使用Node js从FTP服务器下载文件到客户端

Question

System architecture

System consist of 3 components

1: FTP server : Used to store files. Can only be accessed by Node.js app. No direct access.

2: Node.js : Provides an API to interact with FTP server . Only way to interact with FTP server . Node.js app have no collection of files stored on FTP. Only provides method to work with FTP. Node.js app should not store any file uploaded from it and download from it.

3: Client : A user how will upload or download a file to FTP server by using Node.js app .

What I have done :

I am able to download the file stored on FTP by using basic-ftp package. Here is the code for download file function.

async function downloadFile(folderPath, fileName, writeStream) {
    console.log(folderPath);
    console.log(fileName);
    const client = new ftp.Client()
    // client.ftp.verbose = true
    try {
        await client.access({
            'host': process.env.FTP_HOST,
            'user': process.env.FTP_USER,
            'password': process.env.FTP_PASSWORD,
        });
        await client.ensureDir(folderPath);
        await client.downloadTo(writeStream, fileName);
    }
    catch(err) {
        console.log(err)
    }
    client.close()
}

The file is download to the directory named /downloads on Node.js server. What I want to do actually is download the file directly to client computer. To download the file directly to client, I have tried streaming the writeStream object from download method. Here is the code for that

app.post("/download/file", urlencodedParser, (req, res, next) => {
    var writeStream = fs.createWriteStream('./downloads/'+req.body.fileName);
    writeStream.on("data", (data) => {
      res.write(data);
    })
    writeStream.on("close", () => {
      res.end()
    })

    res.setHeader('Transfer-Encoding', 'chunked');
    downloadFile(req.body.folderName, req.body.fileName, writeStream);
})

This does not work. It always ends in error with downloading the file completely.

Another approach I tried is to generate a URL for the file and client will click the URL to download the file. Problem with this approach is the file is not complete by the time I start downloading which results in incomplete file download. For example, If the size of file is 10MB and only 2 MB was download by the time client clicked the link, it will download only 2MB file not 10MB.

Goal :

Download the file to client(browser) from a FTP server through Node js.

Requirement :

Download the file stored on FTP server directly to client through Node js.

Constraints :

Client does not have access to FTP server.

The only way to access the server is through Node js app.

Answer 1

You can try to indicate res as an output stream directly. That way you will simply redirect a stream from an ftp to a client:

async function downloadFile(fileName, writeStream) {
    console.log(fileName);
    const client = new ftp.Client()
    // client.ftp.verbose = true
    try {
        await client.access({
            'host': process.env.FTP_HOST,
            'user': process.env.FTP_USER,
            'password': process.env.FTP_PASSWORD,
        });
        await client.downloadTo(writeStream, fileName);
    }
    catch(err) {
        console.log(err)
    }
    client.close()
}

app.post("/download/file", urlencodedParser, (req, res, next) => {
    downloadFile(req.body.fileName, res);
})