Enhance favicon handling with content type detection

- Added a new variable to store the content type for the favicon.
- Updated the favicon loading mechanism to determine the content type based on the file extension.
- Adjusted the default fallback to use an embedded favicon.ico instead of orly.png.
- Modified the favicon handler to set the appropriate content type when serving the favicon.

main.go

@@ -41,6 +41,9 @@ var orlyFavicon []byte
 // faviconData holds the favicon data to serve
 var faviconData []byte
 
+// faviconContentType holds the content type for the favicon
+var faviconContentType string
+
 func main() {
 	ctx, cancel := signal.NotifyContext(context.Background(), os.Interrupt)
 	defer cancel()
@@ -60,7 +63,7 @@ type C struct {
 	WTo     time.Duration `env:"REVERSE_WTO" usage:"maximum duration before timing out write of the response" default:"5m"`
 	Idle    time.Duration `env:"REVERSE_IDLE" usage:"how long idle connection is kept before closing (set rto, wto to 0 to use this)"`
 	Certs   []string      `env:"REVERSE_CERTS" usage:"certificates and the domain they match: eg: mleku.dev:/path/to/cert - this will indicate to load two, one with extension .key and one with .crt, each expected to be PEM encoded TLS private and public keys, respectively"`
-	Favicon string        `env:"REVERSE_FAVICON" usage:"path to custom favicon file to serve as favicon.ico (overrides default orly.png)"`
+	Favicon string        `env:"REVERSE_FAVICON" usage:"path to custom favicon file to serve as favicon.ico (overrides default favicon.ico)"`
 }
 
 // GetEnv checks if the first command line argument is "env" and returns
@@ -855,8 +858,9 @@ func NostrDNS(hn, ba string, mux *http.ServeMux) (err error) {
 // loadFavicon loads the favicon data from the configured file or uses the default
 func loadFavicon(faviconPath string) error {
 	if faviconPath == "" {
-		// Use default orly.png
-		faviconData = orlyFavicon
+		// Use default embedded favicon.ico
+		faviconData = defaultFavicon
+		faviconContentType = "image/x-icon"
 		return nil
 	}
 
@@ -870,18 +874,36 @@ func loadFavicon(faviconPath string) error {
 	}
 
 	faviconData = data
+
+	// Determine content type based on file extension
+	ext := strings.ToLower(filepath.Ext(faviconPath))
+	switch ext {
+	case ".ico":
+		faviconContentType = "image/x-icon"
+	case ".png":
+		faviconContentType = "image/png"
+	case ".gif":
+		faviconContentType = "image/gif"
+	case ".jpg", ".jpeg":
+		faviconContentType = "image/jpeg"
+	case ".svg":
+		faviconContentType = "image/svg+xml"
+	default:
+		faviconContentType = "image/x-icon" // default fallback
+	}
+
 	log.I.Ln("loaded custom favicon from", faviconPath)
 	return nil
 }
 
 // addFaviconHandler adds a favicon handler for the given hostname that serves
-// the configured favicon as favicon.ico
+// the configured favicon (default favicon.ico or custom file) as favicon.ico
 func addFaviconHandler(hostname string, mux *http.ServeMux) {
 	mux.HandleFunc(
 		hostname+"/favicon.ico",
 		func(w http.ResponseWriter, r *http.Request) {
 			log.I.Ln("serving favicon for", hostname)
-			w.Header().Set("Content-Type", "image/png")
+			w.Header().Set("Content-Type", faviconContentType)
 			w.Header().Set("Content-Length", fmt.Sprint(len(faviconData)))
 			w.Header().Set("Cache-Control", "public, max-age=31536000") // 1 year cache
 			if _, err := w.Write(faviconData); err != nil {