code: func headersToSlice(header http.Header) []interface{} {
  	res := make([]interface{}, 2*len(header))
  	i := 0
  	for k, v := range header {
  		res[i] = k
  		if len(v) == 1 {
  			res[i+1] = v[0]
  		} else {
  			res[i+1] = v
  		}
  		i += 2
  	}
  	return res
  }
docs: // headersToSlice produces a loggable slice from a HTTP header.