add 'DirOptions.PushTargets' for http/2 push on index(es) - #1562

Former-commit-id: 5a3f626ba0fbcf10be979b5a800eba51e88602cd

_examples/file-server/http2push/main.go

@@ -0,0 +1,35 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+)
+
+var opts = iris.DirOptions{
+	IndexName: "/index.html",
+	// Optionally register files (map's absolute values) to be served
+	// when a specific path (map's key WITHOUT prefix) is requested
+	// is fired before client asks (HTTP/2 Push).
+	// E.g. "/" (which serves the `IndexName` if not empty).
+	//
+	// Note: Requires running server under TLS,
+	// that's why we use ListenAndServeTLS below.
+	PushTargets: map[string][]string{
+		"/": {
+			"/public/favicon.ico",
+			"/public/js/main.js",
+			"/public/css/main.css",
+		},
+	},
+	Compress: true,
+	ShowList: true,
+}
+
+func main() {
+	app := iris.New()
+	app.HandleDir("/public", "./assets", opts)
+
+	// Open your browser's Network tools,
+	// navigate to https://127.0.0.1/public.
+	// you should see `Initiator` tab:  "Push / public".
+	app.Run(iris.TLS(":443", "mycert.crt", "mykey.key"))
+}