def push(id, body)
      before = @wallets.acq(id) { |w| w.exists? ? w.digest : '' }
      after = OpenSSL::Digest::SHA256.new(body).hexdigest
      if before == after
        @log.debug("Duplicate of #{id} ignored #{Size.new(body.length)}")
        return []
      end
      @log.debug("New content for #{id} arrived #{Size.new(body.length)}")
      @entrance.push(id, body)
    end
def push(id, body)
      before = @wallets.acq(id) { |w| w.exists? ? w.digest : '' }
      after = OpenSSL::Digest::SHA256.new(body).hexdigest
      if before == after
        @log.debug("Duplicate of #{id} ignored #{Size.new(body.length)}")
        return []
      end
      @log.debug("New content for #{id} arrived #{Size.new(body.length)}")
      @entrance.push(id, body)
    end
Returns a list of modifed wallets (as Zold::Id)