hello_world/
hello_world.rs

1//! Hello World Example - Minimal fastapi_rust Application
2//!
3//! This example demonstrates the most basic fastapi_rust setup:
4//! - Creating an application with a single GET endpoint
5//! - Defining a simple request handler
6//! - Testing with the built-in TestClient
7//!
8//! # Running This Example
9//!
10//! ```bash
11//! cargo run --example hello_world
12//! ```
13//!
14//! # Expected Output
15//!
16//! ```text
17//! GET / -> 200 OK
18//! Response: Hello, World!
19//! ```
20
21// Import the core types from fastapi
22use fastapi::core::{
23    App,            // The application builder and container
24    Request,        // Incoming HTTP request
25    RequestContext, // Request context (contains Cx, request ID, etc.)
26    Response,       // HTTP response to send back
27    ResponseBody,   // Response body types
28    TestClient,     // Built-in test client for making requests
29};
30
31/// A simple request handler that returns "Hello, World!"
32///
33/// # Parameters
34///
35/// - `_ctx`: The request context (unused in this simple example)
36/// - `_req`: The incoming request (unused - we return the same response for any request)
37///
38/// # Returns
39///
40/// An HTTP 200 OK response with "Hello, World!" as the body.
41///
42/// # Note
43///
44/// Handlers in fastapi_rust are functions that take a RequestContext
45/// and mutable Request, and return a Response. They can be sync or async.
46fn hello_handler(_ctx: &RequestContext, _req: &mut Request) -> std::future::Ready<Response> {
47    // Create a 200 OK response with a plain text body
48    std::future::ready(Response::ok().body(ResponseBody::Bytes(b"Hello, World!".to_vec())))
49}
50
51fn main() {
52    println!("fastapi_rust Hello World Example");
53    println!("================================\n");
54
55    // Build the application
56    //
57    // App::builder() creates a new application builder that lets you:
58    // - Add routes for different HTTP methods
59    // - Configure middleware
60    // - Set application state
61    // - Define exception handlers
62    let app = App::builder()
63        // Register a GET handler for the root path "/"
64        //
65        // This is equivalent to:
66        //   @app.get("/")
67        //   def hello():
68        //       return "Hello, World!"
69        // in Python FastAPI
70        .get("/", hello_handler)
71        // Build the final immutable App
72        .build();
73
74    println!("App created with {} route(s)\n", app.route_count());
75
76    // Create a test client to make requests to our app
77    //
78    // TestClient wraps any Handler (including App) and provides
79    // a convenient API for making HTTP requests in tests.
80    let client = TestClient::new(app);
81
82    // Make a GET request to "/"
83    println!("Making request: GET /");
84    let response = client.get("/").send();
85
86    // Check the response
87    println!(
88        "GET / -> {} {}",
89        response.status().as_u16(),
90        response.status().canonical_reason()
91    );
92    println!("Response: {}\n", response.text());
93
94    // Verify success
95    assert_eq!(response.status().as_u16(), 200);
96    assert_eq!(response.text(), "Hello, World!");
97
98    // Try a path that doesn't exist - should get 404
99    println!("Making request: GET /not-found");
100    let response = client.get("/not-found").send();
101    println!(
102        "GET /not-found -> {} {}",
103        response.status().as_u16(),
104        response.status().canonical_reason()
105    );
106    assert_eq!(response.status().as_u16(), 404);
107
108    println!("\nAll assertions passed!");
109}
hello_world/hello_world.rs

hello_world/
hello_world.rs
