilityCfg = baseCfg { configServerTraceHeader = Just $ mk "X-Request-
 testCfgServerTiming :: AppConfig
 testCfgServerTiming = baseCfg { configDbPlanEnabled = True }
 
+testCfgExactCountEnable :: AppConfig
+testCfgExactCountEnable = baseCfg { configDbExactCountEnable = False }
+
 analyzeTable :: Text -> IO ()
 analyzeTable tableName =
   void $ readProcess "psql" ["-U", "postgres", "--set", "ON_ERROR_STOP=1", "-a", "-c", toS $ "ANALYZE test.\"" <> tableName <> "\""] []