How can I make my GCloud Function open a new SSH connection to consume a SFTP server?

My setup requires a Google Function to do some stuff and upload the result to a SFTP server. I'm currently using the basic sftp and crypto/ssh packages to achieve this. Locally, after some debugging, I was able to retrieve the server's pubkey.

When deploying to GCloud nothing works, of course.

This is what handles the connection on my function

func Connect(host string, port string, user string, password string) (*ssh.Client, error) {
	hostKey := getHostKey(host)

	var auths []ssh.AuthMethod

	// Use password authentication if provided
	if password != "" {
		auths = append(auths, ssh.Password(password))
	}

	config := &ssh.ClientConfig{
		User:            user,
		HostKeyCallback: ssh.FixedHostKey(hostKey),
		Auth:            auths,
	}

	cipherOrder := config.Ciphers
	config.Ciphers = append(cipherOrder, "aes128-cbc", "3des-cbc")

	sshConn, err := ssh.Dial("tcp", host+":"+port, config)
	if err != nil {
		return nil, err
	}

	return sshConn, nil
}

func getHostKey(host string) ssh.PublicKey {
	file, err := os.Open("/root/.ssh/known_hosts")
	if err != nil {
		fmt.Fprintf(os.Stderr, "Unable to read known_hosts file: %v\n", err)
		os.Exit(1)
	}
	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 {
				fmt.Fprintf(os.Stderr, "Error parsing %q: %v\n", fields[2], err)
				os.Exit(1)
			}
			break
		}
	}

	if hostKey == nil {
		fmt.Fprintf(os.Stderr, "No hostkey found for %s", host)
		os.Exit(1)
	}

	return hostKey
}

The known_hosts file doesn't exist. I don't have the pubkey of the server, but with Filezilla I can connect to it just fine.

I had to specify those cyphers because a barebone ssh hostname would return Unable to negotiate... error

Is there any other way to do this? I'm thinking about uploading my own known_hosts file but it doesn't sound like a great solution.

I was probably over engineering it.

Setting the ssh.ClientConfig like this solved the problem:

config := &ssh.ClientConfig{
		User:            user,
		Auth:            auths,
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
}

Anyway I also found a nicer package to easily handle SSH connection, simplessh.

conn, _ := simplessh.ConnectWithPassword(host, user, pass)

client, _ := sftp.NewClient(conn.SSHClient)