From a659b61323b075cb38ad03aa43749e52eb4948e0 Mon Sep 17 00:00:00 2001
From: Mayank Patel <maknahar@yahoo.in>
Date: Wed, 30 Aug 2017 11:09:17 +0530
Subject: [PATCH] Fix #271:  Return 405 instead of 404 when request method
 doesn't match the route

---
 mux.go      | 33 +++++++++++++++++++++++++++++++++
 mux_test.go | 39 +++++++++++++++++++++++++++++++++++++++
 old_test.go |  8 +-------
 route.go    | 16 ++++++++++++++++
 4 files changed, 89 insertions(+), 7 deletions(-)

diff --git a/mux.go b/mux.go
index aa19597..fb69196 100644
--- a/mux.go
+++ b/mux.go
@@ -13,6 +13,10 @@ import (
 	"strings"
 )
 
+var (
+	ErrMethodMismatch = errors.New("method is not allowed")
+)
+
 // NewRouter returns a new router instance.
 func NewRouter() *Router {
 	return &Router{namedRoutes: make(map[string]*Route), KeepContext: false}
@@ -39,6 +43,10 @@ func NewRouter() *Router {
 type Router struct {
 	// Configurable Handler to be used when no route matches.
 	NotFoundHandler http.Handler
+
+	// Configurable Handler to be used when the request method does not match the route.
+	MethodNotAllowedHandler http.Handler
+
 	// Parent route, if this is a subrouter.
 	parent parentRoute
 	// Routes to be matched, in order.
@@ -65,6 +73,11 @@ func (r *Router) Match(req *http.Request, match *RouteMatch) bool {
 		}
 	}
 
+	if match.MatchErr == ErrMethodMismatch && r.MethodNotAllowedHandler != nil {
+		match.Handler = r.MethodNotAllowedHandler
+		return true
+	}
+
 	// Closest match for a router (includes sub-routers)
 	if r.NotFoundHandler != nil {
 		match.Handler = r.NotFoundHandler
@@ -105,9 +118,15 @@ func (r *Router) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 		req = setVars(req, match.Vars)
 		req = setCurrentRoute(req, match.Route)
 	}
+
+	if handler == nil && match.MatchErr == ErrMethodMismatch {
+		handler = methodNotAllowedHandler()
+	}
+
 	if handler == nil {
 		handler = http.NotFoundHandler()
 	}
+
 	if !r.KeepContext {
 		defer contextClear(req)
 	}
@@ -344,6 +363,11 @@ type RouteMatch struct {
 	Route   *Route
 	Handler http.Handler
 	Vars    map[string]string
+
+	// MatchErr is set to appropriate matching error
+	// It is set to ErrMethodMismatch if there is a mismatch in
+	// the request method and route method
+	MatchErr error
 }
 
 type contextKey int
@@ -545,3 +569,12 @@ func matchMapWithRegex(toCheck map[string]*regexp.Regexp, toMatch map[string][]s
 	}
 	return true
 }
+
+// methodNotAllowed replies to the request with an HTTP status code 405.
+func methodNotAllowed(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(http.StatusMethodNotAllowed)
+}
+
+// methodNotAllowedHandler returns a simple request handler
+// that replies to each request with a status code 405.
+func methodNotAllowedHandler() http.Handler { return http.HandlerFunc(methodNotAllowed) }
diff --git a/mux_test.go b/mux_test.go
index f6cfb44..413f13f 100644
--- a/mux_test.go
+++ b/mux_test.go
@@ -1871,3 +1871,42 @@ func newRequest(method, url string) *http.Request {
 	}
 	return req
 }
+
+func TestNoMatchMethodErrorHandler(t *testing.T) {
+	func1 := func(w http.ResponseWriter, r *http.Request) {}
+
+	r := NewRouter()
+	r.HandleFunc("/", func1).Methods("GET", "POST")
+
+	req, _ := http.NewRequest("PUT", "http://localhost/", nil)
+	match := new(RouteMatch)
+	matched := r.Match(req, match)
+
+	if matched {
+		t.Error("Should not have matched route for methods")
+	}
+
+	if match.MatchErr != ErrMethodMismatch {
+		t.Error("Should get ErrMethodMismatch error")
+	}
+
+	resp := NewRecorder()
+	r.ServeHTTP(resp, req)
+	if resp.Code != 405 {
+		t.Errorf("Expecting code %v", 405)
+	}
+
+	//Add matching route now
+	r.HandleFunc("/", func1).Methods("PUT")
+
+	match = new(RouteMatch)
+	matched = r.Match(req, match)
+
+	if !matched {
+		t.Error("Should have matched route for methods")
+	}
+
+	if match.MatchErr != nil {
+		t.Error("Should not have any matching error. Found:", match.MatchErr)
+	}
+}
diff --git a/old_test.go b/old_test.go
index 9bdc5e5..3751e47 100644
--- a/old_test.go
+++ b/old_test.go
@@ -121,12 +121,7 @@ func TestRouteMatchers(t *testing.T) {
 		var routeMatch RouteMatch
 		matched := router.Match(request, &routeMatch)
 		if matched != shouldMatch {
-			// Need better messages. :)
-			if matched {
-				t.Errorf("Should match.")
-			} else {
-				t.Errorf("Should not match.")
-			}
+			t.Errorf("Expected: %v\nGot: %v\nRequest: %v %v", shouldMatch, matched, request.Method, url)
 		}
 
 		if matched {
@@ -188,7 +183,6 @@ func TestRouteMatchers(t *testing.T) {
 	match(true)
 
 	// 2nd route --------------------------------------------------------------
-
 	// Everything match.
 	reset2()
 	match(true)
diff --git a/route.go b/route.go
index 6d4a07a..6863adb 100644
--- a/route.go
+++ b/route.go
@@ -52,12 +52,27 @@ func (r *Route) Match(req *http.Request, match *RouteMatch) bool {
 	if r.buildOnly || r.err != nil {
 		return false
 	}
+
+	var matchErr error
+
 	// Match everything.
 	for _, m := range r.matchers {
 		if matched := m.Match(req, match); !matched {
+			if _, ok := m.(methodMatcher); ok {
+				matchErr = ErrMethodMismatch
+				continue
+			}
+			matchErr = nil
 			return false
 		}
 	}
+
+	if matchErr != nil {
+		match.MatchErr = matchErr
+		return false
+	}
+
+	match.MatchErr = nil
 	// Yay, we have a match. Let's collect some info about it.
 	if match.Route == nil {
 		match.Route = r
@@ -68,6 +83,7 @@ func (r *Route) Match(req *http.Request, match *RouteMatch) bool {
 	if match.Vars == nil {
 		match.Vars = make(map[string]string)
 	}
+
 	// Set variables.
 	if r.regexp != nil {
 		r.regexp.setMatch(req, match, r)