Automattic/node-canvas

Assertion failure when drawing after calling canvas.toBuffer() for PDF or SVG canvas

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#1,195 建立於 2018年7月2日

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 (0 留言) (0 反應) (0 負責人)JavaScript (9,524 star) (1,140 fork)batch import
BugHelp wanted

描述

Steps to Reproduce

const canvas = createCanvas(200,200,"svg")
const ctx = canvas.getContext("2d");
canvas.toBuffer()
ctx.fillRect(10,10,100,100) 
canvas.toBuffer()

results in

File: cairo-surface.c, Line 385

Expression: ! surface->finished

toBuffer has a call to cairo_surface_finish. After calling cairo_surface_finish() the only valid operations on a surface are getting and setting user, referencing and destroying, and flushing and finishing it.

We should at least catch that failure so the process doesn't crash. I don't see a way to actually let the canvas continue to be usable for drawing though. (Thought there might be an easy way to copy the content, but not seeing one.)

Your Environment

  • Version of node-canvas (e.g. 1.4.0): master @ b10d204
  • Environment (e.g. node 4.2.0 on Mac OS X 10.8): node 8.x, Win10 x64

貢獻者指南

技術棧
javascriptnodejs
領域
backend
議題類型
bug
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
half day
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
fresh
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
clear
前置要求
Basic knowledge of Node.js native addonsFamiliarity with Cairo graphics library
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
40
研究方向
The issue is caused by calling cairo surface finish() in toBuffer(), which marks the surface as finished, preventing further drawing. The fix should add error handling around the Cairo surface finish call in the toBuffer implementation. Check the Node.js binding code for toBuffer in the node canvas repository, likely in src/Canvas.cc or similar. Consider using cairo surface copy page or other methods to avoid finishing the surface prematurely. Also look at the referenced line in cairo surface.c to understand the assertion.