http: multiple response.WriteHeader calls about gziphandler

[MarufSaidov6]

hihihi

[tmthrgd]

Caveat emptor: I have nothing to do with this library. That being said, the following example works perfectly fine.

The first bug in the above example is that you're not actually using the gzip handler because you are registering it with http.DefaultServeMux but then explicitly passing a handler into http.ListenAndServe (which is very good practice IMO).

The second bug in the above example is that the notFoundHandler doesn't set the Content-Type before it writes the error message. <speculation> This leaves it too late for the GzipHandler to set the Content-Type header but the http.Server does it's own sniffing and infers the incorrect mime-type application/x-gzip. </speculation> The built-in http.Error method does set the Content-Type header before it calls WriteHeader and thus avoids this problem.

Working example:

package main

import (
	"fmt"
	"net/http"

	"github.com/gorilla/mux"
	"github.com/NYTimes/gziphandler"
)

func main() {
	r := mux.NewRouter()
	r.HandleFunc("/", homeHandler)
	r.NotFoundHandler = http.HandlerFunc(notFoundHandler)
	http.ListenAndServe(":3333", gziphandler.GzipHandler(r))
}

func homeHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Hello, World!\n")
}

func notFoundHandler(w http.ResponseWriter, r *http.Request) {
	http.Error(w, "404 - Not Found!", http.StatusNotFound)
}