Proxy pattern

Description

• proxy object controls the creation of and access to subject object
• proxy and subject objects share the same interface

Proxy vs decorator pattern

• Decorator informs and empowers its client, it adds known functionalities to an object
• Proxy restricts and disempowers its client, it controls access to an object with unknown functionalities like authentication

Exemple

public class User { public string Name { get; set; } }

IUserClient.cs

public interface IUserClient { IReadOnlyList<User> GetUsers(); }

UserClient.cs

public class UserClient : IUserClient { public IReadOnlyList<User> GetUsers() { return new[] { new User { Name = "Nicolas" }, new User { Name = "Paul" } }; } }

ProxyUserClient

public class ProxyUserClient : IUserClient { private UserClient userClient; public bool Authenticate(string userName, string password) { if (userName == "Nicolas" && password == "0000") { userClient = new UserClient(); return true; } return false; } public IReadOnlyList<User> GetUsers() { if (userClient == null) { return null; } else { return userClient.GetUsers(); } } }

IUserClient userClient = new UserClient(); // call GetUsers from UserClient: no restrictions var users = userClient.GetUsers(); Console.WriteLine(string.Join('\n', users.Select(x => $"{x.Name}"))); userClient = new ProxyUserClient(); // call GetUsers from ProxyUserClient: authentication restriction users = userClient.GetUsers(); if (users == null) Console.WriteLine("You to authenticate first."); else Console.WriteLine(string.Join('\n', users.Select(x => $"{x.Name}"))); // authentication ((ProxyUserClient)userClient).Authenticate("Nicolas", "0000"); users = userClient.GetUsers(); if (users == null) Console.WriteLine("You to authenticate first."); else Console.WriteLine(string.Join('\n', users.Select(x => $"{x.Name}")));