I'm stuck with json.marshal in go

I'm complete newbie in go, started few days ago. I want to connect to mongodb, search, create a service and use it for angular. I've done almost everything but I have problem with json.marshal(). Can someone tell me what am I doing wrong, or is there a better way? thx

The error is
"./main.go:96: multiple-value json.Marshal() in single-value context"

package main
import (
"encoding/json"
"flag"
"fmt"
"github.com/gorilla/mux"
"labix.org/v2/mgo"
"labix.org/v2/mgo/bson"
"log"
"net/http"
)
type warrior struct {
Name       string        `json:"name"`
LowDamage  int           `json:"low_damage"`
HighDamage int           `json:"high_damage"`
Health     int           `json:"health"`
HealthLeft int           `json:"health_left"`
Armor      int           `json:"armor"`
Id         bson.ObjectId "_id,omitempty"
}
func getWarriors(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Type", "application/json")
w.WriteHeader(200)
w.Write(mongo())
}
func main() {
// command line flags
port := flag.Int("port", 5001, "port to serve on")
dir := flag.String("random message 1", "web/", "random message 2")
flag.Parse()
// handle all requests by serving a file of the same name
fs := http.Dir(*dir)
fileHandler := http.FileServer(fs)
// ROUTES
router := mux.NewRouter()
router.Handle("/", http.RedirectHandler("/static/", 302))
router.HandleFunc("/warriors", getWarriors).Methods("GET")
router.PathPrefix("/static/").Handler(http.StripPrefix("/static", fileHandler))
http.Handle("/", router)
log.Printf("Running on port %d\n", *port)
addr := fmt.Sprintf("127.0.0.1:%d", *port)
err := http.ListenAndServe(addr, nil)
fmt.Println(err.Error())
}
func mongo() []byte {
session, err := mgo.Dial("mongodb://localhost:27017/test")
if err != nil {
panic(err)
}
defer session.Close()
// Optional. Switch the session to a monotonic behavior.
session.SetMode(mgo.Monotonic, true)
// select dm + table name
c := session.DB("test").C("warriors")
e := warrior{
Name:       "first event",
LowDamage:  2,
HighDamage: 4,
Health:     40,
HealthLeft: 40,
Armor:      1,
}
// insert data
err = c.Insert(e)
if err != nil {
panic(err)
}
// search show results []warrior{} for all warrior{}
result := []warrior{}
// err = c.Find(bson.M{"name": "first event"}).One(&result)
err = c.Find(bson.M{"name": "first event"}).Limit(10).All(&result)
if err != nil {
panic(err)
}
b := json.Marshal(result)
log.Println("JSON:", result)
return b
}

Look at the documentation of this function: http://golang.org/pkg/encoding/json/#Marshal

func Marshal(v interface{}) ([]byte, error)

It returns two values. The problem here is that you just give it one variable to get those two values:

b := json.Marshal(result)

So you just have to correct it this way:

b, err := json.Marshal(result)