HTTP Closures

gistfile1.go

package main

import (
	"net/http"
	"database/sql"
	"fmt"
	"log"
	"os"
)

func helloHandler(db *sql.DB) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    		var name string
    		// Execute the query.
    		row := db.QueryRow("SELECT myname FROM mytable")
    		if err := row.Scan(&name); err != nil {
        		http.Error(w, err.Error(), 500)
        		return
    		}
    		// Write it back to the client.
    		fmt.Fprintf(w, "hi %s!\n", name)
    	})
}

func withMetrics(l *log.Logger, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		began := time.Now()
		next.ServeHTTP(w, r)
		l.Printf("%s %s took %s", r.Method, r.URL, time.Since(began))
	})
}

func main() {
	// Open our database connection.
	db, err := sql.Open("postgres", "…")
	if err != nil {
		log.Fatal(err)
	}
	// Create our logger
	logger := log.New(os.Stdout, "", 0)
	// Register our handler.
	http.Handle("/hello", helloHandler(db))
	// Register our handler with metrics logging
	http.Handle("/hello_again", withMetrics(logger, helloHandler(db)))
	http.ListenAndServe(":8080", nil)
}

and how do you write a test against the handler hellohandler using this approach?

The main issue with the @tsenart method is if both your handlers and handles live in a separate package from your main database instance. This still requires creating a struct or global variable in order to pass the database to these functions from main. Hence, I don't consider it a very realistic solution for large projects. In terms of package layout and compartmentalization, the method used here looks very nice: https://hackernoon.com/make-yourself-a-go-web-server-with-mongodb-go-on-go-on-go-on-48f394f24e

Diving into best practices to separate DB from code for scalability/flexibility, and came here from ben johnson's post (https://medium.com/@benbjohnson/structuring-applications-in-go-3b04be4ff091). Thank you for putting this together. Is there any blog posts on how to write tests against this approach? Thanks!

+1 very helpful

smarter way to organize golang code

and how do you write a test against the handler hellohandler using this approach?

Execute helloHandler and put the returned HandlerFunc into a var

and how do you write a test against the handler hellohandler using this approach?

Execute helloHandler and put the returned HandlerFunc into a var

I guess writing unit test this way is again unrealistic, just imagine if there are thousands of handlers to be tested.