Method Resolve

core/remotes/docker/resolver.go:236–445

(ctx context.Context, ref string)

var _ remotes.ResolverWithOptions = &dockerResolver{}

func (r *dockerResolver) Resolve(ctx context.Context, ref string) (string, ocispec.Descriptor, error) {
	base, err := r.resolveDockerBase(ref)
	if err != nil {
		return "", ocispec.Descriptor{}, err
	}
	refspec := base.refspec
	if refspec.Object == "" {
		return "", ocispec.Descriptor{}, reference.ErrObjectRequired
	}

	var (
		paths [][]string
		dgst  = refspec.Digest()
		caps  = HostCapabilityPull
	)

	if dgst != "" {
		if err := dgst.Validate(); err != nil {
			// need to fail here, since we can't actually resolve the invalid
			// digest.
			return "", ocispec.Descriptor{}, err
		}

		// turns out, we have a valid digest, make a url.
		paths = append(paths, []string{"manifests", dgst.String()})

		// fallback to blobs on not found.
		paths = append(paths, []string{"blobs", dgst.String()})
	} else {
		// Add
		paths = append(paths, []string{"manifests", refspec.Object})
		caps |= HostCapabilityResolve
	}

	hosts := base.filterHosts(caps)
	if len(hosts) == 0 {
		return "", ocispec.Descriptor{}, fmt.Errorf("no resolve hosts: %w", errdefs.ErrNotFound)
	}

	ctx, err = ContextWithRepositoryScope(ctx, refspec, false)
	if err != nil {
		return "", ocispec.Descriptor{}, err
	}

	var (
		// firstErr is the most relevant error encountered during resolution.
		// We use this to determine the error to return, making sure that the
		// error created furthest through the resolution process is returned.
		firstErr         error
		firstErrPriority int
	)

	nextHostOrFail := func(i int) string {
		if i < len(hosts)-1 {
			return "trying next host"
		}
		return "fetch failed"
	}