Retrieve image from multer-GridFs-storage and mongoose

i'm stuck at displaying an image that i uploaded to mongodb with multer-gridfs-storage.

the problem is, i'm supposed to have binary data in every chunks and i want to join them to make the final file and encode it to base64

mongodb tell it's binary data but i'm not very sure mongodb chunks

here is my code:

multer.js:

const multer = require("multer");
const { GridFsStorage } = require("multer-gridfs-storage");
const db = require("../utils/database").db;


const storage = new GridFsStorage({ db });

module.exports = {
  upload: multer({
    storage: storage,
  })
};

my function to reassemble the file:

const getImage = (fileName) => {
  return files
    .find({ filename: fileName })
    .then((file) => {
      const id = mongoose.Types.ObjectId(file[0]._id);
      return chunks
        .find({ files_id: id })
        .then((chunks) => {
          if (!chunks || chunks.length === 0) {
            console.log("No data found");
          }
          let fileData = [];
          for (let i = 0; i < chunks.length; i++) {
            //This is in Binary JSON or BSON format, which is stored
            //in fileData array in base64 endocoded string format
            fileData.push(chunks[i].data.toString('base64');
          }

          //Display the chunks using the data URI format
          return (finalFile =
            "data:" + file[0].contentType + ";base64," + fileData.join(""));
        })
        .catch((err) => {
          console.log(err);
        });
    })
    .catch((err) => {
      console.log(err);
    });
};

and i have this kind of result with .toString('base64')

���R3\x17�\x18��bC4%\x19�rS5&񒢂��cDT6\'7\x1A�s�E���dUte�89\x11\x00\x02\x01\x02\x04\x03\x05\x07\x02\x04\x04\x05\x02\x03\x01\x11\x00\x01\x02\x11\x03!1\x12\x04AQ\x05aq"\x13\x06������2�\x07�B#\x14�R3\x15br$4\b�\x16���C%�S\x17D5&�c��s�Td6\t��\x00\f\x03\x01\x00\x02\x

and without .toString('base64')

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

thanks for your help !

Ok, i figured out what was the problem,

in my model chunks.js

const mongoose = require("mongoose");

const Schema = mongoose.Schema;

const chunks = new Schema({
  files_id: {
    type: mongoose.Schema.Types.ObjectId,
  },
  n: {
    type: Number,
  },
  data: {
    type: String,
  },
});

module.exports = mongoose.model("fs.chunks", chunks);

i had the type of data in 'String" instead of "Buffer"

it just work as expected with this

const mongoose = require("mongoose");

const Schema = mongoose.Schema;

const chunks = new Schema({
  files_id: {
    type: mongoose.Schema.Types.ObjectId,
  },
  n: {
    type: Number,
  },
  data: {
    type: Buffer,
  },
});

module.exports = mongoose.model("fs.chunks", chunks);