使用node.js和google app enginge下载ftp-data

Question

我在通过运行在Google应用引擎中的节点api从ftp服务器下载ftp数据（在这种情况下为pdf）时遇到问题。到目前为止，这是我的代码：

const Client = require('node-ftp')
const streams = require('memory-streams')

exports.downloadRekla = async function (req, res, next) {

let writer = new streams.WritableStream();

let c = new Client();
let config = {
    host: "xxx",
    user: "xxx",
    password: "xxx",
    secure: false
}
c.on('ready', function () {
    c.get(`${req.params.banr}_Reklamation.pdf`, function (err, stream) { 

        if (err) {
            // FTP Code 550 = Requested action not taken. File unavailable (e.g., file not found, no access).
            if (err.code == 550) {
                // Don't send if no file with this name exists
                console.log(`${req.params.banr}_Reklamation.pdf nicht vorhanden.`);
                res.status(200).send();
                c.end();
            } else {
                throw err;
            }
        } else {

            stream.once('close', function () {
                writer.end();
                console.log('send res');
                res.send(writer.toBuffer());
                c.end();
                console.log('bye');
            });
            console.log('write data in writable stream');
            stream.pipe(writer);    
            console.log('done writing stuff in stream')
        }
    });
});

c.on('error', function () {
    console.log('close connection');
    c.end();
    setTimeout(() => {
         console.log('attempting to reconnect');
    c.connect(config);
    console.log('reconnected');
    }, 2000);

});

console.log('attempting to connect to ftp server');
c.connect(config);
console.log('connected');}

问题是，我没有得到任何回应，只有502错误的网关...我在这里做错的任何见解？

此外，计划是将pdf数据写入可写流中，将其转换为缓冲区，然后在前端使用该数据制成pdf。