feat: validation, postgress connection,

projects/greenlight/cmd/api/main.go

@@ -1,12 +1,17 @@
 package main
 
 import (
+	"context"
+	"database/sql"
 	"flag"
 	"fmt"
 	"log"
 	"net/http"
 	"os"
 	"time"
+
+	"github.com/joho/godotenv"
+	_ "github.com/lib/pq"
 )
 
 // Declare a string containing the application version number. Later in the book we'll
@@ -22,6 +27,9 @@ const version = "1.0.0"
 type config struct {
 	port int
 	env  string
+	db   struct {
+		dsn string
+	}
 }
 
 // Define an application struct to hold the dependencies for our HTTP handlers, helpers,
@@ -33,13 +41,38 @@ type application struct {
 }
 
 func main() {
+	logger := log.New(os.Stdout, "", log.Ldate|log.Ltime)
 	var cfg config
 
+	err := godotenv.Load()
+	if err != nil {
+		logger.Fatal(err)
+	}
+	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")
+
 	flag.Parse()
 
-	logger := log.New(os.Stdout, "", log.Ldate|log.Ltime)
+	// 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.Fatal(err)
+	}
+
+	// Defer a call to db.Close() so that the connection pool is closed before the
+	// main() function exits.
+	defer db.Close()
+
+	// Also log a message to say that the connection pool has been successfully
+	// established.
+	logger.Printf("database connection pool established")
 
 	app := &application{
 		config: cfg,
@@ -56,6 +89,31 @@ func main() {
 	}
 
 	logger.Printf("starting %s server on %s", cfg.env, srv.Addr)
-	err := srv.ListenAndServe()
+	err = srv.ListenAndServe()
 	logger.Fatal(err)
 }
+
+func openDB(cfg config) (*sql.DB, error) {
+	// Use sql.Open() to create an empty connection pool, using the DSN from the config
+	// struct.
+	db, err := sql.Open("postgres", cfg.db.dsn)
+	if err != nil {
+		return nil, err
+	}
+
+	// Create a context with a 5-second timeout deadline.
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	// Use PingContext() to establish a new connection to the database, passing in the
+	// context we created above as a parameter. If the connection couldn't be
+	// established successfully within the 5 second deadline, then this will return an
+	// error.
+	err = db.PingContext(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	// Return the sql.DB connection pool.
+	return db, nil
+}