SSR performance issue with HTML in markdown

[jsonmaur]

I've found a strange bug in v6.6.8 that is seriously impacting performance during SSR. When the markdown contents have a specific combination of colons and HTML, it sometimes takes around 30-40 seconds to render (on a 2.6GHz i5 Mac Mini), and will occasionally completely freeze. It also pushes the CPU usage to 100% for the entire duration of the program.

We had some auto-triggered builds that were generating large static markdown sites, and the builds started to freeze and timeout since 6.6.8 was released. I've put together a simple example that is able to replicate this on a small scale:

index.js

import fs from 'fs'
import React from 'react'
import Markdown from 'markdown-to-jsx'
import { renderToString } from 'react-dom/server'

// renders immediately
const good = `# This is a normal markdown file. <a href="/">Foo Bar</a>`
console.log(renderToString(<Markdown>{good}</Markdown>))

// takes a long time with high CPU
const bad = `Lorum *ipsum*: <a href="" style="float: right"><small>foo</small></a><span style="float: right"><small>&nbsp;</small></span><a href="" style="float: right"><small>bar</small></a>`
console.log(renderToString(<Markdown>{bad}</Markdown>))

package.json

{
  "scripts": {
    "start": "babel-node index.js"
  },
  "dependencies": {
    "babel-cli": "6.26.0",
    "babel-core": "6.26.3",
    "babel-preset-env": "1.7.0",
    "babel-preset-react": "6.24.1",
    "markdown-to-jsx": "6.6.8",
    "react": "16.4.1",
    "react-dom": "16.4.1"
  },
  "babel": {
    "presets": [
      "env",
      "react"
    ]
  }
}

I haven't been able to nail down exactly which part of the bad markdown string is causing the issue, as removing different pieces will make the render time fluctuate--sometimes making it longer, sometimes shorter. It's weird. Downgrading to v6.6.7 fixes the issue.

[quantizor]

Might be a funky regex recursion situation. I’ll take a look!

[quantizor]

Fixed in 6.6.9