metadata: define content sharing policy

This changeset modifies the metadata store to allow one to set a
"content sharing policy" that defines how blobs are shared between
namespaces in the content store.

The default mode "shared" will make blobs available in all namespaces
once it is pulled into any namespace.  The blob will be pulled into
the namespace if a writer is opened with the "Expected" digest that
is already present in the backend.

The alternative mode, "isolated" requires that clients prove they have
access to the content by providing all of the content to the ingest
before the blob is added to the namespace.

Both modes share backing data, while "shared" will reduce total
bandwidth across namespaces, at the cost of allowing access to any
blob just by knowing its digest.

Note: Most functional codes and changelog of this commit originate from
Stephen J Day <stephen.day@docker.com>, see
40455aade8

Fixes #1713 Fixes #2865

Signed-off-by: Eric Lin <linxiulei@gmail.com>

content/testsuite/testsuite.go

@@ -38,8 +38,16 @@ import (
 	"gotest.tools/assert"
 )
 
+const (
+	emptyDigest = "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+)
+
+// StoreInitFn initializes content store with given root and returns a function for
+// destroying the content store
+type StoreInitFn func(ctx context.Context, root string) (context.Context, content.Store, func() error, error)
+
 // ContentSuite runs a test suite on the content store given a factory function.
-func ContentSuite(t *testing.T, name string, storeFn func(ctx context.Context, root string) (context.Context, content.Store, func() error, error)) {
+func ContentSuite(t *testing.T, name string, storeFn StoreInitFn) {
 	t.Run("Writer", makeTest(t, name, storeFn, checkContentStoreWriter))
 	t.Run("UpdateStatus", makeTest(t, name, storeFn, checkUpdateStatus))
 	t.Run("CommitExists", makeTest(t, name, storeFn, checkCommitExists))
@@ -52,10 +60,18 @@ func ContentSuite(t *testing.T, name string, storeFn func(ctx context.Context, r
 	t.Run("SmallBlob", makeTest(t, name, storeFn, checkSmallBlob))
 	t.Run("Labels", makeTest(t, name, storeFn, checkLabels))
 
+	t.Run("CommitErrorState", makeTest(t, name, storeFn, checkCommitErrorState))
+}
+
+// ContentCrossNSSharedSuite runs a test suite under shared content policy
+func ContentCrossNSSharedSuite(t *testing.T, name string, storeFn StoreInitFn) {
 	t.Run("CrossNamespaceAppend", makeTest(t, name, storeFn, checkCrossNSAppend))
 	t.Run("CrossNamespaceShare", makeTest(t, name, storeFn, checkCrossNSShare))
+}
 
-	t.Run("CommitErrorState", makeTest(t, name, storeFn, checkCommitErrorState))
+// ContentCrossNSIsolatedSuite runs a test suite under isolated content policy
+func ContentCrossNSIsolatedSuite(t *testing.T, name string, storeFn StoreInitFn) {
+	t.Run("CrossNamespaceIsolate", makeTest(t, name, storeFn, checkCrossNSIsolate))
 }
 
 // ContextWrapper is used to decorate new context used inside the test
@@ -890,6 +906,38 @@ func checkCrossNSAppend(ctx context.Context, t *testing.T, cs content.Store) {
 
 }
 
+func checkCrossNSIsolate(ctx context.Context, t *testing.T, cs content.Store) {
+	wrap, ok := ctx.Value(wrapperKey{}).(ContextWrapper)
+	if !ok {
+		t.Skip("multiple contexts not supported")
+	}
+
+	var size int64 = 1000
+	b, d := createContent(size)
+	ref := fmt.Sprintf("ref-%d", size)
+	t1 := time.Now()
+
+	if err := content.WriteBlob(ctx, cs, ref, bytes.NewReader(b), ocispec.Descriptor{Size: size, Digest: d}); err != nil {
+		t.Fatal(err)
+	}
+	t2 := time.Now()
+
+	ctx2, done, err := wrap(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer done(ctx2)
+
+	t3 := time.Now()
+	w, err := cs.Writer(ctx2, content.WithRef(ref), content.WithDescriptor(ocispec.Descriptor{Size: size, Digest: d}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t4 := time.Now()
+
+	checkNewlyCreated(t, w, t1, t2, t3, t4)
+}
+
 func checkStatus(t *testing.T, w content.Writer, expected content.Status, d digest.Digest, preStart, postStart, preUpdate, postUpdate time.Time) {
 	t.Helper()
 	st, err := w.Status()
@@ -934,6 +982,29 @@ func checkStatus(t *testing.T, w content.Writer, expected content.Status, d dige
 	}
 }
 
+func checkNewlyCreated(t *testing.T, w content.Writer, preStart, postStart, preUpdate, postUpdate time.Time) {
+	t.Helper()
+	st, err := w.Status()
+	if err != nil {
+		t.Fatalf("failed to get status: %v", err)
+	}
+
+	wd := w.Digest()
+	if wd != emptyDigest {
+		t.Fatalf("unexpected digest %v, expected %v", wd, emptyDigest)
+	}
+
+	if st.Offset != 0 {
+		t.Fatalf("unexpected offset %v", st.Offset)
+	}
+
+	if runtime.GOOS != "windows" {
+		if st.StartedAt.After(postUpdate) || st.StartedAt.Before(postStart) {
+			t.Fatalf("unexpected started at time %s, expected between %s and %s", st.StartedAt, postStart, postUpdate)
+		}
+	}
+}
+
 func checkInfo(ctx context.Context, cs content.Store, d digest.Digest, expected content.Info, c1, c2, u1, u2 time.Time) error {
 	info, err := cs.Info(ctx, d)
 	if err != nil {