Prevent multiple concurrent requests for packages

Fixes #38
Fixes #41

server/middleware/parseURL.js

@@ -3,28 +3,26 @@ const { parsePackageURL } = require('./PackageUtils')
 /**
  * Parse and validate the URL.
  */
-function parseURL() {
-  return function (req, res, next) {
-    let url
-    try {
-      url = parsePackageURL(req.url)
-    } catch (error) {
-      return res.status(403).send(`Invalid URL: ${req.url}`)
-    }
-
-    if (url == null)
-      return res.status(403).send(`Invalid URL: ${req.url}`)
-
-    req.packageName = url.packageName
-    req.packageVersion = url.packageVersion
-    req.packageSpec = `${req.packageName}@${req.packageVersion}`
-    req.pathname = url.pathname
-    req.filename = url.filename
-    req.search = url.search
-    req.query = url.query
-
-    next()
+function parseURL(req, res, next) {
+  let url
+  try {
+    url = parsePackageURL(req.url)
+  } catch (error) {
+    return res.status(403).send(`Invalid URL: ${req.url}`)
   }
+
+  if (url == null)
+    return res.status(403).send(`Invalid URL: ${req.url}`)
+
+  req.packageName = url.packageName
+  req.packageVersion = url.packageVersion
+  req.packageSpec = `${req.packageName}@${req.packageVersion}`
+  req.pathname = url.pathname
+  req.filename = url.filename
+  req.search = url.search
+  req.query = url.query
+
+  next()
 }
 
 module.exports = parseURL