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

Former-commit-id: 940f07fdb1184266dc315441fb91afa5754092fa

_examples/file-server/embedding-gzipped-files-into-app/main.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+)
+
+// NOTE: need different tool than the "embedding-files-into-app" example.
+//
+// Follow these steps first:
+// $ go get -u github.com/kataras/bindata/cmd/bindata
+// $ bindata ./assets/...
+// $ go run .
+// $ ./embedding-gzipped-files-into-app
+// "physical" files are not used, you can delete the "assets" folder and run the example.
+
+func newApp() *iris.Application {
+	app := iris.New()
+
+	// Note the `GzipAsset` and `GzipAssetNames` are different from go-bindata's `Asset`,
+	// do not set the `Compress` option to true, instead
+	// use the `AssetValidator` option to manually set the content-encoding to "gzip".
+	app.HandleDir("/static", "./assets", iris.DirOptions{
+		Asset:      GzipAsset,
+		AssetInfo:  GzipAssetInfo,
+		AssetNames: GzipAssetNames,
+		AssetValidator: func(ctx iris.Context, name string) bool {
+			ctx.Header("Vary", "Accept-Encoding")
+			ctx.Header("Content-Encoding", "gzip")
+			return true
+		},
+	})
+	return app
+}
+
+func main() {
+	app := newApp()
+
+	// http://localhost:8080/static/css/bootstrap.min.css
+	// http://localhost:8080/static/js/jquery-2.1.1.js
+	// http://localhost:8080/static/favicon.ico
+	app.Listen(":8080")
+}