Pass custom settings to the DB's SESSION (#1063)

- allows queries to refer to current_setting('app.settings.foo') to retrieve variables
- useful for 12-factor apps (app data can be in environment)
- provides workaround for AWS Relational Database Service (RDS) not
  allowing `ALTER DATABASE SET 'app.[KEY]' TO '[VALUE]'` on database.

test/Feature/QuerySpec.hs

@@ -699,7 +699,6 @@ spec = do
           { matchStatus = 200
           , matchHeaders = []
           }
-
     it "multiple cookies ends up as claims" $
       request methodPost "/rpc/get_guc_value" [("Cookie","acookie=cookievalue;secondcookie=anothervalue")]
         [json| {"name":"request.cookie.secondcookie"} |]
@@ -708,7 +707,15 @@ spec = do
           { matchStatus = 200
           , matchHeaders = []
           }
-
+    it "app settings available" $
+      request methodPost "/rpc/get_guc_value" []
+        [json| { "name": "app.settings.app_host" } |]
+          `shouldRespondWith`
+          [str|"localhost"|]
+          { matchStatus  = 200
+          , matchHeaders = [ matchContentTypeJson ]
+          }
+    
   describe "values with quotes in IN and NOT IN" $ do
     it "succeeds when only quoted values are present" $ do
       get "/w_or_wo_comma_names?name=in.\"Hebdon, John\"" `shouldRespondWith`

test/Main.hs

@@ -6,8 +6,8 @@ import SpecHelper
 import qualified Hasql.Pool as P
 
 import PostgREST.App (postgrest)
-import PostgREST.Config (pgVersion96)
-import PostgREST.DbStructure (getDbStructure, getPgVersion)
+import PostgREST.Config (pgVersion96, configSettings)
+import PostgREST.DbStructure (getDbStructure, getPgVersion, fillSessionWithSettings)
 import PostgREST.Types (DbStructure(..))
 import Data.Function (id)
 import Data.IORef
@@ -58,7 +58,9 @@ main = do
       asymJwkApp           = return $ postgrest (testCfgAsymJWK testDbConn)     refDbStructure pool $ pure ()
       nonexistentSchemaApp = return $ postgrest (testNonexistentSchemaCfg testDbConn)   refDbStructure pool $ pure ()
 
-  let reset = resetDb testDbConn
+  let reset :: IO ()
+      reset = P.use pool (fillSessionWithSettings (configSettings $ testCfg testDbConn)) >> resetDb testDbConn
+
       actualPgVersion = pgVersion dbStructure
       pg96spec | actualPgVersion >= pgVersion96 = [("Feature.PgVersion96Spec"  , Feature.PgVersion96Spec.spec)]
                | otherwise = []

test/SpecHelper.hs

@@ -73,6 +73,9 @@ _baseCfg =  -- Connection Settings
             10 Nothing (Just "test.switch_role")
             -- Debug Settings
             True
+            [ ("app.settings.app_host", "localhost")
+            , ("app.settings.external_api_secret", "0123456789abcdef")
+            ]
 
 testCfg :: Text -> AppConfig
 testCfg testDbConn = _baseCfg { configDatabase = testDbConn }