refactor!: add read-only interfaces

content.go

@@ -60,7 +60,7 @@ type ResolveOptions struct {
 }
 
 // Resolve resolves a descriptor with provided reference from the target.
-func Resolve(ctx context.Context, target Target, ref string, opts ResolveOptions) (ocispec.Descriptor, error) {
+func Resolve(ctx context.Context, target ReadOnlyTarget, ref string, opts ResolveOptions) (ocispec.Descriptor, error) {
 	if opts.TargetPlatform == nil {
 		return target.Resolve(ctx, ref)
 	}

content/graph.go

@@ -40,6 +40,12 @@ type GraphStorage interface {
 	PredecessorFinder
 }
 
+// ReadOnlyGraphStorage represents a read-only GraphStorage.
+type ReadOnlyGraphStorage interface {
+	ReadOnlyStorage
+	PredecessorFinder
+}
+
 // Successors returns the nodes directly pointed by the current node.
 // In other words, returns the "children" of the current descriptor.
 func Successors(ctx context.Context, fetcher Fetcher, node ocispec.Descriptor) ([]ocispec.Descriptor, error) {

content/storage.go

@@ -41,8 +41,13 @@ type Pusher interface {
 // accessed via Descriptors.
 // The storage is designed to handle blobs of large sizes.
 type Storage interface {
-	Fetcher
+	ReadOnlyStorage
 	Pusher
+}
+
+// ReadOnlyStorage represents a read-only Storage.
+type ReadOnlyStorage interface {
+	Fetcher
 
 	// Exists returns true if the described content exists.
 	Exists(ctx context.Context, target ocispec.Descriptor) (bool, error)

copy.go

@@ -54,12 +54,12 @@ type CopyOptions struct {
 	// When MapRoot is provided, the descriptor resolved from the source
 	// reference will be passed to MapRoot, and the mapped descriptor will be
 	// used as the root node for copy.
-	MapRoot func(ctx context.Context, src content.Storage, root ocispec.Descriptor) (ocispec.Descriptor, error)
+	MapRoot func(ctx context.Context, src content.ReadOnlyStorage, root ocispec.Descriptor) (ocispec.Descriptor, error)
 }
 
 // getPlatformFromConfig returns a platform object which is made up from the
 // fields in config blob.
-func getPlatformFromConfig(ctx context.Context, src content.Storage, desc ocispec.Descriptor, targetConfigMediaType string) (*ocispec.Platform, error) {
+func getPlatformFromConfig(ctx context.Context, src content.ReadOnlyStorage, desc ocispec.Descriptor, targetConfigMediaType string) (*ocispec.Platform, error) {
 	if desc.MediaType != targetConfigMediaType {
 		return nil, fmt.Errorf("mismatch MediaType %s: expect %s", desc.MediaType, targetConfigMediaType)
 	}
@@ -81,7 +81,7 @@ func getPlatformFromConfig(ctx context.Context, src content.Storage, desc ocispe
 // selectPlatform implements platform filter and returns the descriptor of the
 // first matched manifest if the root is a manifest list. If the root is a
 // manifest, then return the root descriptor if platform matches.
-func selectPlatform(ctx context.Context, src content.Storage, root ocispec.Descriptor, p *ocispec.Platform) (ocispec.Descriptor, error) {
+func selectPlatform(ctx context.Context, src content.ReadOnlyStorage, root ocispec.Descriptor, p *ocispec.Platform) (ocispec.Descriptor, error) {
 	switch root.MediaType {
 	case docker.MediaTypeManifestList, ocispec.MediaTypeImageIndex:
 		manifests, err := content.Successors(ctx, src, root)
@@ -131,7 +131,7 @@ func selectPlatform(ctx context.Context, src content.Storage, root ocispec.Descr
 // - Otherwise ErrUnsupported will be returned.
 func (opts *CopyOptions) WithTargetPlatform(p *ocispec.Platform) {
 	mapRoot := opts.MapRoot
-	opts.MapRoot = func(ctx context.Context, src content.Storage, root ocispec.Descriptor) (desc ocispec.Descriptor, err error) {
+	opts.MapRoot = func(ctx context.Context, src content.ReadOnlyStorage, root ocispec.Descriptor) (desc ocispec.Descriptor, err error) {
 		if mapRoot != nil {
 			if root, err = mapRoot(ctx, src, root); err != nil {
 				return ocispec.Descriptor{}, err
@@ -168,7 +168,7 @@ type CopyGraphOptions struct {
 // The destination reference will be the same as the source reference if the
 // destination reference is left blank.
 // Returns the descriptor of the root node on successful copy.
-func Copy(ctx context.Context, src Target, srcRef string, dst Target, dstRef string, opts CopyOptions) (ocispec.Descriptor, error) {
+func Copy(ctx context.Context, src ReadOnlyTarget, srcRef string, dst Target, dstRef string, opts CopyOptions) (ocispec.Descriptor, error) {
 	if src == nil {
 		return ocispec.Descriptor{}, errors.New("nil source target")
 	}
@@ -208,15 +208,15 @@ func Copy(ctx context.Context, src Target, srcRef string, dst Target, dstRef str
 
 // CopyGraph copies a rooted directed acyclic graph (DAG) from the source CAS to
 // the destination CAS.
-func CopyGraph(ctx context.Context, src, dst content.Storage, root ocispec.Descriptor, opts CopyGraphOptions) error {
+func CopyGraph(ctx context.Context, src content.ReadOnlyStorage, dst content.Storage, root ocispec.Descriptor, opts CopyGraphOptions) error {
 	// use caching proxy on non-leaf nodes
 	proxy := cas.NewProxy(src, cas.NewMemory())
 	return copyGraph(ctx, src, dst, proxy, root, opts)
 }
 
 // copyGraph copies a rooted directed acyclic graph (DAG) from the source CAS to
 // the destination CAS with specified caching.
-func copyGraph(ctx context.Context, src, dst content.Storage, proxy *cas.Proxy, root ocispec.Descriptor, opts CopyGraphOptions) error {
+func copyGraph(ctx context.Context, src content.ReadOnlyStorage, dst content.Storage, proxy *cas.Proxy, root ocispec.Descriptor, opts CopyGraphOptions) error {
 	// track content status
 	tracker := status.NewTracker()
 
@@ -301,7 +301,7 @@ func copyGraph(ctx context.Context, src, dst content.Storage, proxy *cas.Proxy,
 }
 
 // doCopyNode copies a single content from the source CAS to the destination CAS.
-func doCopyNode(ctx context.Context, src, dst content.Storage, desc ocispec.Descriptor) error {
+func doCopyNode(ctx context.Context, src content.ReadOnlyStorage, dst content.Storage, desc ocispec.Descriptor) error {
 	rc, err := src.Fetch(ctx, desc)
 	if err != nil {
 		return err
@@ -316,7 +316,7 @@ func doCopyNode(ctx context.Context, src, dst content.Storage, desc ocispec.Desc
 
 // copyNode copies a single content from the source CAS to the destination CAS,
 // and apply the given options.
-func copyNode(ctx context.Context, src, dst content.Storage, desc ocispec.Descriptor, opts CopyGraphOptions) error {
+func copyNode(ctx context.Context, src content.ReadOnlyStorage, dst content.Storage, desc ocispec.Descriptor, opts CopyGraphOptions) error {
 	if opts.PreCopy != nil {
 		if err := opts.PreCopy(ctx, desc); err != nil {
 			if err == graph.ErrSkipDesc {
@@ -353,7 +353,7 @@ func copyCachedNodeWithReference(ctx context.Context, src *cas.Proxy, dst regist
 }
 
 // resolveRoot resolves the source reference to the root node.
-func resolveRoot(ctx context.Context, src Target, srcRef string, proxy *cas.Proxy) (ocispec.Descriptor, error) {
+func resolveRoot(ctx context.Context, src ReadOnlyTarget, srcRef string, proxy *cas.Proxy) (ocispec.Descriptor, error) {
 	refFetcher, ok := src.(registry.ReferenceFetcher)
 	if !ok {
 		return src.Resolve(ctx, srcRef)

copy_test.go

@@ -540,7 +540,7 @@ func TestCopy_WithOptions(t *testing.T) {
 	// test copy with media type filter
 	dst := memory.New()
 	opts := oras.DefaultCopyOptions
-	opts.MapRoot = func(ctx context.Context, src content.Storage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
+	opts.MapRoot = func(ctx context.Context, src content.ReadOnlyStorage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
 		if root.MediaType == ocispec.MediaTypeImageIndex {
 			return root, nil
 		} else {
@@ -580,7 +580,7 @@ func TestCopy_WithOptions(t *testing.T) {
 	preCopyCount := int64(0)
 	postCopyCount := int64(0)
 	opts = oras.CopyOptions{
-		MapRoot: func(ctx context.Context, src content.Storage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
+		MapRoot: func(ctx context.Context, src content.ReadOnlyStorage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
 			manifests, err := content.Successors(ctx, src, root)
 			if err != nil {
 				return ocispec.Descriptor{}, errdef.ErrNotFound
@@ -645,7 +645,7 @@ func TestCopy_WithOptions(t *testing.T) {
 	// test copy with root filter, but no matching node can be found
 	dst = memory.New()
 	opts = oras.CopyOptions{
-		MapRoot: func(ctx context.Context, src content.Storage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
+		MapRoot: func(ctx context.Context, src content.ReadOnlyStorage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
 			if root.MediaType == "test" {
 				return root, nil
 			} else {
@@ -826,7 +826,7 @@ func TestCopy_WithTargetPlatformOptions(t *testing.T) {
 	// index, but there is no matching node. Should return not found error.
 	dst = memory.New()
 	opts = oras.CopyOptions{
-		MapRoot: func(ctx context.Context, src content.Storage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
+		MapRoot: func(ctx context.Context, src content.ReadOnlyStorage, root ocispec.Descriptor) (ocispec.Descriptor, error) {
 			if root.MediaType == ocispec.MediaTypeImageIndex {
 				return root, nil
 			} else {

extendedcopy.go

@@ -56,15 +56,15 @@ type ExtendedCopyGraphOptions struct {
 	Depth int
 	// FindPredecessors finds the predecessors of the current node.
 	// If FindPredecessors is nil, src.Predecessors will be adapted and used.
-	FindPredecessors func(ctx context.Context, src content.GraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error)
+	FindPredecessors func(ctx context.Context, src content.ReadOnlyGraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error)
 }
 
 // ExtendedCopy copies the directed acyclic graph (DAG) that are reachable from
 // the given tagged node from the source GraphTarget to the destination Target.
 // The destination reference will be the same as the source reference if the
 // destination reference is left blank.
 // Returns the descriptor of the tagged node on successful copy.
-func ExtendedCopy(ctx context.Context, src GraphTarget, srcRef string, dst Target, dstRef string, opts ExtendedCopyOptions) (ocispec.Descriptor, error) {
+func ExtendedCopy(ctx context.Context, src ReadOnlyGraphTarget, srcRef string, dst Target, dstRef string, opts ExtendedCopyOptions) (ocispec.Descriptor, error) {
 	if src == nil {
 		return ocispec.Descriptor{}, errors.New("nil source graph target")
 	}
@@ -93,7 +93,7 @@ func ExtendedCopy(ctx context.Context, src GraphTarget, srcRef string, dst Targe
 
 // ExtendedCopyGraph copies the directed acyclic graph (DAG) that are reachable
 // from the given node from the source GraphStorage to the destination Storage.
-func ExtendedCopyGraph(ctx context.Context, src content.GraphStorage, dst content.Storage, node ocispec.Descriptor, opts ExtendedCopyGraphOptions) error {
+func ExtendedCopyGraph(ctx context.Context, src content.ReadOnlyGraphStorage, dst content.Storage, node ocispec.Descriptor, opts ExtendedCopyGraphOptions) error {
 	roots, err := findRoots(ctx, src, node, opts)
 	if err != nil {
 		return err
@@ -111,7 +111,7 @@ func ExtendedCopyGraph(ctx context.Context, src content.GraphStorage, dst conten
 
 // findRoots finds the root nodes reachable from the given node through a
 // depth-first search.
-func findRoots(ctx context.Context, storage content.GraphStorage, node ocispec.Descriptor, opts ExtendedCopyGraphOptions) (map[descriptor.Descriptor]ocispec.Descriptor, error) {
+func findRoots(ctx context.Context, storage content.ReadOnlyGraphStorage, node ocispec.Descriptor, opts ExtendedCopyGraphOptions) (map[descriptor.Descriptor]ocispec.Descriptor, error) {
 	visited := make(map[descriptor.Descriptor]bool)
 	roots := make(map[descriptor.Descriptor]ocispec.Descriptor)
 	addRoot := func(key descriptor.Descriptor, val ocispec.Descriptor) {
@@ -122,7 +122,7 @@ func findRoots(ctx context.Context, storage content.GraphStorage, node ocispec.D
 
 	// if FindPredecessors is not provided, use the default one
 	if opts.FindPredecessors == nil {
-		opts.FindPredecessors = func(ctx context.Context, src content.GraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+		opts.FindPredecessors = func(ctx context.Context, src content.ReadOnlyGraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
 			return src.Predecessors(ctx, desc)
 		}
 	}
@@ -182,7 +182,7 @@ func findRoots(ctx context.Context, storage content.GraphStorage, node ocispec.D
 // FilterArtifactType first.
 func (opts *ExtendedCopyGraphOptions) FilterAnnotation(key string, regex *regexp.Regexp) {
 	fp := opts.FindPredecessors
-	opts.FindPredecessors = func(ctx context.Context, src content.GraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+	opts.FindPredecessors = func(ctx context.Context, src content.ReadOnlyGraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
 		var predecessors []ocispec.Descriptor
 		var err error
 		if fp == nil {
@@ -237,7 +237,7 @@ func (opts *ExtendedCopyGraphOptions) FilterAnnotation(key string, regex *regexp
 // FilterArtifactType first.
 func (opts *ExtendedCopyGraphOptions) FilterArtifactType(regex *regexp.Regexp) {
 	fp := opts.FindPredecessors
-	opts.FindPredecessors = func(ctx context.Context, src content.GraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+	opts.FindPredecessors = func(ctx context.Context, src content.ReadOnlyGraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
 		var predecessors []ocispec.Descriptor
 		var err error
 		if fp == nil {

extendedcopy_test.go

@@ -568,7 +568,7 @@ func TestExtendedCopyGraph_WithFindPredecessorsOption(t *testing.T) {
 	// test extended copy by descs[3] with media type filter
 	dst := memory.New()
 	opts := oras.ExtendedCopyGraphOptions{
-		FindPredecessors: func(ctx context.Context, src content.GraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
+		FindPredecessors: func(ctx context.Context, src content.ReadOnlyGraphStorage, desc ocispec.Descriptor) ([]ocispec.Descriptor, error) {
 			predecessors, err := src.Predecessors(ctx, desc)
 			if err != nil {
 				return nil, err

internal/cas/proxy.go

@@ -30,17 +30,17 @@ import (
 // cache the fetched content.
 // The subsequent fetch call will read from the local cache.
 type Proxy struct {
-	content.Storage
+	content.ReadOnlyStorage
 	Cache       content.Storage
 	StopCaching bool
 }
 
 // NewProxy creates a proxy for the `base` storage, using the `cache` storage as
 // the cache.
-func NewProxy(base, cache content.Storage) *Proxy {
+func NewProxy(base content.ReadOnlyStorage, cache content.Storage) *Proxy {
 	return &Proxy{
-		Storage: base,
-		Cache:   cache,
+		ReadOnlyStorage: base,
+		Cache:           cache,
 	}
 }
 
@@ -55,7 +55,7 @@ func (p *Proxy) Fetch(ctx context.Context, target ocispec.Descriptor) (io.ReadCl
 		return rc, nil
 	}
 
-	rc, err = p.Storage.Fetch(ctx, target)
+	rc, err = p.ReadOnlyStorage.Fetch(ctx, target)
 	if err != nil {
 		return nil, err
 	}
@@ -99,7 +99,7 @@ func (p *Proxy) FetchCached(ctx context.Context, target ocispec.Descriptor) (io.
 	if exists {
 		return p.Cache.Fetch(ctx, target)
 	}
-	return p.Storage.Fetch(ctx, target)
+	return p.ReadOnlyStorage.Fetch(ctx, target)
 }
 
 // Exists returns true if the described content exists.
@@ -108,5 +108,5 @@ func (p *Proxy) Exists(ctx context.Context, target ocispec.Descriptor) (bool, er
 	if err == nil && exists {
 		return true, nil
 	}
-	return p.Storage.Exists(ctx, target)
+	return p.ReadOnlyStorage.Exists(ctx, target)
 }

internal/cas/proxy_test.go

@@ -34,13 +34,13 @@ func TestProxyCache(t *testing.T) {
 		Size:      int64(len(content)),
 	}
 
-	s := NewProxy(NewMemory(), NewMemory())
 	ctx := context.Background()
-
-	err := s.Push(ctx, desc, bytes.NewReader(content))
+	base := NewMemory()
+	err := base.Push(ctx, desc, bytes.NewReader(content))
 	if err != nil {
-		t.Fatal("Proxy.Push() error =", err)
+		t.Fatal("Memory.Push() error =", err)
 	}
+	s := NewProxy(base, NewMemory())
 
 	// first fetch
 	exists, err := s.Exists(ctx, desc)
@@ -68,7 +68,7 @@ func TestProxyCache(t *testing.T) {
 
 	// repeated fetch should not touch base CAS
 	// nil base will generate panic if the base CAS is touched
-	s.Storage = nil
+	s.ReadOnlyStorage = nil
 
 	exists, err = s.Exists(ctx, desc)
 	if err != nil {
@@ -94,23 +94,6 @@ func TestProxyCache(t *testing.T) {
 	}
 }
 
-func TestProxyPushPassThrough(t *testing.T) {
-	content := []byte("hello world")
-	desc := ocispec.Descriptor{
-		MediaType: "test",
-		Digest:    digest.FromBytes(content),
-		Size:      int64(len(content)),
-	}
-
-	s := NewProxy(NewMemory(), nil)
-	ctx := context.Background()
-
-	err := s.Push(ctx, desc, bytes.NewReader(content))
-	if err != nil {
-		t.Fatal("Proxy.Push() error =", err)
-	}
-}
-
 func TestProxy_FetchCached_NotCachedContent(t *testing.T) {
 	content := []byte("hello world")
 	desc := ocispec.Descriptor{
@@ -119,13 +102,13 @@ func TestProxy_FetchCached_NotCachedContent(t *testing.T) {
 		Size:      int64(len(content)),
 	}
 
-	s := NewProxy(NewMemory(), NewMemory())
 	ctx := context.Background()
-
-	err := s.Push(ctx, desc, bytes.NewReader(content))
+	base := NewMemory()
+	err := base.Push(ctx, desc, bytes.NewReader(content))
 	if err != nil {
-		t.Fatal("Proxy.Push() error =", err)
+		t.Fatal("Memory.Push() error =", err)
 	}
+	s := NewProxy(base, NewMemory())
 
 	// FetchCached should fetch from the base CAS
 	exists, err := s.Exists(ctx, desc)
@@ -170,13 +153,13 @@ func TestProxy_FetchCached_CachedContent(t *testing.T) {
 		Size:      int64(len(content)),
 	}
 
-	s := NewProxy(NewMemory(), NewMemory())
 	ctx := context.Background()
-
-	err := s.Push(ctx, desc, bytes.NewReader(content))
+	base := NewMemory()
+	err := base.Push(ctx, desc, bytes.NewReader(content))
 	if err != nil {
-		t.Fatal("Proxy.Push() error =", err)
+		t.Fatal("Memory.Push() error =", err)
 	}
+	s := NewProxy(base, NewMemory())
 
 	// first fetch
 	exists, err := s.Exists(ctx, desc)
@@ -204,7 +187,7 @@ func TestProxy_FetchCached_CachedContent(t *testing.T) {
 
 	// the subsequent FetchCached should not touch base CAS
 	// nil base will generate panic if the base CAS is touched
-	s.Storage = nil
+	s.ReadOnlyStorage = nil
 
 	exists, err = s.Exists(ctx, desc)
 	if err != nil {
@@ -238,13 +221,13 @@ func TestProxy_StopCaching(t *testing.T) {
 		Size:      int64(len(content)),
 	}
 
-	s := NewProxy(NewMemory(), NewMemory())
 	ctx := context.Background()
-
-	err := s.Push(ctx, desc, bytes.NewReader(content))
+	base := NewMemory()
+	err := base.Push(ctx, desc, bytes.NewReader(content))
 	if err != nil {
-		t.Fatal("Proxy.Push() error =", err)
+		t.Fatal("Memory.Push() error =", err)
 	}
+	s := NewProxy(base, NewMemory())
 
 	// FetchCached should fetch from the base CAS
 	exists, err := s.Exists(ctx, desc)