Break middleware out into separate files

server/middleware/fetchPackage.js

@@ -0,0 +1,70 @@
+const fs = require('fs')
+const path = require('path')
+const tmpdir = require('os-tmpdir')
+const { maxSatisfying: maxSatisfyingVersion } = require('semver')
+const { createPackageURL } = require('./PackageUtils')
+const { getPackageInfo, getPackage } = require('./RegistryUtils')
+
+function checkLocalCache(dir, callback) {
+  fs.stat(path.join(dir, 'package.json'), function (error, stats) {
+    callback(stats && stats.isFile())
+  })
+}
+
+function createTempPath(name) {
+  return path.join(tmpdir(), `unpkg-${name}`)
+}
+
+/**
+ * Fetch the package from the registry and store a local copy on disk.
+ * Redirect if the URL does not specify an exact req.packageVersion number.
+ */
+function fetchPackage(registryURL) {
+  return function (req, res, next) {
+    req.packageDir = createTempPath(req.packageSpec)
+
+    // TODO: fix race condition! (see #38)
+    // TODO: ensure req.packageInfo is always populated so we can re-use later
+    checkLocalCache(req.packageDir, function (isCached) {
+      if (isCached)
+        return next() // Best case: we already have this package on disk.
+
+      // Fetch package info from NPM.
+      getPackageInfo(registryURL, req.packageName, function (error, packageInfo) {
+        if (error)
+          return res.status(500).send(error.message || error)
+
+        if (packageInfo == null || packageInfo.versions == null)
+          return res.status(404).send(`Cannot find package "${req.packageName}"`)
+
+        const { versions, 'dist-tags': tags } = packageInfo
+
+        if (req.packageVersion in versions) {
+          // A valid request for a package we haven't downloaded yet.
+          const packageConfig = versions[req.packageVersion]
+          const tarballURL = packageConfig.dist.tarball
+
+          getPackage(tarballURL, req.packageDir, function (error) {
+            if (error) {
+              res.status(500).send(error.message || error)
+            } else {
+              next()
+            }
+          })
+        } else if (req.packageVersion in tags) {
+          res.redirect(createPackageURL(req.packageName, tags[req.packageVersion], req.filename, req.search))
+        } else {
+          const maxVersion = maxSatisfyingVersion(Object.keys(versions), req.packageVersion)
+
+          if (maxVersion) {
+            res.redirect(createPackageURL(req.packageName, maxVersion, req.filename, req.search))
+          } else {
+            res.status(404).send(`Cannot find package ${req.packageSpec}`)
+          }
+        }
+      })
+    })
+  }
+}
+
+module.exports = fetchPackage