节点 FTP: 循环内的多个异步调用

Question

我知道这是我自己遇到的一些异步难题，但我正在尝试从 npm 的各种 FTP 包的任何 .list 方法的回调中下载多个文件。

所以像这样（注意：JSFTP 这里只是 node-ftp 的包装，我遇到了同样的问题）：

  ftp = new JSFTP(conf.FTPConfig)
  ftp.ls(conf.remoteFolder, (err, fileList) => {
    if (err) return console.error(err)

    for (let i=0; i<fileList.length; i++){
      file = fileList[i]
      ftp.get(file.name, `./Downloaded/${file.name}`, err => {
        if (err) return console.error(err)
        console.log(`${file.name} copied.`)
      })
    }
  })

如果我不使用循环，只下载一个文件，一切正常。但是在循环中，我不断收到以下错误并且我没有收到任何文件（除了一个或两个空文件占位符）：

（简而言之）：Error: 503 Bad sequence of commands，再往下：'Probably trying a PASV operation while one is in progress

看起来它在循环内启动了我所有的 .get 调用（显然没有等待它们中的任何一个完成，这很好），但是实际上没有执行所有 .get 调用方法？他们不应该只是运行并行、异步吗？

{ Error: 503 Bad sequence of commands.
    at Ftp.parse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:257:11)
    at Ftp.parseResponse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:174:8)
    at Stream.<anonymous> (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:146:24)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at ResponseParser.reemit (C:\Git\SenecaFTP\FTPMonitor\node_modules\duplexer\index.js:70:25)
    at emitOne (events.js:96:13)
    at ResponseParser.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:172:18)
    at ResponseParser.Readable.push (_stream_readable.js:130:10) code: 503 }
{ Error: 503 Bad sequence of commands.
    at Ftp.parse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:257:11)
    at Ftp.parseResponse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:174:8)
    at Stream.<anonymous> (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:146:24)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at ResponseParser.reemit (C:\Git\SenecaFTP\FTPMonitor\node_modules\duplexer\index.js:70:25)
    at emitOne (events.js:96:13)
    at ResponseParser.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:172:18)
    at ResponseParser.Readable.push (_stream_readable.js:130:10) code: 503 }
{ Error: 503 Bad sequence of commands.
    at Ftp.parse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:257:11)
    at Ftp.parseResponse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:174:8)
    at Stream.<anonymous> (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:146:24)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at ResponseParser.reemit (C:\Git\SenecaFTP\FTPMonitor\node_modules\duplexer\index.js:70:25)
    at emitOne (events.js:96:13)
    at ResponseParser.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:172:18)
    at ResponseParser.Readable.push (_stream_readable.js:130:10) code: 503 }
{ Error: 503 Bad sequence of commands.
    at Ftp.parse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:257:11)
    at Ftp.parseResponse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:174:8)
    at Stream.<anonymous> (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:146:24)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at ResponseParser.reemit (C:\Git\SenecaFTP\FTPMonitor\node_modules\duplexer\index.js:70:25)
    at emitOne (events.js:96:13)
    at ResponseParser.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:172:18)
    at ResponseParser.Readable.push (_stream_readable.js:130:10) code: 503 }
{ Error: 503 Bad sequence of commands.
    at Ftp.parse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:257:11)
    at Ftp.parseResponse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:174:8)
    at Stream.<anonymous> (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:146:24)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at ResponseParser.reemit (C:\Git\SenecaFTP\FTPMonitor\node_modules\duplexer\index.js:70:25)
    at emitOne (events.js:96:13)
    at ResponseParser.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:172:18)
    at ResponseParser.Readable.push (_stream_readable.js:130:10) code: 503 }
{ Error: 503 Bad sequence of commands.
    at Ftp.parse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:257:11)
    at Ftp.parseResponse (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:174:8)
    at Stream.<anonymous> (C:\Git\SenecaFTP\FTPMonitor\node_modules\jsftp\lib\jsftp.js:146:24)
    at emitOne (events.js:96:13)
    at Stream.emit (events.js:188:7)
    at ResponseParser.reemit (C:\Git\SenecaFTP\FTPMonitor\node_modules\duplexer\index.js:70:25)
    at emitOne (events.js:96:13)
    at ResponseParser.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:172:18)
    at ResponseParser.Readable.push (_stream_readable.js:130:10) code: 503 }
{ Error: connect ECONNREFUSED 192.168.100.161:61229
    at Object.exports._errnoException (util.js:1007:11)
    at exports._exceptionWithHostPort (util.js:1030:20)
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1080:14)
  code: 'ECONNREFUSED',
  errno: 'ECONNREFUSED',
  syscall: 'connect',
  address: '192.168.100.161',
  port: 61229,
  msg: 'Probably trying a PASV operation while one is in progress' }

Answer 1

在查看 jsftp 的源代码后，它似乎创建了一个连接并仅使用一个套接字：https://github.com/sergi/jsftp/blob/master/lib/jsftp.js#L120

这意味着它不会为每个命令创建一个新连接，而是使用一个连接来发送命令。基本上，您可以通过为每个要上传的文件创建一个新的 SFTP 实例来规避这种情况。

基本上将代码修改为：

ftp = new JSFTP(conf.FTPConfig)
  ftp.ls(conf.remoteFolder, (err, fileList) => {
    if (err) return console.error(err)

    for (let i=0; i<fileList.length; i++){
      file = fileList[i]
      new JSFTP(conf.FTPConfig).get(file.name, `./Downloaded/${file.name}`, err => {
        if (err) return console.error(err)
        console.log(`${file.name} copied.`)
      })
    }
  })

但是我建议使用某种流控制库，例如 async 或使用基于承诺的解决方案，因为它可能更易于管理。

在 SO 上也有类似的问题，使用我提到的 async 模块的类似解决方案：Downloading multiple file from ftp site using node js

节点 FTP: 循环内的多个异步调用

Node FTP: Multiple asynchronous calls inside loop

ftp

asynchronous

node.js

node-ftp