Solved-Assignment 8: Rust and WebAssembly -Solution

Description

Question 1: WebAssembly is a small, well-defined language. It is specified using mainly sequent

calculus. You can find the specification here:

https://webassembly.github.io/spec/core/valid/instructions.html

Given this specification and notational conventions, we define several lower-level functions in WebAssembly. Write sequent calculus definitions for the following functions;

a- “The instruction t.const results in the same generic type.”

b- “The instruction t.add takes two generic values and returns the same generic type”

c- “The instruction t.eq takes two generic values and returns in an i32 value.” Yes, WebAssembly implements Boolean as an Integer.

Question 2: Consider the following piece of code:

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, Error = ()> {

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))

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ECE 421 | Exploring Software Development Domains
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

51 type BoxFut = Box, Error = hyper::Error>
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?

Does this code use Async/IO, if not, how would you change the program to use it? Question 3:

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ECE 421 | Exploring Software Development Domains

Question 3: 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. 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.

Question 4: Consider the following program:

a- What is nighty channel in Rust (check Playground)
b- What are unstable features?
c- Why can playground run this code (think O.S.)
d- What is the output from this code?
e- Provide comments for the lines ending in #

#![feature(asm)]
fn main() {

let message = String::from(“James, you are completely mad\n”); syscall(message);
}

#[cfg(target_os = “linux”)]
fn syscall(message: String) {
let msg_ptr = message.as_ptr();
let len = message.len();
unsafe {
asm!(”
mov $$1, %rax #

mov $$1, %rdi #
mov $0, %rsi #
mov $1, %rdx #
syscall #
”

:
: “r”(msg_ptr), “r”(len)

)
}
}

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