code: func (swap *Swap) GetPeerBalance(peer enode.ID) (int64, error) {
  	swap.lock.RLock()
  	defer swap.lock.RUnlock()
  	if p, ok := swap.balances[peer]; ok {
  		return p, nil
  	}
  	return 0, errors.New("Peer not found")
  }
docs: //GetPeerBalance returns the balance for a given peer