Passing in parameters to a http.HandlerFunc - http

Question

I'm using Go's built in http server and pat to respond to some URLs:
mux.Get("/products", http.HandlerFunc(index))
func index(w http.ResponseWriter, r *http.Request) {
// Do something.
}
I need to pass in an extra parameter to this handler function - an interface.
func (api Api) Attach(resourceManager interface{}, route string) {
// Apply typical REST actions to Mux.
// ie: Product - to /products
mux.Get(route, http.HandlerFunc(index(resourceManager)))
// ie: Product ID: 1 - to /products/1
mux.Get(route+"/:id", http.HandlerFunc(show(resourceManager)))
}
func index(w http.ResponseWriter, r *http.Request, resourceManager interface{}) {
managerType := string(reflect.TypeOf(resourceManager).String())
w.Write([]byte(fmt.Sprintf("%v", managerType)))
}
func show(w http.ResponseWriter, r *http.Request, resourceManager interface{}) {
managerType := string(reflect.TypeOf(resourceManager).String())
w.Write([]byte(fmt.Sprintf("%v", managerType)))
}
How can I send in an extra paramter to the handler function?

Answer 1

You should be able to do what you wish by using closures.
Change func index() to the following (untested):
func index(resourceManager interface{}) http.HandlerFunc {
return func(w http.ResponseWriter, r *http.Request) {
managerType := string(reflect.TypeOf(resourceManager).String())
w.Write([]byte(fmt.Sprintf("%v", managerType)))
}
}
And then do the same to func show()

Answer 2

Another option is to use types implementing http.Handler directly rather than only using functions. For example:
type IndexHandler struct {
resourceManager interface{}
}
func (ih IndexHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
managerType := string(reflect.TypeOf(ih.resourceManager).String())
w.Write([]byte(fmt.Sprintf("%v", managerType)))
}
...
mux.Get(route, IndexHandler{resourceManager})
This kind of pattern can be useful if you want to refactor your ServeHTTP handler method into multiple methods.