added filtering by artifact type with regex

extendedcopy.go

@@ -17,13 +17,16 @@ package oras
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"regexp"
 
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+	artifactspec "github.com/oras-project/artifacts-spec/specs-go/v1"
 	"oras.land/oras-go/v2/content"
 	"oras.land/oras-go/v2/internal/copyutil"
 	"oras.land/oras-go/v2/internal/descriptor"
+	"oras.land/oras-go/v2/registry"
 )
 
 var (
@@ -196,3 +199,75 @@ func findRoots(ctx context.Context, storage content.GraphStorage, node ocispec.D
 	}
 	return roots, nil
 }
+
+// FilterArtifactType will configure opts.FindPredecessors to filter the predecessors
+// whose artifact type matches a given regex pattern.
+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) {
+		var predecessors []ocispec.Descriptor
+		var err error
+		if fp == nil {
+			// if src is a ReferrerFinder, use Referrers() to filter the predecessors.
+			rf, ok := src.(registry.ReferrerFinder)
+			if ok {
+				predecessors, err = findReferrersAndFilter(rf, ctx, desc, regex)
+				if err != nil {
+					return predecessors, nil
+				}
+			} else {
+				predecessors, err = src.Predecessors(ctx, desc)
+			}
+		} else {
+			predecessors, err = fp(ctx, src, desc)
+		}
+		if err != nil {
+			return nil, err
+		}
+		var filtered []ocispec.Descriptor
+		// for each predecessor, decode the manifest and check its artifact type.
+		for _, p := range predecessors {
+			if p.MediaType == artifactspec.MediaTypeArtifactManifest {
+				if err = func() error {
+					rc, err := src.Fetch(ctx, p)
+					if err != nil {
+						return err
+					}
+					defer rc.Close()
+					var manifest artifactspec.Manifest
+					if err := json.NewDecoder(rc).Decode(&manifest); err != nil {
+						return err
+					}
+					if regex.MatchString(manifest.ArtifactType) {
+						filtered = append(filtered, p)
+					}
+					return nil
+				}(); err != nil {
+					return nil, err
+				}
+			}
+		}
+		return filtered, nil
+	}
+}
+
+// findReferrersAndFilter filters the predecessors with Referrers.
+func findReferrersAndFilter(rf registry.ReferrerFinder, ctx context.Context, desc ocispec.Descriptor, regex *regexp.Regexp) ([]ocispec.Descriptor, error) {
+	var predecessors []ocispec.Descriptor
+	if err := rf.Referrers(ctx, desc, "", func(referrers []artifactspec.Descriptor) error {
+		// for each page of the results, do the following:
+		for _, referrer := range referrers {
+			if regex.MatchString(referrer.ArtifactType) {
+				predecessors = append(predecessors, ocispec.Descriptor{
+					MediaType: referrer.MediaType,
+					Digest:    referrer.Digest,
+					Size:      referrer.Size,
+				})
+			}
+		}
+		return nil
+	}); err != nil {
+		return nil, err
+	}
+	return predecessors, nil
+}