Description
Software Construction, Verification and Evolution
Question 1: Consider the following piece of code (use crate: hyper=”0.12.35″):
1 use hyper::rt::Future;
2 use hyper::service::service_fn_ok;
3 use hyper::{Body, Request, Response, Server};
7
8 fn main() {
9 let addr = ([127, 0, 0, 1], 3000).into();
10 let server = Server::bind(&addr)
11 .serve(|| {
12 service_fn(service_router)
13 })
14 .map_err(|e| eprintln!(“server error: {}”, e));
15
16 println!(“Listening on http://{}”, addr);
17 hyper::rt::run(server);
18 }
19
20 fn svc_wait(t: u64) -> impl Future
21 println!(“[start] waiting…”);
22 let when = Instant::now() + Duration::from_millis(t);
23 Delay::new(when)
24 .map_err(|e| panic!(“timer failed; err={:?}”, e))
25 .and_then(|_| {
26 println!(“[end] waiting”);
27 Ok(())
28 })
29 }
30
31
32 fn fetch_data() -> impl Future
34 let uri: Uri = “http://httpbin.org/get”.parse().expect(“Cannot parse 35
URL”);
36 Client::new()
37 .get(uri)
38 // Future is polled here
39 .and_then(|res| {
40 res.into_body().concat2()
41 })
42 .map_err(|err| println!(“error: {}”, err))
43 .map(|body| {
44 let decoded: RespStruct =
45 serde_json::from_slice(&body).expect(“Couldn’t deserialize”);
46 future::ok(decoded)
47 })
48 }
49
50
1
ECE 522 | Software Construction, Verification and Evolution
51 type BoxFut = Box
52 + Send>;
53
54
55 fn service_router(req: Request) -> BoxFut {
56 let mut response = Response::new(Body::empty());
57
58 match (req.method(), req.uri().path()) {
60
61
62 (&Method::GET, “/wait”) => {
63 let r = svc_wait(1500);
64 hyper::rt::spawn(r);
65 *response.body_mut() = Body::from(format!(“Triggered waiting
66 {}ms”, 1500));
67 }
68
69
70 (&Method::GET, “/fetch”) => {
71 let r = fetch_data().map(|x| {
72 println!(“got data: {:?}”, x);
73 });
74 hyper::rt::spawn(r);
75 *response.body_mut() = Body::from(“Sent request to external
76 webservice”);
77 }
78
79 // … more routers
80 }
81 eprintln!(“Returning a response”);
82 Box::new(future::ok(response))
83 }
a- Explain what do the numbers mean in line 9.
b- The function in line 20 uses Future; what is Future?
c- What does http://httpbin.org do (line 34)?
d- Give a definition for the body variable in line 45.
e- Explain the BoxFut type in line 51
f- Should BoxFut (Line 51) implement the Sync trait?
g- Should BoxFut (Line 51) use a lifetime?
h- At some points, you will be using the following instruction:
$ curl localhost:3000/wait
What does curl do?
i- Does this code use Async/IO, if not, how would you change the program to use it?
Question 2: Libra (libra.org) is a major new product from Facebook. Libra is a cryptocurrency
platform. Facebook expect to make billions from Libra and revolutionize the financial industry.
2
ECE 522 | Software Construction, Verification and Evolution
a- What language is Libra written in?
b- Discuss the technical reasons why this choice of language suits the application and its objectives.
c- Libra uses many standard packages, including lazy_static, tokio, failure, etc. Briefly, describe
each of these packages.
3
