docker/docker_image_src.go
func (s *dockerImageSource) getSignaturesFromLookaside(ctx context.Context, instanceDigest *digest.Digest) ([][]byte, error) {
	manifestDigest, err := s.manifestDigest(ctx, instanceDigest)
	if err != nil {
		return nil, err
	}

	// NOTE: Keep this in sync with docs/signature-protocols.md!
	signatures := [][]byte{}
	for i := 0; ; i++ {
		url := signatureStorageURL(s.c.signatureBase, manifestDigest, i)
		if url == nil {
			return nil, errors.Errorf("Internal error: signatureStorageURL with non-nil base returned nil")
		}
		signature, missing, err := s.getOneSignature(ctx, url)
		if err != nil {
			return nil, err
		}
		if missing {
			break
		}
		signatures = append(signatures, signature)
	}
	return signatures, nil
}
func (s *dockerImageSource) getSignaturesFromLookaside(ctx context.Context, instanceDigest *digest.Digest) ([][]byte, error) {
	manifestDigest, err := s.manifestDigest(ctx, instanceDigest)
	if err != nil {
		return nil, err
	}

	// NOTE: Keep this in sync with docs/signature-protocols.md!
	signatures := [][]byte{}
	for i := 0; ; i++ {
		url := signatureStorageURL(s.c.signatureBase, manifestDigest, i)
		if url == nil {
			return nil, errors.Errorf("Internal error: signatureStorageURL with non-nil base returned nil")
		}
		signature, missing, err := s.getOneSignature(ctx, url)
		if err != nil {
			return nil, err
		}
		if missing {
			break
		}
		signatures = append(signatures, signature)
	}
	return signatures, nil
}
// getSignaturesFromLookaside implements GetSignatures() from the lookaside location configured in s.c.signatureBase,
// which is not nil.