Better dev server integration

server/middleware/assetsManifest.js

@@ -0,0 +1,26 @@
+/**
+ * An express middleware that sets req.manifest from the build manifest
+ * in the given file. Should be used in production together with
+ * https://github.com/soundcloud/chunk-manifest-webpack-plugin
+ * to get consistent hashes.
+ */
+function assetsManifest(webpackManifestFile) {
+  let manifest;
+  try {
+    manifest = JSON.parse(fs.readFileSync(webpackManifestFile, "utf8"));
+  } catch (error) {
+    invariant(
+      false,
+      'assetsManifest middleware cannot read the manifest file "%s"; ' +
+        "run `yarn build` before starting the server",
+      webpackManifestFile
+    );
+  }
+
+  return (req, res, next) => {
+    req.manifest = manifest;
+    next();
+  };
+}
+
+module.exports = assetsManifest;