Nén Giảm Dung Lượng File PDF Trong JavaScript & Node.js

import { exec } from 'child_process';
import util from 'util';
import fs from 'fs';

const execAsync = util.promisify(exec);

export async function compressPdfWithGhostscript(
  inputPath: string,
  outputPath: string,
  quality: 'screen' | 'ebook' | 'printer' = 'ebook'
): Promise<{ originalSize: number; compressedSize: number; savingsRatio: string }> {
  // -dPDFSETTINGS:
  // /screen = lowest quality, smallest size (72 dpi)
  // /ebook  = moderate quality, great for web reading (150 dpi)
  // /printer = high quality (300 dpi)
  const gsCommand = [
    'gs',
    '-sDEVICE=pdfwrite',
    '-dCompatibilityLevel=1.4',
    `-dPDFSETTINGS=/${quality}`,
    '-dNOPAUSE',
    '-dQUIET',
    '-dBATCH',
    `-sOutputFile="${outputPath}"`,
    `"${inputPath}"`,
  ].join(' ');

  await execAsync(gsCommand);

  const origStats = fs.statSync(inputPath);
  const compStats = fs.statSync(outputPath);
  const savings = (((origStats.size - compStats.size) / origStats.size) * 100).toFixed(1);

  return {
    originalSize: origStats.size,
    compressedSize: compStats.size,
    savingsRatio: `${savings}%`,
  };
}

import { PDFDocument } from 'pdf-lib';

export async function optimizePdfInMemory(pdfBytes: Uint8Array): Promise<Uint8Array> {
  const pdfDoc = await PDFDocument.load(pdfBytes);
  // Re-saving with object stream optimization
  return await pdfDoc.save({ useObjectStreams: true });
}