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Request-Endpoint-Response (REPR) Pattern

Overview

The Request-Endpoint-Response (REPR) pattern is a simple but important concept in modern web and API design. The pattern is a way of describing how communication works in web applications and APIs.

At its core:

  1. A client makes a request
  2. The request is sent to a defined endpoint (a URL or route)
  3. The server processes the request and sends back a response

This is the fundamental interaction model for REST APIs, web services, and most HTTP-based systems.

How It Works

1. Request

  • Sent by a client (browser, mobile app, backend service).
  • Contains method (GET, POST, PUT, DELETE), headers, and sometimes a body (e.g., JSON payload).

2. Endpoint

  • A URL path on the server that defines what the request is targeting.
  • Example: /api/customers/123 → endpoint to retrieve customer with ID 123.

3. Response

  • The server sends back data (JSON, HTML, XML, file, etc.) or status codes (e.g., 200 OK, 404 Not Found, 500 Server Error).

Advantages

  • Simplicity: Clear flow of request → endpoint → response.
  • Consistency: Clients always know what to expect.
  • Scalability: Easy to extend by adding new endpoints.
  • Interoperability: Works with any client that speaks HTTP (browsers, apps, services).

Drawbacks

  • Rigid structure: Not ideal for highly dynamic interactions (e.g., streaming, real-time).
  • Overfetching/underfetching: Fixed endpoints may not return exactly what the client needs (GraphQL addresses this).
  • Statelessness: Each request is independent; maintaining state requires extra effort (sessions, tokens, etc.).

Example in C# (.NET Web API)

[ApiController]
[Route("api/[controller]")]
public class CustomersController : ControllerBase
{
    // Endpoint: GET /api/customers/123
    [HttpGet("{id}")]
    public IActionResult GetCustomer(int id)
    {
        var customer = new { Id = id, Name = "Alice", Email = "alice@example.com" };

        // Response: 200 OK with JSON data
        return Ok(customer);
    }
}

Flow:

  1. Request: GET /api/customers/123
  2. Endpoint: api/customers/{id} handled by GetCustomer
  3. Response: 200 OK { "id": 123, "name": "Alice", "email": "alice@example.com" }

When to Use the REPR Pattern

  • When building REST APIs or HTTP-based services
  • For CRUD operations (Create, Read, Update, Delete)
  • When you need a standard, predictable interaction model

For more complex, real-time, or flexible querying needs, alternatives like GraphQL or WebSockets may be better.

Summary

The Request-Endpoint-Response (REPR) pattern is the backbone of REST APIs and web apps: a client sends a request to a defined endpoint, and the server returns a response. It’s simple, scalable, and universal for HTTP communication.