remote: add maybePathMetadata serializer

hnix-store-remote/src/System/Nix/Store/Remote/Serializer.hs

@@ -94,6 +94,8 @@ module System.Nix.Store.Remote.Serializer
   , gcResult
   -- *** Missing
   , missing
+  -- *** Maybe (Metadata StorePath)
+  , maybePathMetadata
   ) where
 
 import Control.Monad.Except (MonadError, throwError, )
@@ -562,9 +564,11 @@ pathMetadata = Serializer
 
       metadataReferences <- getS $ hashSet storePath
       metadataRegistrationTime <- getS time
-      metadataNarBytes <- (\case
+      metadataNarBytes <-
-                      0 -> Nothing
+        (\case
-                      size -> Just size) <$> getS int
+          0 -> Nothing
+          size -> Just size
+        ) <$> getS int
       metadataTrust <- getS storePathTrust
 
       metadataSigs <- getS $ set narSignature
@@ -1343,6 +1347,7 @@ data ReplySError
   | ReplySError_PrimPut SError
   | ReplySError_DerivationOutput SError
   | ReplySError_GCResult SError
+  | ReplySError_Metadata SError
   | ReplySError_Missing SError
   | ReplySError_Realisation SError
   | ReplySError_RealisationWithId SError
@@ -1476,3 +1481,19 @@ missing = mapErrorS ReplySError_Missing $ Serializer
       putS int missingDownloadSize
       putS int missingNarSize
   }
+
+-- *** Maybe (Metadata StorePath)
+
+maybePathMetadata
+  :: HasStoreDir r
+  => NixSerializer r ReplySError (Maybe (Metadata StorePath))
+maybePathMetadata = mapErrorS ReplySError_Metadata $ Serializer
+  { getS = do
+      valid <- getS bool
+      if valid
+      then pure <$> getS pathMetadata
+      else pure Nothing
+  , putS = \case
+      Nothing -> putS bool False
+      Just pm -> putS bool True >> putS pathMetadata pm
+  }

hnix-store-remote/src/System/Nix/Store/Remote/Types/StoreReply.hs

@@ -4,6 +4,7 @@ module System.Nix.Store.Remote.Types.StoreReply
 
 import System.Nix.Build (BuildResult)
 import System.Nix.StorePath (HasStoreDir(..), StorePath)
+import System.Nix.StorePath.Metadata (Metadata)
 import System.Nix.Store.Remote.Serializer
 import System.Nix.Store.Remote.Types.GC (GCResult)
 import System.Nix.Store.Remote.Types.Query.Missing (Missing)
@@ -33,6 +34,9 @@ instance StoreReply GCResult where
 instance StoreReply Missing where
   getReplyS = missing
 
+instance StoreReply (Maybe (Metadata StorePath)) where
+  getReplyS = maybePathMetadata
+
 instance StoreReply StorePath where
   getReplyS = mapPrimE storePath
 

hnix-store-remote/tests/NixSerializerSpec.hs

@@ -152,6 +152,7 @@ spec = parallel $ do
   describe "StoreReply" $ do
     prop "GCResult" $ roundtripSReader @StoreDir gcResult
     prop "Missing" $ roundtripSReader @StoreDir missing
+    prop "Maybe (Metadata StorePath)" $ roundtripSReader @StoreDir maybePathMetadata
 
 restrictProtoVersion :: ProtoVersion -> Some StoreRequest -> Bool
 restrictProtoVersion v (Some (BuildPaths _ _)) | v < ProtoVersion 1 30 = False