节点FTP：循环内有多个异步调用

Question

我知道这是我遇到的一个异步难题，但是我正在尝试从npm的各种FTP软件包中的.list方法的回调中下载多个文件。

所以是这样的（注意：这里的JSFTP只是node-ftp的包装器，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，而仅下载一个文件，则一切正常。 但是通过循环，我不断收到以下错误，但没有任何文件（一个或两个空文件占位符除外）：

（简而言之）： Error: 503 Bad sequence of commands ，以及更进一步的内容： 'Probably trying a PASV operation while one is in progress

看起来它在循环内启动了我的所有.get调用（显然不等待它们中的任何一个完成，这很好），但是随后是否无法以这种方式实际执行所有.get调用？ 他们不应该只是异步并行运行吗？

{ 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的源代码之后，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新的连接，而是使用单个连接来发送命令。 基本上，您可以通过为要上传的每个文件创建一个新的SFTP实例来规避该问题。

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，我建议您使用某种流控制库（例如async或使用基于Promise的解决方案，因为它可能更易于管理。

使用我提到的async模块，使用类似的解决方案在SO上也存在类似的问题： 使用节点js从ftp站点下载多个文件