使用 Node.js、Async 和 Formidable 处理错误

Posted 2023-03-10

【中文标题】使用 Node.js、Async 和 Formidable 处理错误

【英文标题】：Error handling with Node.js, Async and Formidable

【发布时间】：2018-03-11 12:12:29

【问题描述】：

在下面的 sn-p 中，我想验证第一个异步方法中的字段。

如果它们无效，我想立即向用户返回一个错误。

我该怎么做？

var form = new formidable.IncomingForm();

async1.series([
    function (callback) 
        form.parse(req);

        form.on('field', function (name, val) 
            // Get the fields
        );

        form.on('fileBegin', function (name, file) 
            if (file.name !== "") 
                file.path = __dirname + '/upload/' + file.name;
            
        );
        callback();
    ,
    function (callback) 
        form.on('file', function (name, file) 
            try 
                // Do something with the file using the fields retrieved from first async method
            
            catch (err) 
                logger.info(err);
            
        );


        callback();
    
], function (err) 
    //the upload failed, there is nothing we can do, send a 500

    if (err === "uploadFailed") 
        return res.send(500);
    

    if (err) 
        throw err;
    
    return res.status(200);

);

【问题讨论】：

您可以立即从您正在检查字段的 if 块返回带有错误 return callback(err) 的回调，该回调将直接执行您发送 response code 的 callback handler function。

【参考方案1】：

我会将表单检查提取到一个函数中：

var form = new formidable.IncomingForm();

function check(name, cb, err) 
 return new Promise((res,rej) => 
  form.on('field', function(n, val) 
        if(n !== name) return;
        if(cb(val))
          res(val);
        else
          rej(err);
       
   );
 );


form.parse(req);

所以现在我们可以实现检查并使用 Promise.all 来总结它们：

 Promise.all(
   check("username", val => val.length > 4, "username isnt valid"),
   check("password", val => true, "we need a password")
 ).then(_ => res.json(status:200))
  .catch(err => res.json(err));

如果不是所有的参数都已传递，这将无休止地等待。因此，如果它已结束，让我们终止：

const ended = new Promise((_,rej) => form.on("end", () => rej("params required"));

Promise.race(
 ended,
  Promise.all(
   check("username", val => val.length > 4, "username isnt valid"),
   check("password", val => true, "we need a password")
  )
).then(_ => res.json(status:200))
 .catch(err => res.json(err));

因此，我们可以创建良好的数据流。例如：

const login = Promise.all(
  //usable as one liners
 check("username", val => val.length >= 8, "username invalid"),
 //or more extensible
 check("password", val => 
   if( val.length < 8 ) return false;
   //other checks
   console.log(password);
   return true;
 , "password invalid")
//the field values are resolved by the promises so we can summarize them below 
).then(([username,password]) =>
   //a random (maybe async) call to evaluate the credentials
  checkAgainstDB(username,password)
  //we can directly fail here, err is  "password invalid" or "username invalid"
).catch(err => res.json(error:"login failed",details:err));

 //another parameter can be extra handled    
const data = check("something", val => val.length);

//we need to summarize all the possible paths (login /data in this case) to one that generates the result
Promise.race(
 //here we join them together
 Promise.all(login, data)
   .then((l, d) => res.json(whatever),
 //and we use the ended promise ( from above ) to end the whole thing
 ended
  //and at last the errors that can occur if the response ended or that have not been canceled early
).catch(e => res.json(e));

【参考方案2】：

var form = new formidable.IncomingForm();

async1.series([
    function (callback) 
        form.parse(req);

        form.on('field', function (name, val) 
            if (!name || !val) 
              // the moment callback is called with an error, async will stop execution of any of the steps
              // in the series and execute the function provided as the last argument
              // idimoatic node, when calling the callback with instance of Error
              return callback(new Error('InvalidParams'));
            

            /**
             * This is from async documentation: https://caolan.github.io/async/docs.html#series
             * Run the functions in the tasks collection in series, each one running once the previous function 
             * has completed. If any functions in the series pass an error to its callback, no more functions are 
             * run, and callback is immediately called with the value of the error. Otherwise, callback receives 
             * an array of results when tasks have completed.
             */
        );

        form.on('fileBegin', function (name, file) 
            if (file.name !== "") 
                file.path = __dirname + '/upload/' + file.name;
            
        );

        form.on('end', function () 
          // call callback with null to specify there's no error
          // if there are some results, call it like callback(null, results);
          return callback(null);
        );

        // if you call the callback immediately after registering event handlers for on('field') etc,
        // there will be no time for those events to be triggered, by that time, this function will be 
        // done executing.
        //callback();
    ,
    function (callback) 
        form.on('file', function (name, file) 
            try 
                // Do something with the file using the fields retrieved from first async method
            
            catch (err) 
                logger.info(err);
                return callback(err);
            
        );

        // This should also not be called immediately
        //callback();
    
], function (err) 
    //the upload failed, there is nothing we can do, send a 500

    if (err === "uploadFailed") 
        return res.send(500);
    

    if (err.message === 'InvalidParams') 
      // This will be immediately returned to the user.
      return res.sendStatus(400);
    

    if (err) 
      // I'm not sure if this was just for the example, but if not, you should not be throwing an error
      // at run time. 
        throw err;
    
    return res.status(200);

);

我在代码中添加了一些 cmets，我需要显示在何处以及如何创建错误以及如何立即将其冒泡给用户。

参考：Async Documentation

附：代码片段不可运行，但它具有更好的代码表示。

-- 编辑--

从评论中了解更多后，添加另一个sn-p。您不合理地混合了回调和事件处理。您可以只将回调传递给 form.parse 并在收集所有字段时调用回调。您可以进行验证、立即返回错误或直接处理表单字段。

form.parse(req, function(err, fields, files) 
  if (err) return res.sendStatus(400);
  if (fields.areNotValid()) return res.sendStatus(400);
  // parse fields
);

或者，您可以为其注册事件处理程序。流入的所有事件都将同时处理，例如 async.series。

var form = new formidable.IncomingForm();

form.parse(req);
form.on('field', (name, val) => 
  if (!name || val) 
    console.log('InvalidParams')
    return res.sendStatus(400);
  
);
form.on('fileBegin', (name, file) => 
  if (file.name !== "") 
    file.path = __dirname + '/upload/' + file.name;
  
);
form.on('file', (name, file) => 

);
form.on('error', (err) => 
  console.log('ParsingError');
  return res.sendStatus(400);
)
form.on('end', () => 
  if (res.headersSent) 
    console.log('Response sent already')
   else 
    // handle what you want to handle at the end of the form when all task in series are finished
    return res.sendStatus(200);
  
);

【讨论】：

这会在我们返回错误时导致 callback() is already called 错误。 form.on('end') 中的回调抛出错误

@Robben_Ford_Fan_boy 明白了！我现在更好地理解了这个问题并更新了我的答案。请检查修改，如果有帮助，请告诉我。

【参考方案3】：

我假设这是一个验证的好地方，因为这是字段进入的时候：

form.on('field', function (name, val) 
    //if values are null
    if (!name || !val) 
        //pass the callback an error 
        return callback("Values are null")
    
    // Get the fields
);

如果这有帮助，请告诉我。

【讨论】：

错误被抛出到哪里？有没有办法将错误返回给 API 调用？

在我的代码中，我相信它会通过错误参数发送到异步系列中的最后一个函数。要将其发送到 API 调用（我假设类似 Express），也许您可​​以执行 'return res.send('Values are null')