feat: support deletion for memory graph

Signed-off-by: Xiaoxuan Wang <[email protected]>

internal/container/set/set.go

@@ -33,3 +33,8 @@ func (s Set[T]) Contains(item T) bool {
 	_, ok := s[item]
 	return ok
 }
+
+// Delete deletes an item from the set.
+func (s Set[T]) Delete(item T) {
+	delete(s, item)
+}

internal/container/set/set_test.go

@@ -52,4 +52,12 @@ func TestSet(t *testing.T) {
 	if got, want := len(set), 2; got != want {
 		t.Errorf("len(Set) = %v, want %v", got, want)
 	}
+	// test deleting a key
+	set.Delete(key1)
+	if got, want := set.Contains(key1), false; got != want {
+		t.Errorf("Set.Contains(%s) = %v, want %v", key1, got, want)
+	}
+	if got, want := len(set), 1; got != want {
+		t.Errorf("len(Set) = %v, want %v", got, want)
+	}
 }

internal/graph/deletablememory.go

@@ -0,0 +1,144 @@
+/*
+Copyright The ORAS Authors.
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package graph
+
+import (
+	"context"
+	"errors"
+	"sync"
+
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	"oras.land/oras-go/v2/content"
+	"oras.land/oras-go/v2/errdef"
+	"oras.land/oras-go/v2/internal/container/set"
+	"oras.land/oras-go/v2/internal/descriptor"
+	"oras.land/oras-go/v2/internal/status"
+	"oras.land/oras-go/v2/internal/syncutil"
+)
+
+// DeletableMemory is a memory based PredecessorFinder.
+type DeletableMemory struct {
+	nodes        map[descriptor.Descriptor]ocispec.Descriptor // nodes saves the map keys of ocispec.Descriptor
+	predecessors map[descriptor.Descriptor]set.Set[descriptor.Descriptor]
+	successors   map[descriptor.Descriptor]set.Set[descriptor.Descriptor]
+	lock         sync.RWMutex
+}
+
+// NewDeletableMemory creates a new DeletableMemory.
+func NewDeletableMemory() *DeletableMemory {
+	return &DeletableMemory{
+		nodes:        make(map[descriptor.Descriptor]ocispec.Descriptor),
+		predecessors: make(map[descriptor.Descriptor]set.Set[descriptor.Descriptor]),
+		successors:   make(map[descriptor.Descriptor]set.Set[descriptor.Descriptor]),
+	}
+}
+
+// Index indexes predecessors for each direct successor of the given node.
+func (m *DeletableMemory) Index(ctx context.Context, fetcher content.Fetcher, node ocispec.Descriptor) error {
+	_, err := m.index(ctx, fetcher, node)
+	return err
+}
+
+// Index indexes predecessors for all the successors of the given node.
+func (m *DeletableMemory) IndexAll(ctx context.Context, fetcher content.Fetcher, node ocispec.Descriptor) error {
+	// track content status
+	tracker := status.NewTracker()
+	var fn syncutil.GoFunc[ocispec.Descriptor]
+	fn = func(ctx context.Context, region *syncutil.LimitedRegion, desc ocispec.Descriptor) error {
+		// skip the node if other go routine is working on it
+		_, committed := tracker.TryCommit(desc)
+		if !committed {
+			return nil
+		}
+		successors, err := m.index(ctx, fetcher, desc)
+		if err != nil {
+			if errors.Is(err, errdef.ErrNotFound) {
+				// skip the node if it does not exist
+				return nil
+			}
+			return err
+		}
+		if len(successors) > 0 {
+			// traverse and index successors
+			return syncutil.Go(ctx, nil, fn, successors...)
+		}
+		return nil
+	}
+	return syncutil.Go(ctx, nil, fn, node)
+}
+
+// Predecessors returns the nodes directly pointing to the current node.
+// Predecessors returns nil without error if the node does not exists in the
+// store.
+// Like other operations, calling Predecessors() is go-routine safe. However,
+// it does not necessarily correspond to any consistent snapshot of the stored
+// contents.
+func (m *DeletableMemory) Predecessors(_ context.Context, node ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+	m.lock.RLock()
+	defer m.lock.RUnlock()
+	key := descriptor.FromOCI(node)
+	set, exists := m.predecessors[key]
+	if !exists {
+		return nil, nil
+	}
+	var res []ocispec.Descriptor
+	for k := range set {
+		res = append(res, m.nodes[k])
+	}
+	return res, nil
+}
+
+// Remove removes the node from its predecessors and successors.
+func (m *DeletableMemory) Remove(ctx context.Context, node ocispec.Descriptor) error {
+	nodeKey := descriptor.FromOCI(node)
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	// remove the node from its successors' predecessor list
+	for successorKey := range m.successors[nodeKey] {
+		m.predecessors[successorKey].Delete(nodeKey)
+	}
+	delete(m.successors, nodeKey)
+	return nil
+}
+
+// index indexes predecessors for each direct successor of the given node.
+func (m *DeletableMemory) index(ctx context.Context, fetcher content.Fetcher, node ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+	successors, err := content.Successors(ctx, fetcher, node)
+	if err != nil {
+		return nil, err
+	}
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	// index the node
+	nodeKey := descriptor.FromOCI(node)
+	m.nodes[nodeKey] = node
+
+	// index the successors and predecessors
+	successorSet := set.New[descriptor.Descriptor]()
+	m.successors[nodeKey] = successorSet
+	for _, successor := range successors {
+		successorKey := descriptor.FromOCI(successor)
+		successorSet.Add(successorKey)
+		predecessorSet, exists := m.predecessors[successorKey]
+		if !exists {
+			predecessorSet = set.New[descriptor.Descriptor]()
+			m.predecessors[successorKey] = predecessorSet
+		}
+		predecessorSet.Add(nodeKey)
+	}
+	return successors, nil
+}