ECE421-Assignment 8 Rust and WebAssembly Solved

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<Item = (), Error = () {

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<Item = future::FutureResult<RespStruct, 33         String, 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))
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<dyn Future<Item = Response<Body, Error = hyper::Error

52                                                                                     + Send;

53  

54  

55         fn service_router(req: Request<Body) - 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:

 

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) 

        )

    }

}