diff --git a/.github/workflows/CI.yaml b/.github/workflows/CI.yaml
index 56e5832..d8df207 100644
--- a/.github/workflows/CI.yaml
+++ b/.github/workflows/CI.yaml
@@ -19,7 +19,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@v3
         with:
-          go-version: '1.20'
+          go-version: '1.21'
 
       - name: Setup necessary packages
         run: |
diff --git a/.github/workflows/codecov.yaml b/.github/workflows/codecov.yaml
index be556f6..d617e55 100644
--- a/.github/workflows/codecov.yaml
+++ b/.github/workflows/codecov.yaml
@@ -19,7 +19,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@v3
         with:
-          go-version: '1.20'
+          go-version: '1.21'
 
       - name: Setup necessary packages
         run: |
diff --git a/Dockerfile b/Dockerfile
index 052a98a..f0aab14 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,4 +1,4 @@
-FROM golang:1.20-bookworm as builder
+FROM golang:1.21-bookworm as builder
 
 ARG IMG_PATH=/opt/pics
 ARG EXHAUST_PATH=/opt/exhaust
diff --git a/config/config.go b/config/config.go
index f2cf158..9cf6003 100644
--- a/config/config.go
+++ b/config/config.go
@@ -51,18 +51,18 @@ WantedBy=multi-user.target`
 )
 
 var (
-	ConfigPath  string
-	Jobs        int
-	DumpSystemd bool
-	DumpConfig  bool
-	ShowVersion bool
-	ProxyMode   bool
-	Prefetch    bool
-	Config      jsonFile
-	Version     = "0.9.8"
-	WriteLock   = cache.New(5*time.Minute, 10*time.Minute)
-	RemoteRaw   = "./remote-raw"
-	Metadata    = "./metadata"
+	ConfigPath     string
+	Jobs           int
+	DumpSystemd    bool
+	DumpConfig     bool
+	ShowVersion    bool
+	ProxyMode      bool
+	Prefetch       bool
+	Config         jsonFile
+	Version        = "0.9.9"
+	WriteLock      = cache.New(5*time.Minute, 10*time.Minute)
+	RemoteRaw      = "./remote-raw"
+	Metadata       = "./metadata"
 	LocalHostAlias = "local"
 )
 
diff --git a/helper/helper.go b/helper/helper.go
index 89aa870..8965d58 100644
--- a/helper/helper.go
+++ b/helper/helper.go
@@ -9,6 +9,8 @@ import (
 	"time"
 	"webp_server_go/config"
 
+	"slices"
+
 	"github.com/h2non/filetype"
 
 	"github.com/cespare/xxhash"
@@ -83,14 +85,13 @@ func ImageExists(filename string) bool {
 }
 
 func CheckAllowedType(imgFilename string) bool {
-	for _, allowedType := range config.Config.AllowedTypes {
-		if allowedType == "*" {
-			return true
-		}
-		allowedType = "." + strings.ToLower(allowedType)
-		if strings.HasSuffix(strings.ToLower(imgFilename), allowedType) {
-			return true
-		}
+	if config.Config.AllowedTypes[0] == "*" {
+		return true
+	}
+	imgFilenameExtension := strings.ToLower(path.Ext(imgFilename))
+	imgFilenameExtension = strings.TrimPrefix(imgFilenameExtension, ".") // .jpg -> jpg
+	if slices.Contains(config.Config.AllowedTypes, imgFilenameExtension) {
+		return true
 	}
 	return false
 }
@@ -137,19 +138,20 @@ func GuessSupportedFormat(header *fasthttp.RequestHeader) []string {
 		supported["avif"] = true
 	}
 
-	// chrome on iOS will not send valid image accept header
-	if strings.Contains(ua, "iPhone OS 14") || strings.Contains(ua, "CPU OS 14") ||
-		strings.Contains(ua, "iPhone OS 15") || strings.Contains(ua, "CPU OS 15") ||
-		strings.Contains(ua, "iPhone OS 16") || strings.Contains(ua, "CPU OS 16") ||
-		strings.Contains(ua, "iPhone OS 17") || strings.Contains(ua, "CPU OS 17") ||
-		strings.Contains(ua, "Android") || strings.Contains(ua, "Linux") {
-		supported["webp"] = true
+	supportedWebPs := []string{"iPhone OS 14", "CPU OS 14", "iPhone OS 15", "CPU OS 15", "iPhone OS 16", "CPU OS 16", "iPhone OS 17", "CPU OS 17"}
+	for _, version := range supportedWebPs {
+		if strings.Contains(ua, version) {
+			supported["webp"] = true
+			break
+		}
 	}
 
-	// iOS 16 supports AVIF
-	if strings.Contains(ua, "iPhone OS 16") || strings.Contains(ua, "CPU OS 16") ||
-		strings.Contains(ua, "iPhone OS 17") || strings.Contains(ua, "CPU OS 17") {
-		supported["avif"] = true
+	supportedAVIFs := []string{"iPhone OS 16", "CPU OS 16", "iPhone OS 17", "CPU OS 17"}
+	for _, version := range supportedAVIFs {
+		if strings.Contains(ua, version) {
+			supported["avif"] = true
+			break
+		}
 	}
 
 	// save true value's key to slice