Prevent multiple concurrent requests for package info

server/PackageInfo.js

@@ -0,0 +1,68 @@
+require('isomorphic-fetch')
+const PackageInfoCache = require('./PackageInfoCache')
+const createMutex = require('./createMutex')
+
+const RegistryURL = process.env.NPM_REGISTRY_URL || 'https://registry.npmjs.org'
+
+function fetchPackageInfo(packageName) {
+  console.log(`Fetching info for package ${packageName} from NPM`)
+
+  let encodedPackageName
+  if (packageName.charAt(0) === '@') {
+    encodedPackageName = `@${encodeURIComponent(packageName.substring(1))}`
+  } else {
+    encodedPackageName = encodeURIComponent(packageName)
+  }
+
+  const url = `${RegistryURL}/${encodedPackageName}`
+
+  return fetch(url, {
+    headers: { 'Accept': 'application/json' }
+  }).then(function (response) {
+    return response.status === 404 ? null : response.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 one 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) {
+      callback(error)
+    } else if (value) {
+      callback(null, value === PackageNotFound ? null : value)
+    } else {
+      fetchMutex(packageName, callback)
+    }
+  })
+}
+
+module.exports = {
+  get: getPackageInfo
+}

server/PackageInfoCache.js

@@ -0,0 +1,29 @@
+const redis = require('redis')
+
+const RedisURL = process.env.OPENREDIS_URL || 'redis://localhost:6379'
+
+const db = redis.createClient(RedisURL)
+
+function createKey(packageName) {
+  return 'packageInfo-' + packageName
+}
+
+function set(packageName, value, expiry, callback) {
+  db.setex(createKey(packageName), expiry, JSON.stringify(value), callback)
+}
+
+function get(packageName, callback) {
+  db.get(createKey(packageName), function (error, value) {
+    callback(error, value && JSON.parse(value))
+  })
+}
+
+function del(packageName, callback) {
+  db.del(createKey(packageName), callback)
+}
+
+module.exports = {
+  set,
+  get,
+  del
+}

server/createMutex.js

@@ -0,0 +1,21 @@
+function createMutex(doWork) {
+  const mutex = {}
+
+  return function (key, callback) {
+    if (mutex[key]) {
+      mutex[key].push(callback)
+    } else {
+      mutex[key] = [ function () {
+        delete mutex[key]
+      }, callback ]
+
+      doWork(key, function (error, value) {
+        mutex[key].forEach(function (callback) {
+          callback(error, value)
+        })
+      })
+    }
+  }
+}
+
+module.exports = createMutex

server/index.js

@@ -102,7 +102,6 @@ const defaultServerConfig = {
   publicDir: 'public',
 
   // for the middleware
-  registryURL: process.env.REGISTRY_URL || 'https://registry.npmjs.org',
   autoIndex: !process.env.DISABLE_INDEX,
   blacklist: require('./PackageBlacklist').blacklist
 }

server/middleware/RegistryCache.js

@@ -1,27 +0,0 @@
-const redis = require('redis')
-
-const RedisURL = process.env.OPENREDIS_URL || 'redis://localhost:6379'
-
-const db = redis.createClient(RedisURL)
-
-const createKey = (key) => 'registryCache-' + key
-
-const set = (key, value, expiry) => {
-  db.setex(createKey(key), expiry, JSON.stringify(value))
-}
-
-const get = (key, callback) => {
-  db.get(createKey(key), (error, value) => {
-    callback(error, value && JSON.parse(value))
-  })
-}
-
-const del = (key) => {
-  db.del(createKey(key))
-}
-
-module.exports = {
-  set,
-  get,
-  del
-}

server/middleware/RegistryUtils.js

@@ -2,57 +2,8 @@ require('isomorphic-fetch')
 const gunzip = require('gunzip-maybe')
 const mkdirp = require('mkdirp')
 const tar = require('tar-fs')
-const RegistryCache = require('./RegistryCache')
 
-const getPackageInfoFromRegistry = (registryURL, 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(response => (
-    response.status === 404 ? null : response.json()
-  ))
-}
-
-const PackageNotFound = 'PackageNotFound'
-
-const getPackageInfo = (registryURL, packageName, callback) => {
-  RegistryCache.get(packageName, (error, value) => {
-    if (error) {
-      callback(error)
-    } else if (value) {
-      callback(null, value === PackageNotFound ? null : value)
-    } else {
-      getPackageInfoFromRegistry(registryURL, packageName).then(value => {
-        if (value == null) {
-          // Keep 404s in the cache 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.
-          RegistryCache.set(packageName, PackageNotFound, 300)
-        } else {
-          // Keep package.json in the cache for a minute.
-          RegistryCache.set(packageName, value, 60)
-        }
-
-        callback(null, value)
-      }, error => {
-        // Do not cache errors.
-        RegistryCache.del(packageName)
-        callback(error)
-      })
-    }
-  })
-}
-
-const normalizeTarHeader = (header) => {
+function normalizeTarHeader(header) {
   // Most packages have header names that look like "package/index.js"
   // so we shorten that to just "index.js" here. A few packages use a
   // prefix other than "package/". e.g. the firebase package uses the
@@ -61,7 +12,7 @@ const normalizeTarHeader = (header) => {
   return header
 }
 
-const getPackage = (tarballURL, outputDir, callback) => {
+function getPackage(tarballURL, outputDir, callback) {
   mkdirp(outputDir, (error) => {
     if (error) {
       callback(error)
@@ -92,6 +43,5 @@ const getPackage = (tarballURL, outputDir, callback) => {
 }
 
 module.exports = {
-  getPackageInfo,
   getPackage
 }

server/middleware/fetchPackage.js

@@ -2,8 +2,9 @@ const fs = require('fs')
 const path = require('path')
 const tmpdir = require('os-tmpdir')
 const { maxSatisfying: maxSatisfyingVersion } = require('semver')
+const PackageInfo = require('../PackageInfo')
 const { createPackageURL } = require('./PackageUtils')
-const { getPackageInfo, getPackage } = require('./RegistryUtils')
+const { getPackage } = require('./RegistryUtils')
 
 function checkLocalCache(dir, callback) {
   fs.stat(path.join(dir, 'package.json'), function (error, stats) {
@@ -19,20 +20,20 @@ function createTempPath(name) {
  * Fetch the package from the registry and store a local copy on disk.
  * Redirect if the URL does not specify an exact req.packageVersion number.
  */
-function fetchPackage(registryURL) {
+function fetchPackage() {
   return function (req, res, next) {
     req.packageDir = createTempPath(req.packageSpec)
 
     // TODO: fix race condition! (see #38)
-    // TODO: ensure req.packageInfo is always populated so we can re-use later
     checkLocalCache(req.packageDir, function (isCached) {
       if (isCached)
         return next() // Best case: we already have this package on disk.
 
-      // Fetch package info from NPM.
-      getPackageInfo(registryURL, req.packageName, function (error, packageInfo) {
-        if (error)
-          return res.status(500).send(error.message || error)
+      PackageInfo.get(req.packageName, function (error, packageInfo) {
+        if (error) {
+          console.error(error)
+          return res.status(500).send(`Cannot get info for package "${req.packageName}"`)
+        }
 
         if (packageInfo == null || packageInfo.versions == null)
           return res.status(404).send(`Cannot find package "${req.packageName}"`)

server/middleware/index.js

@@ -25,8 +25,7 @@ const serveFile = require('./serveFile')
  * /history@latest/umd/History.min.js (redirects to version)
  * /history@^1/umd/History.min.js (redirects to max satisfying version)
  */
-const createRequestHandler = (options = {}) => {
-  const registryURL = options.registryURL || 'https://registry.npmjs.org'
+function createRequestHandler(options = {}) {
   const autoIndex = options.autoIndex !== false
   const maximumDepth = options.maximumDepth || Number.MAX_VALUE
   const blacklist = options.blacklist || []
@@ -36,9 +35,9 @@ const createRequestHandler = (options = {}) => {
   app.use(
     parseURL(),
     checkBlacklist(blacklist),
-    fetchPackage(registryURL),
+    fetchPackage(),
     findFile(),
-    serveFile(registryURL, autoIndex, maximumDepth)
+    serveFile(autoIndex, maximumDepth)
   )
 
   return app

server/middleware/serveFile.js

@@ -1,5 +1,5 @@
 const path = require('path')
-const { getPackageInfo } = require('./RegistryUtils')
+const PackageInfo = require('../PackageInfo')
 const { generateMetadata } = require('./MetadataUtils')
 const { generateDirectoryIndexHTML } = require('./IndexUtils')
 const { sendFile } = require('./ResponseUtils')
@@ -7,9 +7,9 @@ const { sendFile } = require('./ResponseUtils')
 /**
  * Send the file, JSON metadata, or HTML directory listing.
  */
-function serveFile(registryURL, autoIndex, maximumDepth) {
+function serveFile(autoIndex, maximumDepth) {
   return function (req, res, next) {
-    // TODO: change query param from "json" => "meta"
+    // TODO: change query param from "json" to "meta"
     if (req.query.json != null) {
       generateMetadata(req.packageDir, req.file, req.stats, maximumDepth, function (error, metadata) {
         if (metadata) {
@@ -22,8 +22,7 @@ function serveFile(registryURL, autoIndex, maximumDepth) {
       // TODO: use res.sendFile instead of our own custom function?
       sendFile(res, path.join(req.packageDir, req.file), req.stats, 31536000)
     } else if (autoIndex && req.stats.isDirectory()) {
-      // TODO: re-use packageInfo from fetchPackage middleware
-      getPackageInfo(registryURL, req.packageName, function (error, packageInfo) {
+      PackageInfo.get(req.packageName, function (error, packageInfo) {
         if (error) {
           res.status(500).send(`Cannot generate index page for ${req.packageSpec}${req.filename}`)
         } else {