setup 404 NotFound handler on a gorilla mux router

Question

Here is my code about a small demonstration webserver written with the Go language and the gorilla mux package :

package main

import (
    "fmt"
    "github.com/gorilla/mux"
    "net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    fmt.Fprintf(w, "Hi there, I love %s!", vars["username"])
}

func homeHandler(w http.ResponseWriter, r *http.Request) {
    if r.URL.Path != "/" {
        errorHandler(w, r, http.StatusNotFound)
        return
    }
    vars := mux.Vars(r)
    fmt.Fprintf(w, "Hi there, I love %s!", vars["username"])
}

func main() {
    r := mux.NewRouter()
    r.HandleFunc("/help/{username}/", handler)
    http.Handle("/", r)
    http.ListenAndServe(":8080", nil)
}

But I don't find a way on how to implement a custom 404 page.

But I can't make a r.HandleFunc("/",...) but it will be too greedy.

For serving a custom error page yourself, see [httprouter configuring NotFound](http://stackoverflow.com/questions/30500322/httprouter-configuring-notfound/30500491#30500491). — icza, Apr 25 '17 at 14:26

score 13 · Accepted Answer · answered Apr 25 '17 at 14:26

13

The Router exports a NotFoundHandler field which you can set to your custom handler.

r := mux.NewRouter()
r.NotFoundHandler = MyCustom404Handler

answered Apr 25 '17 at 14:26

mkopriva

35,176
4
57
71

eexit · Answer 2 · 2019-07-15T17:11:30.440

11

Sometimes, you spend a lot of time building a stack of middleware that does many things like logging, sending metrics and so... And the default 404 handler just skips all the middlewares.

I was able to solve this issue by re-setting the default 404 handler like this:

router := mux.NewRouter()
router.Use(someMiddleware())
// Re-define the default NotFound handler
router.NotFoundHandler = router.NewRoute().HandlerFunc(http.NotFound).GetHandler()

Now, the 404 default handler is also going thru all the middlewares.

edited Jul 15 '19 at 17:11

answered Jul 08 '19 at 14:54

eexit

138
2
8

Cool solution. But you have to do this assigning either after declaring your real routes or by using `BuildOnly()` method to prevent this route from acting like a wildcard. – Berkant İpek Aug 02 '19 at 10:09
Works, but You should define this NotFoundHandler registered once all the handlers are registered, otherwise, it will override all the handlers – sharath chandra Jul 14 '21 at 09:10

score 2 · Answer 3 · answered Apr 25 '17 at 14:25

2

Set the NotFoundHandler to a handler method that returns your custom 404 page.

answered Apr 25 '17 at 14:25

Jonathan Hall

75,165
16
143
189

score 2 · Answer 4 · answered Jul 20 '21 at 18:32

2

r := mux.NewRouter()

h := http.HandlerFunc(NotFound)
r.NotFoundHandler = h
    
func NotFound(w http.ResponseWriter, r *http.Request) {
        
}

answered Jul 20 '21 at 18:32

Faruk AK

249
2
6

Please add some explanation about what this does – Matiiss Jul 20 '21 at 22:31

setup 404 NotFound handler on a gorilla mux router

4 Answers4