add Cache304 as an alternative to the server-side kataras/iris/cache middleware - it can perform better with less server overheat but it comes with a cost of 304 instead of 200 so custom clients must make that check

Former-commit-id: b0ba68c528c870fe060e2825c35689771a1d3680

_examples/cache/client-side/main.go

@@ -6,22 +6,34 @@
 package main
 
 import (
-	"fmt"
 	"time"
 
 	"github.com/kataras/iris"
 )
 
-var modtime = time.Now()
-
-func greet(ctx iris.Context) {
-	ctx.Header("X-Custom", "my  custom header")
-	response := fmt.Sprintf("Hello World! %s", time.Now())
-	ctx.WriteWithExpiration([]byte(response), modtime)
-}
+const refreshEvery = 10 * time.Second
 
 func main() {
 	app := iris.New()
+	app.Use(iris.Cache304(refreshEvery))
+	// same as:
+	// app.Use(func(ctx iris.Context) {
+	// 	now := time.Now()
+	// 	if modified, err := ctx.CheckIfModifiedSince(now.Add(-refresh)); !modified && err == nil {
+	// 		ctx.WriteNotModified()
+	// 		return
+	// 	}
+
+	// 	ctx.SetLastModified(now)
+
+	// 	ctx.Next()
+	// })
+
 	app.Get("/", greet)
 	app.Run(iris.Addr(":8080"))
 }
+
+func greet(ctx iris.Context) {
+	ctx.Header("X-Custom", "my  custom header")
+	ctx.Writef("Hello World! %s", time.Now())
+}