unpkg/server/middleware/utils/getPackageInfo.js

require('isomorphic-fetch')
const createCache = require('./createCache')
const createMutex = require('./createMutex')

const RegistryURL = process.env.NPM_REGISTRY_URL || 'https://registry.npmjs.org'

const PackageInfoCache = createCache('packageInfo')

function fetchPackageInfo(packageName) {
  console.log(`info: Fetching package info for ${packageName}`)

  let encodedPackageName
  if (packageName.charAt(0) === '@') {
    encodedPackageName = `@${encodeURIComponent(packageName.substring(1))}`
  } else {
    encodedPackageName = encodeURIComponent(packageName)
  }

  const url = `${RegistryURL}/${encodedPackageName}`

  return fetch(url, {
    headers: {
      Accept: 'application/json'
    }
  }).then(function(res) {
    return res.status === 404 ? null : res.json()
  })
}

const PackageNotFound = 'PackageNotFound'

// This mutex prevents multiple concurrent requests to
// the registry for the same package info.
const fetchMutex = createMutex(function(packageName, callback) {
  fetchPackageInfo(packageName).then(
    function(value) {
      if (value == null) {
        // Cache 404s for 5 minutes. This prevents us from making
        // unnecessary requests to the registry for bad package names.
        // In the worst case, a brand new package's info will be
        // available within 5 minutes.
        PackageInfoCache.set(packageName, PackageNotFound, 300, function() {
          callback(null, value)
        })
      } else {
        // Cache valid package info for 1 minute.
        PackageInfoCache.set(packageName, value, 60, function() {
          callback(null, value)
        })
      }
    },
    function(error) {
      // Do not cache errors.
      PackageInfoCache.del(packageName, function() {
        callback(error)
      })
    }
  )
})

function getPackageInfo(packageName, callback) {
  PackageInfoCache.get(packageName, function(error, value) {
    if (error || value != null) {
      callback(error, value === PackageNotFound ? null : value)
    } else {
      fetchMutex(packageName, packageName, callback)
    }
  })
}

module.exports = getPackageInfo