go-playground/projects/greenlight/cmd/api/main.go

package main

import (
	"context"
	"database/sql"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"time"

	"github.com/joho/godotenv"
	_ "github.com/lib/pq"
	"greenlight.debuggingjon.dev/internal/data"
	"greenlight.debuggingjon.dev/internal/jsonlog"
)

// Declare a string containing the application version number. Later in the book we'll
// generate this automatically at build time, but for now we'll just store the version
// number as a hard-coded global constant.
const version = "1.0.0"

// Define a config struct to hold all the configuration settings for our application.
// For now, the only configuration settings will be the network port that we want the
// server to listen on, and the name of the current operating environment for the
// application (development, staging, production, etc.). We will read in these
// configuration settings from command-line flags when the application starts.
type config struct {
	port int
	env  string
	db   struct {
		dsn          string
		maxOpenConns int
		maxIdleConns int
		maxIdleTime  string
	}
}

// Define an application struct to hold the dependencies for our HTTP handlers, helpers,
// and middleware. At the moment this only contains a copy of the config struct and a
// logger, but it will grow to include a lot more as our build progresses.
type application struct {
	config config
	logger *jsonlog.Logger
	models data.Models
}

func main() {
	var cfg config

	// Initialize a new jsonlog.Logger which writes any messages *at or above* the INFO
	// severity level to the standard out stream.
	logger := jsonlog.New(os.Stdout, jsonlog.LevelInfo)

	err := godotenv.Load()
	if err != nil {
		logger.PrintFatal(err, nil)
	}
	dsn := os.Getenv("DATABASE_DSN")

	flag.IntVar(&cfg.port, "port", 4000, "API server port")
	flag.StringVar(&cfg.env, "env", "development", "Environment (development|staging|production)")
	// Read the DSN value from the db-dsn command-line flag into the config struct. We
	// default to using our development DSN if no flag is provided.
	flag.StringVar(&cfg.db.dsn, "db-dsn", dsn, "PostgreSQL DSN (Default from DATABASE_DSN in .env)")
	// Read the connection pool settings from command-line flags into the config struct.
	// Notice the default values that we're using?
	flag.IntVar(&cfg.db.maxOpenConns, "db-max-open-conns", 25, "PostgreSQL max open connections")
	flag.IntVar(&cfg.db.maxIdleConns, "db-max-idle-conns", 25, "PostgreSQL max idle connections")
	flag.StringVar(&cfg.db.maxIdleTime, "db-max-idle-time", "15m", "PostgreSQL max connection idle time")

	flag.Parse()

	// Call the openDB() helper function (see below) to create the connection pool,
	// passing in the config struct. If this returns an error, we log it and exit the
	// application immediately.
	db, err := openDB(cfg)
	if err != nil {
		logger.PrintFatal(err, nil)
	}

	// Defer a call to db.Close() so that the connection pool is closed before the
	// main() function exits.
	defer func() {
		if closeErr := db.Close(); closeErr != nil && err == nil {
			err = closeErr
		}
	}()
	// Also log a message to say that the connection pool has been successfully
	// established.
	logger.PrintInfo("database connection pool established", nil)

	app := &application{
		config: cfg,
		logger: logger,
		models: data.NewModels(db),
	}

	// Use the httprouter instance returned by app.routes() as the server handler.
	srv := &http.Server{
		Addr:         fmt.Sprintf(":%d", cfg.port),
		Handler:      app.routes(),
		IdleTimeout:  time.Minute,
		ErrorLog:     log.New(logger, "", 0),
		ReadTimeout:  10 * time.Second,
		WriteTimeout: 30 * time.Second,
	}

	logger.PrintInfo("starting server", map[string]string{
		"addr": srv.Addr,
		"env":  cfg.env,
	})
	err = srv.ListenAndServe()
	logger.PrintFatal(err, nil)
}

func openDB(cfg config) (*sql.DB, error) {
	db, err := sql.Open("postgres", cfg.db.dsn)
	if err != nil {
		return nil, err
	}

	// Set the maximum number of open (in-use + idle) connections in the pool. Note that
	// passing a value less than or equal to 0 will mean there is no limit.
	db.SetMaxOpenConns(cfg.db.maxOpenConns)

	// Set the maximum number of idle connections in the pool. Again, passing a value
	// less than or equal to 0 will mean there is no limit.
	db.SetMaxIdleConns(cfg.db.maxIdleConns)

	// Use the time.ParseDuration() function to convert the idle timeout duration string
	// to a time.Duration type.
	duration, err := time.ParseDuration(cfg.db.maxIdleTime)
	if err != nil {
		return nil, err
	}

	// Set the maximum idle timeout.
	db.SetConnMaxIdleTime(duration)

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	err = db.PingContext(ctx)
	if err != nil {
		return nil, err
	}

	return db, nil
}