The proxy design pattern belongs to the structural group that controls the creation and access of objects. A proxy is usually a simple small object between the client code and the real (more complex) object that controls access to the real object. When the conditions are right, the proxy will delegate the client’s request to the actual object for processing.
What is a Proxy Design Pattern in C#?
Imagine a one-stop shop in public offices (like in wards). Although there are many people in the ward in charge of different fields of work, the one-stop shop is the only place where people come into contact.
This department receives all requests from people and checks relevant documents. If the documents are complete and appropriate, the one-stop shop will transfer the documents to the person in charge of the right job for settlement. If the paperwork is incomplete or has errors, the one-stop shop will return it and ask for it to be completed before receiving it.
So what good is this model? Please understand that handling each job at the request of the people is not simple. It takes time and effort. If things go straight to the immediate department, they may have to do things that aren’t really their area of expertise, like checking paperwork. Meanwhile, if the paperwork arrives correctly, they can start their work right away and focus on that.
When there are results from the specialized department, the one-stop-shop will return the results to the people on behalf of the people. At the same time, this department can make additional requests from the people related to the main results.
The one-stop shop works on the idea of a proxy design pattern: controlling access to a specific service; activate the service only when the incoming request matches; perform additional services upon completion of the request.
Now back to the programming world. Imagine the process of accessing a database.
You can allow the client to directly call the database access code.
Problem Solved by Proxy Pattern
However, accessing the database is often complicated, time consuming and processing resources. If the client is not eligible for access or the client’s request does not match, letting the client directly execute the data access code causes a waste of resources.
At this point the proxy model becomes very suitable: a lightweight object (proxy) now stands between the client and the data access code. The proxy checks all conditions before calling the data access code on behalf of the client.
Solution with The Proxy Pattern
UML Diagram of The Proxy Design Pattern in C#
Below is a UML diagram of the Proxy design pattern.
In the above design, there are a few points to note:
Subject is the class that actually helps you handle the request. However, client code will not be able to directly work with objects of this class.
ISubject is an interface with the same method descriptions as that of Subject. In the above diagram, both Subject and ISubject have a Request method. The client will contain (has-a) a variable of type ISubject (and this variable will point to a proxy object).
Proxy is a class that implements the ISubject interface. An object of the Proxy will be contained and used by the client instead of the object of the Subject. Subject methods are called through the Proxy object. In other words, the object of the Proxy will call the actual method of the Subject on behalf of the client.
As you can see, the design diagram of Proxy is quite simple. The key point is that the proxy must have the same method description as the real Subject, while also blocking between the client and the Subject. Client does not call Subject directly, but calls through Proxy. The proxy calls the Subject on behalf of the client. Through this process, the Proxy controls access to the Subject.
Implementing the Proxy Design Pattern in C#
Once you understand the general principle of Proxy, now let’s write a simple program that implements this design pattern.
The program below repeats the design shown above. The program simulates simple account registration from the command line interface.
using System;
using Framework;
namespace P01_Concept
{
class Subject : ISubject
{
public void Request(string name)
{
ViewHelper.WriteLine($"Hello, {name}. I'm the real subject. I'm doing my job for you", ConsoleColor.Cyan);
}
}
interface ISubject
{
void Request(string name);
}
class Proxy : ISubject
{
private readonly Subject _subject;
public Proxy() => _subject = new Subject();
public Proxy(Subject subject) => _subject = subject;
public void Request(string name)
{
ViewHelper.WriteLine($"Hello, {name}. I'm the proxy. Your request will be processing now. Thank you!", ConsoleColor.Yellow);
_subject.Request(name);
ViewHelper.WriteLine($"Greating! I'm the proxy again. Your work is done, {name}. Goodbye!", ConsoleColor.Green);
}
}
class Program
{
static ISubject _proxy = new Proxy();
static void Main(string[] args)
{
var app = new Application
{
Title = "PROXY DESIGN PATTERN",
Config = RegisterRoutes
};
app.Run();
}
private static void RegisterRoutes()
{
var router = Router.Instance;
router.Register(
route: "register",
action: (p) => { CreateAccount(p["name"]); },
"Request to register a new account in the system.rnSyntax: register ? name = ..."
);
}
private static void CreateAccount(string name)
{
_proxy.Request(name);
}
}
}
The results of running the program are as follows:
The above simple program re-implements the presented UML design. You will notice that the client code (the Program class) contains the object of the Proxy. It also calls the Proxy’s Request method.
However, the Proxy adds its own directive before and after the actual execution of the Subject. In real situations, this is where the code that controls accessing the actual object is written, as well as performing additional operations.
Use Cases for the Proxy Design Pattern in C#
Scenario 1: Accessing Expensive Resources
In certain situations, accessing resources can be a resource-intensive operation, leading to performance issues. The Proxy Design Pattern can help address this challenge by introducing a proxy that optimizes resource usage.
- Illustration of a resource-intensive operation:
Consider a scenario where an application needs to retrieve large files from a remote server. This process may involve significant network latency and consume substantial bandwidth. Directly accessing these resources each time they are required could lead to delays and inefficiencies.
- Implementation of a proxy to optimize resource usage:
To tackle this issue, the Proxy Design Pattern can be employed. A proxy is created as an intermediary between the client and the remote server. When the client requests a file, the proxy intercepts the request and performs additional operations to optimize resource usage. For example, it could implement a caching mechanism to store frequently accessed files locally, reducing the need for repeated remote requests.
B. Scenario 2: Implementing Security Measures
Security is a critical aspect of software development. The Proxy Design Pattern can be instrumental in enforcing authentication and authorization measures, ensuring that only authorized users can access certain objects.
- Demonstrating how a proxy can enforce authentication and authorization:
Consider an application that provides access to sensitive data, such as financial information or personal records. It is imperative to restrict access to these resources to authorized users only. The Proxy Design Pattern can help by implementing a proxy that verifies the user’s credentials before allowing access to the requested object.
- Code snippets showcasing security-related proxy implementation:
In the context of security, the proxy acts as a gatekeeper. It authenticates the user, validates their permissions, and grants or denies access accordingly. By encapsulating these security checks within the proxy, the underlying real subject remains protected from unauthorized access attempts.
For instance, the proxy can prompt the user to provide their credentials, verify them against a database or authentication service, and only if the user is authorized, forward the request to the real subject to retrieve the sensitive data.
By leveraging the Proxy Design Pattern in this manner, developers can strengthen the security of their applications and prevent unauthorized access to critical resources.
Advantages of Using the Proxy Design Pattern
- Enhanced Performance and Resource Utilization:
- By implementing a proxy, resource-intensive operations can be optimized, leading to improved performance and reduced latency.
- Caching mechanisms within the proxy can reduce the frequency of expensive operations, resulting in faster response times.
- Improved Security and Access Control:
- The proxy acts as a gatekeeper, enforcing authentication and authorization checks, ensuring that only authorized users can access sensitive objects.
- Security measures implemented within the proxy help protect the underlying real subject from unauthorized access attempts.
Limitations of the Proxy Design Pattern
- Additional Complexity and Overhead:
- Implementing the Proxy Design Pattern introduces additional layers and components, which can increase code complexity and maintenance efforts.
- The proxy might need to perform additional operations, leading to potential performance overhead, especially in scenarios where real-time access is critical.
- Potential Impact on Performance in Certain Scenarios:
- If the proxy design is not implemented efficiently, it can introduce overhead and impact performance, particularly when dealing with high-volume or time-sensitive operations.
- Careful consideration must be given to ensure that the proxy implementation does not become a bottleneck in the system.
Advantages and Limitations of the Proxy Design Pattern
The Proxy Design Pattern in C# offers several advantages that make it a valuable tool for controlling object access in software development.
Enhanced Performance and Resource Utilization:
By implementing the Proxy Design Pattern, developers can optimize resource usage and improve overall system performance. The proxy acts as an intermediary, allowing it to perform additional operations to enhance efficiency.
For example, a proxy can implement a caching mechanism that stores frequently accessed data locally. This reduces the need for repeated expensive operations, such as fetching data from a remote server. Instead, the proxy can quickly retrieve the data from its cache, resulting in faster response times and reduced latency.
Improved Security and Access Control:
Another significant advantage of the Proxy Design Pattern is its ability to enforce authentication and authorization measures. The proxy acts as a gatekeeper, verifying the user’s credentials and permissions before granting access to the requested object.
By encapsulating security checks within the proxy, developers can protect sensitive resources from unauthorized access attempts. This helps ensure that only authorized users can interact with critical data or functionalities, enhancing the overall security of the application.
Limitations of the Proxy Design Pattern
While the Proxy Design Pattern offers numerous advantages, it is essential to consider its limitations to make informed decisions about its usage in software development.
Additional Complexity and Overhead:
Implementing the Proxy Design Pattern introduces additional layers and components, which can increase code complexity and maintenance efforts. Developers need to carefully design and manage the proxy to ensure its effectiveness and minimize potential complexities.
Furthermore, depending on the specific implementation, the proxy may need to perform additional operations, such as caching or security checks. These operations can introduce overhead and potentially impact the overall system performance. Therefore, it is crucial to strike a balance between the benefits gained from using the proxy and the additional complexity it introduces.
Potential Impact on Performance in Certain Scenarios:
While the Proxy Design Pattern can enhance performance in many cases, it is important to consider specific scenarios where its implementation might have an adverse effect.
For example, in situations where real-time access to objects is critical, the additional operations performed by the proxy could introduce delays. If not carefully managed, the proxy implementation may become a bottleneck, negatively impacting system performance.
It is essential to analyze the requirements and characteristics of the system to determine whether the Proxy Design Pattern is suitable for a particular use case. Performance considerations, scalability needs, and the trade-off between added complexity and benefits should be carefully evaluated.
Conclusion
In this lesson we learned the proxy design pattern and its basic implementation in C#. There are several situations where Proxy can be used:
- You need to control object access;
- You only want to create objects when absolutely necessary;
- Object consumes a lot of resources to initialize and operate;
- Perform additional tasks each time the client accesses the object.
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