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

package main

import (
	"context"
	"database/sql"
	"expvar"
	"flag"
	"fmt"
	"os"
	"runtime"
	"strings"
	"sync"
	"time"

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

var (
	buildTime string
	version   string
)

// 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
	}
	// Add a new limiter struct containing fields for the requests-per-second and burst
	// values, and a boolean field which we can use to enable/disable rate limiting
	// altogether.
	limiter struct {
		rps     float64
		burst   int
		enabled bool
	}
	smtp struct {
		host     string
		port     int
		username string
		password string
		sender   string
	}
	// Add a cors struct and trustedOrigins field with the type []string.
	cors struct {
		trustedOrigins []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
	mailer mailer.Mailer
	wg     sync.WaitGroup
}

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")

	// Create command line flags to read the setting values into the config struct.
	// Notice that we use true as the default for the 'enabled' setting?
	flag.Float64Var(&cfg.limiter.rps, "limiter-rps", 2, "Rate limiter maximum requests per second")
	flag.IntVar(&cfg.limiter.burst, "limiter-burst", 4, "Rate limiter maximum burst")
	flag.BoolVar(&cfg.limiter.enabled, "limiter-enabled", true, "Enable rate limiter")

	// Read the SMTP server configuration settings into the config struct, using the
	// Mailtrap settings as the default values. IMPORTANT: If you're following along,
	// make sure to replace the default values for smtp-username and smtp-password
	// with your own Mailtrap credentials.
	flag.StringVar(&cfg.smtp.host, "smtp-host", "sandbox.smtp.mailtrap.io", "SMTP host")
	flag.IntVar(&cfg.smtp.port, "smtp-port", 2525, "SMTP port")
	flag.StringVar(&cfg.smtp.username, "smtp-username", "3d946287da35ea", "SMTP username")
	flag.StringVar(&cfg.smtp.password, "smtp-password", "d06a774b484ca3", "SMTP password")
	flag.StringVar(&cfg.smtp.sender, "smtp-sender", "Greenlight <no-reply@greenlight.debuggingjon.dev>", "SMTP sender")

	// Use the flag.Func() function to process the -cors-trusted-origins command line
	// flag. In this we use the strings.Fields() function to split the flag value into a
	// slice based on whitespace characters and assign it to our config struct.
	// Importantly, if the -cors-trusted-origins flag is not present, contains the empty
	// string, or contains only whitespace, then strings.Fields() will return an empty
	// []string slice.
	flag.Func("cors-trusted-origins", "Trusted CORS origins (space separated)", func(val string) error {
		cfg.cors.trustedOrigins = strings.Fields(val)
		return nil
	})

	// Create a new version boolean flag with the default value of false.
	displayVersion := flag.Bool("version", false, "Display version and exit")

	flag.Parse()

	// If the version flag value is true, then print out the version number and
	// immediately exit.
	if *displayVersion {
		fmt.Printf("Version:\t%s\n", version)
		// Print out the contents of the buildTime variable.
		fmt.Printf("Build time:\t%s\n", buildTime)
		os.Exit(0)
	}

	// 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)

	// Publish a new "version" variable in the expvar handler containing our application
	// version number (currently the constant "1.0.0").
	expvar.NewString("version").Set(version)
	expvar.Publish("goroutines", expvar.Func(func() any {
		return runtime.NumGoroutine()
	}))

	// Publish the database connection pool statistics.
	expvar.Publish("database", expvar.Func(func() any {
		return db.Stats()
	}))

	// Publish the current Unix timestamp.
	expvar.Publish("timestamp", expvar.Func(func() any {
		return time.Now().Unix()
	}))

	app := &application{
		config: cfg,
		logger: logger,
		models: data.NewModels(db),
		mailer: mailer.New(cfg.smtp.host, cfg.smtp.port, cfg.smtp.username, cfg.smtp.password, cfg.smtp.sender),
	}

	err = app.serve()
	if err != nil {
		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
}