Roll back on db errors

postgrest.cabal

@@ -40,6 +40,7 @@ executable postgrest
                      , http-types
                      , interpolatedstring-perl6
                      , jwt
+                     , mtl
                      , optparse-applicative >= 0.11 && < 0.13
                      , parsec
                      , postgrest
@@ -92,6 +93,7 @@ library
                      , http-types
                      , interpolatedstring-perl6
                      , jwt
+                     , mtl
                      , optparse-applicative
                      , parsec
                      , regex-tdfa
@@ -173,6 +175,7 @@ Test-Suite spec
                      , interpolatedstring-perl6
                      , jwt
                      , monad-control
+                     , mtl
                      , optparse-applicative
                      , parsec
                      , process

src/PostgREST/Main.hs

@@ -14,6 +14,7 @@ import           PostgREST.Middleware
 import           PostgREST.Types                      (DbStructure)
 
 import           Control.Monad
+import           Control.Monad.Error.Class            (catchError, throwError)
 import           Data.Monoid                          ((<>))
 import           Data.String.Conversions              (cs)
 import           Data.Time.Clock.POSIX                (getPOSIXTime)
@@ -95,5 +96,9 @@ postgrest conf dbStructure pool =
 
     let handleReq = runWithClaims conf time (app dbStructure conf body) req
     resp <- either pgErrResponse id <$> P.use pool
-      (HT.run handleReq HT.ReadCommitted HT.Write)
+      (rollbackOnError $ HT.run handleReq HT.ReadCommitted HT.Write)
     respond resp
+
+ where
+  rollbackOnError :: H.Session a -> H.Session a
+  rollbackOnError = (`catchError` ((H.sql "rollback;" >>) . throwError))