one common http handler instead of several

Is it possible to not copy paste expression commonHanlder(handler1), commonHanlder(handler2) ... commonHanlder(handlerN) in this code:

rtr.HandleFunc("/", commonHanlder(handler1)).Methods("GET")
rtr.HandleFunc("/page2", commonHanlder(handler2)).Methods("GET")

and set it in one place like

http.ListenAndServe(":3000", commonHanlder(http.DefaultServeMux))

But this variant is not working and gives two errors on compile:

./goRelicAndMux.go:20: cannot use http.DefaultServeMux (type *http.ServeMux) as type gorelic.tHTTPHandlerFunc in argument to commonHanlder
./goRelicAndMux.go:20: cannot use commonHanlder(http.DefaultServeMux) (type gorelic.tHTTPHandlerFunc) as type http.Handler in argument to http.ListenAndServe:
    gorelic.tHTTPHandlerFunc does not implement http.Handler (missing ServeHTTP method)

The full code:

package main

import (
	"github.com/gorilla/mux"
	"github.com/yvasiyarov/gorelic"
	"log"
	"net/http"
)

func main() {
	initNewRelic()
	rtr := mux.NewRouter()
	var commonHanlder = agent.WrapHTTPHandlerFunc

	rtr.HandleFunc("/", commonHanlder(handler1)).Methods("GET")
	rtr.HandleFunc("/page2", commonHanlder(handler2)).Methods("GET")

	http.Handle("/", rtr)
	log.Println("Listening...")
	http.ListenAndServe(":3000", http.DefaultServeMux)
}

func handler1(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("mainPage"))
}

func handler2(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("page 2"))
}

var agent *gorelic.Agent

func initNewRelic() {
	agent = gorelic.NewAgent()
	agent.Verbose = true
	agent.NewrelicName = "test"
	agent.NewrelicLicense = "new relic key"
	agent.Run()
}

It seems like you want to call commonHandler on the root of your application and have it work for all. Since you are using mux, just wrap the mux router once.

func main() {
    initNewRelic()
    rtr := mux.NewRouter()
    var commonHandler = agent.WrapHTTPHandler

    rtr.HandleFunc("/", handler1).Methods("GET")
    rtr.HandleFunc("/page2", handler2).Methods("GET")

    http.Handle("/", commonHandler(rtr))
    log.Println("Listening...")
    http.ListenAndServe(":3000", nil)
}

I also removed the http.DefaultServeMux reference in ListenAndServe since passing nil will automatically use the default.