Merge pull request #519 from outline/jori/prefetch

Added link=“prefetch” tags

server/utils/prefetchTags.js

@@ -0,0 +1,35 @@
+// @flow
+import React from 'react';
+import fs from 'fs';
+import path from 'path';
+import webpackConfig from '../../webpack.config';
+
+const PUBLIC_PATH = webpackConfig.output.publicPath;
+
+const prefetchTags = [
+  <link rel="dns-prefetch" href={process.env.AWS_S3_UPLOAD_BUCKET_URL} />,
+];
+
+try {
+  const manifest = fs.readFileSync(
+    path.join(__dirname, '../../dist/manifest.json'),
+    'utf8'
+  );
+  const manifestData = JSON.parse(manifest);
+  Object.values(manifestData).forEach(filename => {
+    if (typeof filename !== 'string') return;
+    if (filename.endsWith('.js')) {
+      prefetchTags.push(
+        <link rel="prefetch" href={`${PUBLIC_PATH}${filename}`} as="script" />
+      );
+    } else if (filename.endsWith('.css')) {
+      prefetchTags.push(
+        <link rel="prefetch" href={`${PUBLIC_PATH}${filename}`} as="style" />
+      );
+    }
+  });
+} catch (_e) {
+  // no-op
+}
+
+export default prefetchTags;