golang.org/x/crypto/ssh 新连接时怎么保存HOSTKEY到known_hosts文件

使用golang.org/x/crypto/ssh 连接远程时， 如果是第一次连接， 且known_hosts文件中没有保存远程主机的KEY， 就报错: “no hostkey for 192.168.1.100” 怎么在第一次连接时自动保存key到known_hosts文件? 没有看到crypto/ssh源文件中有这样的方法。

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 func getHostKey(host string) (ssh.PublicKey, error) {
        file, err := os.Open(filepath.Join(os.Getenv("HOME"), ".ssh", "known_hosts"))
        if err != nil {
                return nil, err
        }
        defer file.Close()

        scanner := bufio.NewScanner(file)
        var hostKey ssh.PublicKey
        for scanner.Scan() {
                fields := strings.Split(scanner.Text(), " ")
                if len(fields) != 3 {
                        continue
                }
                if strings.Contains(fields[0], host) {
                        var err error
                        hostKey, _, _, _, err = ssh.ParseAuthorizedKey(scanner.Bytes())
                        if err != nil {
                                return nil, errors.New(fmt.Sprintf("error parsing %q: %v", fields[2], err))
                        }
                        break
                }
        }

        if hostKey == nil {
                return nil, errors.New(fmt.Sprintf("no hostkey for %s", host))
        }
        return hostKey, nil
}

func main() {

        hostKey, err := getHostKey("192.168.1.100")
        if err != nil {
                        panic(err)
        }

        config := &ssh.ClientConfig{
                User: "root",
                Auth: []ssh.AuthMethod{
                        ssh.Password("xxxxxx"),
                },
                //HostKeyCallback: ssh.InsecureIgnoreHostKey(),   //这个可以， 但是不够安全
                HostKeyCallback: ssh.FixedHostKey(hostKey),
                Timeout:         30 * time.Second,
        }
        client, err := ssh.Dial("tcp", "192.168.1.100:22", config)
        if err != nil {
                panic("Failed to dial: " + err.Error())
        }

        session, err := client.NewSession()
        if err != nil {
                panic("Failed to create session: " + err.Error())
        }
        defer session.Close()

        var b bytes.Buffer
        session.Stdout = &b
        if err := session.Run("ls"); err != nil {
                panic("Failed to run: " + err.Error())
        }
        fmt.Println(b.String())

}

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