HTTP.2 Push Headers

lib/render.js

@@ -54,13 +54,14 @@ export async function render (req, res) {
       res.statusCode = 404
       return res.end()
     }
-    const { html, error, redirected } = await this.renderRoute(req.url, context)
+    const { html, error, redirected, resourceHints } = await this.renderRoute(req.url, context)
     if (redirected) {
       return html
     }
     if (error) {
       res.statusCode = context.nuxt.error.statusCode || 500
     }
+    // ETag header
     if (!error && this.options.render.etag) {
       const etag = generateETag(html, this.options.render.etag)
       if (fresh(req.headers, { etag })) {
@@ -72,6 +73,18 @@ export async function render (req, res) {
     }
     res.setHeader('Content-Type', 'text/html; charset=utf-8')
     res.setHeader('Content-Length', Buffer.byteLength(html))
+    // Parse resourceHints to extract HTTP.2 prefetch/push headers
+    // https://w3c.github.io/preload/#server-push-http-2
+    const regex = /link rel="([^"]*)" href="([^"]*)" as="([^"]*)"/g
+    const pushAssets = []
+    let m
+    while (m = regex.exec(resourceHints)) { // eslint-disable-line no-cond-assign
+      const [_, rel, href, as] = m
+      if (rel === 'preload') {
+        pushAssets.push(`<${href}>; rel=${rel}; as=${as}`)
+      }
+    }
+    res.setHeader('Link', pushAssets)
     res.end(html, 'utf8')
     return html
   } catch (err) {
@@ -106,7 +119,8 @@ export async function renderRoute (url, context = {}) {
   if (this._routerBaseSpecified) {
     HEAD += `<base href="${this.options.router.base}">`
   }
-  HEAD += context.renderResourceHints() + context.renderStyles()
+  const resourceHints = context.renderResourceHints()
+  HEAD += resourceHints + context.renderStyles()
   APP += `<script type="text/javascript">window.__NUXT__=${serialize(context.nuxt, { isJSON: true })}</script>`
   APP += context.renderScripts()
   const html = this.appTemplate({
@@ -117,6 +131,7 @@ export async function renderRoute (url, context = {}) {
   })
   return {
     html,
+    resourceHints,
     error: context.nuxt.error,
     redirected: context.redirected
   }