Original http status text by `http.Hijacker`.

main.go

package main

import (
	"fmt"
	"log"
	"net/http"
)

func indexHandler(w http.ResponseWriter, req *http.Request) {
	hj, ok := w.(http.Hijacker)
	if !ok {
		http.Error(w, "webserver doesn't support hijacking", http.StatusInternalServerError)
		return
	}
	conn, bufrw, err := hj.Hijack()
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	defer conn.Close()

	fmt.Fprint(bufrw, `HTTP/1.1 808 Double Not Found
Date: Wed, 26 Nov 2014 03:37:57 GMT
Content-Length: 26
Content-Type: application/json; charset=utf-8

{"error_message":"error?"}`)
	bufrw.Flush()
}

func main() {
	http.HandleFunc("/", indexHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
}