Method digest

pkg/remote/pull.go:173–209

digest resolves the remote digest, matching crane.Digest behavior. When a platform is set, it resolves indexes to the platform-specific image digest; otherwise it uses a cheap HEAD request and falls back to GET if HEAD fails.

(ctx context.Context, ref name.Reference)

// platform is set, it resolves indexes to the platform-specific image digest;
// otherwise it uses a cheap HEAD request and falls back to GET if HEAD fails.
func (s *session) digest(ctx context.Context, ref name.Reference) (string, error) {
	if s.opts.Platform != nil {
		d, err := s.get(ctx, ref)
		if err != nil {
			return "", err
		}
		if !d.MediaType.IsIndex() {
			return d.Digest.String(), nil
		}
		img, err := d.Image()
		if err != nil {
			return "", err
		}
		digest, err := img.Digest()
		if err != nil {
			return "", err
		}
		return digest.String(), nil
	}

	var desc *v1.Descriptor
	err := s.withFallback(func(p *remote.Puller) error {
		var headErr error
		desc, headErr = p.Head(ctx, ref)
		return headErr
	})
	if err == nil {
		return desc.Digest.String(), nil
	}

	// HEAD failed (e.g. registry doesn't support it); fall back to GET.
	d, getErr := s.get(ctx, ref)
	if getErr != nil {
		return "", getErr
	}
	return d.Digest.String(), nil
}

// image fetches the manifest and returns a lazy v1.Image whose layer reads
// reuse this session's authenticated fetcher.