check-links.js

const { readdir, stat, readFile } = require('fs').promises
const { resolve } = require('path')
const http = require('http')
const https = require('https')

// Recursively search for files matching the pattern in a directory
const searchRecursive = async (dir, pattern) => {
  let results = []
  const files = await readdir(dir)

  await Promise.all(
    files.map(async (dirInner) => {
      const resolvedPath = resolve(dir, dirInner)
      const statResult = await stat(resolvedPath)

      if (statResult.isDirectory()) {
        const nestedResults = await searchRecursive(resolvedPath, pattern)
        results = results.concat(nestedResults)
      }
      if (statResult.isFile() && resolvedPath.endsWith(pattern)) {
        results.push(resolvedPath)
      }
    })
  )
  return results
}

const checkLinks = async () => {
  const files = await searchRecursive('./src/book', '.mdx')
  const externalLinksList = []

  // Loop through the mdx files to find all links
  let count = 0
  await Promise.all(
    files.map(async (file) => {
      const content = await readFile(file, 'utf-8')
      const array = content.split('\n')
      const reBrackets = /\((.*?)\)/g

      array.forEach((line) => {
        let found
        while ((found = reBrackets.exec(line)) !== null) {
          const t = found[1].split(' ', 1)[0]
          if (t.includes('/')) {
            if (t.startsWith('http') && !t.includes('localhost')) {
              count++
              externalLinksList.push({ link: t, file })
            }
          }
        }
      })
    })
  )

  // Send HTTP/HTTPS HEAD request to check if the link exists
  const sendHTTPRequest = (linkURL) => {
    return new Promise((resolve) => {
      const client = linkURL.startsWith('https') ? https : http
      const req = client.request(
        linkURL,
        { method: 'HEAD', timeout: 5000 },
        (res) => {
          resolve(res.statusCode)
        }
      )
      req.on('error', () => resolve(null))
      req.end()
    })
  }

  // Check all external links with a queue
  const queue = []
  const concurrency = 5

  for (const { link, file } of externalLinksList) {
    const promise = sendHTTPRequest(link).then((statusCode) => {
      if (statusCode === 404) {
        console.log(`Broken link: ${link}\n\tFound in file: ${file}`)
      }
    })
    queue.push(promise)

    if (queue.length >= concurrency) {
      await Promise.race(queue)
      queue.splice(
        queue.findIndex((p) => p === promise),
        1
      )
    }
  }

  await Promise.all(queue)
  console.log('External Links found:', count)
}

checkLinks()