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_rust::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
51#[allow(clippy::needless_pass_by_value)]
52fn check_eq<T: PartialEq + std::fmt::Debug>(left: T, right: T, message: &str) -> bool {
53    if left == right {
54        true
55    } else {
56        eprintln!("Check failed: {message}. left={left:?} right={right:?}");
57        false
58    }
59}
60
61fn main() {
62    println!("fastapi_rust Hello World Example");
63    println!("================================\n");
64
65    // Build the application
66    //
67    // App::builder() creates a new application builder that lets you:
68    // - Add routes for different HTTP methods
69    // - Configure middleware
70    // - Set application state
71    // - Define exception handlers
72    let app = App::builder()
73        // Register a GET handler for the root path "/"
74        //
75        // This is equivalent to:
76        //   @app.get("/")
77        //   def hello():
78        //       return "Hello, World!"
79        // in Python FastAPI
80        .get("/", hello_handler)
81        // Build the final immutable App
82        .build();
83
84    println!("App created with {} route(s)\n", app.route_count());
85
86    // Create a test client to make requests to our app
87    //
88    // TestClient wraps any Handler (including App) and provides
89    // a convenient API for making HTTP requests in tests.
90    let client = TestClient::new(app);
91
92    // Make a GET request to "/"
93    println!("Making request: GET /");
94    let response = client.get("/").send();
95
96    // Check the response
97    println!(
98        "GET / -> {} {}",
99        response.status().as_u16(),
100        response.status().canonical_reason()
101    );
102    println!("Response: {}\n", response.text());
103
104    // Verify success
105    if !check_eq(response.status().as_u16(), 200, "GET / should return 200") {
106        return;
107    }
108    if !check_eq(response.text(), "Hello, World!", "GET / should return body") {
109        return;
110    }
111
112    // Try a path that doesn't exist - should get 404
113    println!("Making request: GET /not-found");
114    let response = client.get("/not-found").send();
115    println!(
116        "GET /not-found -> {} {}",
117        response.status().as_u16(),
118        response.status().canonical_reason()
119    );
120    if !check_eq(
121        response.status().as_u16(),
122        404,
123        "Unknown routes should return 404",
124    ) {
125        return;
126    }
127
128    println!("\nAll assertions passed!");
129}
hello_world/hello_world.rs

hello_world/
hello_world.rs
