在我的node.js应用程序中，我使用ssh 2-sftp-client每5秒上传一张图片。
上传工作正常，但在重复该功能时，我收到错误消息

node .\upload.js
uploaded screenshot to server as test_screenshot_uploadI3Mjc.png (first run)
Error: connect: An existing SFTP connection is already defined (second run)

我的代码是：

let Client = require('ssh2-sftp-client');
let sftp = new Client();

function uploadScreenshot() {
    randomNumber = Buffer.from(Math.random().toString()).toString("base64").substring(10,15);
    filename = "test_screenshot_upload"+randomNumber+".png";
    sftp.connect({
      host: 'ssh.strato.de',
      port: '22',
      username: 'user',
      password: 'pass'
  }).then(() => {
    sftp.put('screenshot.png', '/path/folder/folder/'+filename);
  }).then(data => {
      console.log("uploaded screenshot to server as " + filename);
  }).catch(err => {
    console.log(err, 'catch error');
  });  
}

function foo() {
    uploadScreenshot();
    setInterval(foo, 5000);
}

foo();

我试着在sftp.put后添加sftp.end();，但是没有用。你能给予我一个提示吗？我做错了什么？