Use ExceptT in readSnapshot, fix typos

Author: geo2a

ouroboros-consensus/src/ouroboros-consensus/Ouroboros/Consensus/Storage/LedgerDB/Snapshots.hs

@@ -37,7 +37,7 @@ import           Codec.Serialise.Decoding (Decoder)
 import qualified Codec.Serialise.Decoding as Dec
 import           Codec.Serialise.Encoding (Encoding)
 import           Control.Monad (forM, void)
-import           Control.Monad.Except (ExceptT (..))
+import           Control.Monad.Except (ExceptT (..), throwError, withExceptT)
 import           Control.Tracer
 import           Data.Bits
 import qualified Data.ByteString.Builder as BS
@@ -196,10 +196,10 @@ diskSnapshotIsTemporary = not . diskSnapshotIsPermanent
 
 data ReadSnapshotErr =
     -- | Error while de-serialising data
-    ReadSnaphotFailed ReadIncrementalErr
+    ReadSnapshotFailed ReadIncrementalErr
     -- | Checksum of read snapshot differs from the one tracked by
     --   the corresponding '.checksum' file
-  | ReadSnaphotDataCorruption
+  | ReadSnapshotDataCorruption
     -- | A '.checksum' file does not exist for a @'DiskSnapshot'@
   | ReadSnapshotNoChecksumFile FsPath
     -- | A '.checksum' file exists for a @'DiskSnapshot'@, but its contents is invalid
@@ -219,13 +219,11 @@ readSnapshot ::
   -> ExceptT ReadSnapshotErr m (ExtLedgerState blk)
 readSnapshot someHasFS decLedger decHash snapshotName = do
   !snapshotCRC <- readCRC someHasFS (snapshotToChecksumPath snapshotName)
-  ExceptT $
-    readIncremental someHasFS decoder (snapshotToPath snapshotName) >>= \case
-       Left e  -> pure $ Left (ReadSnaphotFailed e)
-       Right (ledgerState, checksumAsRead) ->
-           if checksumAsRead /= snapshotCRC
-           then pure $ Left ReadSnaphotDataCorruption
-           else pure (Right ledgerState)
+  (ledgerState, checksumAsRead) <- withExceptT ReadSnapshotFailed . ExceptT $
+    readIncremental someHasFS decoder (snapshotToPath snapshotName)
+  if checksumAsRead /= snapshotCRC
+       then throwError ReadSnapshotDataCorruption
+       else pure ledgerState
   where
     decoder :: Decoder s (ExtLedgerState blk)
     decoder = decodeSnapshotBackwardsCompatible (Proxy @blk) decLedger decHash