code: def push(id, body)
        before = @zache.get(id.to_s, lifetime: @period) { '' }
        after = hash(id, body)
        if before == after
          @log.debug("Spam of #{id} ignored; the wallet content of #{Size.new(body.length)} \
  and '#{after[0..8]}' hash has already been seen #{Age.new(@zache.mtime(id.to_s))} ago")
          return []
        end
        @zache.put(id.to_s, after)
        @entrance.push(id, body)
      end
docs: Returns a list of modifed wallets (as Zold::Id)