Negroni golang mgo middleware example

app.go

package main

import (
	"github.com/codegangsta/negroni"
	"github.com/gorilla/context"
	"github.com/unrolled/render"
	"labix.org/v2/mgo"
	"labix.org/v2/mgo/bson"
	"log"
	"net/http"
	"os"
)

type key int

const db key = 0

func GetDb(r *http.Request) *mgo.Database {
	if rv := context.Get(r, db); rv != nil {
		return rv.(*mgo.Database)
	}
	return nil
}

func SetDb(r *http.Request, val *mgo.Database) {
	context.Set(r, db, val)
}

type Site struct {
	Env  string
	Id   bson.ObjectId `bson:"_id"`
	Name string        `bson:"name"`
}

func getSite(db *mgo.Database) *Site {
	var aSite Site
	sites := db.C("COLLECTION__NAME")

	err := sites.Find(bson.M{"name": "some site name"}).One(&aSite)
	if err != nil {
		log.Print(err)
	}
	aSite.Env = os.Getenv("APP_ENV")
	return &aSite
}

func MongoMiddleware() negroni.HandlerFunc {
	database := os.Getenv("DB_NAME")
	session, err := mgo.Dial("127.0.0.1:27017")

	if err != nil {
		panic(err)
	}

	return negroni.HandlerFunc(func(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
		reqSession := session.Clone()
		defer reqSession.Close()
		db := reqSession.DB(database)
		SetDb(r, db)
		next(rw, r)
	})
}

func main() {
	r := render.New(render.Options{
		Layout: "index",
		Delims: render.Delims{"[[", "]]"},
	})

	mux := http.NewServeMux()

	mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
		db := GetDb(req)
		site := getSite(db)
		r.HTML(w, http.StatusOK, "home", site)
	})

	n := negroni.Classic()
	n.Use(MongoMiddleware())
	n.UseHandler(mux)
	n.Run(":3200")
}

use n.UseHandler(context.ClearHandler(mux)) on line 80 to avoid memory leak

@Adesegun thanks that was very important point.

Why doesn't defer reqSession.Close() in the middleware closes the session before handler can use it?

Should line 49 be somehow moved from to main -- Does calling mgo.Dial per request affect performance? Or is this somehow cached away.

From mgo Dial DocumentationThis method is generally called just once for a given cluster. Further sessions to the same cluster are then established using the New or Copy methods on the obtained session. This will make them share the underlying cluster, and manage the pool of connections appropriately.