Http: multiple response.WriteHeader calls

[nyrf]

package main

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

func main() {
	r := mux.NewRouter()
	r.HandleFunc("/", wrapController("Home", &TODO{}))
	http.ListenAndServe(":3000", r)
}

// TODO
type TODO struct {
	BaseController
}

func (t *TODO) Home() {
	t.Response.Write([]byte("todo home"))
}

// Helper
func handleController(w http.ResponseWriter, req *http.Request, fn string, ctrl Controller) {
	ctrl.New(w, req)
	in := make([]reflect.Value, 0)
	reflect.ValueOf(ctrl).MethodByName(fn).Call(in)
}
func wrapController(fn string, ctrl Controller) func(http.ResponseWriter, *http.Request) {
	return func(w http.ResponseWriter, req *http.Request) {
		handleController(w, req, fn, ctrl)
	}
}

// Controller
type Controller interface {
	New(http.ResponseWriter, *http.Request)
}

type BaseController struct {
	Request  *http.Request
	Response http.ResponseWriter
}

func (b *BaseController) New(w http.ResponseWriter, r *http.Request) {
	b.Request = r
	b.Response = w
}

When run wrk -t12 -c900 -d10s http://localhost:3000, got errors http: multiple response.WriteHeader calls, i can’t find how to fix it,thanks.

[matt (Matt Holt)]

I suspect it’s because you’re using the same Controller for all requests. When you do &TODO{} in your main(), that only creates one Controller and all requests share the same one.

By the way, this is very unusual Go code. Can I ask why you’re doing this?

[nyrf]

I want to write a mini framework to learn go. I referenced some code from https://github.com/astaxie/beego

[matt (Matt Holt)]

Run your program with the -race flag and see if it finds any race conditions first. I’m suspicious of that Controller.

[nyrf]

@matt

-race

Thanks, i tried, but nothing happend,

[nyrf]

Solved. Use sync.RWMutex can fix this.Thanks.

[matt (Matt Holt)]

Remember to mark your reply as the answer (click the chrck mark) so others who find this thread can find the answer quickly

[nyrf]

OK, thank you.

[elithrar (Matt Silverlock)]

@nyrf

Solved. Use sync.RWMutex can fix this.Thanks.

This is a very odd design (as @mholt points out) - in fact, it’s pretty dangerous as you have one controller instance and will leak data across requests (as you are finding out).

Sharing the same controller across requests is not how to write a Go HTTP server.

Take a look at these articles and move away from the “Controller” pattern —which doesn’t port well to Go, as you’re finding:

• Writing Web Applications - The Go Programming Language (a simple web application example)
• LearnServerProgramming · golang/go Wiki · GitHub (a list of web server programming resources, inc. the above link)

[nyrf]

@elithrar Thanks, because i learned golfing from beego, so my code referenced from https://github.com/astaxie/beego and https://github.com/astaxie/build-web-application-with-golang/blob/master/en/13.2.md