index.js

const fs = require('fs')
const { performance } = require('perf_hooks')
const globby = require('globby')

const { mergeWithDefaultPolicies, createFileProcessor, buildCSPArray, splitToGlobalAndLocal } = require('./functions.js')

module.exports = {
  onPostBuild: async ({ inputs }) => {
    const startTime = performance.now()

    const {
      buildDir,
      exclude,
      policies,
      disablePolicies,
      disableGeneratedPolicies,
      reportOnly,
      reportURI,
      reportTo,
      generateForAllFiles,
      debug,
    } = inputs

    const mergedPolicies = mergeWithDefaultPolicies(policies)

    const htmlFiles = `${buildDir}/**/**.html`
    const excludeFiles = (exclude || []).map((filePath) => `!${buildDir}/${filePath.replace(/^!/, '')}`)
    console.info(`Excluding ${excludeFiles.length} ${excludeFiles.length === 1 ? 'file' : 'files'}`)

    const lookup = [htmlFiles].concat(excludeFiles)
    const paths = await globby(lookup)
    console.info(`Found ${paths.length} HTML ${paths.length === 1 ? 'file' : 'files'}`)

    if (debug === true) {
      console.log('Lookup:', lookup)
      console.log('Paths:', paths)

      const excludedLookup = (exclude || []).map((filePath) => `${buildDir}/${filePath.replace(/^!/, '')}`)
      const excludedPaths = await globby(excludedLookup)

      console.log(`Excluded ${excludedPaths.length} ${excludedPaths.length === 1 ? 'path' : 'paths'}`)
      console.log('Excluded:', excludedPaths)
    }

    const processFile = createFileProcessor(buildDir, disableGeneratedPolicies, generateForAllFiles)

    const processedFileHeaders = await Promise.all(
      paths.map(path => fs.promises.readFile(path, 'utf-8').then(processFile(path)))
    )

    const { globalHeaders, localHeaders } = processedFileHeaders
      .reduce(splitToGlobalAndLocal, { globalHeaders: [], localHeaders: [] })

    const file = globalHeaders.concat(...localHeaders)
      .map(({ webPath, cspObject }) => {
        const cspArray = buildCSPArray(mergedPolicies, disablePolicies, cspObject)
        if (reportURI) {
          cspArray.push(`report-uri ${reportURI};`)
        }
        if (reportTo) {
          cspArray.push(`report-to ${reportTo};`)
        }
        const cspString = cspArray.join(' ')
        const headerType = reportOnly ? 'Content-Security-Policy-Report-Only' : 'Content-Security-Policy'

        return `${webPath}\n  ${headerType}: ${cspString}`
      }).join('\n')

    fs.appendFileSync(`${buildDir}/_headers`, file)

    const completedTime = performance.now() - startTime
    console.info(`Saved at ${buildDir}/_headers - ${(completedTime / 1000).toFixed(2)} seconds`)
  },
}