Fast path for setting headers.

- No heap allocation
- No indirection
- CanonicalMIMEHeaderKey() is not called

render/html.go

@@ -30,7 +30,7 @@ type (
 	}
 )
 
-const htmlContentType = "text/html; charset=utf-8"
+var htmlContentType = []string{"text/html; charset=utf-8"}
 
 func (r HTMLProduction) Instance(name string, data interface{}) Render {
 	return HTML{
@@ -58,6 +58,6 @@ func (r HTMLDebug) loadTemplate() *template.Template {
 }
 
 func (r HTML) Write(w http.ResponseWriter) error {
-	w.Header().Set("Content-Type", htmlContentType)
+	w.Header()["Content-Type"] = htmlContentType
 	return r.Template.ExecuteTemplate(w, r.Name, r.Data)
 }