code: func (ec *Client) NetworkID(ctx context.Context) (*big.Int, error) {
  	version := new(big.Int)
  	var ver string
  	if err := ec.c.CallContext(ctx, &ver, "net_version"); err != nil {
  		return nil, err
  	}
  	if _, ok := version.SetString(ver, 10); !ok {
  		return nil, fmt.Errorf("invalid net_version result %q", ver)
  	}
  	return version, nil
  }
docs: // State Access
  // NetworkID returns the network ID (also known as the chain ID) for this chain.