preload artwork images on /artworks/*

cache http headers

what the cache

main.go

@@ -40,6 +40,7 @@ func CanRequestSkipLimiter(c *fiber.Ctx) bool {
 }
 
 func CanRequestSkipLogger(c *fiber.Ctx) bool {
+	// return false
 	path := c.Path()
 	return CanRequestSkipLimiter(c) ||
 		strings.HasPrefix(path, "/proxy/i.pximg.net/")
@@ -189,6 +190,7 @@ func main() {
 				},
 				Expiration:   5 * time.Minute,
 				CacheControl: true,
+				StoreResponseHeaders: true,
 
 				KeyGenerator: func(c *fiber.Ctx) string {
 					key := utils.CopyString(c.OriginalURL())
@@ -207,6 +209,8 @@ func main() {
 		))
 	}
 
+	// redirect any round with ?r=url
+	// could this be unsafe with cross-site scripting?
 	server.Use(func(c *fiber.Ctx) error {
 		ret := c.Query("r")
 		if ret != "" {

pages/artwork.go

@@ -24,7 +24,11 @@ func ArtworkPage(c *fiber.Ctx) error {
 		metaDescription += "#" + i.Name + ", "
 	}
 
-	// todo: passing ArtWorkData{} here will not work. maybe lowercase?
+	// monkey patching. assuming illust.Images[_].Large is used
+	for _, img := range illust.Images {
+		PreloadImage(c, img.Large)
+	}
+
 	return c.Render("artwork", fiber.Map{
 		"Illust":          illust,
 		"Title":           illust.Title,

pages/utils.go

@@ -0,0 +1,11 @@
+package pages
+
+import (
+	"fmt"
+
+	"github.com/gofiber/fiber/v2"
+)
+
+func PreloadImage(c *fiber.Ctx, url string) {
+	c.Response().Header.Add("Link", fmt.Sprintf("<%s>; rel=preload; as=image", url))
+}

serve/preload.go

@@ -0,0 +1,60 @@
+package serve
+
+import (
+	"bytes"
+	"io"
+	"log"
+	"strings"
+
+	"github.com/gofiber/fiber/v2"
+	"golang.org/x/net/html"
+)
+
+// not working as middleware for some reason
+
+func Rewrite_Link_preload(c *fiber.Ctx) error {
+	err := c.Next()
+	if err != nil {
+		return err
+	}
+
+	contentType := string(c.Response().Header.ContentType())
+	// log.Print("ct ", contentType)
+	if contentType == "text/html; charset=utf-8" {
+		images_to_preload := []string{}
+
+		// here, the response body is not valid
+		// no idea how to get c.Render to work here.
+		// reading gofiber's code, c.Render uses bytebufferpool
+		// i fail to understand how that makes sense
+		z := html.NewTokenizer(bytes.NewReader(c.Response().Body()))
+	scan_tokens:
+		for {
+			token_type := z.Next()
+			switch token_type {
+			case html.ErrorToken:
+				err := z.Err()
+				if err == io.EOF {
+					break scan_tokens
+				}
+				return err
+			case html.StartTagToken, html.SelfClosingTagToken, html.EndTagToken:
+				tag_name, hasAttr := z.TagName()
+				log.Print("tag name ", string(tag_name))
+				if string(tag_name) == "img" && hasAttr {
+					for hasAttr {
+						var key, val []byte
+						key, val, hasAttr = z.TagAttr()
+						log.Print("key val ", string(key), string(val))
+						if string(key) == "src" && strings.HasPrefix(string(val), "/proxy/i.pximg.net/img-master/") {
+							images_to_preload = append(images_to_preload, string(val))
+						}
+					}
+				}
+			}
+		}
+		log.Print("preload ", images_to_preload)
+	}
+
+	return nil
+}

tests/test.go

@@ -0,0 +1 @@
+package tests