From cfe84bf67c3a81e3fd94484d736deaa23815073c Mon Sep 17 00:00:00 2001
From: Nova Kwok <n0vad3v@riseup.net>
Date: Tue, 30 Jun 2020 17:58:58 +0800
Subject: [PATCH] Try add Etag on response  by nova

---
 helper.go | 14 +++++++++++++-
 router.go |  8 ++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/helper.go b/helper.go
index b17a143..5125b76 100644
--- a/helper.go
+++ b/helper.go
@@ -2,11 +2,14 @@ package main
 
 import (
 	"fmt"
-	log "github.com/sirupsen/logrus"
+	"hash/crc32"
+	"io/ioutil"
 	"net/http"
 	"os"
 	"path"
 	"path/filepath"
+
+	log "github.com/sirupsen/logrus"
 	"strings"
 )
 
@@ -61,6 +64,15 @@ func GenWebpAbs(RawImagePath string, ExhaustPath string, ImgFilename string, req
 	return cwd, WebpAbsolutePath
 }
 
+func GenEtag(ImgAbsPath string) string {
+	data, err := ioutil.ReadFile(ImgAbsPath)
+	if err != nil {
+		log.Info(err)
+	}
+	crc := crc32.ChecksumIEEE(data)
+	return fmt.Sprintf(`W/"%d-%08X"`, len(data), crc)
+}
+
 func goOrigin(UA string) bool {
 	// for more information, please check test case
 	if strings.Contains(UA, "Firefox") || strings.Contains(UA, "Chrome") {
diff --git a/router.go b/router.go
index ef0788d..f0183ee 100644
--- a/router.go
+++ b/router.go
@@ -23,6 +23,10 @@ func Convert(ImgPath string, ExhaustPath string, AllowedTypes []string, QUALITY
 		done := goOrigin(UA)
 		if done {
 			log.Infof("A Safari/IE/whatever user has arrived...%s", UA)
+			// Check for Safari users. If they're Safari, just simply ignore everything.
+
+			etag := GenEtag(RawImageAbs)
+			c.Set("ETag", etag)
 			c.SendFile(RawImageAbs)
 			return
 		}
@@ -46,6 +50,8 @@ func Convert(ImgPath string, ExhaustPath string, AllowedTypes []string, QUALITY
 			log.Warn(msg)
 			c.Send(msg)
 			if ImageExists(RawImageAbs) {
+				etag := GenEtag(RawImageAbs)
+				c.Set("ETag", etag)
 				c.SendFile(RawImageAbs)
 			}
 			return
@@ -95,6 +101,8 @@ func Convert(ImgPath string, ExhaustPath string, AllowedTypes []string, QUALITY
 			}
 			finalFile = WebpAbsPath
 		}
+		etag := GenEtag(finalFile)
+		c.Set("ETag", etag)
 		c.SendFile(finalFile)
 	}
 }