code: func ValidServiceName(service string) error {
  	// Blank service names are not allowed.
  	if service == "" {
  		return ErrUnsetService
  	}
  
  	// Service names must consist of the characters [a-z0-9-]
  	for _, r := range service {
  		if (r < 'a' || r > 'z') && (r < '0' || r > '9') && r != '-' {
  			return ErrInvalidService
  		}
  	}
  
  	return nil
  }
docs: // ValidServiceName returns nil if service is valid. Otherwise returns an error.