dagger/dagger · error

no media type is stored for %q

Error message

no media type is stored for %q

What it means

getBlobDesc reconstructs an OCI descriptor from a blob's content-store metadata. The blob's media type is stored as a label (blobMediaTypeLabel) on the content record; if the record exists but lacks that label, the media type cannot be recovered and this error is thrown. It indicates the blob was stored without full descriptor metadata, typically by older versions or by paths that wrote blobs directly.

Source

Thrown at engine/snapshots/refs.go:545

		}
		if isContinue, err := walkBlobVariantsOnly(ctx, cs, c, f, visited); !isContinue || err != nil {
			return isContinue, err
		}
	}
	return true, nil
}

func getBlobDesc(ctx context.Context, cs content.Store, dgst digest.Digest) (ocispecs.Descriptor, error) {
	info, err := cs.Info(ctx, dgst)
	if err != nil {
		return ocispecs.Descriptor{}, err
	}
	if info.Labels == nil {
		return ocispecs.Descriptor{}, errors.Errorf("no blob metadata is stored for %q", info.Digest)
	}
	mt, ok := info.Labels[blobMediaTypeLabel]
	if !ok {
		return ocispecs.Descriptor{}, errors.Errorf("no media type is stored for %q", info.Digest)
	}
	desc := ocispecs.Descriptor{
		Digest:    info.Digest,
		Size:      info.Size,
		MediaType: mt,
	}
	for k, v := range info.Labels {
		if strings.HasPrefix(k, blobAnnotationsLabelPrefix) {
			if desc.Annotations == nil {
				desc.Annotations = make(map[string]string)
			}
			desc.Annotations[strings.TrimPrefix(k, blobAnnotationsLabelPrefix)] = v
		}
	}
	if len(desc.URLs) == 0 {
		// If there are no URL's, there is no reason to have this be non-dsitributable
		desc.MediaType = layerToDistributable(desc.MediaType)
	}

View on GitHub (pinned to 82ba2681db)

Solutions

1. Re-push or re-ingest the affected blob so addBlobDescToInfo writes the media-type label
2. Run a migration/GC-prune of the content store to drop legacy unlabeled blobs
3. Skip blobs missing the label in walkBlobVariantsOnly rather than failing the whole walk

Example fix

// before
desc, err := getBlobDesc(ctx, cs, dgst) // errors on unlabeled blob
// after
if _, err := cs.Info(ctx, dgst); err == nil {
    info, _ := cs.Info(ctx, dgst)
    if info.Labels == nil || info.Labels[blobMediaTypeLabel] == "" {
        info = addBlobDescToDesc(desc, info) // backfill label before querying
        cs.Update(ctx, info, "labels."+blobMediaTypeLabel)
    }
}
desc, err := getBlobDesc(ctx, cs, dgst)

info, err := cs.Info(ctx, dgst)
if err != nil { return err }
if info.Labels == nil || info.Labels[blobMediaTypeLabel] == "" {
    // legacy/unlabeled blob: backfill or skip
    info = addBlobDescToInfo(desc, info)
    if _, err := cs.Update(ctx, info, "labels."+blobMediaTypeLabel); err != nil { return err }
}

func hasBlobMediaType(info content.Info) bool {
    return info.Labels != nil && info.Labels[blobMediaTypeLabel] != ""
}

desc, err := getBlobDesc(ctx, cs, dgst)
if err != nil && strings.Contains(err.Error(), "no media type is stored") {
    // fall back to default layer media type or skip variant
}

When it happens

Trigger: Calling getBlobDesc (via ociDesc or walkBlobVariantsOnly) on a content-store blob whose Info.Labels map exists but has no blobMediaTypeLabel key — e.g. blobs ingested by a containerd/dagger version that did not stamp media-type labels, or GC-rebuilt metadata.

Common situations: Upgrading from an older engine whose stored blobs predate the blobMediaTypeLabel convention; inspecting/exporting caches created by another tool that populated the content store directly.

Related errors

• read index blob: %w
• stat host manifest %s: %w
• read host image index blob: %w
• error writing manifest list blob %s
• error writing manifest blob %s

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/3d87304ea42588ac. Report an issue: GitHub.