Dotnet | Request Pipeline

A request in .NET Core (now commonly called ASP.NET Core) flows through a well-defined pipeline. Think of it as a chain of steps that process an HTTP request and produce a response.

Here’s the flow in a clear, conceptual way:

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1. Client Sends HTTP Request

A browser, mobile app, or API client sends an HTTP request:

• URL (e.g., /api/products)
• Method (GET, POST, etc.)
• Headers, body

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2. Web Server (Kestrel)

The request first hits the built-in web server:

• Kestrel
• It listens for incoming HTTP requests and forwards them to the app

Optionally, Kestrel can sit behind:

• IIS
• Nginx

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3. Middleware Pipeline (Core of the Flow)

This is the most important part.

Middleware are components executed in sequence. Each one can:

• Handle the request
• Modify it
• Pass it to the next middleware

Typical pipeline setup (in Program.cs):

app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers();

Flow inside middleware:

Request → Middleware 1 → Middleware 2 → Middleware 3 → Endpoint
                                      ← Response flows back

Common middleware:

• Exception handling
• Static files
• Routing
• Authentication & Authorization

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4. Routing

Routing determines which endpoint should handle the request.

• Matches URL pattern
• Maps to a controller/action or minimal API

Example:

[HttpGet("products/{id}")]
public IActionResult GetProduct(int id)

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5. Endpoint Execution

Once matched, the request reaches:

Option A: Controllers (MVC/Web API)

• Controller class handles request
• Action method executes logic

Option B: Minimal APIs

app.MapGet("/hello", () => "Hello World");

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6. Model Binding & Validation

Before the action runs:

• Data from request (JSON, query, route) is converted into C# objects
• Validation attributes are applied

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7. Business Logic & Services

Inside the action:

• Calls services (via Dependency Injection)
• Interacts with database, APIs, etc.

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8. Response Creation

The action returns:

• JSON (Ok(object))
• View (MVC)
• Status codes

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9. Response Travels Back Through Middleware

The response goes back through the same middleware in reverse order:

• Logging
• Error handling
• Response modification

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10. Response Sent to Client

Finally:

• Kestrel sends the HTTP response back to the client

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Quick Summary (Flow)

Client → Kestrel → Middleware → Routing → Endpoint → Business Logic
       ←──────────── Response (back through middleware) ───────────

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Key Concepts to Remember

• Middleware = pipeline backbone
• Routing decides where to go
• Controllers/Endpoints handle logic
• Dependency Injection is used everywhere