HTTP Range Request: Tải Từng Phần Tệp Với Mã HTTP 206 Partial Content

# Yêu cầu chỉ 500 byte đầu tiên (để kiểm tra magic header)
curl -r 0-499 -i "https://filedummy.dev/api/download?type=pdf&size=10mb"

import fs from 'fs';
import { IncomingMessage, ServerResponse } from 'http';

export function handleRangeRequest(req: IncomingMessage, res: ServerResponse, filePath: string) {
  const stat = fs.statSync(filePath);
  const total = stat.size;
  const range = req.headers.range;

  if (!range) {
    res.writeHead(200, {
      'Content-Length': total,
      'Content-Type': 'application/pdf',
      'Accept-Ranges': 'bytes',
    });
    fs.createReadStream(filePath).pipe(res);
    return;
  }

  const parts = range.replace(/bytes=/, '').split('-');
  const start = parseInt(parts[0], 10);
  const end = parts[1] ? parseInt(parts[1], 10) : total - 1;
  const chunksize = end - start + 1;

  res.writeHead(206, {
    'Content-Range': `bytes ${start}-${end}/${total}`,
    'Accept-Ranges': 'bytes',
    'Content-Length': chunksize,
    'Content-Type': 'application/pdf',
  });

  const stream = fs.createReadStream(filePath, { start, end });
  stream.pipe(res);
}