feat: add vary header helper

internal/server/static_delivery.go

@@ -0,0 +1,18 @@
+package server
+
+import (
+	"net/http"
+	"strings"
+)
+
+//nolint:unused
+func addVary(header http.Header, value string) {
+	for _, line := range header.Values("Vary") {
+		for _, existing := range strings.Split(line, ",") {
+			if strings.EqualFold(strings.TrimSpace(existing), value) {
+				return
+			}
+		}
+	}
+	header.Add("Vary", value)
+}