Split up fetchFile middleware into 2

server/middleware/fetchPackage.js

@@ -0,0 +1,99 @@
+const semver = require("semver");
+
+const createPackageURL = require("../utils/createPackageURL");
+const getPackageInfo = require("./utils/getPackageInfo");
+const getPackage = require("./utils/getPackage");
+
+function tagRedirect(req, res) {
+  // Cache tag redirects for 1 minute.
+  res
+    .set({
+      "Cache-Control": "public, max-age=60",
+      "Cache-Tag": "redirect,tag-redirect"
+    })
+    .redirect(
+      302,
+      createPackageURL(
+        req.packageName,
+        req.packageInfo["dist-tags"][req.packageVersion],
+        req.filename,
+        req.search
+      )
+    );
+}
+
+function semverRedirect(req, res) {
+  const maxVersion = semver.maxSatisfying(
+    Object.keys(req.packageInfo.versions),
+    req.packageVersion
+  );
+
+  if (maxVersion) {
+    // Cache semver redirects for 1 minute.
+    res
+      .set({
+        "Cache-Control": "public, max-age=60",
+        "Cache-Tag": "redirect,semver-redirect"
+      })
+      .redirect(
+        302,
+        createPackageURL(req.packageName, maxVersion, req.filename, req.search)
+      );
+  } else {
+    res
+      .status(404)
+      .type("text")
+      .send(`Cannot find package ${req.packageSpec}`);
+  }
+}
+
+/**
+ * Fetch the package metadata and tarball from npm. Redirect to the exact
+ * version if the request targets a tag or uses a semver version.
+ */
+function fetchPackage(req, res, next) {
+  getPackageInfo(req.packageName, (error, packageInfo) => {
+    if (error) {
+      console.error(error);
+
+      return res
+        .status(500)
+        .type("text")
+        .send(`Cannot get info for package "${req.packageName}"`);
+    }
+
+    if (packageInfo == null || packageInfo.versions == null) {
+      return res
+        .status(404)
+        .type("text")
+        .send(`Cannot find package "${req.packageName}"`);
+    }
+
+    req.packageInfo = packageInfo;
+
+    if (req.packageVersion in req.packageInfo.versions) {
+      // A valid request for a package we haven't downloaded yet.
+      req.packageConfig = req.packageInfo.versions[req.packageVersion];
+
+      getPackage(req.packageConfig, (error, outputDir) => {
+        if (error) {
+          console.error(error);
+
+          res
+            .status(500)
+            .type("text")
+            .send(`Cannot fetch package ${req.packageSpec}`);
+        } else {
+          req.packageDir = outputDir;
+          next();
+        }
+      });
+    } else if (req.packageVersion in req.packageInfo["dist-tags"]) {
+      tagRedirect(req, res);
+    } else {
+      semverRedirect(req, res);
+    }
+  });
+}
+
+module.exports = fetchPackage;