code: func isBrokenOpenSSHVersion(versionStr string) bool {
  	i := strings.Index(versionStr, openSSHPrefix)
  	if i < 0 {
  		return false
  	}
  	i += len(openSSHPrefix)
  	j := i
  	for ; j < len(versionStr); j++ {
  		if versionStr[j] < '0' || versionStr[j] > '9' {
  			break
  		}
  	}
  	version, _ := strconv.Atoi(versionStr[i:j])
  	return version < 6
  }
docs: // isBrokenOpenSSHVersion returns true if the given version string
  // specifies a version of OpenSSH that is known to have a bug in port
  // forwarding.