code: func (m *Monitor) getOpenBlockNumber(
  	el *data.JobEthLog) (block uint32, ok bool, err error) {
  	var event string
  	switch el.Topics[0] {
  	case eth.ServiceChannelToppedUp:
  		event = logChannelToppedUp
  	case eth.ServiceChannelCloseRequested:
  		event = logChannelCloseRequested
  	case eth.ServiceCooperativeChannelClose:
  		event = logCooperativeChannelClose
  	case eth.ServiceUnCooperativeChannelClose:
  		event = logUnCooperativeChannelClose
  	default:
  		return
  	}
  
  	if event != "" {
  		block, err = m.blockNumber(el.Data,
  			logChannelToppedUp)
  		ok = true
  	}
  	return
  }
docs: // getOpenBlockNumber extracts the Open_block_number field of a given
  // channel-related EthLog. Returns false in case it failed, i.e.
  // the event has no such field.