使用 Node.js 将上传的文件流转发到另一台服务器

Question

我正在构建一个连接到 DMS (Alfresco) 的 Angular / Node.js 应用程序。服务器端 Node.js / Express 层充当代理，向客户端隐藏 Alfresco 的复杂性：

Angular client <--> Node backend <--> Alfresco

这个问题仅与 Node.js 后端有关。

上传文件时，我想将传入的文件直接转发到 Alfresco，而不临时将其存储在磁盘上。使用临时磁盘存储，这可以按预期工作：

const fileUpload = require('express-fileupload');
const FormData = require('form-data');

// app is the express object
app.use(fileUpload({ createParentPath: true }));

app.post('/file', async (req, res) => {

    // filedata is the FormData field of the client containing the actual file
    let file = req.files.filedata;
    let tmpPath = __dirname + '/tmp/' + file.name;

    // save the file temporarily on the server
    file.mv(tmpPath, async function(err) {

        // create a new FormData Object for the upload to the DMS
        const formData = new FormData();
        formData.append('name', name);
        // creates an fs.ReadStream object which is inherited from stream.Readable
        formData.append('filedata', fs.createReadStream(tmpPath));
    
        // upload the file to the DMS
        let response = await axios.post('/files/...', formData, { headers: formData.getHeaders() });
        
        // remove the temporary file
        fs.rm(tmpPath, () => {

            // return the answer of the DMS to the client
            res.send(response.data);
        });
    });
});

现在我想避免磁盘访问并将文件直接转发到 DMS。考虑到 在 Node.js 中将缓冲区转换为 ReadableStream 我尝试了以下三种替代方案。

const { Readable } = require('stream');

app.post('/file', async (req, res) => {
    let file = req.files.fileData;

    // create a new FormData Object for the upload to the DMS
    const formData = new FormData();
    formData.append('name', name);

    /* alternatives starting here */
    // Source: https://stackoverflow.com/questions/13230487/
    
    // #1
    const readable = new Readable();
    readable._read = () => {};
    readable.push(file.data);
    readable.push(null);
    
    // #2
    const readable = new Readable();
    readable._read = () => {};
    const buffer = new Buffer(file.data, 'utf-8');
    readable.push(buffer);  
    readable.push(null);
    
    // #3
    const readable = Readable.from(file.data);

    /* alternatives ending here */

    // put the Readable into the FormData object
    formData.append('filedata', readable);

    // upload the file to the DMS
    let response = await axios.post('/files/...', formData, { headers: formData.getHeaders() });

    // return the answer of the DMS to the client
    res.send(response.data);
});

无论我尝试什么选择，Alfresco 总是抱怨，必填字段会丢失。尽管如此，还是提供了所有必填字段，因为临时存储文件的示例工作正常。我认为，Alfresco 无法处理我提供的流，并且我无法完全理解流在这种情况下如何工作。我应该采取什么不同的做法？

请注意，为了可读性，所有错误处理以及 Alfresco 请求配置/API URL 均被省略。

Answer 1

尝试提供文件相关信息，例如文件名、knownLength 等。

let file = req.files.fileData;

const formData = new FormData();
// buffer with file related info
formData.append(name, file.data, {
    filename: file.name,
    contentType: file.mimetype,
    knownLength: file.size
});

// upload the file to the DMS
let response = await axios.post('/files/...', formData, {headers: formData.getHeaders() });

// return the answer of the DMS to the client
res.send(response.data);