Merge 2 log files in nodejs - node.js

Question

I have a file saved in my server, suppose its path is data/x.log. I upload a new file to the server:
import { Injectable } from '#angular/core';
import { HttpClient } from '#angular/common/http';
import { Observable } from 'rxjs';
import { IResponse } from 'src/app/interfaces/response.interface';
import { environment } from 'src/environments/environment';
const ENDPOINT = environment.apiUrl + '/log';
#Injectable()
export class HttpUploadService {
constructor(
private http: HttpClient,
) { }
public uploadLogFile(file: File): Observable<IResponse> {
const baseUrl: string = ENDPOINT;
const postData = new FormData();
postData.append('file', file);
return this.http.post<IResponse>(baseUrl, { postData });
}
}
This is also a log file. My order is to merge these 2 files to the same location data/x.log path.
The merge is like append. just add the second file content after the first one.
How can I do it my server code with node.js?
This is my controller for this:
const saveLogFile = async (req, res) => {
}
In my first approach I tried to do it with multer package:
const storage = multer.diskStorage({
destination(req, file, cb) {
cb(null, './data');
},
filename(req, file, cb) {
cb(null, `x.log`);
}
});
But as far as I know it will just override the file content with no merge.
How can I do it?

Answer 1

I haven't heard of upload libraries supporting append. You'd most likely have to do it manually without using a library that automatically stores files on disk.
You could, for example, use busboy to access the incoming file as a stream and then append it to your desired file. Once you get a hold of the incoming stream, you can append to an existing file with something like:
const fs = require("fs");
const destination = fs.createWriteStream("data/x.log", {
flags: "a" // "a" for append
});
incomingFile.pipe(destination);