The PDF file created by createPDFStream becomes larger in size, and createWriteStream is very slow #2615

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1. 948764321

   added

   Bug

   on Aug 21, 2026
2. chearon commented on Aug 25, 2026

   

   chearon

   on Aug 25, 2026

   Collaborator

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   Can you provide a minimal script to reproduce the problem? Also, does the issue happen in 3.2.3 or just 4.0.0-rc3?
3. 948764321 commented on Sep 2, 2026

   

   948764321

   on Sep 2, 2026

   Author

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   Can you provide a minimal script to reproduce the problem? Also, does the issue happen in 3.2.3 or just 4.0.0-rc3?

   // Minimal repro: node-canvas 4.0.0-rc3 PDF export is slow and huge vs 3.2.3
   // Run:  npm i canvas@3.2.3     && node repro-issue.js
   //       npm i canvas@4.0.0-rc3 && node repro-issue.js
   'use strict'
   const fs = require('fs')
   const { createCanvas } = require('canvas')
   const version = require('canvas/package.json').version
   
   const PAGES = 10          // A4 pages
   const LINES = 45          // body text lines per page
   const BODY = '汉字性能测试：落霞与孤鹜齐飞，秋水共长天一色，共二十五个全角字符。'
   const out = `out-${version}.pdf`
   
   async function main() {
     const t0 = Date.now()
     const canvas = createCanvas(595.28, 841.89, 'pdf')
     const ctx = canvas.getContext('2d')
     ctx.textDrawingMode = 'glyph'
   
     for (let p = 0; p < PAGES; p++) {
       if (p > 0) ctx.addPage(595.28, 841.89)
       ctx.fillStyle = '#ffffff'
       ctx.fillRect(0, 0, 595.28, 841.89)
       ctx.fillStyle = '#000000'
       ctx.font = 'bold 16px "sans-serif"'
       ctx.fillText(`Heading ${p + 1}`, 72, 80)
       ctx.font = '10.5px "sans-serif"'
       for (let i = 0; i < LINES; i++) ctx.fillText(`${BODY} (${i + 1})`, 72, 120 + i * 16)
       ctx.strokeStyle = '#333333'
       ctx.lineWidth = 0.5
       ctx.strokeRect(72, 780, 451, 60)
     }
     const drawMs = Date.now() - t0
   
     const t1 = Date.now()
     await new Promise((res, rej) => {
       const ws = fs.createWriteStream(out)
       const s = canvas.createPDFStream()
       s.on('error', rej); ws.on('error', rej); ws.on('finish', res)
       s.pipe(ws)
     })
     const exportMs = Date.now() - t1
   
     console.log(JSON.stringify({
       version, pages: PAGES, linesPerPage: LINES,
       drawMs, exportMs, totalMs: drawMs + exportMs,
       pdfMB: +(fs.statSync(out).size / 1048576).toFixed(2),
     }, null, 2))
   }
   
   main().catch(e => { console.error(e); process.exit(1) })

   result

   {
     "version": "4.0.0-rc3",
     "pages": 10,
     "linesPerPage": 45,
     "drawMs": 2422,
     "exportMs": 3240,
     "totalMs": 5662,
     "pdfMB": 26.91
   }
   
   {
     "version": "3.2.3",
     "pages": 10,
     "linesPerPage": 45,
     "drawMs": 113,
     "exportMs": 29,
     "totalMs": 142,
     "pdfMB": 0.076
   }