code: func (p *PilosaKeyMapper) MapRequest(body []byte) ([]byte, error) {
  	log.Printf("mapping request: '%s'", body)
  	query, err := pql.ParseString(string(body))
  	if err != nil {
  		return nil, errors.Wrap(err, "parsing string")
  	}
  	for _, call := range query.Calls {
  		err := p.mapCall(call)
  		if err != nil {
  			return nil, errors.Wrap(err, "mapping call")
  		}
  	}
  	log.Printf("mapped request: '%s'", query.String())
  	return []byte(query.String()), nil
  }
docs: // MapRequest takes a request body and returns a mapped version of that body.