code: func (b *DescribedBlob) PermanodeFile() (path []blob.Ref, fi *camtypes.FileInfo, ok bool) {
  	if b == nil || b.Permanode == nil {
  		return
  	}
  	if contentRef := b.Permanode.Attr.Get("camliContent"); contentRef != "" {
  		if cdes := b.Request.DescribedBlobStr(contentRef); cdes != nil && cdes.File != nil {
  			return []blob.Ref{b.BlobRef, cdes.BlobRef}, cdes.File, true
  		}
  	}
  	return
  }
docs: // PermanodeFile returns in path the blobref of the described permanode
  // and the blobref of its File camliContent.
  // If b isn't a permanode, or doesn't have a camliContent that
  // is a file blob, ok is false.