Ubuntu – Node.js Multer: Intermittent File Upload Failures – Files Not Uploading to Server Randomly

I am facing an intermittent issue with file uploads using Multer in my Node.js application. The issue is that files are not always being uploaded to the server, and the req.files array sometimes contains only partial information about the files.

Description of the Issue:
In my application, users upload files through a browser, which are then saved in the state in React.js. The file types can be .pdf, .jpg, .step, .stp, .iges, .stl, etc. The following code is used to handle file selection and save the files in the state:

Note: I am using React DropZone for file uploading

const onSelectFile = async (filesData, ext) => {
  try {
    setIsQuoteChanged(true);
    const filesCollection = [...files];

    for (let file of filesData) {
      const singleValue = {
        selectedFile: file,
        partFileName: file?.path || file?.name,
        ...commandFields
      };

      valueCollection.push(singleValue);

      filesCollection.push({
        ...file,
        isNotFromMongoDB: true
      });
    }

    setFiles(filesCollection);
  } catch (err) {
    //Error handling
  }
};

When it’s time to submit the form, the following code appends the files to formData and makes the API call:

const saveApiCall = (user, updateType) => {
    return new Promise(async (resolve, reject) => {
      try {
        setLoading(true);
 
        let formData = new FormData();
        files.map((val, i) => {
          formData.append('selectedFile', val?.selectedFile || val)
        })

        for (const key in twoDFiles) {
          const value = twoDFiles[key];
          formData.append('twoDFiles', value?.file);
        }

        formData.append('twoDFilesData', JSON.stringify(twoDFiles))
        //other formdata appends.....

        if (_id) {
          const updateResponse = await postApi(`comman/update-quote/${_id}`, formData, token);
          return resolve(updateResponse.data);
        } else {
          const response = await postApi('comman/save-quote', formData, token);
          return resolve(response.data);
        }
      } catch (err) {
        //Error handling
      }
    })
  }


//code for postApi
export const postApi = async (endPoint, payload,token) => {
  return new Promise(async (resolve, reject) => {
    try {
      //code for headers

      let response = await axios.post(`${config.backEnd}/${endPoint}`, payload, { headers: header });
      return resolve(response.data);
    } catch (error) {
      return reject(error);
    }
  });
}

Backend Code:
Here’s the backend route handling the file upload using Multer:

const multer = require('multer');
const multerIns = multer();
const storage = multer.diskStorage({
  destination: (req, file, cb) => cb(null, 'public/uploads/'),
  filename: (req, file, cb) => cb(null, Date.now() + file.originalname),
});
const upload = multer({ storage: storage });


router.post('/save-quote', multerIns.any(), async (req, res) => {
  try {
    // code for userdata
    const response = await CommonController.createQuote(req.body, req.files, userData.userType)
    return res.status(200).send({ status: true, message: 'save data', data: response })
  } catch (err) {
    //error handling
  }
})

Issue:
Out of 100%, the code works fine in 95% of situations. However, at certain random moments, the files data is not available in req.files. Instead of receiving the complete file information, I get:

{
  path: <File name>
}

and the files are not available on the server. This issue is intermittent and cannot be replicated at will but is occurring more frequently in production, causing significant business impact.

Environment:
Node.js version: v18.14.0
Multer version: ^1.4.5-lts.1
Operating System: Ubuntu 20.04.5 LTS

Steps to Reproduce:
Set up a basic Node.js server with the above code.
Use an API client (e.g., Postman) to upload files repeatedly.
Observe that some files do not appear in the uploads/ directory.

Any insights or suggestions would be greatly appreciated. Thank you!

What I’ve Tried:
Ensured the upload directory exists and has the correct permissions.
Checked server logs for any errors (none found).
Increased the logging level to debug but still no useful information.

Questions:
What could be causing these random failures in file uploads?
Are there any known issues with Multer or its configuration that might lead to this behavior?
What additional debugging steps can I take to identify the root cause?