Use generics in readAllLayerStores

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

check.go

@@ -160,10 +160,10 @@ func (s *store) Check(options *CheckOptions) (CheckReport, error) {
 
 	// Walk the list of layer stores, looking at each layer that we didn't see in a
 	// previously-visited store.
-	if errored, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
+	if _, _, err := readAllLayerStores(s, func(store roLayerStore) (struct{}, bool, error) {
 		layers, err := store.Layers()
 		if err != nil {
-			return true, err
+			return struct{}{}, true, err
 		}
 		isReadWrite := roLayerStoreIsReallyReadWrite(store)
 		readWriteDesc := ""
@@ -337,7 +337,7 @@ func (s *store) Check(options *CheckOptions) (CheckReport, error) {
 		// At this point we're out of things that we can be sure will work in read-only
 		// stores, so skip the rest for any stores that aren't also read-write stores.
 		if !isReadWrite {
-			return false, nil
+			return struct{}{}, false, nil
 		}
 		// Content and mount checks are also things that we can only be sure will work in
 		// read-write stores.
@@ -439,8 +439,8 @@ func (s *store) Check(options *CheckOptions) (CheckReport, error) {
 			err := fmt.Errorf("%slayer %s: %w", readWriteDesc, parent, ErrLayerMissing)
 			report.Layers[id] = append(report.Layers[id], err)
 		}
-		return false, nil
+		return struct{}{}, false, nil
-	}); errored {
+	}); err != nil {
 		return CheckReport{}, err
 	}
 
@@ -630,13 +630,13 @@ func (s *store) Check(options *CheckOptions) (CheckReport, error) {
 	// Now go back through all of the layer stores, and flag any layers which don't belong
 	// to an image or a container, and has been around longer than we can reasonably expect
 	// such a layer to be present before a corresponding image record is added.
-	if errored, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
+	if _, _, err := readAllLayerStores(s, func(store roLayerStore) (struct{}, bool, error) {
 		if isReadWrite := roLayerStoreIsReallyReadWrite(store); !isReadWrite {
-			return false, nil
+			return struct{}{}, false, nil
 		}
 		layers, err := store.Layers()
 		if err != nil {
-			return true, err
+			return struct{}{}, true, err
 		}
 		for _, layer := range layers {
 			maximumAge := defaultMaximumUnreferencedLayerAge
@@ -654,8 +654,8 @@ func (s *store) Check(options *CheckOptions) (CheckReport, error) {
 				}
 			}
 		}
-		return false, nil
+		return struct{}{}, false, nil
-	}); errored {
+	}); err != nil {
 		return CheckReport{}, err
 	}
 

check_test.go

@@ -80,11 +80,11 @@ func TestCheckDetectWriteable(t *testing.T) {
 	require.NoError(t, err, "unexpected error initializing test store")
 	s, ok := stoar.(*store)
 	require.True(t, ok, "unexpected error making type assertion")
-	done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
+	_, done, err := readAllLayerStores(s, func(store roLayerStore) (struct{}, bool, error) {
 		if roLayerStoreIsReallyReadWrite(store) { // implicitly checking that the type assertion in this function doesn't panic
 			sawRWlayers = true
 		}
-		return false, nil
+		return struct{}{}, false, nil
 	})
 	assert.False(t, done, "unexpected error from readAllLayerStores")
 	assert.NoError(t, err, "unexpected error from readAllLayerStores")

store.go

@@ -1149,38 +1149,39 @@ func (s *store) allLayerStores() ([]roLayerStore, error) {
 // readAllLayerStores processes allLayerStores() in order:
 // It locks the store for reading, checks for updates, and calls
 //
-//	(done, err) := fn(store)
+//	(data, done, err) := fn(store)
 //
 // until the callback returns done == true, and returns the data from the callback.
 //
-// If reading any layer store fails, it immediately returns (true, err).
+// If reading any layer store fails, it immediately returns ({}, true, err).
 //
-// If all layer stores are processed without setting done == true, it returns (false, nil).
+// If all layer stores are processed without setting done == true, it returns ({}, false, nil).
 //
 // Typical usage:
 //
-//	var res T = failureValue
+//	if res, done, err := s.readAllLayerStores(store, func(…) {
-//	if done, err := s.readAllLayerStores(store, func(…) {
 //		…
 //	}; done {
 //		return res, err
 //	}
-func (s *store) readAllLayerStores(fn func(store roLayerStore) (bool, error)) (bool, error) {
+func readAllLayerStores[T any](s *store, fn func(store roLayerStore) (T, bool, error)) (T, bool, error) {
+	var zeroRes T // A zero value of T
+
 	layerStores, err := s.allLayerStores()
 	if err != nil {
-		return true, err
+		return zeroRes, true, err
 	}
 	for _, s := range layerStores {
 		store := s
 		if err := store.startReading(); err != nil {
-			return true, err
+			return zeroRes, true, err
 		}
 		defer store.stopReading()
-		if done, err := fn(store); done {
+		if res, done, err := fn(store); done {
-			return true, err
+			return res, true, err
 		}
 	}
-	return false, nil
+	return zeroRes, false, nil
 }
 
 // writeToLayerStore is a helper for working with store.getLayerStore():
@@ -1828,19 +1829,17 @@ func (s *store) SetMetadata(id, metadata string) error {
 }
 
 func (s *store) Metadata(id string) (string, error) {
-	var res string
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) (string, bool, error) {
-
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		if store.Exists(id) {
-			var err error
+			res, err := store.Metadata(id)
-			res, err = store.Metadata(id)
+			return res, true, err
-			return true, err
 		}
-		return false, nil
+		return "", false, nil
 	}); done {
 		return res, err
 	}
 
+	var res string
 	if done, err := s.readAllImageStores(func(store roImageStore) (bool, error) {
 		if store.Exists(id) {
 			var err error
@@ -1937,17 +1936,15 @@ func (s *store) ImageBigData(id, key string) ([]byte, error) {
 // named data associated with an layer.
 func (s *store) ListLayerBigData(id string) ([]string, error) {
 	foundLayer := false
-	var res []string
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) ([]string, bool, error) {
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		data, err := store.BigDataNames(id)
 		if err == nil {
-			res = data
+			return data, true, nil
-			return true, nil
 		}
 		if store.Exists(id) {
 			foundLayer = true
 		}
-		return false, nil
+		return nil, false, nil
 	}); done {
 		return res, err
 	}
@@ -1961,17 +1958,15 @@ func (s *store) ListLayerBigData(id string) ([]string, error) {
 // associated with a layer.
 func (s *store) LayerBigData(id, key string) (io.ReadCloser, error) {
 	foundLayer := false
-	var res io.ReadCloser
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) (io.ReadCloser, bool, error) {
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		data, err := store.BigData(id, key)
 		if err == nil {
-			res = data
+			return data, true, nil
-			return true, nil
 		}
 		if store.Exists(id) {
 			foundLayer = true
 		}
-		return false, nil
+		return nil, false, nil
 	}); done {
 		return res, err
 	}
@@ -2204,18 +2199,20 @@ func (s *store) SetContainerBigData(id, key string, data []byte) error {
 }
 
 func (s *store) Exists(id string) bool {
-	var res = false
+	found, _, err := readAllLayerStores(s, func(store roLayerStore) (bool, bool, error) {
-
-	if done, _ := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		if store.Exists(id) {
-			res = true
+			return true, true, nil
-			return true, nil
 		}
-		return false, nil
+		return false, false, nil
-	}); done {
+	})
-		return res
+	if err != nil {
+		return false
+	}
+	if found {
+		return true
 	}
 
+	var res = false
 	if done, _ := s.readAllImageStores(func(store roImageStore) (bool, error) {
 		if store.Exists(id) {
 			res = true
@@ -2345,18 +2342,16 @@ func (s *store) updateNames(id string, names []string, op updateNameOperation) e
 }
 
 func (s *store) Names(id string) ([]string, error) {
-	var res []string
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) ([]string, bool, error) {
-
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		if l, err := store.Get(id); l != nil && err == nil {
-			res = l.Names
+			return l.Names, true, nil
-			return true, nil
 		}
-		return false, nil
+		return nil, false, nil
 	}); done {
 		return res, err
 	}
 
+	var res []string
 	if done, err := s.readAllImageStores(func(store roImageStore) (bool, error) {
 		if i, err := store.Get(id); i != nil && err == nil {
 			res = i.Names
@@ -2378,18 +2373,16 @@ func (s *store) Names(id string) ([]string, error) {
 }
 
 func (s *store) Lookup(name string) (string, error) {
-	var res string
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) (string, bool, error) {
-
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		if l, err := store.Get(name); l != nil && err == nil {
-			res = l.ID
+			return l.ID, true, nil
-			return true, nil
 		}
-		return false, nil
+		return "", false, nil
 	}); done {
 		return res, err
 	}
 
+	var res string
 	if done, err := s.readAllImageStores(func(store roImageStore) (bool, error) {
 		if i, err := store.Get(name); i != nil && err == nil {
 			res = i.ID
@@ -2782,14 +2775,12 @@ func (s *store) Unmount(id string, force bool) (bool, error) {
 }
 
 func (s *store) Changes(from, to string) ([]archive.Change, error) {
-	var res []archive.Change
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) ([]archive.Change, bool, error) {
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		if store.Exists(to) {
-			var err error
+			res, err := store.Changes(from, to)
-			res, err = store.Changes(from, to)
+			return res, true, err
-			return true, err
 		}
-		return false, nil
+		return nil, false, nil
 	}); done {
 		return res, err
 	}
@@ -2797,16 +2788,17 @@ func (s *store) Changes(from, to string) ([]archive.Change, error) {
 }
 
 func (s *store) DiffSize(from, to string) (int64, error) {
-	var res int64 = -1
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) (int64, bool, error) {
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		if store.Exists(to) {
-			var err error
+			res, err := store.DiffSize(from, to)
-			res, err = store.DiffSize(from, to)
+			return res, true, err
-			return true, err
 		}
-		return false, nil
+		return -1, false, nil
 	}); done {
-		return res, err
+		if err != nil {
+			return -1, err
+		}
+		return res, nil
 	}
 	return -1, ErrLayerUnknown
 }
@@ -2895,16 +2887,16 @@ func (s *store) ApplyDiff(to string, diff io.Reader) (int64, error) {
 
 func (s *store) layersByMappedDigest(m func(roLayerStore, digest.Digest) ([]Layer, error), d digest.Digest) ([]Layer, error) {
 	var layers []Layer
-	if _, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
+	if _, _, err := readAllLayerStores(s, func(store roLayerStore) (struct{}, bool, error) {
 		storeLayers, err := m(store, d)
 		if err != nil {
 			if !errors.Is(err, ErrLayerUnknown) {
-				return true, err
+				return struct{}{}, true, err
 			}
-			return false, nil
+			return struct{}{}, false, nil
 		}
 		layers = append(layers, storeLayers...)
-		return false, nil
+		return struct{}{}, false, nil
 	}); err != nil {
 		return nil, err
 	}
@@ -2929,16 +2921,17 @@ func (s *store) LayersByUncompressedDigest(d digest.Digest) ([]Layer, error) {
 }
 
 func (s *store) LayerSize(id string) (int64, error) {
-	var res int64 = -1
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) (int64, bool, error) {
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		if store.Exists(id) {
-			var err error
+			res, err := store.Size(id)
-			res, err = store.Size(id)
+			return res, true, err
-			return true, err
 		}
-		return false, nil
+		return -1, false, nil
 	}); done {
-		return res, err
+		if err != nil {
+			return -1, err
+		}
+		return res, nil
 	}
 	return -1, ErrLayerUnknown
 }
@@ -2983,13 +2976,13 @@ func (s *store) ContainerParentOwners(id string) ([]int, []int, error) {
 
 func (s *store) Layers() ([]Layer, error) {
 	var layers []Layer
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
+	if _, done, err := readAllLayerStores(s, func(store roLayerStore) (struct{}, bool, error) {
 		storeLayers, err := store.Layers()
 		if err != nil {
-			return true, err
+			return struct{}{}, true, err
 		}
 		layers = append(layers, storeLayers...)
-		return false, nil
+		return struct{}{}, false, nil
 	}); done {
 		return nil, err
 	}
@@ -3021,14 +3014,12 @@ func (s *store) Containers() ([]Container, error) {
 }
 
 func (s *store) Layer(id string) (*Layer, error) {
-	var res *Layer
+	if res, done, err := readAllLayerStores(s, func(store roLayerStore) (*Layer, bool, error) {
-	if done, err := s.readAllLayerStores(func(store roLayerStore) (bool, error) {
 		layer, err := store.Get(id)
 		if err == nil {
-			res = layer
+			return layer, true, nil
-			return true, nil
 		}
-		return false, nil
+		return nil, false, nil
 	}); done {
 		return res, err
 	}