Consolidate url parse/create in PackageURL module

server/PackageURL.js

@@ -0,0 +1,74 @@
+const url = require('url')
+
+const URLFormat = /^\/((?:@[^\/@]+\/)?[^\/@]+)(?:@([^\/]+))?(\/.*)?$/
+
+function decodeParam(param) {
+  if (param) {
+    try {
+      return decodeURIComponent(param) : ''
+    } catch (error) {
+      // Ignore param parsing errors.
+    }
+  }
+
+  return null
+}
+
+const ValidQueryKeys = {
+  main: true,
+  meta: true,
+  json: true
+}
+
+function queryIsValid(query) {
+  return Object.keys(query).every(function (key) {
+    return ValidQueryKeys[key]
+  })
+}
+
+function parsePackageURL(packageURL) {
+  const { pathname, search, query } = url.parse(packageURL, true)
+
+  // Do not allow unrecognized query parameters because
+  // some people use them to bust the cache.
+  if (!queryIsValid(query))
+    return null
+
+  const match = URLFormat.exec(pathname)
+
+  if (match == null)
+    return null
+
+  const packageName = match[1]
+  const packageVersion = decodeParam(match[2]) || 'latest'
+  const filename = decodeParam(match[3])
+
+  return {          // If the URL is /@scope/name@version/file.js?main=browser:
+    pathname,       // /@scope/name@version/path.js
+    search,         // ?main=browser
+    query,          // { main: 'browser' }
+    packageName,    // @scope/name
+    packageVersion, // version
+    filename        // /file.js
+  }
+}
+
+function createPackageURL(packageName, version, filename, search) {
+  let pathname = `/${packageName}`
+
+  if (version != null)
+    pathname += `@${version}`
+
+  if (filename)
+    pathname += filename
+
+  if (search)
+    pathname += search
+
+  return pathname
+}
+
+module.exports = {
+  parse: parsePackageURL,
+  create: createPackageURL
+}