Example for "Build Your Own Web Framework in Go" articles

main.go

package main

import (
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"net/http"
	"time"

	"github.com/gorilla/context"
	"github.com/julienschmidt/httprouter"
	"github.com/justinas/alice"
)

func recoverHandler(next http.Handler) http.Handler {
	fn := func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if err := recover(); err != nil {
				log.Printf("panic: %+v", err)
				http.Error(w, http.StatusText(500), 500)
			}
		}()

		next.ServeHTTP(w, r)
	}

	return http.HandlerFunc(fn)
}

func loggingHandler(next http.Handler) http.Handler {
	fn := func(w http.ResponseWriter, r *http.Request) {
		t1 := time.Now()
		next.ServeHTTP(w, r)
		t2 := time.Now()
		log.Printf("[%s] %q %v\n", r.Method, r.URL.String(), t2.Sub(t1))
	}

	return http.HandlerFunc(fn)
}

func aboutHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "You are on the about page.")
}

func indexHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Welcome!")
}

type appContext struct {
	db *sql.DB
}

func (c *appContext) authHandler(next http.Handler) http.Handler {
	fn := func(w http.ResponseWriter, r *http.Request) {
		authToken := r.Header.Get("Authorization")
		user, err := map[string]interface{}{}, errors.New("test")
		// user, err := getUser(c.db, authToken)
		log.Println(authToken)

		if err != nil {
			http.Error(w, http.StatusText(401), 401)
			return
		}

		context.Set(r, "user", user)
		next.ServeHTTP(w, r)
	}

	return http.HandlerFunc(fn)
}

func (c *appContext) adminHandler(w http.ResponseWriter, r *http.Request) {
	user := context.Get(r, "user")
	// Maybe other operations on the database
	json.NewEncoder(w).Encode(user)
}

func (c *appContext) teaHandler(w http.ResponseWriter, r *http.Request) {
	params := context.Get(r, "params").(httprouter.Params)
	log.Println(params.ByName("id"))
	// tea := getTea(c.db, params.ByName("id"))
	json.NewEncoder(w).Encode(nil)
}

// We could also put *httprouter.Router in a field to not get access to the original methods (GET, POST, etc. in uppercase)
type router struct {
	*httprouter.Router
}

func (r *router) Get(path string, handler http.Handler) {
	r.GET(path, wrapHandler(handler))
}

func NewRouter() *router {
	return &router{httprouter.New()}
}

func wrapHandler(h http.Handler) httprouter.Handle {
	return func(w http.ResponseWriter, r *http.Request, ps httprouter.Params) {
		context.Set(r, "params", ps)
		h.ServeHTTP(w, r)
	}
}

func main() {
	// db := sql.Open("postgres", "...")
	appC := appContext{nil}
	commonHandlers := alice.New(context.ClearHandler, loggingHandler, recoverHandler)
	router := NewRouter()
	router.Get("/admin", commonHandlers.Append(appC.authHandler).ThenFunc(appC.adminHandler))
	router.Get("/about", commonHandlers.ThenFunc(aboutHandler))
	router.Get("/", commonHandlers.ThenFunc(indexHandler))
	router.Get("/teas/:id", commonHandlers.ThenFunc(appC.teaHandler))
	http.ListenAndServe(":8080", router)
}

@nmerouze thank you, very interesting articles and code!
I'm new to Go, so forgive what is probably a silly question: I'm trying to adapt this code to move some handlers to a different package, say I want to move the teaHandler handler to an "api" package.
Could you provide some hints on how to do this? The best result I can get is that my method is undefined 😊

@trapias if you are moving code to a different package, you will need to import that package in order to have access to it.

Something like the following:

import (
    "github.com/username/project/api" // or...
    "go-path-src-directory/project/api" // or...
    "./api"
)

func foo() {
    api.Handler()
}

@nmerouze

How do you get a reference to the http.ResponseWriter and http.Request in the loggingHandler function?

func loggingHandler(next http.Handler) http.Handler {
    fn := func(w http.ResponseWriter, r *http.Request) {
        t1 := time.Now()
        next.ServeHTTP(w, r)
        t2 := time.Now()
        log.Printf("[%s] %q %v\n", r.Method, r.URL.String(), t2.Sub(t1))
    }

    return http.HandlerFunc(fn)
}

You are creating an anonymous function and then passing to http.HandlerFunc, where does the writer and request get set?

@diogogmt

the loggingHandler is essentially middleware

func loggingHandler(next http.Handler) http.Handler {
  fn := func(w http.ResponseWriter, r *http.Request) {
      t1 := time.Now()
      next.ServeHTTP(w, r)
      t2 := time.Now()
      log.Printf("[%s] %q %v\n", r.Method, r.URL.String(), t2.Sub(t1))
}

  return http.HandlerFunc(fn)
 }

func indexHandler(w http.ResponseWriter, r *http.Request) {
  fmt.Fprintf(w, "Index Handler")
}

func main() {
  index := http.HandlerFunc(indexHandler)
  http.Handle("/", loggingHandler(index))
  log.Fatal(http.ListenAndServe(":9000", nil))
}