Node JS：我应该使用 Promise 来执行预处理吗？

Question

NodeJS + Express。我正在努力实现以下目标：

• 客户端使用以下 JSON 文档 data={text: "I love Stackoverflow", shouldPreprocess: <true or false>} 发送 post 请求；
• 我需要调用外部 WebSocket 服务对文本进行情感分析并将结果返回为 JSON，例如{sentiment: '正面'};
• 但是，如果 shouldPreprocess 为 true，我应该先调用另一个预处理服务；

问题：

1. 我不确定执行此操作的正确方法是什么，但这里有两次尝试。我觉得他们俩都很老套。
2. 我不确定如何处理来自客户端的无效输入。详情如下。

router.post('/analyse', function (req, res, next) {
    const data = req.body;

    if (typeof data.text === 'undefined' || typeof data.shouldPreprocess === 'undefined') {
        return next(new Error('Please provide text and flag'));
    }

    analyseSentiment(data.text, data.shouldPreprocess)
        .then(doc => res.json(doc))
        .catch(err => next(err));
});

function analyseSentiment(text, shouldPreprocess) {
    let promise;
    if (shouldPreprocess === true) {
        textP = preprocess(text);
    } else promise = new Promise((res, req) => res(text));
    return textP
        .then(text => axios.post(<URL to sentiment analyser>, text))

function preprocess(text) {
    const ws = WebSocket(<URL of preprocessor>);
    // But what if I wanted to check for some property of text here and throw an error
    // that gets sent to the client, just as I do in the main function, i.e. in router.post above?
    ws.on('open', () => ws.send(text));
    return new Promise((res, rej) => ws.on('message', preprocText => res(preprocText)));
}

所以这是第一种方式。感觉很奇怪，因为我在 analyseSentiment 中创建了一个只返回文本的无用承诺，这样我就有了一种统一的方式来处理预处理和非预处理场景。另请参阅上面函数preprocess 中的评论中的问题。

第二种方法是在router.post 中做所有事情，例如：

router.post('/analyse', function (req, res, next) {
    const data = req.body;

    if (typeof data.text === 'undefined' || typeof data.shouldPreprocess === 'undefined') {
        return next(new Error('Please provide text and flag'));
    }

    if (data.shouldPreprocess) {
        preprocess(data.text)
            .then(text => axios.post(<URL to sentiment analyser>, text)))
            .then(doc => res.json(doc))
            .catch(err => next(err));
    } else {
        axios.post(<URL to sentiment analyser>, text)
            .then(doc => res.json(doc))
            .catch(err => next(err));
    }

});

但是当然有重复的代码片段。

谢谢！

Answer 1

我会利用在 Express 中可以将多个函数作为请求处理程序传递的事实。当你不带参数地调用next() 时，它们将被一个接一个地调用。

示例实现：

router.post('/analyse', validate, preprocess, analyse)

function validate (req, res, next) {
  let text = req.body.text
  let preprocess = req.body.shouldPreprocess
  if (typeof text === 'string' &&
      text.length > 0 &&
      text.length < 400 &&
      typeof preprocess === 'boolean') {
    next() // validation complete, go to the next request handler
  } else {
    return res.status(400).json({ reason: 'Please provide text and flag' })
  }
}

function preprocess (req, res, next) {
  if (req.body.shouldPreprocess) {
    const ws = WebSocket(<URL of preprocessor>)

    ws.on('open', () => ws.send(text))
    ws.on('message', preprocessed_text => {
      // check for some properties of text
      // this function is not implemented here
      if (validatePreprocessedText(preprocessed_text) {
        // send error to client
        return res.status(400).json({ reason: 'Malformed preprocessing result.' })
      }
      // seems legit, go on...
      res.locals.text_to_analyze = preprocessed_text
      next()
    }
    ws.on('error', next) // or return res.status(500).json({ reason: 'whatever...' })
  } else {
    res.locals.text_to_analyze = req.body.text
    next() // nothing to see here, move on...
  }
}

function analyse (req, res, next) {
  axios.post(<URL to sentiment analyser>, res.locals.text_to_analyze)
    .then(reply => res.json(reply.data))
    .catch(error => {
      console.log(error)
      res.status(500).json({ reason: 'Sentiment service has blown up.' })
    })
}

我希望这会有所帮助！ :)

Answer 2

您可能希望将预处理和验证解耦为express middlewares，并将它们放在主处理程序的前面，这可能如下所示：

const validate = (req, res, next) => {
  const data = req.body;

  if (typeof data.text === 'undefined' || typeof data.shouldPreprocess === 'undefined') {
    return next(new Error('Please provide text and flag'));
  }
  return next();
}

const preprocess = (req, res, next) => {
  if (req.body.shouldPreprocess) {
    const ws = WebSocket('<URL of preprocessor>');
    ws.on('message', preprocText => {
      req.body.text = preprocText;
      next();
    });
  } else {
    next()
  }
}

router.post('/analyse', validate, preprocess, function (req, res, next) {
  const text = req.body.text;

  axios.post('<URL to sentiment analyser>', text)
    .then(doc => res.json(doc))
    .catch(err => next(err));
});