feat(gatsby): add cache control headers to serve command

packages/gatsby/src/commands/serve.ts

@@ -10,6 +10,7 @@ import report from "gatsby-cli/lib/reporter"
 import multer from "multer"
 import pathToRegexp from "path-to-regexp"
 import cookie from "cookie"
+import minimatch from "minimatch"
 
 import telemetry from "gatsby-telemetry"
 
@@ -85,6 +86,36 @@ const matchPathRouter = (
   return next()
 }
 
+const setCacheHeaders = (
+  req: express.Request,
+  res: express.Response,
+  next: express.NextFunction
+): void => {
+  function match(pattern: string, options: minimatch.IOptions = {}): boolean {
+    return minimatch(req.path, pattern, options)
+  }
+
+  if (req.method !== `GET`) {
+    next()
+    return
+  }
+
+  if ((match(`/static/**`) || match(`/**.+(js|css)`)) && !match(`/sw.js`)) {
+    res.header(
+      `Cache-control`,
+      `cache-control: public, max-age=31536000, immutable`
+    )
+
+    next()
+    return
+  }
+
+  res.header(`Cache-control`, `public, max-age=0, must-revalidate`)
+
+  next()
+  return
+}
+
 module.exports = async (program: IServeProgram): Promise<void> => {
   telemetry.trackCli(`SERVE_START`)
   telemetry.startBackgroundUpdate()
@@ -110,6 +141,7 @@ module.exports = async (program: IServeProgram): Promise<void> => {
   app.use(telemetry.expressMiddleware(`SERVE`))
 
   router.use(compression())
+  app.use(setCacheHeaders)
   router.use(express.static(`public`, { dotfiles: `allow` }))
   const matchPaths = await readMatchPaths(program)
   router.use(matchPathRouter(matchPaths, { root }))