1package mux
2
3import (
4	"net/http"
5	"strings"
6)
7
8// MiddlewareFunc is a function which receives an http.Handler and returns another http.Handler.
9// Typically, the returned handler is a closure which does something with the http.ResponseWriter and http.Request passed
10// to it, and then calls the handler passed as parameter to the MiddlewareFunc.
11type MiddlewareFunc func(http.Handler) http.Handler
12
13// middleware interface is anything which implements a MiddlewareFunc named Middleware.
14type middleware interface {
15	Middleware(handler http.Handler) http.Handler
16}
17
18// Middleware allows MiddlewareFunc to implement the middleware interface.
19func (mw MiddlewareFunc) Middleware(handler http.Handler) http.Handler {
20	return mw(handler)
21}
22
23// Use appends a MiddlewareFunc to the chain. Middleware can be used to intercept or otherwise modify requests and/or responses, and are executed in the order that they are applied to the Router.
24func (r *Router) Use(mwf ...MiddlewareFunc) {
25	for _, fn := range mwf {
26		r.middlewares = append(r.middlewares, fn)
27	}
28}
29
30// useInterface appends a middleware to the chain. Middleware can be used to intercept or otherwise modify requests and/or responses, and are executed in the order that they are applied to the Router.
31func (r *Router) useInterface(mw middleware) {
32	r.middlewares = append(r.middlewares, mw)
33}
34
35// CORSMethodMiddleware automatically sets the Access-Control-Allow-Methods response header
36// on requests for routes that have an OPTIONS method matcher to all the method matchers on
37// the route. Routes that do not explicitly handle OPTIONS requests will not be processed
38// by the middleware. See examples for usage.
39func CORSMethodMiddleware(r *Router) MiddlewareFunc {
40	return func(next http.Handler) http.Handler {
41		return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
42			allMethods, err := getAllMethodsForRoute(r, req)
43			if err == nil {
44				for _, v := range allMethods {
45					if v == http.MethodOptions {
46						w.Header().Set("Access-Control-Allow-Methods", strings.Join(allMethods, ","))
47					}
48				}
49			}
50
51			next.ServeHTTP(w, req)
52		})
53	}
54}
55
56// getAllMethodsForRoute returns all the methods from method matchers matching a given
57// request.
58func getAllMethodsForRoute(r *Router, req *http.Request) ([]string, error) {
59	var allMethods []string
60
61	for _, route := range r.routes {
62		var match RouteMatch
63		if route.Match(req, &match) || match.MatchErr == ErrMethodMismatch {
64			methods, err := route.GetMethods()
65			if err != nil {
66				return nil, err
67			}
68
69			allMethods = append(allMethods, methods...)
70		}
71	}
72
73	return allMethods, nil
74}
75