javascript - Node : Wait for all foreach with Promises to finish but never actually finishes

Question

我正在使用 Nodejs。我有一个异步的 forEach，因为我必须在 forEach 中等待结果。结果，我需要等待 forEach 完成，然后继续处理循环的结果。我找到了几种等待 forEach 的解决方案，其中之一是使用 Promises。虽然我做了，并且创建了这些 promise ，但是，forEach(以及 promise )完成后的代码从未真正执行(未打印 console.log)。并且 NodeJS 函数刚刚结束，没有任何错误。

这是我的代码:

var Client = require('ssh2').Client;

// eslint-disable-next-line no-undef
var csv = require("csvtojson");
// eslint-disable-next-line no-undef
var fs = require("fs");
// eslint-disable-next-line no-undef
const config = require('./config.json');
// eslint-disable-next-line no-undef
const os = require('os');
let headerRow = [];
let sumTxAmount = 0;

const filenameShortened = 'testFile';

let csvLists = [];
let csvFile;

const options = {
    flags: 'r',
    encoding: 'utf8',
    handle: null,
    mode: 0o664,
    autoClose: true
}

var conn = new Client();

async function start() {
    const list = await getCSVList();
    let content = fs.readFileSync('./temp.json', 'utf8');
    content = JSON.parse(content);
    var promises = list.map(function(entry) {
        return new Promise(async function (resolve, reject) {
            if (!content['usedFiles'].includes(entry.filename)) {
                const filename = entry.filename;
                csvFile = await getCsv(filename);
                csvLists.push(csvFile);
                console.log('here');
                resolve();
            } else {
                resolve();
            }
        })
    });
    console.log(promises)
    Promise.all(promises)
        .then(function() {
            console.log(csvLists.length, 'length');
        })
        .catch(console.error);
}

start();

“这里”被打印一次(不是 8 次，因为数组长度是 8)，但是创建了 8 个 promise 。我打印数组长度的下半部分没有执行。

谁能告诉我我做错了什么？我是否错误地使用了 Promises 和 forEach，因为我必须在 forEach 中执行等待？

注意:getCSVList() 和 getCsv() 是从 sftp 服务器获取 Csvs 的函数:

function getCSVList() {
    return new Promise((resolve, reject) => {
            conn.on('ready', function () {
                conn.sftp(function (err, sftp) {
                        if (err) throw err;
                        sftp.readdir(config.development.pathToFile, function (err, list) {
                            if(err) {
                                console.log(err);
                                conn.end();
                                reject(err);
                            } else {
                                console.log('resolved');
                                conn.end();
                                resolve(list);
                            }
                        })
                })
            }).connect({
                host: config.development.host,
                port: config.development.port, // Normal is 22 port
                username: config.development.username,
                password: config.development.password
                // You can use a key file too, read the ssh2 documentation
            });
    })
}

function getCsv(filename) {
    return new Promise((resolve, reject) => {
        conn.on('ready', function () {
        conn.sftp(function (err, sftp) {
            if (err) reject(err);
            let csvFile = sftp.createReadStream(`${config.development.pathToFile}/${filename}`, options);
            // console.log(csvFile);
            conn.end();
            resolve(csvFile);
        })
    }).connect({
        host: config.development.host,
        port: config.development.port, // Normal is 22 port
        username: config.development.username,
        password: config.development.password
        // You can use a key file too, read the ssh2 documentation
    });
});
} 

我的控制台中所有控制台日志的输出是:

`➜ node server.js
resolved
[ Promise { <pending> },
  Promise { <pending> },
  Promise { <pending> },
  Promise { <pending> },
  Promise { <pending> },
  Promise { <pending> },
  Promise { <pending> },
  Promise { <pending> } ]
here`

Answer 1

将您的问题分解成多个部分，确认它们在整个过程中都有效。

除其他外，您没有正确使用流。

我用 ssh2-sftp-client 制作了一个工作示例，因此您可以将其用作起点。

---

工作示例:

var fs = require('fs'); var _ = require('underscore');
var SFTPClient = require('ssh2-sftp-client');
const CONFIG = {
 "SSH_CONN_OPTS":{"host":"XXXXXXXX","port":22,"username":"XXXXXXXX","password":"XXXXXXXX"},
 "CSV_DIRECTORY":"/var/www/html"
}
//---------------
//.:The order-logic of the script is here
function StartScript(){
 console.log("[i] SSH Connection")
 LoadValidationFile(()=>{
  InitializeSFTP(()=>{ console.log("[+] SSH Connection Established")
   ListRemoteDirectory((list)=>{ console.log(`[i] Total Files @ ${CONFIG.CSV_DIRECTORY} : ${list.length}`)
    //console.log(list) //:now you have a 'list' of file_objects, you can iterate over to check the filename
    var csvFileList = [] //store the names of the files you will request after
    _.each(list,(list_entry)=>{ console.log(list_entry)
     if(!CONFIG.USED_FILES.includes(list_entry.name)){ csvFileList.push(list_entry.name) }
    }) 
    //:now loop over the new final list of files you have just validated for future fetch 
    GenerateFinalOutput(csvFileList)
   })
  })
 })
}
//.:Loads your validation file
function LoadValidationFile(cb){
 fs.readFile(__dirname+'/temp.json','utf8',(err,data)=>{ if(err){throw err}else{
  var content = JSON.parse(data)
  CONFIG.USED_FILES = content.usedFiles
  cb()
 }})
}
//.:Connects to remote server using CONFIG.SSH_CONN_OPTS
function InitializeSFTP(cb){
 global.SFTP = new SFTPClient();
 SFTP.connect(CONFIG.SSH_CONN_OPTS)
 .then(()=>{cb()})
 .catch((err)=>{console.log("[!] InitializeSFTP :",err)})
}
//.:Get a list of files from a remote directory
function ListRemoteDirectory(cb){
 SFTP.list(`${CONFIG.CSV_DIRECTORY}`)
     .then((list)=>{cb(list)})
     .catch((err)=>{console.log("[!] ListRemoteDirectory :",err)})
}
//.:Get target file from remote directory
function GetRemoteFile(filename,cb){
 SFTP.get(`${CONFIG.CSV_DIRECTORY}/${filename}`)
     .then((data)=>{cb(data.toString("utf8"))}) //convert it to a parsable string
     .catch((err)=>{console.log("[!] ListRemoteDirectory :",err)})
}
//-------------------------------------------
var csvLists = []
function GenerateFinalOutput(csv_files,current_index){ if(!current_index){current_index=0}
 if(current_index!=csv_files.length){ //:loop
  var csv_file = csv_files[current_index]
  console.log(`[i] Loop Step #${current_index+1}/${csv_files.length} : ${csv_file}`)
  GetRemoteFile(csv_file,(csv_data)=>{
   if(csv_data){csvLists.push(csv_data)}
   current_index++
   GenerateFinalOutput(csv_files,current_index)
  })
 }else{ //:completed
  console.log("[i] Loop Completed")
  console.log(csvLists)
 }
}
//------------
StartScript()

祝你好运!