Fix replace with compliant image mediatype (#4077)

* Fix replace with non compliant image mediatypes

Signed-off-by: Stef Graces <stefgraces@hotmail.com>

* Add test for signature mediatype

Signed-off-by: Stef Graces <stefgraces@hotmail.com>

---------

Signed-off-by: Stef Graces <stefgraces@hotmail.com>

Author: stgrace

pkg/oci/mutate/signatures.go

@@ -17,10 +17,10 @@ package mutate
 
 import (
 	v1 "github.com/google/go-containerregistry/pkg/v1"
-	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/sigstore/cosign/v2/internal/pkg/now"
 	"github.com/sigstore/cosign/v2/pkg/oci"
+	"github.com/sigstore/cosign/v2/pkg/oci/empty"
 )
 
 const maxLayers = 1000
@@ -83,7 +83,7 @@ func ReplaceSignatures(base oci.Signatures) (oci.Signatures, error) {
 			Annotations: ann,
 		})
 	}
-	img, err := mutate.Append(empty.Image, adds...)
+	img, err := mutate.Append(empty.Signatures(), adds...)
 	if err != nil {
 		return nil, err
 	}

pkg/oci/mutate/signatures_test.go

@@ -20,6 +20,7 @@ import (
 	"testing"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 	"github.com/sigstore/cosign/v2/pkg/oci"
 	"github.com/sigstore/cosign/v2/pkg/oci/empty"
 	"github.com/sigstore/cosign/v2/pkg/oci/static"
@@ -87,6 +88,34 @@ func TestAppendSignatures(t *testing.T) {
 	}
 }
 
+func TestReplaceSignatures(t *testing.T) {
+	base := empty.Signatures()
+
+	s1, err := static.NewSignature([]byte{}, "s1")
+	if err != nil {
+		t.Fatalf("NewSignature() = %v", err)
+	}
+
+	oneSig, err := AppendSignatures(base, false, s1)
+	if err != nil {
+		t.Fatalf("AppendSignatures() = %v", err)
+	}
+	replaceSig, err := ReplaceSignatures(oneSig)
+	if err != nil {
+		t.Fatalf("ReplaceSignatures() = %v", err)
+	}
+	if sl, err := replaceSig.Get(); err != nil {
+		t.Fatalf("Get() = %v", err)
+	} else if got, want := len(sl), 1; got != want {
+		t.Errorf("len(Get()) = %d, wanted %d", got, want)
+	}
+	if mt, err := replaceSig.MediaType(); err != nil {
+		t.Fatalf("MediaType() = %v", err)
+	} else if got, want := mt, types.OCIManifestSchema1; got != want {
+		t.Errorf("MediaType() = %v, wanted %v", got, want)
+	}
+}
+
 func TestGet(t *testing.T) {
 	tests := []struct {
 		name         string