If you use upb, an allocator is optional - you can provide a presized block to upb_Arena and a NULL upb_alloc. Of course, you'll still fail to parse a message w

If you use upb, an allocator is optional - you can provide a presized block to upb_Arena and a NULL upb_alloc. Of course, you'll still fail to parse a message with an in memory representation larger than your region.