main.go

package main

import (
	"log"
	"net/http"
)

func main() {
	fs := interceptHandler(http.FileServer(http.Dir(".")), defaultErrorHandler)
	log.Fatal(http.ListenAndServe(":80", fs))
}

type interceptResponseWriter struct {
	http.ResponseWriter
	errH func(http.ResponseWriter, int)
}

func (w *interceptResponseWriter) WriteHeader(status int) {
	if status >= http.StatusBadRequest {
		w.errH(w.ResponseWriter, status)
		w.errH = nil
	} else {
		w.ResponseWriter.WriteHeader(status)
	}
}

type ErrorHandler func(http.ResponseWriter, int)

func (w *interceptResponseWriter) Write(p []byte) (n int, err error) {
	if w.errH == nil {
		return len(p), nil
	}
	return w.ResponseWriter.Write(p)
}

func defaultErrorHandler(w http.ResponseWriter, status int) {
	log.Print("error handler called")
	http.Error(w, "foo", status)
}

func interceptHandler(next http.Handler, errH ErrorHandler) http.Handler {
	if errH == nil {
		errH = defaultErrorHandler
	}
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		next.ServeHTTP(&interceptResponseWriter{w, errH}, r)
	})
}

How to use http.Redirect instead of http.Error in function defaultErrorHandler?
I can not figure out how to send the r *http.Request around this whole wrapper
Thnx