DirOptions.PushTargets: add example for https://github.com/kataras/iris/issues/1562

Former-commit-id: 940f07fdb1184266dc315441fb91afa5754092fa

_examples/file-server/http2push-embedded-gzipped/main.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+)
+
+// Follow the steps below:
+// $ go get -u github.com/kataras/bindata/cmd/bindata
+//
+// $ bindata -prefix "../http2push/" ../http2push/assets/...
+// # OR if the ./assets directory was inside this example foder:
+// # bindata ./assets/...
+//
+// $ go run .
+// Physical files are not used, you can delete the "assets" folder and run the example.
+
+var opts = iris.DirOptions{
+	IndexName: "/index.html",
+	PushTargets: map[string][]string{
+		"/": {
+			"/public/favicon.ico",
+			"/public/js/main.js",
+			"/public/css/main.css",
+		},
+	},
+	Compress:   false, // SHOULD be set to false, files already compressed.
+	ShowList:   true,
+	Asset:      GzipAsset,
+	AssetInfo:  GzipAssetInfo,
+	AssetNames: GzipAssetNames,
+	// Required for pre-compressed files:
+	AssetValidator: func(ctx iris.Context, _ string) bool {
+		ctx.Header("Vary", "Content-Encoding")
+		ctx.Header("Content-Encoding", "gzip")
+		return true
+	},
+}
+
+func main() {
+	app := iris.New()
+	app.HandleDir("/public", "./assets", opts)
+
+	app.Run(iris.TLS(":443", "../http2push/mycert.crt", "../http2push/mykey.key"))
+}