How can I convert a file from an external link to a buffer using Nest.js?

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To convert a file from an external link to a buffer using Nest.js, you can use the built-in http or https module in Node.js to make a GET request to the external link and then convert the response data into a buffer using the Buffer.from() method. Here's an example implementation:

import { Injectable } from '@nestjs/common';
import { http, https } from 'follow-redirects';
import { Buffer } from 'buffer';

@Injectable()
export class FileService {
  async getFileFromURL(url: string): Promise<Buffer> {
    const isHTTPS = url.startsWith('https://');
    const client = isHTTPS ? https : http;
    return new Promise<Buffer>((resolve, reject) => {
      const req = client.get(url, (res) => {
        const chunks = [];
        res.on('data', (chunk) => chunks.push(chunk));
        res.on('end', () => {
          const buffer = Buffer.concat(chunks);
          resolve(buffer);
        });
      });
      req.on('error', (err) => reject(err));
    });
  }
}

Here, we define a getFileFromURL method in a FileService class that takes a URL string as input and returns a Promise that resolves to a buffer. In the method, we first check whether the URL starts with https:// or http:// and use the respective Node.js module to make a GET request to the URL. We then listen for the response data event and push each chunk of data into an array. When the response end event is emitted, we concatenate all the data chunks into a single buffer using Buffer.concat() and resolve the Promise with it. If there's an error during the request, we reject the Promise with the error object.