# tor-rtmock
Support for mocking with `tor-rtcompat` asynchronous runtimes.
## Overview
The `tor-rtcompat` crate defines a `Runtime` trait that represents
most of the common functionality of . This crate provides mock
implementations that override a `Runtime`, in whole or in part,
for testing purposes.
This crate is part of
[Arti](https://gitlab.torproject.org/tpo/core/arti/), a project to
implement [Tor](https://www.torproject.org/) in Rust.
It is used to write tests for higher-level
crates in Arti that rely on asynchronous runtimes.
This crate should only be used for writing tests.
The principal entrypoint for writing tests is [`MockRuntime`],
particularly [`test_with_various`](MockRuntime::test_with_various).
It supports mocking the passage of time
(via [`SimpleMockTimeProvider`](simple_time::SimpleMockTimeProvider)
and
[`MockExecutor`](task::MockExecutor)),
and impersonating the internet (via [`MockNetRuntime`]).
## Comprehensive example
Suppose you've written a function that relies on making a
connection to the network and possibly timing out.
With `tor-rtmock` you can test this function,
replacing the internet, _and_ the passage of time.
The test runs instantly, without actually blocking,
even though it tests a timeout.
And it tests the function against your mocked server,
without making any actual network connections.
```rust
# #[cfg(miri)] // miri cannot do CLOCK_REALTIME
# return;
use tor_rtcompat::{Runtime, SleepProviderExt as _n};
use std::{io, net::{IpAddr, SocketAddr}, time::Duration};
use futures::{channel::oneshot, io::{AsyncReadExt as _, AsyncWriteExt as _}, poll};
use futures::StreamExt as _;
use std::io::ErrorKind;
use tor_rtmock::{MockRuntime, /*MockNetRuntime,*/ net::MockNetwork};
use tor_rtcompat::{NetStreamProvider as _, NetStreamListener as _};
// Code to be tested:
/// Connects to `addr`, says hello, and returns whatever the server sent back
async fn converse(runtime: impl Runtime, addr: &SocketAddr) -> io::Result<Vec<u8>> {
let delay = Duration::new(5,0);
runtime.timeout(delay, async {
let mut conn = runtime.connect(addr).await?;
conn.write_all(b"Hello world!\r\n").await?;
conn.flush().await?;
let mut response = vec![];
conn.read_to_end(&mut response).await?;
io::Result::Ok(response)
}).await?
}
// In test module:
// We wrap it up with views onto a nonempty one we're using for the test:
let fake_internet = MockNetwork::new();
// Make a view that pretends we're at the server address
let sip: IpAddr = "198.51.100.99".parse().unwrap();
let srt = fake_internet.builder().add_address(sip).runtime(rt.clone());
// Make a view that pretends we're at the client address
let cip: IpAddr = "198.51.100.7".parse().unwrap();
let crt = fake_internet.builder().add_address(cip).runtime(rt.clone());
// Helper to spawn a task to execute `converse` and report its results
//
// Returns a oneshot::Receiver that becomes ready when `converse` has returned
let spawn_test = |saddr| {
let (ret_tx, ret_rx) = oneshot::channel();
let crt = crt.clone();
rt.spawn_identified("function under test", async move {
let ret = converse(crt, &saddr).await;
ret_tx.send(ret).unwrap();
});
ret_rx
};
eprintln!("First test. Nothing is listening.");
let saddr = SocketAddr::new(sip, 1);
let ret = spawn_test(saddr).await.unwrap();
assert_eq!(ret.unwrap_err().kind(), ErrorKind::ConnectionRefused);
eprintln!("Second test. Listening, but no-one picks up the phone: timeout.");
let saddr = SocketAddr::new(sip, 2);
let listener = srt.listen(&saddr).await.unwrap();
let mut ret_fut = spawn_test(saddr);
rt.progress_until_stalled().await; // let it run as far as it can get
assert!(ret_fut.try_recv().unwrap().is_none()); // it hasn't completed right away
assert!(poll!(&mut ret_fut).is_pending()); // alternative check, works with any future
rt.advance_by(Duration::from_secs(4)).await; // run for 4 seconds, < timeout
assert!(ret_fut.try_recv().unwrap().is_none()); // it still hasn't completed
rt.advance_by(Duration::from_secs(1)).await; // run for 1 more, reaching timeout
let ret = ret_fut.try_recv().unwrap().unwrap();
assert_eq!(ret.unwrap_err().kind(), ErrorKind::TimedOut);
eprintln!("Third test. Working.");
let saddr = SocketAddr::new(sip, 3);
let listener = srt.listen(&saddr).await.unwrap();
let mut incoming_streams = listener.incoming();
let mut ret_fut = spawn_test(saddr);
let (mut conn, caddr) = incoming_streams.next().await.unwrap().unwrap();
eprintln!("listener accepted from {caddr:?}");
assert_eq!(caddr.ip(), cip);
let expect = b"Hello world!\r\n";
let mut output = vec![b'X'; expect.len()];
conn.read_exact(&mut output).await.unwrap();
eprintln!("listener received {output:?}");
assert_eq!(output, expect);
let reply_data = b"reply data";
conn.write(reply_data).await.unwrap();
conn.close().await.unwrap();
let ret = ret_fut.await.unwrap();
assert_eq!(ret.unwrap(), reply_data);
});
```
License: MIT OR Apache-2.0