آموزش دیزاین پترن پروکسی (Proxy) در گولنگ

package main
 
import (
 "database/sql"
 "errors"
 "fmt"
 "time"
 
 _ "github.com/mattn/go-sqlite3"
)
 
// Database defines the interface that the real database and proxy will implement.
type Database interface {
 Connect() (*sql.DB, error)
}
 
// RealDatabase implements the Database interface and represents the actual database resource.
type RealDatabase struct{}
 
func (r *RealDatabase) Connect() (*sql.DB, error) {
 db, err := sql.Open("sqlite3", "test.db")
 if err != nil {
  return nil, err
 }
 // Simulate a slow connection by waiting for a few seconds.
 time.Sleep(2 * time.Second)
 return db, nil
}
 
// ProxyDatabase implements the Database interface and provides a surrogate or placeholder for the real database connection.
type ProxyDatabase struct {
 realDatabase *RealDatabase
}
 
func (p *ProxyDatabase) Connect() (*sql.DB, error) {
 if p.realDatabase == nil {
  p.realDatabase = &RealDatabase{}
 }
 // Perform some security checks before allowing access to the real database.
 // For example, check if the user is authorized to access the database.
 if !isUserAuthorized() {
  return nil, errors.New("user is not authorized to access the database")
 }
 // Log the access to the database.
 fmt.Println("User accessed the database at", time.Now().Format(time.RFC3339))
 return p.realDatabase.Connect()
}
 
func isUserAuthorized() bool {
 // Perform some logic to determine if the user is authorized to access the database.
 return true
}
 
func main() {
 var db Database = &ProxyDatabase{}
 connection, err := db.Connect()
 if err != nil {
  fmt.Println("Failed to connect to the database:", err)
  return
 }
 defer connection.Close()
 // Use the database connection.
 fmt.Println("Successfully connected to the database.")
}
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