feat: defer function, add info to string var dsn

projects/greenlight/cmd/api/main.go

@@ -54,7 +54,7 @@ func main() {
 	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.StringVar(&cfg.db.dsn, "db-dsn", dsn, "PostgreSQL DSN (From DATABASE_DSN in .env)")
 
 	flag.Parse()
 
@@ -68,8 +68,11 @@ func main() {
 
 	// Defer a call to db.Close() so that the connection pool is closed before the
 	// main() function exits.
-	defer db.Close()
-
+	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.Printf("database connection pool established")