Maintain backward compatibility on GUC headers feature

If pg version >= 9.6 is detected the feature is enabled,
also all of the 9.6 dependent tests are moved to their own spec.

src/PostgREST/App.hs

@@ -84,12 +84,9 @@ postgrest conf refDbStructure pool worker =
                   (iTarget apiRequest) (iAction apiRequest)
             response <- P.use pool $ HT.transaction HT.ReadCommitted txMode handleReq
             return $ either (pgError authed) identity response
-        when (isResponse503 response) worker
+        when (responseStatus response == status503) worker
         respond response
 
-isResponse503 :: Response -> Bool
-isResponse503 resp = statusCode (responseStatus resp) == 503
-
 transactionMode :: DbStructure -> Target -> Action -> H.Mode
 transactionMode structure target action =
   case action of
@@ -252,6 +249,7 @@ app dbStructure conf apiRequest =
                          singular paramsAsSingleObject
                          (contentType == CTTextCSV)
                          (contentType == CTOctetStream) _isReadOnly bField
+                         (pgVersion dbStructure)
               let (tableTotal, queryTotal, body, jsonHeaders) =
                     fromMaybe (Just 0, 0, "[]", "[]") row
                   (status, contentRange) = rangeHeader queryTotal tableTotal

src/PostgREST/Config.hs

@@ -19,11 +19,12 @@ module PostgREST.Config ( prettyVersion
                         , readOptions
                         , corsPolicy
                         , minimumPgVersion
-                        , PgVersion (..)
+                        , pgVersion96
                         , AppConfig (..)
                         )
        where
 
+import           PostgREST.Types             (PgVersion(..))
 import           Control.Applicative
 import           Control.Monad                (fail)
 import           Control.Lens                 (preview)
@@ -211,11 +212,9 @@ pathParser =
     metavar "FILENAME" <>
     help "Path to configuration file"
 
-data PgVersion = PgVersion {
-  pgvNum  :: Int32
-, pgvName :: Text
-}
-
 -- | Tells the minimum PostgreSQL version required by this version of PostgREST
 minimumPgVersion :: PgVersion
 minimumPgVersion = PgVersion 90300 "9.3"
+
+pgVersion96 :: PgVersion
+pgVersion96 = PgVersion 90600 "9.6"

src/PostgREST/DbStructure.hs

@@ -8,6 +8,7 @@ module PostgREST.DbStructure (
 , accessibleTables
 , accessibleProcs
 , schemaDescription
+, getPgVersion
 ) where
 
 import qualified Hasql.Decoders                as HD
@@ -29,8 +30,8 @@ import           GHC.Exts                      (groupWith)
 import           Protolude
 import           Unsafe (unsafeHead)
 
-getDbStructure :: Schema -> H.Session DbStructure
-getDbStructure schema = do
+getDbStructure :: Schema -> PgVersion -> H.Session DbStructure
+getDbStructure schema pgVer = do
   tabs <- H.query () allTables
   cols <- H.query () $ allColumns tabs
   syns <- H.query () $ allSynonyms cols
@@ -48,6 +49,7 @@ getDbStructure schema = do
     , dbRelations = rels'
     , dbPrimaryKeys = keys'
     , dbProcs = procs
+    , pgVersion = pgVer
     }
 
 decodeTables :: HD.Result [Table]
@@ -706,3 +708,9 @@ synonymFromRow allCols (s1,t1,c1,s2,t2,c2) = (,) <$> col1 <*> col2
     col1 = findCol s1 t1 c1
     col2 = findCol s2 t2 c2
     findCol s t c = find (\col -> (tableSchema . colTable) col == s && (tableName . colTable) col == t && colName col == c) allCols
+
+getPgVersion :: H.Session PgVersion
+getPgVersion = H.query () $ H.statement sql HE.unit versionRow False
+  where
+    sql = "SELECT current_setting('server_version_num')::integer, current_setting('server_version')"
+    versionRow = HD.singleRow $ PgVersion <$> HD.value HD.int4 <*> HD.value HD.text

src/PostgREST/QueryBuilder.hs

@@ -31,6 +31,7 @@ import qualified Hasql.Decoders          as HD
 
 import qualified Data.Aeson              as JSON
 
+import           PostgREST.Config        (pgVersion96)
 import           PostgREST.RangeQuery    (NonnegRange, rangeLimit, rangeOffset, allRange)
 import           Data.Functor.Contravariant (contramap)
 import qualified Data.HashMap.Strict     as HM
@@ -143,9 +144,9 @@ createWriteStatement selectQuery mutateQuery wantSingle wantHdrs asCsv rep pKeys
     | otherwise = asJsonF
 
 type ProcResults = (Maybe Int64, Int64, ByteString, ByteString)
-callProc :: QualifiedIdentifier -> JSON.Object -> Bool -> SqlQuery -> SqlQuery ->
-  Bool -> Bool -> Bool -> Bool -> Bool -> Bool -> Maybe FieldName -> H.Query () (Maybe ProcResults)
-callProc qi params returnsScalar selectQuery countQuery countTotal isSingle paramsAsJson asCsv asBinary isReadOnly binaryField =
+callProc :: QualifiedIdentifier -> JSON.Object -> Bool -> SqlQuery -> SqlQuery -> Bool ->
+  Bool -> Bool -> Bool -> Bool -> Bool -> Maybe FieldName -> PgVersion -> H.Query () (Maybe ProcResults)
+callProc qi params returnsScalar selectQuery countQuery countTotal isSingle paramsAsJson asCsv asBinary isReadOnly binaryField pgVer =
   unicodeStatement sql HE.unit decodeProc True
   where
     sql =
@@ -155,7 +156,7 @@ callProc qi params returnsScalar selectQuery countQuery countTotal isSingle para
          {countResultF} AS total_result_set,
          1 AS page_total,
          {scalarBodyF} AS body,
-         {responseHeaders} AS headers
+         {responseHeaders} AS response_headers
        FROM ({selectQuery}) _postgrest_t;|]
      else [qc|
        WITH {sourceCTEName} AS (select * from {fromQi qi}({_args}))
@@ -163,7 +164,7 @@ callProc qi params returnsScalar selectQuery countQuery countTotal isSingle para
          {countResultF} AS total_result_set,
          pg_catalog.count(_postgrest_t) AS page_total,
          {bodyF} AS body,
-         {responseHeaders} AS headers
+         {responseHeaders} AS response_headers
        FROM ({selectQuery}) _postgrest_t;|]
 
     countResultF = if countTotal then "( "<> countQuery <> ")" else "null::bigint" :: Text
@@ -172,7 +173,10 @@ callProc qi params returnsScalar selectQuery countQuery countTotal isSingle para
                 else intercalate "," $ map _assignment (HM.toList params)
     _procName = qiName qi
     _assignment (n,v) = pgFmtIdent n <> ":=" <> insertableValue v
-    responseHeaders = "coalesce(nullif(current_setting('response.headers', true), ''), '[]')" :: Text -- nullif is used because of https://gist.github.com/steve-chavez/8d7033ea5655096903f3b52f8ed09a15
+    responseHeaders =
+      if pgVer >= pgVersion96
+        then "coalesce(nullif(current_setting('response.headers', true), ''), '[]')" :: Text -- nullif is used because of https://gist.github.com/steve-chavez/8d7033ea5655096903f3b52f8ed09a15
+        else "'[]'" :: Text
     decodeProc = HD.maybeRow procRow
     procRow = (,,,) <$> HD.nullableValue HD.int8 <*> HD.value HD.int8
                     <*> HD.value HD.bytea <*> HD.value HD.bytea

src/PostgREST/Types.hs

@@ -31,6 +31,7 @@ data DbStructure = DbStructure {
 , dbRelations   :: [Relation]
 , dbPrimaryKeys :: [PrimaryKey]
 , dbProcs       :: M.HashMap Text ProcDescription
+, pgVersion     :: PgVersion
 } deriving (Show, Eq)
 
 data PgArg = PgArg {
@@ -271,3 +272,8 @@ toMime CTSingularJSON    = "application/vnd.pgrst.object+json"
 toMime CTOctetStream     = "application/octet-stream"
 toMime CTAny             = "*/*"
 toMime (CTOther ct)      = ct
+
+data PgVersion = PgVersion {
+  pgvNum  :: Int32
+, pgvName :: Text
+} deriving (Eq, Ord, Show)